June 11, 2014
Two Venomous Snakes That Evolved Separately Are Strikingly Similar
Gerard LeBlond for www.redorbit.com - Your Universe Online
North American and Australian snakes evolved independently, but into similar body types over millions of years. These snakes are stout-bodied and highly camouflaged, which help them move and ambush prey more efficiently. As well, these rattlesnakes of North America and death adders of Australia are slender, fast-moving burrowers.A phenomenon called convergence is where two species evolve independently, but feature similar body forms in response to ecological conditions. Although the snakes are similar in appearance, a new study shows that look-alike snakes on two different continents differ in one major characteristic: their diet.
The paper’s authors are Michael Grundler and co-author Daniel Rabosky, both from the University of Michigan. Rabosky is an evolutionary biologist and Grundler is a doctoral student. They published the paper online, June 10 in the journal Proceedings of the Royal Society B.
“Most biologists tend to assume that convergence in body form for a group of organisms implies that they must be ecologically similar. But our study shows that there is almost no overlap in diet between many of the snakes that are morphologically very similar,” Rabosky explains.
There are at least seven distinct groups of advanced snakes in North America. One major group, the elapids, inhabited Australia around 12 million years ago. Elapids include king cobras, coral snakes, mambas and kraits. They have hollow, fixed fangs for injecting venom and are found worldwide.
Elapids from Australia evolved over millions of years in a process called adaptive radiation, splitting into about 100 different species of snakes, including some of the most venomous species -- taipans, brown snakes, death adders and tiger snakes. During this process, the Australian snakes evolved into similar body forms as the North American snakes.
For the study, Grundler and Rabosky compared the snakes by analyzing 786 specimens characterizing 248 different species from the University of Michigan Museum of Zoology, the Field Museum of Natural History and the Western Australian Museum.
“We found that the morphologies of Australia elapid snakes have evolved into the same types of body forms seen across a much more diverse set of snakes from North America. For example, Australia has the death adder, a stout-bodied ambush predator that looks, for all practical purposes, like a typical viper,” Grundler said.
“Vipers are a family of fanged, venomous snakes that includes pit vipers such as rattlesnakes, copperheads and bushmasters. But the death adder is not a viper and is in fact much more closely related to other Australian elapid snakes, most of which look nothing like vipers,” he added.
The two researchers studied literature on the feeding habits of snakes on both continents, which were placed into eight categories: invertebrates like insects, earthworms, mollusks and crustaceans; fish; amphibians; lizards and snakes; lizard and snake eggs; birds; bird eggs; and mammals.
The findings suggest the Australian and North American snakes are similar in appearance, but differ substantially in their diet. In North America, small snakes living in sand eat spiders, scorpions, slugs and centipedes, while the similar snake in Australia, mainly feeds on lizards and other snakes.
The authors believe the physical similarities are a reflection of evolutionary advantages for locomotion, foraging or habitat use.
LEARN MORE ABOUT SNAKES - National Audubon Society Field Guide to North American Reptiles and Amphibians