Just when you thought evolution couldn't get attacked by anyone else, a zoologist writing in Science and his colleagues are contending that changing winter conditions due to global warming are causing Scotland's wild Soay sheep to get smaller despite the evolutionary benefits of having a large body. Yep, climate change can trump natural selection, it turns out.
So much for adapting to the environment. Too bad Darwin didn't know about CO2.
"Sheep are getting smaller. Well, at least the wild Soay sheep living on a remote Scottish island are. But according to classic evolutionary theory, they should have been getting bigger, because larger sheep tend to be more likely to survive and reproduce than smaller ones, and offspring tend to resemble their parents," said study author Tim Coulson, professor of population biology at Imperial College London who teaches courses in ecology, evolution and conservation.
"Our findings have solved a paradox that has tormented biologists for years – why predictions did not match observation. Biologists have realized that ecological and evolutionary processes are intricately intertwined, and they now have a way of dissecting out the contribution of each. Unfortunately it is too early to tell whether a warming world will lead to pocket-sized sheep," Coulson said.
Coulson and his colleagues analyzed body-weight measurements and life-history data (which record the timing of key milestones throughout an individual's life), for the female members of a population of Soay sheep. The sheep live on the island of Hirta in the St. Kilda archipelago and have been studied closely since 1985.
The researchers plugged their data into a numerical model that they say predicts how a trait such as body size will change over time due to natural selection and other factors that influence survival and reproduction in the wild. They selected body size because it is a heritable trait, and because the sheep have, on average, been decreasing in size for the last 25 years.
Their results lead them to state that the decrease is primarily an ecological response to environmental variation over the last 25 years. Evolutionary change has contributed relatively little.
More specifically, lambs are not growing as quickly as they once did. As winters have become shorter and milder, due to global climate change, lambs now do not need to put on as much as weight in the first months of life to survive to their first birthday. So, even the slower-growing ones now have a chance of surviving, according to Coulson.
Also contributing to this trend is what Coulson and his colleagues call the "young mum effect." The researchers found that younger mothers are physically unable to produce offspring that are as big as they were at birth. The reasons behind this are still unclear, but the young mum effect counters the effect of natural selection, which favors larger lambs, the authors report.
Article: Arpat Ozgul , Shripad Tuljapurkar, Tim G. Benton, Josephine M. Pemberton, Tim H. Clutton-Brock, Tim Coulson, 'The Dynamics of Phenotypic Change and the Shrinking Sheep of St. Kilda', Published Online July 2, 2009 Science DOI: 10.1126/science.1173668
This research was funded by the Natural Environment Research Council and the National Institute on Aging, NIH.
So much for adapting to the environment. Too bad Darwin didn't know about CO2.
"Sheep are getting smaller. Well, at least the wild Soay sheep living on a remote Scottish island are. But according to classic evolutionary theory, they should have been getting bigger, because larger sheep tend to be more likely to survive and reproduce than smaller ones, and offspring tend to resemble their parents," said study author Tim Coulson, professor of population biology at Imperial College London who teaches courses in ecology, evolution and conservation.
"Our findings have solved a paradox that has tormented biologists for years – why predictions did not match observation. Biologists have realized that ecological and evolutionary processes are intricately intertwined, and they now have a way of dissecting out the contribution of each. Unfortunately it is too early to tell whether a warming world will lead to pocket-sized sheep," Coulson said.
Coulson and his colleagues analyzed body-weight measurements and life-history data (which record the timing of key milestones throughout an individual's life), for the female members of a population of Soay sheep. The sheep live on the island of Hirta in the St. Kilda archipelago and have been studied closely since 1985.
The researchers plugged their data into a numerical model that they say predicts how a trait such as body size will change over time due to natural selection and other factors that influence survival and reproduction in the wild. They selected body size because it is a heritable trait, and because the sheep have, on average, been decreasing in size for the last 25 years.
Their results lead them to state that the decrease is primarily an ecological response to environmental variation over the last 25 years. Evolutionary change has contributed relatively little.
More specifically, lambs are not growing as quickly as they once did. As winters have become shorter and milder, due to global climate change, lambs now do not need to put on as much as weight in the first months of life to survive to their first birthday. So, even the slower-growing ones now have a chance of surviving, according to Coulson.
Also contributing to this trend is what Coulson and his colleagues call the "young mum effect." The researchers found that younger mothers are physically unable to produce offspring that are as big as they were at birth. The reasons behind this are still unclear, but the young mum effect counters the effect of natural selection, which favors larger lambs, the authors report.
Article: Arpat Ozgul , Shripad Tuljapurkar, Tim G. Benton, Josephine M. Pemberton, Tim H. Clutton-Brock, Tim Coulson, 'The Dynamics of Phenotypic Change and the Shrinking Sheep of St. Kilda', Published Online July 2, 2009 Science DOI: 10.1126/science.1173668
This research was funded by the Natural Environment Research Council and the National Institute on Aging, NIH.
1) First, why even bother to study the growth rate of Soay Sheep. I'm all for science, but sometimes I wonder what these studies are for and how much money they spend that could go towards much more beneficial research. I'm sure there's some federal grant money involved in this, happy to see my tax dollars at work.
2) Climate change isn't "trumping" natural selection, it IS natural selection. This is a crazy statement for a scientist to make really. natural selection includes all factors in nature, including climate. While the cause of the temperature change may be in dispute (_possibly_ caused by human activity) this is irrelevant to his argument. The sheep are reacting to their environment, just as natural selection theorizes. "So much for adapting to the environment." - so what are they doing if not 'adapting to the environment'???
3) Saying their predictions don't match observations is a "paradox" is a bit of an overstatement. My guess is 80% of the predictions of species development don't match observations, I'm pretty sure we're not at that level of sophistication yet.
4) "Biologists have realized that ecological and evolutionary processes are intricately intertwined, and they now have a way of dissecting out the contribution of each." - I'm not a biologist, so chime in if you are, but do they really think their dissection process is infallible? again, I'm pretty sure we're not there yet. And let's not even comment on the "pocket sized sheep". Can I get some of this grant money?
5) "the young mum effect" - this guy seems to be witnessing natural selection in action, admits the reasons for this effect are unclear, and still, paradoxically, states that this effect "counters" the effect of natural selection.
This wouldn't be so bad if it wasn't being repeated on BBC on the hour.
- Confused.