MUTATIONS RESPONSIBLE FOR ENVIRONMENTAL ADAPTATIONS
While my blog is rooted on Lake Malawi cichlids biodiversity, sometimes I find stories which are indirectly related to the issue of rapid radiation of Lake Malawi cichlids. As we may all know the puzzle in cichlid evolution is to solve the oring of this stunning biodiversity of Lake Malawi. Among the factors responsible for this puzzle are mate choice basing on the male breeding colour morphs. Today, the study in bacteria has managed to locate the mutations which are responsible for phenotypic changes due to environment. In simplistic sense, think of colour morphs in cichlids and water levels or environment or geographic locations in Lake Malawi, is it possible to indetify the mutations responsible?? Think of red tops (P. zebra), blue tops (P. zebra), blue black tops (P. zebra) and C. afra. Is it possible to locate the mutations responsible??
Now read on the story below:
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Researchers for the first time have tracked the specific genetic mutations -- occurring over just a few generations -- that allow bacteria to respond to environmental changes, they report online in Nature today (November 4).
"We showed how evolution happens in real time," said Hubertus Beaumont, a biologist from Leiden University in the Netherlands and first author on the study.
Studies have shown bacteria and other organisms can switch back and forth between phenotypes to better survive in new environments. For instance, Beaumont said, many bacteria switch their surface antigens when invading a host, so they can avoid being attacked, and certain desert plants are programmed to germinate seeds at random time intervals, increasing their chances of encountering rain. "This bet-hedging strategy is very simple, but captures the essence of evolution." Beaumont said. "Natural selection in these uncertain environments causes an organism to evolve protective traits." Exactly how such phenotypic adaptability emerges, however, was unknown.
In order to observe how bet-hedging evolves, Beaumont and his colleague Paul Rainey at Massey University in New Zealand observed Pseudomonas fluorescens, a common rod-shaped bacterium, in a new type of environment. They already knew that the bacteria grow well in a test tube that's shaken manually or in an incubator that allows oxygen to circulate in the culture. So instead of shaking the test tube, a condition to which the bacteria are well-adapted, the researchers watched the bacteria grow in non-shaken test tubes.
As expected, some of the bacteria adapted to the novel environment, forming colonies with an advantageous "wrinkly" morphology as opposed to the ancestral bacteria, which grew smoothly. The team identified these new colony types in the test tube and transferred them to fresh tubes, repeating this process 15 times to select for the new variations. Eventually, the bacteria evolved the ability to rapidly switch their phenotypes between the "wrinkly" and "smooth" cell-types to prepare themselves to cope with the different environments.
"I find these results really intriguing," said Martin Ackermann, an environmental microbiologist at Eidgenössische Technische Hochschule Zurich (or ETH Zurich) in Switzerland who was not involved in the research. "It is amazing to see that phenotypic switching can evolve so rapidly, in the course of a just a few rounds of selection. As far as I know, this has not been observed before."
Beaumont and Rainey then sequenced the evolved bacterial genome and found all the mutations that had arisen and that might have contributed to this new trait. The team identified nine mutations distinguishing bet-hedgers from their ancestors. They pinpointed one specific mutation as the one which allows the phenotype to switch back and forth between different morphologies, while the other mutations, they found, were essential for growing the new type of bacteria.
"It's yet another beautiful study at multiple levels from Paul Rainey's team," said Richard Lenski, a microbial ecologist at Michigan State University who didn't participate in the research, in an email. "This is a neat demonstration that the evolution of bet-hedging was contingent on other mutations that had occurred earlier in the lineage." These earlier changes improved the fitness of the bacteria at each stage.
"The results thus suggest that phenotypic switching is a strategy that can readily evolve," and may capture the earliest evolutionary solutions to life in fluctuating environments, Ackerman wrote in an email.
Wednesday, November 4, 2009
Friday, October 23, 2009
Malawi at the root of humankind 6 MYA
Malawi could be the cradle of humankind-researcher
KARONGA, Malawi (Reuters) - The latest discovery of pre-historic tools and remains of hominids in Malawi's remote northern district of Karonga provides further proof that the area could be the cradle of humankind, a leading German researcher said.
Professor Friedemann Schrenk of the Goethe University in Frankfurt told Reuters that two students working on the excavation site last month had discovered prehistoric tools and a tooth of an hominid.
"This latest discovery of prehistoric tools and remains of hominids provides additional proof to the theory that the Great Rift Valley of Africa and perhaps the excavation site near Karonga can be considered the cradle of humankind," Schrenk said.
A hominid is a member of a family of primates which includes humans and their prehistoric ancestors.
The discovery was at Malema excavation site, 10 km (6 miles) from Karonga.
The site also contains some of the earliest dinosaurs which lived between 100 million and 140 million years ago and early hominids believed to have lived between a million and 6 million years ago.
He is leading a team of researchers from Europe and Africa to establish an African center for interdisciplinary studies on mammal and hominid evolution in the southern African nation.
Karonga is about 615 km (380 miles) north of the capital Lilongwe and is near the border with Tanzania.
KARONGA, Malawi (Reuters) - The latest discovery of pre-historic tools and remains of hominids in Malawi's remote northern district of Karonga provides further proof that the area could be the cradle of humankind, a leading German researcher said.
Professor Friedemann Schrenk of the Goethe University in Frankfurt told Reuters that two students working on the excavation site last month had discovered prehistoric tools and a tooth of an hominid.
"This latest discovery of prehistoric tools and remains of hominids provides additional proof to the theory that the Great Rift Valley of Africa and perhaps the excavation site near Karonga can be considered the cradle of humankind," Schrenk said.
A hominid is a member of a family of primates which includes humans and their prehistoric ancestors.
The discovery was at Malema excavation site, 10 km (6 miles) from Karonga.
The site also contains some of the earliest dinosaurs which lived between 100 million and 140 million years ago and early hominids believed to have lived between a million and 6 million years ago.
He is leading a team of researchers from Europe and Africa to establish an African center for interdisciplinary studies on mammal and hominid evolution in the southern African nation.
Karonga is about 615 km (380 miles) north of the capital Lilongwe and is near the border with Tanzania.
Wednesday, October 14, 2009
Pheromones may not initiate sexual attraction and mating
This story was taken from science magazine on as is basis, but found it interesting as I am working on mate choice of Lake Malawi cichlids as well. The role of chemical cues in cichlid mate choice has already being suggested but their relationship with the pheromeones (hydrocarbones) is yet to be told. The following study in drosophila has worked on such untouched components.
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Pheromones may not initiate sexual attraction and mating, as commonly believed, new research suggests. Instead, the chemical signals may help flies distinguish between different genders and species while choosing a mate, researchers report in this week's issue of Nature.
This is the first time a study has deciphered the chemical dialogue happening between flies as they mate," said Nicolas Gompel, a geneticist at the Institut de Biologie du Developpement de Marseille-Luminy in France, who was not involved with the research but wrote an accompanying commentary on the paper. "The research challenges the common belief that pheromones are essential to initiate courtship... and suggests that instead, [they] play a significant role in mate identification and selection."
Scientists have long understood that pheromones, hydrocarbons produced by an animal or insect that trigger reactions in another individual, play a role in mating. But they've been unable to identify the role of individual pheromones because the hydrocarbons are often secreted as blends, comprised of up to 30 molecules, and function in conjunction with other signals. In order to study individual pheromones, Jean-Christophe Billeter from the University of Toronto at Mississauga and his colleagues genetically engineered adult Drosophila melanogaster without oenocytes, cells that secret hydrocarbons. The oenocyte-less flies were "blank slates," said Joel Levine, a geneticist from the University of Toronto and coauthor of the study, allowing the team to imprint one pheromone at a time.
Because pheromones have been generally believed to stimulate mating, Billeter and his colleagues expected that flies lacking hydrocarbons would be sexually unappealing to males. To their surprise, quite the opposite happened: wild-type males were hyperattracted to oenocyte-less flies. The wild-type males also ignored gender, choosing to mate with both unscented males and females over other wild-types. These results led the researchers to conclude that pheromones may not stimulate mating, but may instead act to slow down male mating attempts to allow the female to assess her partner's suitability. They also concluded that hydrocarbons help flies distinguish between sexes.
Billeter and his colleagues then tested the effect of individual pheromones on mate selection and copulation attempts. Researchers treated unscented D. melanogaster with wild-type levels of cVA, a hydrocarbon males are known to coat on females to deter further mating attempts. As expected, cVA effectively created a "chemical chastity belt," said Gompel.
Researchers then treated unscented flies with 7,11-heptacosadiene (7,11-HD), a pheromone thought to act as an aphrodisiac for flies. Although 7,11-HD alone did not stimulate additional mating attempts, when applied over cVA, it helped diminish the inhibiting effect of the compound, allowing females to broadcast their mating availability. The findings suggested that mating doesn't depend on just one pheromone relaying a message of availability, but instead on a complex mixture of attractive and aversive signals.
7,11-HD also seemed to act as a species barrier in mating. Unscented D. melanogaster females treated with the hydrocarbon attracted males of the same species, but deterred D. simulans and D. yakuba males.
"It's neat that one hydrocarbon (7, 11-HD) acts both as an aphrodisiac to males of D. melanogaster and also as a key compound causing males of other closely related species in the genus to reject her," said Tristram Wyatt, an evolutionary biologist at the University of Oxford. "It's surprising at first sight, but perhaps it's another example of evolution resulting in simple solutions, two effects for one."
Billeter's study isn't the first time that the pheromone-less flies have been shown to be hyperattractive. Fabrice Savarit from the Universite Paris Sud and colleagues reported similar results in 1999. "One of the main differences between our study and Billeter's is his team was able to cleanly get rid of oenocytes," said Matthew Cobb, an evolutionary neurobiologist at the University of Manchester in England and coauthor of the 1999 study. "We produced pheromone-less flies in a roundabout way by overexpressing the UAS-tra transgene. Billeter's methodology is much more precise and reproducible." Billeter's study was also able to produce pheromone-less male flies, something Cobb's team failed to do.
Wyatt agreed, noting that the "blank canvas" flies will be invaluable "in further researching the neural circuits involved in sex and species recognition in these flies."
Cobb also noted that while hydrocarbons excreted by oenocytes may not initiate mating in flies, other pheromones might. In their 1999 study, Savarit and his colleagues noticed there was still a small amount of pheromones on their supposedly hydrocarbon-less female flies. Cobb noticed a similar trend in Billeter's data. "It seems even after they wiped out all the oenocytes in flies, there is a tiny -- we're talking less than 10 millivolts -- but significant amount of hydrocarbons still present," he said. "These might be ancestral pheromones, or not, but either way it is very intriguing."
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Pheromones may not initiate sexual attraction and mating, as commonly believed, new research suggests. Instead, the chemical signals may help flies distinguish between different genders and species while choosing a mate, researchers report in this week's issue of Nature.
This is the first time a study has deciphered the chemical dialogue happening between flies as they mate," said Nicolas Gompel, a geneticist at the Institut de Biologie du Developpement de Marseille-Luminy in France, who was not involved with the research but wrote an accompanying commentary on the paper. "The research challenges the common belief that pheromones are essential to initiate courtship... and suggests that instead, [they] play a significant role in mate identification and selection."
Scientists have long understood that pheromones, hydrocarbons produced by an animal or insect that trigger reactions in another individual, play a role in mating. But they've been unable to identify the role of individual pheromones because the hydrocarbons are often secreted as blends, comprised of up to 30 molecules, and function in conjunction with other signals. In order to study individual pheromones, Jean-Christophe Billeter from the University of Toronto at Mississauga and his colleagues genetically engineered adult Drosophila melanogaster without oenocytes, cells that secret hydrocarbons. The oenocyte-less flies were "blank slates," said Joel Levine, a geneticist from the University of Toronto and coauthor of the study, allowing the team to imprint one pheromone at a time.
Because pheromones have been generally believed to stimulate mating, Billeter and his colleagues expected that flies lacking hydrocarbons would be sexually unappealing to males. To their surprise, quite the opposite happened: wild-type males were hyperattracted to oenocyte-less flies. The wild-type males also ignored gender, choosing to mate with both unscented males and females over other wild-types. These results led the researchers to conclude that pheromones may not stimulate mating, but may instead act to slow down male mating attempts to allow the female to assess her partner's suitability. They also concluded that hydrocarbons help flies distinguish between sexes.
Billeter and his colleagues then tested the effect of individual pheromones on mate selection and copulation attempts. Researchers treated unscented D. melanogaster with wild-type levels of cVA, a hydrocarbon males are known to coat on females to deter further mating attempts. As expected, cVA effectively created a "chemical chastity belt," said Gompel.
Researchers then treated unscented flies with 7,11-heptacosadiene (7,11-HD), a pheromone thought to act as an aphrodisiac for flies. Although 7,11-HD alone did not stimulate additional mating attempts, when applied over cVA, it helped diminish the inhibiting effect of the compound, allowing females to broadcast their mating availability. The findings suggested that mating doesn't depend on just one pheromone relaying a message of availability, but instead on a complex mixture of attractive and aversive signals.
7,11-HD also seemed to act as a species barrier in mating. Unscented D. melanogaster females treated with the hydrocarbon attracted males of the same species, but deterred D. simulans and D. yakuba males.
"It's neat that one hydrocarbon (7, 11-HD) acts both as an aphrodisiac to males of D. melanogaster and also as a key compound causing males of other closely related species in the genus to reject her," said Tristram Wyatt, an evolutionary biologist at the University of Oxford. "It's surprising at first sight, but perhaps it's another example of evolution resulting in simple solutions, two effects for one."
Billeter's study isn't the first time that the pheromone-less flies have been shown to be hyperattractive. Fabrice Savarit from the Universite Paris Sud and colleagues reported similar results in 1999. "One of the main differences between our study and Billeter's is his team was able to cleanly get rid of oenocytes," said Matthew Cobb, an evolutionary neurobiologist at the University of Manchester in England and coauthor of the 1999 study. "We produced pheromone-less flies in a roundabout way by overexpressing the UAS-tra transgene. Billeter's methodology is much more precise and reproducible." Billeter's study was also able to produce pheromone-less male flies, something Cobb's team failed to do.
Wyatt agreed, noting that the "blank canvas" flies will be invaluable "in further researching the neural circuits involved in sex and species recognition in these flies."
Cobb also noted that while hydrocarbons excreted by oenocytes may not initiate mating in flies, other pheromones might. In their 1999 study, Savarit and his colleagues noticed there was still a small amount of pheromones on their supposedly hydrocarbon-less female flies. Cobb noticed a similar trend in Billeter's data. "It seems even after they wiped out all the oenocytes in flies, there is a tiny -- we're talking less than 10 millivolts -- but significant amount of hydrocarbons still present," he said. "These might be ancestral pheromones, or not, but either way it is very intriguing."
Thursday, October 1, 2009
Elevated genetic diversity in introduced populations of Cynotilapia afra
Genetic variation in many invasive species shows little or no signs of a founder event, suggesting that high genetic diversity may facilitate establishment success. The rocky-shore, plankton-feeding cichlid fish Cynotilapia afra is endemic to Lake Malawi, but naturally absent from many suitable sites. In the 1960s, this species was introduced to the southern areas of the lake, presumably as a result of the aquarium fish trade. It has now become established on a number of rocky areas within the Lake Malawi National Park. Here, we analysed DNA sequence variation in the mitochondrial control region of six native and four introduced populations of C. afra, and three populations of the closely-related and hybridizing Pseudotropheus zebra. In contrast to previous studies of Lake Malawi rock dwelling cichlids, network analyses suggested that native populations of C. afra showed high levels of lineage sorting in mtDNA. Introduced populations showed higher sequence and haplotype diversity than their native counterparts. Our analyses suggested that the elevated gene diversity was largely attributed to the fact that the introduced C. afra populations were derived from several genetically distinct and geographically separate populations, and to a lesser extent because of introgressive hybridization with native P. zebra. The establishment and spread of C. afra may be partly because of its ability to occupy a vacant ecological niche, but it may also have been facilitated by its enhanced genetic diversity.
Monday, June 22, 2009
LATERAL LINE AS AN ADAPTATION TO FEEDING BAHAVIOUR
We are all fascinated by the jaw morphology adaptation of Lake Malawi cichlids as one of the driving mechanism in their diversity. One of this months published studies has revealed the lateral line to be among the wonders of the feeding behaviour in cichlids.
Working on one of the peacock cichlids of the so called "Alunocara" group, it has been reported that their wide cavity lateral line is responsible for the efficiency of this species in getting food.
Three groups of fish were studied, one with normal cavity, another chemically deformed and last group feeding in the dark. The chemically deformed lateral line failed to ge their prey, while the other two hand their game on spot.
Let us know that this mechanism is widely spread among the deep sea fish, and for the peacocks to posses this adaptation within Lake Malawi system which is suggested to have clear waters and suppossedly clear feeding vision is one of the seven wonders in fish biology and the cichlid system as a whole.
As if this is not enough, on a lighter note this group of "Alunocara" is among the most expensive products of the aquarium trade despite having a wide distribution range within Lake Malawi.
The Lake Malawi biodiversity will never cease to amaze us!
WHATS NEXT THE CICHLIDS WE ARE WATCHING.
Working on one of the peacock cichlids of the so called "Alunocara" group, it has been reported that their wide cavity lateral line is responsible for the efficiency of this species in getting food.
Three groups of fish were studied, one with normal cavity, another chemically deformed and last group feeding in the dark. The chemically deformed lateral line failed to ge their prey, while the other two hand their game on spot.
Let us know that this mechanism is widely spread among the deep sea fish, and for the peacocks to posses this adaptation within Lake Malawi system which is suggested to have clear waters and suppossedly clear feeding vision is one of the seven wonders in fish biology and the cichlid system as a whole.
As if this is not enough, on a lighter note this group of "Alunocara" is among the most expensive products of the aquarium trade despite having a wide distribution range within Lake Malawi.
The Lake Malawi biodiversity will never cease to amaze us!
WHATS NEXT THE CICHLIDS WE ARE WATCHING.
Friday, June 19, 2009
Hatchery breeding for reintroduction into Lake Malawi
Evidence is increasing on the downside of captive breeding aimed for reintroduction into the wild. A study published in Biology Letters suggest that wild born offspring from hatchery raised Steelhead Trout parents has only 37% reproductive fitness as compared to 87% if only one of the parents was wild breed. These differences are still detected even if the fish have spent one generation in the wild.
Lake Malawi holds one of the stunning cichlid biodiversity in the world, however this biodiversity is believed to be only 1 to 2 million years old. In other words is still going through sysnthesis, thus most of the cichlids still interbreed naturally during a secondary contact. The results from the above mentioned study should tell us that one of our cards to mitigate for overfishing of the most sort Tilapia should not be hatchery raised ones, but reinforcement of the fishing season and fishing gear size.
If hatchery breed fingerlings are to be used in Chambo restoration plan, then genetic differences between them and wild types should be well studied. As far as I know the aquaculture stock at the moment may not be the best candidates for this exercise. Molecular studies have already revealed that the aqua stock has a mixed up gene pool, that is neither pure Chambo (O. karongae), nor Makakana (O. mossambicus) to mention a few.
All the evidence points us to one thing, Chambo restoration plan should be based on proper scientifc evidence not emotions or personnal gains if we are aiming to produce and really preserve the original (OK) gene pool, which is tasty and tender as claimed by the Lake shore crew.
On a lighter note, while my emphasis has been on the famous chambo, the same principle should also apply on the red listed Ntchila, Sanjika, Ningwi ect in river shire and its catchment.
Have a nice weekend.
Lake Malawi holds one of the stunning cichlid biodiversity in the world, however this biodiversity is believed to be only 1 to 2 million years old. In other words is still going through sysnthesis, thus most of the cichlids still interbreed naturally during a secondary contact. The results from the above mentioned study should tell us that one of our cards to mitigate for overfishing of the most sort Tilapia should not be hatchery raised ones, but reinforcement of the fishing season and fishing gear size.
If hatchery breed fingerlings are to be used in Chambo restoration plan, then genetic differences between them and wild types should be well studied. As far as I know the aquaculture stock at the moment may not be the best candidates for this exercise. Molecular studies have already revealed that the aqua stock has a mixed up gene pool, that is neither pure Chambo (O. karongae), nor Makakana (O. mossambicus) to mention a few.
All the evidence points us to one thing, Chambo restoration plan should be based on proper scientifc evidence not emotions or personnal gains if we are aiming to produce and really preserve the original (OK) gene pool, which is tasty and tender as claimed by the Lake shore crew.
On a lighter note, while my emphasis has been on the famous chambo, the same principle should also apply on the red listed Ntchila, Sanjika, Ningwi ect in river shire and its catchment.
Have a nice weekend.
Friday, June 5, 2009
THE SCHOOLING AND SHOALING FACTOR
Have we ever asked why do fish move in groups aka schools or shoaling behavior.
No No No the sheep are best at it, when one makes it into the M1 road, yes in Malawi all of them will follow. But, why? If you can not answer this question by studying these mogastrics then that is why our study system the cichlids are the coolest. Yes they are the toughest they can tell you many of the amazing behaviour we have in animal kngdom.
A study published in Current Biology Journal on 29 th Jan 09, tells it all. The secrete is they do their social work best when they are in groups than go it alone stuff. So do not say I did not tell you, social insects also knows these best, ask the bees, fire ants, flying ants ect.
From a blog at the scientist web, here is what they had to say on stickle backs.
read on
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No No No the sheep are best at it, when one makes it into the M1 road, yes in Malawi all of them will follow. But, why? If you can not answer this question by studying these mogastrics then that is why our study system the cichlids are the coolest. Yes they are the toughest they can tell you many of the amazing behaviour we have in animal kngdom.
A study published in Current Biology Journal on 29 th Jan 09, tells it all. The secrete is they do their social work best when they are in groups than go it alone stuff. So do not say I did not tell you, social insects also knows these best, ask the bees, fire ants, flying ants ect.
From a blog at the scientist web, here is what they had to say on stickle backs.
read on
==========
Thursday, April 23, 2009
Nuts at dawn: Britain's squirrels fight for survival
Deep in the heart of England's seemingly peaceful countryside, a fierce battle for survival is being waged between the domestic red squirrel, its tougher grey cousin -- and a new mutant arrival.
Where there were once 3.5 million red squirrels in Britain, only about 150,000 remain. About 75 percent of these live in the wild in Scotland, while most of the rest are protected in nature reserves in northern England.
A plethora of organisations comprising hundreds of members have sprung up in their support, and in recent months they have stepped up their efforts to check the cause of this slaughter -- the grey squirrel.
Imported from the United States in 1876 to populate country estates, the greys were larger and had thicker fur than their English cousins and quickly began to dominate -- so much so that in 1930, it became illegal to release them into the wild.
But the containment policy failed and the greys began to encroach on the reds' territory, with disastrous results.
The reds were less hardy than their American cousins -- they need more space and their food takes longer to ripen -- but it was the squirrel pox virus that did the most harm. Greys are immune, but it proves fatal for reds.
"It can take only one grey squirrel to introduce this virus to a local population of red squirrels, and then the virus can spread throughout the reds with devastating effect," says the group Save our Squirrels (SOS).
As a result, red squirrels -- viewed in the early 20th century as a pest to be hunted down and killed -- have been a protected species since 1981.
At the same time, the reputation of the greys, who now number about 2.5 million in England and Wales, gets worse and worse.
Some organisations believe in radical action. The Red Squirrel Protection Partnership (RSPP), in Northumberland in northern England, has a clear plan -- to trap and kill as many grey squirrels as possible.
According to the RSPP's website, 22,287 squirrels have been killed since January 2007, as supporters act with military-style precision. Some of these end up on the butcher's block or on restaurant menus.
"We only call ourselves the Red Squirrel Protection Partnership because if we called it the Grey Squirrel Annihilation League people might be a bit less sympathetic," supporter Baron Rupert Mitford told the Guardian newspaper.
Public organisations have so far shied away from such a radical solution but the tactic is gaining ground.
For example, the Saving Scotland's Red Squirrels project, launched in February by a coalition of Scottish groups, purports to protect the habitat of red squirrels and "control" the grey population.
A few timid voices defend the greys, however, noting they face a similar fate to the red squirrels at the hand of a new arrival -- the black squirrel.
These are the result of a genetic mutation of the grey squirrels and are spreading across Britain from East Anglia, where the greys were first introduced.
According to a study by Alison Thomas, a geneticist at Anglia Ruskin University in Cambridge, the black squirrel made up almost half the rodent population in some areas at the beginning of 2008.
"The estimate is about 25,000 (black squirrels) today, but the black mutation gene has a dominant aspect which explains their rapid increase," she told AFP.
With a thicker coat and a higher level of testosterone than either the red or grey squirrels, the black mutants have been dubbed the "super-squirrel" and are proving more attractive to females -- ensuring their population flourishes.
Where there were once 3.5 million red squirrels in Britain, only about 150,000 remain. About 75 percent of these live in the wild in Scotland, while most of the rest are protected in nature reserves in northern England.
A plethora of organisations comprising hundreds of members have sprung up in their support, and in recent months they have stepped up their efforts to check the cause of this slaughter -- the grey squirrel.
Imported from the United States in 1876 to populate country estates, the greys were larger and had thicker fur than their English cousins and quickly began to dominate -- so much so that in 1930, it became illegal to release them into the wild.
But the containment policy failed and the greys began to encroach on the reds' territory, with disastrous results.
The reds were less hardy than their American cousins -- they need more space and their food takes longer to ripen -- but it was the squirrel pox virus that did the most harm. Greys are immune, but it proves fatal for reds.
"It can take only one grey squirrel to introduce this virus to a local population of red squirrels, and then the virus can spread throughout the reds with devastating effect," says the group Save our Squirrels (SOS).
As a result, red squirrels -- viewed in the early 20th century as a pest to be hunted down and killed -- have been a protected species since 1981.
At the same time, the reputation of the greys, who now number about 2.5 million in England and Wales, gets worse and worse.
Some organisations believe in radical action. The Red Squirrel Protection Partnership (RSPP), in Northumberland in northern England, has a clear plan -- to trap and kill as many grey squirrels as possible.
According to the RSPP's website, 22,287 squirrels have been killed since January 2007, as supporters act with military-style precision. Some of these end up on the butcher's block or on restaurant menus.
"We only call ourselves the Red Squirrel Protection Partnership because if we called it the Grey Squirrel Annihilation League people might be a bit less sympathetic," supporter Baron Rupert Mitford told the Guardian newspaper.
Public organisations have so far shied away from such a radical solution but the tactic is gaining ground.
For example, the Saving Scotland's Red Squirrels project, launched in February by a coalition of Scottish groups, purports to protect the habitat of red squirrels and "control" the grey population.
A few timid voices defend the greys, however, noting they face a similar fate to the red squirrels at the hand of a new arrival -- the black squirrel.
These are the result of a genetic mutation of the grey squirrels and are spreading across Britain from East Anglia, where the greys were first introduced.
According to a study by Alison Thomas, a geneticist at Anglia Ruskin University in Cambridge, the black squirrel made up almost half the rodent population in some areas at the beginning of 2008.
"The estimate is about 25,000 (black squirrels) today, but the black mutation gene has a dominant aspect which explains their rapid increase," she told AFP.
With a thicker coat and a higher level of testosterone than either the red or grey squirrels, the black mutants have been dubbed the "super-squirrel" and are proving more attractive to females -- ensuring their population flourishes.
Wednesday, January 28, 2009
ECOLOGY, SEXUAL SELECTION, HYBRIDISATION AS SPECIATION MECHANISMS
What? Who said we geographic isolation alone?
The article below has some insights on mechanisms involved in speciation. The high biodiversity of cichlid fishes in great Lake of Malawi is one of the many examples of organisms that have appreciated this mechanisms and produced the unspoken wonders of the world.
Just get a dive in rocky habitats of Cape Maclear, Nkhata Bay, Likoma and Monkey Bay just to mention a few localities and you will appreciate what we are trying to communicate here.
Do not say I did not tell you.
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SEXUAL SELECTION AND SPECIATION
The following points are made by K. Kraaijeveld and A. Pomiankowski (Current Biology 2004 14:R419):1) When Charles Darwin (1809-1882) [1] proposed his theory of sexual selection he was concerned mainly with explaining the widespread occurrence of exaggerated sexual ornaments and courtship displays, as these traits could not easily be explained by natural selection. He also noted that taxonomic groups with more pronounced sexual ornaments tended to have more species. This suggests that sexual selection may elevate the rate at which populations diversify and give rise to new species. A new study [2] of female mate preferences in five populations of an East African cichlid species strongly supports the connection between sexual selection and speciation.2) With the surge of interest in sexual selection over the past few decades, the question of whether it can lead to speciation has also enjoyed renewed attention. A plethora of theoretical models have investigated the connection, and generally concluded that sexual selection can promote speciation (3). The main evolutionary mechanism proposed invokes the rapid coevolution of female mate preferences and male courtship traits, leading to reproductive isolation between groups of individuals. However, empirical evidence in support of the idea is scarce.3) An indirect way this idea has been tested involves looking across broad taxonomic groups for a link between the strength of sexual selection and species number. So far, the evidence from these studies has been conflicting. In birds for example, taxa with greater sexual differences in plumage color -- an indicator of sexual selection -- have higher species numbers compared to sister taxa subject to weaker sexual selection [4,5]. However, surveys in other groups (butterflies, mammals, and spiders) have failed to find such an association, and the positive result in birds has not been replicated in a recent reanalysis. It seems premature to conclude from this that speciation is independent of sexual selection. One reason for the lack of a strong linkage is that sexual selection may promote extinction as well as speciation, if it leads to the evolution of traits maladaptive to male and female survival. Another is that sexual selection can even retard speciation under certain conditions. So in the long term, species numbers may only loosely be connected to sexual selection.4) A more direct way of investigating the connection between sexual selection and speciation is to examine its action in closely related populations. Knight and Turner [2] attempted such a test using populations of the cichlid fish Pseudotropheus zebra from Lake Malawi. The cichlid fishes of the East African lakes, in particular Lake Victoria and Lake Malawi, are renowned for rampant speciation over a very brief period of time -- more than 1000 species have been generated in less than a million years. Some of this diversity is due to ecological specialization, facilitated by the "key innovation" of the cichlid pharyngeal jaw. But many closely related species show practically no differences except in male color, suggesting that sexual selection may be an important additional mechanism of speciation.
References (abridged):1. Darwin, C.R. (1871). The Descent of Man and Selection in Relation to Sex. (London: John Murray)2. Knight, M.E. and Turner, G.F. (2004). Laboratory mating trials indicate incipient speciation by sexual selection among populations of the cichlid fish Pseudotropheus zebra from Lake Malawi. Proc. R. Soc. Lond. B 271, 675-6803. Turelli, M., Barton, N.H., and Coyne, J.A. (2001). Theory and speciation. Trends Ecol. Evol. 16, 330-3434. Barraclough, T.G., Harvey, P.H., and Nee, S. (1995). Sexual selection and taxonomic diversity in passerine birds. Proc. R. Soc. Lond. B 259, 211-2155. Owens, I.P.F., Bennett, P.M., and Harvey, P.H. (1999). Species richness among birds: body size, life history, sexual selection or ecology?. Proc. R. Soc. Lond. B 266, 933-939
ON HABITATS AND ECOLOGICAL SPECIATION.
The following points are made by R. Ogden and R.S. Thorpe (Proc. Nat. Acad. Sci. 2002 99: 13612):1) Understanding speciation processes in rainforests is key to predicting changes in species number and planning conservation strategy (1). Ecological speciation due to divergent natural selection has emerged as an alternative theory to speciation in geographic isolation. Recent studies in support of an ecological gradient model of speciation in rainforests have shown morphological differences between habitats but have not tested for a reduction in gene flow (2,3) or have not reported such a reduction where it has been tested (3,4). Morphological variation along ecological gradients may indicate diversification, but speciation is not an inevitable consequence of population differentiation (5), and molecular evidence of reduced gene flow is needed to strengthen support for the theory of ecological speciation.2) The authors report a study in which molecular markers were used to examine the effects of allopatric divergence and habitat on levels of gene flow in the Caribbean lizard Anolis roquet. Three study transects were constructed to compare variation in microsatellite allele frequencies and morphology across phylogenetic and habitat boundaries in northern Martinique. Results showed reductions in gene flow to be concordant with divergent selection for habitat type. No evidence could be found for divergence in allopatry influencing current gene flow. Morphological data match these findings, with multivariate analysis showing correlation with habitat type but no grouping by phylogenetic lineage. The results support the ecological speciation model of evolutionary divergence, indicating the importance of habitats in biodiversity generation.References (abridged):1. Moritz, C. , Patton, J. L. , Schneider, C. J. & Smith, T. B. (2000) Annu. Rev. Ecol. Syst. 31, 533-5632. Schneider, C. J. , Smith, T. B. , Larison, B. & Moritz, C. (1999) Proc. Natl. Acad. Sci. USA 96, 13869-138733. Smith, T. B. , Schneider, C. J. & Holder, K. (2001) Genetica 112, 383-3984. Smith, T. B. , Wayne, R. K. , Girman, D. J. & Bruford, M. W. (1997) Science 276, 1855-18575. Magurran, A. E. (1998) Philos. Trans. R. Soc. London B 353, 275-286Proc. Nat. Acad. Sci.
HYBRIDS AND SPECIATION
The following points are made by Richard J. Abbott (Science 2003 301:1189):1) Why sex evolved and is maintained in most living organisms remains a key question in evolutionary biology (1). What is indisputable, however, is that sexual reproduction generates new gene combinations, some of which may render the organism better adapted to new environments. The range of different genotypes among offspring increases with the level of genetic divergence between parents. Therefore, matings between different species (that is, interspecific hybridization could potentially generate a vast range of different offspring genotypes, provided that the resulting hybrid zygotes develop and exhibit some fertility. For example, Rieseberg et al (2) describe how hybridization between two sunflower species generated offspring genotypes that are adapted to habitats very different from those occupied by the parents. This resulted in three diploid hybrid sunflower species that are ecologically isolated from each other and their progenitors. The Rieseberg et al findings provide proof that interspecific hybridization can be adaptive.2) In many plant groups, hybridization between different species is prevented by prezygotic barriers. Such barriers may arise when species have their own specific pollinator, occupy a habitat different from other species, or are spatially separate from other species. Under these conditions, postzygotic barriers manifested in the form of embryo abortion or low hybrid viability may be absent or weak. However, prezygotic barriers can be "leaky", especially when habitats are disturbed in some way, so hybrids are sometimes produced that are often sterile or exhibit reduced fertility. Such problems of low fertility can be overcome, either by chromosome doubling (allopolyploidy) or recombination (3), to produce a stable fertile hybrid that is reproductively isolated from its parents by a strong postzygotic barrier (4,5), and which is therefore regarded as a new species.3) Although postzygotic barriers are effective mechanisms of reproductive isolation, they present major obstacles to the establishment of a new hybrid species in the wild. Hybrids are born into populations comprising one or both parent species and will initially be represented as a minority component. Consequently, most matings by a fertile hybrid will be with a parent rather than another hybrid, and will result in the production of no offspring or sterile offspring. The hybrid therefore suffers from what is termed a "minority type disadvantage" (4). It can escape from this predicament by evolving a prezygotic barrier that prevents it from mating with its parents. This can be achieved through uniparental reproduction (asexual reproduction or selfing), by flowering earlier or later, by attracting a different pollinator, by occupying a different habitat (ecological isolation), or through spatial isolation due to geographical separation after dispersal (3). Ecological or spatial isolation will also enable a hybrid to avoid any adverse effects of interspecific competition with a parent.References (abridged):1. S. A. West et al., J. Evol. Biol. 12, 1003 (1999)2. L. H. Rieseberg et al. Science 301, 1211 (2003)3. V. Grant, Plant Speciation (Columbia Univ. Press, New York, ed. 2, 1981) 4. D. A. Levin, The Role of Chromosomal Change in Plant Evolution (Oxford Univ. Press, Oxford, 2002)5. J. F. Gutierrez-Marcos et al., Philos. Trans. R. Soc. London Ser. B 358, 1105 (2003)
The article below has some insights on mechanisms involved in speciation. The high biodiversity of cichlid fishes in great Lake of Malawi is one of the many examples of organisms that have appreciated this mechanisms and produced the unspoken wonders of the world.
Just get a dive in rocky habitats of Cape Maclear, Nkhata Bay, Likoma and Monkey Bay just to mention a few localities and you will appreciate what we are trying to communicate here.
Do not say I did not tell you.
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SEXUAL SELECTION AND SPECIATION
The following points are made by K. Kraaijeveld and A. Pomiankowski (Current Biology 2004 14:R419):1) When Charles Darwin (1809-1882) [1] proposed his theory of sexual selection he was concerned mainly with explaining the widespread occurrence of exaggerated sexual ornaments and courtship displays, as these traits could not easily be explained by natural selection. He also noted that taxonomic groups with more pronounced sexual ornaments tended to have more species. This suggests that sexual selection may elevate the rate at which populations diversify and give rise to new species. A new study [2] of female mate preferences in five populations of an East African cichlid species strongly supports the connection between sexual selection and speciation.2) With the surge of interest in sexual selection over the past few decades, the question of whether it can lead to speciation has also enjoyed renewed attention. A plethora of theoretical models have investigated the connection, and generally concluded that sexual selection can promote speciation (3). The main evolutionary mechanism proposed invokes the rapid coevolution of female mate preferences and male courtship traits, leading to reproductive isolation between groups of individuals. However, empirical evidence in support of the idea is scarce.3) An indirect way this idea has been tested involves looking across broad taxonomic groups for a link between the strength of sexual selection and species number. So far, the evidence from these studies has been conflicting. In birds for example, taxa with greater sexual differences in plumage color -- an indicator of sexual selection -- have higher species numbers compared to sister taxa subject to weaker sexual selection [4,5]. However, surveys in other groups (butterflies, mammals, and spiders) have failed to find such an association, and the positive result in birds has not been replicated in a recent reanalysis. It seems premature to conclude from this that speciation is independent of sexual selection. One reason for the lack of a strong linkage is that sexual selection may promote extinction as well as speciation, if it leads to the evolution of traits maladaptive to male and female survival. Another is that sexual selection can even retard speciation under certain conditions. So in the long term, species numbers may only loosely be connected to sexual selection.4) A more direct way of investigating the connection between sexual selection and speciation is to examine its action in closely related populations. Knight and Turner [2] attempted such a test using populations of the cichlid fish Pseudotropheus zebra from Lake Malawi. The cichlid fishes of the East African lakes, in particular Lake Victoria and Lake Malawi, are renowned for rampant speciation over a very brief period of time -- more than 1000 species have been generated in less than a million years. Some of this diversity is due to ecological specialization, facilitated by the "key innovation" of the cichlid pharyngeal jaw. But many closely related species show practically no differences except in male color, suggesting that sexual selection may be an important additional mechanism of speciation.
References (abridged):1. Darwin, C.R. (1871). The Descent of Man and Selection in Relation to Sex. (London: John Murray)2. Knight, M.E. and Turner, G.F. (2004). Laboratory mating trials indicate incipient speciation by sexual selection among populations of the cichlid fish Pseudotropheus zebra from Lake Malawi. Proc. R. Soc. Lond. B 271, 675-6803. Turelli, M., Barton, N.H., and Coyne, J.A. (2001). Theory and speciation. Trends Ecol. Evol. 16, 330-3434. Barraclough, T.G., Harvey, P.H., and Nee, S. (1995). Sexual selection and taxonomic diversity in passerine birds. Proc. R. Soc. Lond. B 259, 211-2155. Owens, I.P.F., Bennett, P.M., and Harvey, P.H. (1999). Species richness among birds: body size, life history, sexual selection or ecology?. Proc. R. Soc. Lond. B 266, 933-939
ON HABITATS AND ECOLOGICAL SPECIATION.
The following points are made by R. Ogden and R.S. Thorpe (Proc. Nat. Acad. Sci. 2002 99: 13612):1) Understanding speciation processes in rainforests is key to predicting changes in species number and planning conservation strategy (1). Ecological speciation due to divergent natural selection has emerged as an alternative theory to speciation in geographic isolation. Recent studies in support of an ecological gradient model of speciation in rainforests have shown morphological differences between habitats but have not tested for a reduction in gene flow (2,3) or have not reported such a reduction where it has been tested (3,4). Morphological variation along ecological gradients may indicate diversification, but speciation is not an inevitable consequence of population differentiation (5), and molecular evidence of reduced gene flow is needed to strengthen support for the theory of ecological speciation.2) The authors report a study in which molecular markers were used to examine the effects of allopatric divergence and habitat on levels of gene flow in the Caribbean lizard Anolis roquet. Three study transects were constructed to compare variation in microsatellite allele frequencies and morphology across phylogenetic and habitat boundaries in northern Martinique. Results showed reductions in gene flow to be concordant with divergent selection for habitat type. No evidence could be found for divergence in allopatry influencing current gene flow. Morphological data match these findings, with multivariate analysis showing correlation with habitat type but no grouping by phylogenetic lineage. The results support the ecological speciation model of evolutionary divergence, indicating the importance of habitats in biodiversity generation.References (abridged):1. Moritz, C. , Patton, J. L. , Schneider, C. J. & Smith, T. B. (2000) Annu. Rev. Ecol. Syst. 31, 533-5632. Schneider, C. J. , Smith, T. B. , Larison, B. & Moritz, C. (1999) Proc. Natl. Acad. Sci. USA 96, 13869-138733. Smith, T. B. , Schneider, C. J. & Holder, K. (2001) Genetica 112, 383-3984. Smith, T. B. , Wayne, R. K. , Girman, D. J. & Bruford, M. W. (1997) Science 276, 1855-18575. Magurran, A. E. (1998) Philos. Trans. R. Soc. London B 353, 275-286Proc. Nat. Acad. Sci.
HYBRIDS AND SPECIATION
The following points are made by Richard J. Abbott (Science 2003 301:1189):1) Why sex evolved and is maintained in most living organisms remains a key question in evolutionary biology (1). What is indisputable, however, is that sexual reproduction generates new gene combinations, some of which may render the organism better adapted to new environments. The range of different genotypes among offspring increases with the level of genetic divergence between parents. Therefore, matings between different species (that is, interspecific hybridization could potentially generate a vast range of different offspring genotypes, provided that the resulting hybrid zygotes develop and exhibit some fertility. For example, Rieseberg et al (2) describe how hybridization between two sunflower species generated offspring genotypes that are adapted to habitats very different from those occupied by the parents. This resulted in three diploid hybrid sunflower species that are ecologically isolated from each other and their progenitors. The Rieseberg et al findings provide proof that interspecific hybridization can be adaptive.2) In many plant groups, hybridization between different species is prevented by prezygotic barriers. Such barriers may arise when species have their own specific pollinator, occupy a habitat different from other species, or are spatially separate from other species. Under these conditions, postzygotic barriers manifested in the form of embryo abortion or low hybrid viability may be absent or weak. However, prezygotic barriers can be "leaky", especially when habitats are disturbed in some way, so hybrids are sometimes produced that are often sterile or exhibit reduced fertility. Such problems of low fertility can be overcome, either by chromosome doubling (allopolyploidy) or recombination (3), to produce a stable fertile hybrid that is reproductively isolated from its parents by a strong postzygotic barrier (4,5), and which is therefore regarded as a new species.3) Although postzygotic barriers are effective mechanisms of reproductive isolation, they present major obstacles to the establishment of a new hybrid species in the wild. Hybrids are born into populations comprising one or both parent species and will initially be represented as a minority component. Consequently, most matings by a fertile hybrid will be with a parent rather than another hybrid, and will result in the production of no offspring or sterile offspring. The hybrid therefore suffers from what is termed a "minority type disadvantage" (4). It can escape from this predicament by evolving a prezygotic barrier that prevents it from mating with its parents. This can be achieved through uniparental reproduction (asexual reproduction or selfing), by flowering earlier or later, by attracting a different pollinator, by occupying a different habitat (ecological isolation), or through spatial isolation due to geographical separation after dispersal (3). Ecological or spatial isolation will also enable a hybrid to avoid any adverse effects of interspecific competition with a parent.References (abridged):1. S. A. West et al., J. Evol. Biol. 12, 1003 (1999)2. L. H. Rieseberg et al. Science 301, 1211 (2003)3. V. Grant, Plant Speciation (Columbia Univ. Press, New York, ed. 2, 1981) 4. D. A. Levin, The Role of Chromosomal Change in Plant Evolution (Oxford Univ. Press, Oxford, 2002)5. J. F. Gutierrez-Marcos et al., Philos. Trans. R. Soc. London Ser. B 358, 1105 (2003)
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