— Archaeologists find new evidence of animals being introduced to prehistoric Caribbean — An archaeological research team from North Carolina State University, the University of Washington and University of Florida has found one of the most diverse collections of prehistoric…
— Microscopic worms could hold the key to living life on Mars — The astrophysicist Stephen Hawking believes that if humanity is to survive we will have up sticks and colonise space. But is the human body up to the challenge?…
— Chemical warfare of stealthy silverfish — A co-evolutionary arms race exists between social insects and their parasites. Army ants (Leptogenys distinguenda) share their nests with several parasites such as beetles, snails and…
— Stinky frogs are a treasure trove of antibiotic substances — Some of the nastiest smelling creatures on Earth have skin that produces the greatest known variety of anti-bacterial substances that hold promise for becoming new weapons in the battle…
— Genetic code of first arachnid cracked — An international team of scientists - including Ghent VIB scientists - has succeeded in deciphering the genome of the spider mite. This is also the first known genome of an arachnid.…
— How bats 'hear' objects in their path — By placing real and virtual objects in the flight paths of bats, scientists at the Universities of Bristol and Munich have shed new light on how echolocation works. Their research is…
— Counting cats: The endangered snow leopards of the Himalayas — The elusive snow leopard (Panthera uncia) lives high in the mountains across Central Asia. Despite potentially living across 12 countries the actual numbers of this beautiful large…
— Surprise role of nuclear structure protein in development — Scientists have long held theories about the importance of proteins called B-type lamins in the process of embryonic stem cells replicating and differentiating into different varieties…
— Pregnancy is a drag for bottlenose dolphins — Lumbering around during the final weeks before delivery is tough for any pregnant mum. Most females adjust their movements to compensate for the extreme physical changes that accompany…
When animals evolve on islands, size does not matter
A theory explaining the evolution of giant rodents, miniature elephants, and even miniature humans on islands has been called into questions by new research published today in Proceedings of the Royal Society B: Biological Sciences.
The new study refutes the 'island rule' which says that in island environments small mammals such as rodents tend to evolve to be larger, and large mammals such as elephants tend to evolve to be smaller, with the original size of the species being the key determining factor in these changes.
The new research findings suggest that the tendency to either evolve larger or smaller on islands varies from one group of species to another, irrespective of original size. The research team, from Imperial College London, suspect instead that a number of external factors, including the physical environment of the particular island, the availability of prey, the presence of predators and the presence of competing species all play a role in determining the size evolution of island mammals. Dr Shai Meiri from the NERC Centre for Population Biology at Imperial College London, lead author on the paper, explains: 'If the island rule was correct, then most large mammals living on islands would be smaller than their continental relatives, and most small island mammals would be larger those living on continents. Our large dataset of mammal body sizes shows that this isn't the case: there is evidence that most mammal groups show no tendency to consistently either grow larger or smaller, in contradiction to the island rule.'
Dr Meiri, who carried out the work with Professor Andy Purvis and Natalie Cooper from the College's Department of Life Sciences, added: 'The island rule suggests that the smallest mammals such as mice will exhibit the most evolutionary growth on islands, whilst the largest mammals like elephants will dwarf the most, with all mammals in between on a sliding-scale.
'Our analyses showed this isn't the case, and the relationship between mammal size and evolutionary size change on islands is not that straightforward. Crucially, when we examined size change in light of the evolutionary relationship between different species, there was no connection between an evolution towards large size and greater degree of dwarfism on islands, or between evolution towards small size and island gigantism.'
The research team concluded that although there does appear to be a weak correlation between the size of a mammal and how its size then evolves in an island habitat, this reflects some groups' specific tendencies towards gigantism or dwarfism, and not the general course of evolution. 'The course of size evolution is dependent on a complex interplay of many other factors, that have led to the evolution of fascinating miniature and giant species of mammals on islands,' concludes Dr Meiri.
'The island rule: made to be broken?,' Proceedings of the Royal Society B: Biological Sciences, Wednesday 7 November 2007.
Or subscribe for our Newsletter, a free e-mail publication. It is published practically every day.
Normal vision but blind to light
New catfish species named after Frank Gallagher
New bacterial species is found trapped in 120,000-year-old ice
Researchers discover stinging truths about jellyfish blooms in the Bering Sea