Thursday May 12, 2011
Scientists estimate that 17,800 years ago a new subspecies of western gorilla was born. Known today as the Cross River gorilla, this subspecies is one of two subspecies of western gorillas, the other being the western lowland gorilla.
The research team that conducted the study included Olaf Thalmann of the University of Turku in Finland and Linda Vigilant of the Max Planck Institute for Evolutionary Anthropology in Germany. They examined the DNA of living gorillas and museum specimens and found that although Cross River gorillas and western lowland gorillas diverged 17,800 years ago, they have experienced intergreeding periodically since that time.
The research team suggests that during the Pleistocene, fluctations in climate meant that western gorillas were isolated and reunited repeatedly. This cycle, which mirrored the shrinking and expansion of their forest habitat, meant that over time two subspecies of gorillas emerged. The study reveals that the last interbreeding between Cross River gorillas and western lowland gorillas occurred about 420 years ago.
Today, habitat destruction has further fragmented Cross River gorilla habitat. The overall population of Cross River gorillas is separated into about 9 different locations, thus creating subpopulations whose individuals interbreed or migrate between locations only on occasion.
Scientists hope that if these population fragments can be reunited, a threshold population can be maintained within the Cross River gorilla popoulation and extinction can be averted.
Cross River gorillas are among the world's most endangered primates. There are fewer than 300 individuals surviving in the wild. They inhabit isolated pockets of forest along the Cross River in Cameroon and Nigeria.
References
Thalmann, O., L. Vigilant et. al. (2011) Historical sampling reveals dramatic demographic changes in western gorilla populations. BMC Evolutionary Biology. 11:85 doi:10.1186/1471-2148-11-85
Photo © Nicky Lankester.
More About Primates
Wednesday May 4, 2011
Biologists studying the environmental effects of the Chernobyl nuclear disaster have discovered that birds with orange plumage were more affected by radiation than birds of different colors.
The research team, led by Ismael Galvan of the University of Paris-Sur in France, studied 97 species of birds from the Chernobyl area. They found that in general, as levels of radiation levels rose, bird populations declined. But the declines were not even distributed across birds of various plumage colors. Birds with orange and brown feathers (colors that result from the presence of the pigment pheomelanin) suffered more from the ill effects of radiation exposure than birds posessing other pigments.
The researchers concluded that the type of pigmentation a bird posesses may interfere with its ability to combat the negative effects of radioactivity.
The nuclear accident near the Ukrainian city of Chernobyl which took place on April 26, 1986 remains history's worst nuclear disaster. The disaster began when a systems test went awry and a series of power spikes caused an explosion which in turn started a fire. High levels of radioactive material escaped into the atmosphere and a radioactive plume drifted over the western Soviet Union and Europe.
References
Galván, I., Mousseau, T., & Møller, A. (2010) Bird population declines due to radiation exposure at Chernobyl are stronger in species with pheomelanin-based coloration. Oecologia, 165(4), 827-835. DOI: 10.1007/s00442-010-1860-5
Photo © Rafael Palomo Santana.
More About Birds
Monday April 25, 2011
On the Ile auz Aigrettes, a small island off the coast of Mauritius, conservationists have been testing out a controversial new way of putting the pieces of a broken ecosystem back together. The technique, called re-wilding, introduces non-native species to a region as ecological substitutes for native species that have gone extinct.
In 2000, Christine Griffiths of Bristol's School of Biological Sciences and her colleagues introduced Aldabra tortoises to Ile auz Aigrettes. Their hope was that the Aldabra tortoise might fill an ecological role left vacant on the island when native giant tortoises went extinct several decades ago.
When a species goes extinct, it leaves a void in the ecological community in which it lived. Rewilding aims to enable a substitute species to carry on its predicessor's role in the community. The technique is not universally accepted yet and has little evidence to support its value. Skeptics argue that such introductions often cause more trouble than good by disrupting a community, not stablizing it. But Christine Griffith's study reveals that such a conservation scenario can work.
By the early 1980s, the logging industry had decimated Ile auz Aigrettes' ebony forests and had driven the native giant tortoises to extinction. The tortoises had acted as seed dispersers for the ebony trees. When conservationists tried to restore the island's ebony forests, they failed. They needed a replacement seed disperser for the ebony trees to thrive. That's where the Aldabra tortiose comes in.
Like the native tortoises, the Aldabra tortoise is a fruit-eater. So when in 2000, scientists introduced Aldabra tortoises to Ile auz Aigrettes, the found that it took up the former duties of the native tortoises. The Aldabra tortoises ate the ebonly friut, dispsersed the seeds and fostered the widespread establishment of new ebony seedlings.
"Our results demonstrate that the introduction of these effective seed dispersers is aiding the recovery of this critically endangered tree whose seeds were previously seed-dispersal limited. Reversible rewilding experiments such as ours are necessary to investigate whether extinct interactions can be restored," said Chiristine Griffiths.
References
Griffiths, C., Hansen, D., Jones, C., Zuël, N., & Harris, S. (2011) Resurrecting Extinct Interactions with Extant Substitutes. Current Biology. DOI: 10.1016/j.cub.2011.03.042
Photo © Nik Cole. An Aldabra tortoise on Ile auz Aigrettes.
More About Reptiles
Wednesday April 20, 2011
Detecting forgeries isn't just the business of hand-writing experts and forgery sleuths. It turns out some bird species are highly skilled in detecting fraud as well. But for these birds, the forgeries they seek to thwart aren't bad checks or fake money but instead counterfeit eggs. And the forgers of these impostor eggs are laid by opportunistic birds, called brood parasites.
Brood parasites lay their eggs in the nests of host birds with the hope that the host birds will not notice the offending egg and will look after it as their own. Once hatched, a brood parasite chick grows quickly, often out-pacing the growth of host chicks. Brood parasites sometimes even eject the hosts' chicks or eggs from the nest in order to monopolize the host parents' care and attention.
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