Evolution
Published by: The Society for the Study of Evolution
Evolution 60(2):362-369. 2006
doi: http://dx.doi.org/10.1554/05-314.1
SHARED AND UNIQUE FEATURES OF DIVERSIFICATION IN GREATER ANTILLEAN ANOLIS ECOMORPHS
R. Brian Langerhansab, Jason H. Knouftc, Jonathan B. Lososa
aDepartment of Biology, Washington University, St. Louis, Missouri 63130-4899
cDepartment of Ecology and Evolutionary Biology and University of Colorado Museum, University of Colorado, Boulder, Colorado 80309-0265
Abstract
Examples of convergent evolution suggest that natural selection can often produce predictable evolutionary outcomes. However, unique histories among species can lead to divergent evolution regardless of their shared selective pressures—and some contend that such historical contingencies produce the dominant features of evolution. A classic example of convergent evolution is the set of Anolis lizard ecomorphs of the Greater Antilles. On each of four islands, anole species partition the structural habitat into at least four categories, exhibiting similar morphologies within each category. We assessed the relative importance of shared selection due to habitat similarity, unique island histories, and unique effects of similar habitats on different islands in the generation of morphological variation in anole ecomorphs. We found that shared features of diversification across habitats were of greatest importance, but island effects on morphology (reflecting either island effects per se or phylogenetic relationships) and unique aspects of habitat diversification on different islands were also important. There were three distinct cases of island-specific habitat diversification, and only one was confounded by phylogenetic relatedness. The other two unique aspects were not related to shared ancestry but might reflect as-yet-unmeasured environmental differences between islands in habitat characteristics. Quantifying the relative importance of shared and unique responses to similar selective regimes provides a more complete understanding of phenotypic diversification, even in this much-studied system.
C. Benkman
Received: June 9, 2005; Accepted: November 21, 2005
Keywords: Adaptive radiation, Anolis, convergent evolution, diversification, ecomorphology, historical contingency, morphometrics, natural selection
Literature Cited
Fig. 1. Phylogeny of Anolis used in the study. Island of origin and ecomorph category are given for each species. Numbers represent Bayesian posterior probabilities for each node in the pruned tree topology. Branch lengths are relative, with the distance from the root to the tips arbitrarily set to 100 units
Fig. 2. Morphological variation along the first two canonical axes derived from the interaction term (habitat × island) of the MANOVA. Convex polygons (dashed lines) delineate each ecomorph category. Highlighted unique effects represent the three distinct cases identified by the interaction term. Symbols as in Figure 1
Table 1. Results of MANOVA examining morphological variation among 27 species of Greater Antillean Anolis lizards. F-ratios were approximated using Wilks's Λ values. Partial variance explained by each effect was estimated using Wilks's partial η2. Values marked with an asterisk remained significant after accounting for phylogenetic relationships
Table 2. Significance of association between anole morphology and the following factors, controlling for phylogenetic relationships (patristic distance)
Appendix Standardized canonical coefficients for each morphological variable, corresponding to canonical axes derived from each factor of the MANOVA (HD, head depth; JL, jaw length; JW, jaw width; TPW, toe pad width; LN, lamellae number; HL, hindlimb length; FL, forelimb length; PEL, pelvic width; PEC, pectoral width). These coefficients depict the standardized contribution of each morphological trait on each axis, controlling for all other traits. While nine canonical axes were derived for the interaction term, the first three axes captured most of the significant unique features of diversification; thus, we only present results from these three axes. Group differences represent the rank order of species groups relevant to each canonical axis (CG, crown-giant; TC, trunk-crown; TG, trunk-ground; TW, twig; C, Cuba; H, Hispaniola; J, Jamaica; P, Puerto Rico). Bars above groups indicate groups that are not significantly different from each other using Tukey's HSD test
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