Lizards Undergo Rapid Evolution after Introduction to a New Home

April 17, 2008

In 1971, biologists moved five adult pairs of Italian wall lizards from their home island of Pod Kopiste, in the South Adriatic Sea, to the neighboring island of Pod Mrcaru. Now, an international team of researchers has shown that introducing these small, green-backed lizards, Podarcis sicula, to a new environment caused them to undergo rapid and large-scale evolutionary changes.

“Striking differences in head size and shape, increased bite strength and the development of new structures in the lizard’s digestive tracts were noted after only 36 years, which is an extremely short time scale,” says Duncan Irschick, a professor of biology at the University of Massachusetts Amherst. “These physical changes have occurred side-by-side with dramatic changes in population density and social structure.” Results of the study were published March 25 in Proceedings of the National Academy of Sciences.

Researchers returned to the islands twice a year for three years, in the spring and summer of 2004, 2005 and 2006. Captured lizards were transported to a field laboratory and measured for snout-vent length, head dimensions and body mass. Tail clips taken for DNA analysis confirmed that the Pod Mrcaru lizards were genetically identical to the source population on Pod Kopiste.

Observed changes in head morphology were caused by adaptation to a different food source. According to Irschick, lizards on the barren island of Pod Kopiste were well-suited to catching mobile prey, feasting mainly on insects. Life on Pod Mrcaru, where they had never lived before, offered them an abundant supply of plant foods, including the leaves and stems from native shrubs. Analysis of the stomach contents of lizards on Pod Mrcaru showed that their diet included up to two-thirds plants, depending on the season, a large increase over the population of Pod Kopiste.

“As a result, individuals on Pod Mrcaru have heads that are longer, wider and taller than those on Pod Kopiste, which translates into a big increase in bite force,” says Irschick. “Because plants are tough and fibrous, high bite forces allow the lizards to crop smaller pieces from plants, which can help them break down the indigestible cell walls.”

Examination of the lizard’s digestive tracts revealed something even more surprising. Eating more plants caused the development of new structures called cecal valves, designed to slow the passage of food by creating fermentation chambers in the gut, where microbes can break down the difficult to digest portion of plants. Cecal valves, which were found in hatchlings, juveniles and adults on Pod Mrcaru, have never been reported for this species, including the source population on Pod Kopiste.

“These structures actually occur in less than 1 percent of all known species of scaled reptiles,” says Irschick. “Our data shows that evolution of novel structures can occur on extremely short time scales. Cecal valve evolution probably went hand-in-hand with a novel association between the lizards on Pod Mrcaru and microorganisms called nematodes that break down cellulose, which were found in their hindguts.”

Change in diet also affected the population density and social structure of the Pod Mrcaru population. Because plants provide a larger and more predictable food supply, there were more lizards in a given area on Pod Mrcaru. Food was obtained through browsing rather than the active pursuit of prey, and the lizards had given up defending territories.

“What is unique about this finding is that rapid evolution can affect not only the structure and function of a species, but also influence behavioral ecology and natural history,” says Irschick.

Source: University of Massachusetts Amherst

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1 / 5 (4) Apr 18, 2008
No mention is made of the native lizards, and that the changes might be due to breeding between the two.
Eating more plants caused the development of new structures called cecal valves

Did the native lizards have these valves? If so then this statement is pure fabrication. Try giving the whole story for once!

5 / 5 (2) Apr 18, 2008
"Tail clips taken for DNA analysis confirmed that the Pod Mrcaru lizards were genetically identical to the source population on Pod Kopiste."

What part of this isn't clear?
3 / 5 (2) Apr 18, 2008
DGBEACH - since you obviously skimmed this piece, let me answer your 2nd question, quoting the article:
"Cecal valves, which were found in hatchlings, juveniles and adults on Pod Mrcaru, have never been reported for this species, including the source population on Pod Kopiste."
4 / 5 (2) Apr 18, 2008
What is interesting to me: these lizards are identical in DNA yet show physical differences. It makes me wonder if these attributes are available in both the source population and the Pod Mrcaru population. The environment allowed these characteristics to show. (btw, the article states that the environment 'caused' changes. I beleive a more evolutionary term would be 'allowed' or even 'favored')
4 / 5 (1) Apr 18, 2008
Indeed I skimmed over too quickly...apologies. oye
2 / 5 (3) Apr 18, 2008
The statement about being genetically identical is obviously an error. They meant to say that the Pod Mrcaru lizards are most genetically similar to the Pod Kopiste lizards. In fact they may be almost genetically identical except for the few mutations that lead to the morphological changes noted in the article.
4 / 5 (1) Jul 16, 2008
1. How much DNA did they test? Probably just a few genes, as they do for DNA tests with people. It'd be too much work to sequence the whole lizard genome for one study.

2. It's possible for two lizards to be genetically identical in every aspect but still be phenotypically different. Different genes might be epigenetically expressed. If the lizard's ancestors had cecal valves but the genes for such valves had been silenced, the genes could be 'turned back on.' Whales sometimes exhibit vestigial legs in a similar fashion.

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