Showing papers by "Jonathan B. Losos published in 2003"

Tempo and Mode of Evolutionary Radiation in Iguanian Lizards

Abstract: Identification of general properties of evolutionary radiations has been hindered by the lack of a general statistical and phylogenetic approach applicable across diverse taxa. We present a comparative analytical framework for examining phylogenetic patterns of diversification and morphological disparity with data from four iguanian-lizard taxa that exhibit substantially different patterns of evolution. Taxa whose diversification occurred disproportionately early in their evolutionary history partition more of their morphological disparity among, rather than within, subclades. This inverse relationship between timing of diversification and morphological disparity within subclades may be a general feature that transcends the historically contingent properties of different evolutionary radiations.

Phylogenetic comparative methods and the geography of speciation

Abstract: The geography of speciation has long been contentious. In recent years, phylogenetic approaches have been proposed to determine the geographical mode of speciation. If reliable, these methods not only provide a means of settling the debate about the geography of speciation, but also indicate that sympatric speciation is surprisingly common and that peripatric speciation is relatively rare. Similar to any phylogenetic inference, reconstructions of speciation mode are only useful if the underlying assumptions of the method are met. In this case, the key assumption is that the geographical range of both extant and ancestral species at the time of speciation can be inferred from present-day distributions. We discuss whether, and under what circumstances, such assumptions could be met. We conclude that interspecific phylogenies are unable to test alternative hypotheses concerning the geography of speciation rigorously because of the lability of geographical ranges and the lack of correlation between the role of adaptive processes and geographical mode of speciation.

Niche lability in the evolution of a Caribbean lizard community

Abstract: Niche conservatism--the tendency for closely related species to be ecologically similar--is widespread. However, most studies compare closely related taxa that occur in allopatry; in sympatry, the stabilizing forces that promote niche conservatism, and thus inhibit niche shifts, may be countered by natural selection favouring ecological divergence to minimize the intensity of interspecific interactions. Consequently, the relative importance of niche conservatism versus niche divergence in determining community structure has received little attention. Here, we examine a tropical lizard community in which species have a long evolutionary history of ecological interaction. We find that evolutionary divergence overcomes niche conservatism: closely related species are no more ecologically similar than expected by random divergence and some distantly related species are ecologically similar, leading to a community in which the relationship between ecological similarity and phylogenetic relatedness is very weak. Despite this lack of niche conservatism, the ecological structuring of the community has a phylogenetic component: niche complementarity only occurs among distantly related species, which suggests that the strength of ecological interactions among species may be related to phylogeny, but it is not necessarily the most closely related species that interact most strongly.

Phylogenetic analysis of ecological and morphological diversification in Hispaniolan trunk-ground anoles (Anolis cybotes group).

Abstract: Anolis lizards in the Greater Antilles partition the structural microhabitats available at a given site into four to six distinct categories. Most microhabitat specialists, or ecomorphs, have evolved only once on each island, yet closely related species of the same ecomorph occur in different geographic macrohabitats across the island. The extent to which closely related species of the same ecomorph have diverged to adapt to different geographic macrohabitats is largely undocumented. On the island of Hispaniola, members of the Anolis cybotes species group belong to the trunk-ground ecomorph category. Despite evolutionary stability of their trunk-ground microhabitat, populations of the A. cybotes group have undergone an evolutionary radiation associated with geographically distinct macrohabitats. A combined phylogeographic and morphometric study of this group reveals a strong association between macrohabitat type and morphology independent of phylogeny. This association results from long-term morphological evolutionary stasis in populations associated with mesic-forest environments (A. c. cybotes and A. marcanoi) and predictable morphometric changes associated with entry into new macrohabitat types (i.e., xeric forests, high-altitude pine forest, rock outcrops). Phylogeographic analysis of 73 new mitochondrial DNA sequences (1921 aligned sites) sampled from 68 geographic populations representing 12 recognized species and subspecies diagnoses 16 allopatric or parapatric groupings of populations differing from each other by 5-18% sequence divergence. At least some of these groupings appear to have attained species-level divergence from others. Evolutionary specialization to different macrohabitat types may be a major factor in the evolutionary diversification of Greater Antillean anoles.

Ecomorphological Differences in Toepad Characteristics between Mainland and Island Anoles

Abstract: Anoles (Anolis, Chamaeleolis, Chamaelinorops, Phenacosaurus) differ greatly in size and shape of their subdigital toepads. We sampled 79 anole species to address two issues. First, is toepad size significantly related to habitat use? Second, do anoles from mainland Central and South America differ from Caribbean anoles in either the size of their toepads or in the relationship between toepad shape and habitat use? Among all anoles, toepad size increases with both perch height and diameter, although when the effects of body size are removed, these relationships are weakened. Morphological differences exist between toepads of anoles from the two regions. Caribbean anoles have larger toepads relative to snout–vent length and wider pads at larger body sizes compared to mainland species. Relationships between toepad morphology and habitat use characteristics do not differ significantly between the two groups of anoles. However, with effects of size removed, Caribbean anoles have larger and wider toepa...

Effect of immersion in seawater on egg survival in the lizard Anolis sagrei

Abstract: Studies on the lizard, Anolis sagrei, revealed that after Hurricane Floyd devastated the Bahamas in 1999, some populations consisted only of hatchlings. Because the storm surge of the hurricane completely inundated these islands, apparently for up to 6 h, survival of anole eggs in salt water for such periods is implied. To test this hypothesis directly, we placed A. sagrei eggs in saltwater for 3 or 6 h with unimmersed eggs serving as the control. Hatching success and incubation time did not differ among the three treatments. These findings help explain the persistence of anole populations on small islands vulnerable to hurricanes.