Anolis Lizards of the Eastern Caribbean: A Case Study in Evolution. I. Genetic Relationships, Phylogeny, and Colonization Sequence of the Roquet Group

Abstract

Yang, S. Y., M. Soule (Biol. Dept., UCSD, La Jolla, California, 92037), and G. C. Gorman (Biol. Dept., UCLA, Los Angeles, California, 90024) 1974. Anolis lizards of the eastern Caribbean: a case study in evolution. I. Genetic relationships, phylogeny, and colonization sequence of the roquet group. Syst. Zool. 23:387-399.-A phylogeny based upon genetic similarity coupled with information from cytogenetics, behavior, ecological distribution, and geography is developed for the roquet group of Anolis lizards in the southeastern Caribbean region. We postulate that the primary events were stepwise colonization of the three island banks closest to the South American mainland (Grenada, St. Vincent, and St. Lucia). The secondary events were colonization from St. Lucia to the more westerly islands of Blanquilla, and from there to Bonaire; the acquisition of a second on St. Vincent by in situ speciation or by secondary colonization; the colonization of Martinique, Barbados, and the Grenada Bank (the latter for the second time). [Anolis; genetic relationships; phylogeny; colonization.] This paper is an attempt to reconstruct the phylogeny and colonization sequence of a group of insular lizards. The data are genetic similarity estimates for more than 20 loci detected by electrophoresis of water soluble proteins. The results are integrated with information obtained by a variety of approaches during the past decade. Later papers in this series will use the phylogeny herein propounded to help test and develop a general theory of island evolution. Our study is of the Anolis roquet group (Sauria, Iguanidae). The genus is very large (over 200 species); the group under study is well defined osteologically, cytologically, behaviorally, and ecologically. Furthermore, it occupies a discrete set of islands in the southeastern Caribbean region (Fig. 1), a region where no other group of Anolis is represented. The arc of islands that sweeps north and westerly from the continental shelf of South America to the large Antillean island of Puerto Rico is known as the Lesser Antilles. 'Present address: Museum of Vertebrate Zoology, University of California, Berkeley, California. Our area of concern is the southern Lesser Antilles and the islands of Bonaire and Blanquilla, far to the west of the main chain. There are nine species1 in the roquet group distributed on the seven island banks shown in Fig. 1. Each of these banks has endemic forms exclusively. The evolutionary history that we are analyzing is clearly one of sequential colonization between these islands, with presumably little or no input from the mainland following the original colonization, and little or no speciation within an island bank (Gorman and Atkins, 1969). Thorough understanding of the physical geography and geological history of the study area would certainly aid in understanding the evolution of the organisms. We would like to know the maximum ages 1 To avoid semantic problems we are arbitrarily permitting the island bank to define the taxa at the level of species. This seems preferable to the alternative of agonizing over such non-operational criteria as potential fertility of animals on different islands. Admittedly, some of the species are so closely related that they would be referred to as races or subspecies if connecting populations existed.