ScienceDaily (Feb. 22, 2010) — New research on lizards supports an old idea about how species can originate. Morphologically distinct types are often found within species, and biologists have speculated that these "morphs" could be the raw material for speciation. What were once different types of individuals within the same population could eventually evolve into separate species.
Side-blotched lizards have three color morphs with different mating strategies, but in some populations only one morph occurs. This male lizard is from an all-orange population. (Credit: Photo by Ammon Corl)
A new study conducted by researchers at the University of California, Santa Cruz, supports this idea. The study documents the disappearance of certain morphs of the side-blotched lizard in some populations. The researchers reported their findings in a paper published February 17 in the online early edition of Proceedings of the National Academy of Sciences(PNAS).
The side-blotched lizard, Uta stansburiana, has three morphs differing in color and mating behavior. Barry Sinervo, a professor of ecology and evolutionary biology at UCSC, has studied a population of side-blotched lizards near Los Baños, Calif., for over 20 years. Ammon Corl, now a postdoctoral researcher at Uppsala University in Sweden, led the new study as a graduate student at UCSC and is first author of the paper.
Previous work by Sinervo and his colleagues showed that competition among male side-blotched lizards takes the form of a rock-paper-scissors game in which each mating strategy beats and is beaten by one other strategy. Males with orange throats can take territory from blue-throated males because they have more testosterone and body mass. As a result, orange males control large territories containing many females. Blue-throated males cooperate with each other to defend territories and closely guard females, so they are able to beat the sneaking strategy of yellow-throated males. Yellow-throated males are not territorial, but mimic female behavior and coloration to sneak onto the large territories of orange males to mate with females.
"My goal when starting my Ph.D. thesis research was to understand how this fascinating mating system evolved," Corl said. "We studied lizard populations from California to Texas and from Washington State down to Baja California Sur in Mexico."
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Selective loss of polymorphic mating types is associated with rapid phenotypic evolution during morphic speciation
Ammon Corl1,2, Alison R. Davis3, Shawn R. Kuchta4, and Barry Sinervo
-Author Affiliations
Department of Ecology and Evolutionary Biology, EMS A316, University of California, Santa Cruz, CA 95064
↵2Present address: Department of Evolutionary Biology, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden.
↵3Present address: Museum of Vertebrate Zoology, University of California, Berkeley, 3101 Valley Life Sciences Building, Berkeley, CA 94720.
↵4Present address: Dartmouth College, Department of Biological Sciences, Gilman Hall, Hanover, NH 03755.
Edited by David B. Wake, University of California, Berkeley, CA, and approved January 11, 2010 (received for review August 21, 2009)
Abstract
Polymorphism may play an important role in speciation because new species could originate from the distinctive morphs observed in polymorphic populations. However, much remains to be understood about the process by which morphs found new species. To detail the steps of this mode of speciation, we studied the geographic variation and evolutionary history of a throat color polymorphism that distinguishes the “rock-paper-scissors” mating strategies of the side-blotched lizard, Uta stansburiana. We found that the polymorphism is geographically widespread and has been maintained for millions of years. However, there are many populations with reduced numbers of throat color morphs. Phylogenetic reconstruction showed that the polymorphism is ancestral, but it has been independently lost eight times, often giving rise to morphologically distinct subspecies/species. Changes to the polymorphism likely involved selection because the allele for one particular male strategy, the “sneaker” morph, has been lost in all cases. Polymorphism loss was associated with accelerated evolution of male size, female size, and sexual dimorphism, which suggests that polymorphism loss can promote rapid divergence among populations and aid species formation.
lizard morph phylogeny rock-paper-scissors Uta stansburiana
Footnotes
1To whom correspondence should be addressed. E-mail:corl@biology.ucsc.edu.
Author contributions: A.C. and B.S. designed research; A.C., A.R.D., S.R.K., and B.S. performed research; A.C. analyzed data; and A.C. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0909480107/DCSupplemental.
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