Showing papers by "Jonathan B. Losos published in 2006"

Phylogenetic analysis of the evolution of the niche in lizards of the anolis sagrei group

Abstract: Recent advances in ecological niche modeling (ENM) algorithms, in conjunction with increasing availability of geographic information system (GIS) data, allow species' niches to be predicted over broad geographic areas using environmental characteristics associated with point localities for a given species. Consequently, the examination of how niches evolve is now possible using a regionally inclusive multivariate approach to characterize the environmental requirements of a species. Initial work that uses this approach has suggested that niche evolution is characterized by conservatism: the more closely related species are, the more similar are their niches. We applied a phylogenetic approach to examine niche evolution during the radiation of Cuban trunk-ground anoles (Anolis sagrei group), which has produced 15 species in Cuba. We modeled the niche of 11 species within this group using the WhyWhere ENM algorithm and examined the evolution of the niche using a phylogeny based on approximately 1500 base pairs of mitochondrial DNA. No general relationship exists between phylogenetic similarity and niche similarity. Examination of species pairs indicates some examples in which closely related species display niche conservatism and some in which they exhibit highly divergent niches. In addition, some distantly related species exhibit significant niche similarity. Comparisons also revealed a specialist-generalist sister species pair in which the niche of one species is nested within, and much narrower than, the niche of another closely related species.

Rapid temporal reversal in predator-driven natural selection.

Abstract: As the environment changes, will species be able to adapt? By conducting experiments in natural environments, biologists can study how evolutionary processes such as natural selection operate through time. We predicted that the introduction of a terrestrial predator would first select for longer-legged lizards, which are faster, but as the lizards shifted onto high twigs to avoid the predator, selection would reverse toward favoring the shorter-legged individuals better able to locomote there. Our experimental studies on 12 islets confirmed these predictions within a single generation, thus demonstrating the rapidity with which evolutionary forces can change during times of environmental flux.

Intercontinental community convergence of ecology and morphology in desert lizards

Abstract: Evolutionary ecologists have long debated the extent to which communities in similar environments but different geographic regions exhibit convergence. On the one hand, if species' adaptations and community structure are determined by environmental features, convergence would be expected. However, if historical contingencies have long-lasting effects convergence would be unlikely. Most studies to date have emphasized the differences between communities in similar environments and little quantitative evidence for convergence exists. The application of comparative phylogenetic methods to ecological studies provides an opportunity to further investigate hypotheses of convergence. We compared the evolutionary patterns of structural ecology and morphology of 42 species of iguanian lizards from deserts of Australia and North America. Using a comparative approach, we found that evolutionary convergence of ecology and morphology occurs both in overall, community-wide patterns and in terms of pairs of highly similar intercontinental pairs of species. This result indicates that in these desert lizards, deterministic adaptive evolution shapes community patterns and overrides the historical contingencies unique to particular lineages.

Shared and unique features of diversification in greater antillean anolis ecomorphs

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.

Adaptation, Speciation, and Convergence: A Hierarchical Analysis of Adaptive Radiation in Caribbean Anolis Lizards

Abstract: Caribbean Anolis lizards are a classic case of adaptive radiation, repeated four times across islands of the Greater Antilles. On each island, very similar patterns of evolutionary divergence have occurred, resulting in the evolution of the same set of ecological specialists—termed ecomorphs—on each island. However, this is only part of the story of the Caribbean anole radiations. Indeed, much of the species diversity of Caribbean Anolis occurs within clades of ecomorphs, which contain as many as 14 ecologically-similar species on a single island. We ask to what extent the classic model of ecological interactions as the driving force in adaptive radiation can account for this aspect of anole evolutionary diversity. Our answer is that it can in part, but not entirely. More generally, the most complete understanding of evolutionary diversification and radiation is achieved by studying multiple hierarchical evolutionary levels from clades to populations.

What drives variation in habitat use by Anolis lizards: habitat availability or selectivity?

Abstract: Geographic variation in habitat availability may drive geographic variation in a species' habitat use; alterna- tively, species adapted to particular habitat characteristics may use a habitat regardless of its availability within an environ- ment. In this study, we investigated habitat use of two sympatric species of Anolis lizards that are morphologically specialized to use different microhabitats. We examined variation in microhabitat use and availability among four distinct forest types. In each forest type, we quantified available microhabitats (i.e., perch diameter, angle of inclination, and visi- bility), as well as microhabitats actually used by each species. We found that species consistently differed in microhabitat use, corresponding to each species' morphological specializations. However, microhabitat use of both species varied among sites. This variation in Anolis gundlachi Peters, 1876 reflected differences in microhabitat availability, while the variation in Anolis krugi Peters, 1876 resulted from differential microhabitat selectivity. These results indicate that both habitat availability and habitat preferences must be examined in multiple localities for a species to understand the causes of variation in its habitat use. Resume ´ : La variation geographique de la disponibilitedes habitats peut expliquer la variation geographique de l'usage qu'une espece fait de son habitat; d'autre part, une espece adapteeades caracteristiques particulieres de l'habitat peut uti- liser un habitat quelle que soit sa disponibilitedans un milieu. Nous examinons dans notre etude l'utilisation de l'habitat par deux especes sympatriques d'Anolis specialisees par leur morphologie autiliser des microhabitats differents. Nous de ´- terminons la variation dans l'utilisation et la disponibilitedes microhabitats dans quatre types distincts de foret. Dans cha- que type de foret, nous quantifions les microhabitats disponibles (c.-a `-d., diametre des perchoirs, angle d'inclination, visibilite ´) ainsi que les microhabitats actuellement utilises par chaque espece. Les deux especes different constamment dans leur utilisation des microhabitats, de facon qui correspond a leurs specialisations morphologiques. L'utilisation des microhabitats varie, cependant, d'un site aun autre. Chez Anolis gundlachi Peters, 1876, cette variation resulte de la dispo- nibilitedes microhabitats, alors que chez Anolis krugi Peters, 1876 elle s'explique par une selectivitedifferentielle des mi- crohabitats. Ces resultats indiquent que la disponibilitedes habitats ainsi que les preferences d'habitat doivent toutes deux etre examinees en plusieurs sites pour une meme espece, si l'on veut comprendre les causes de la variation de son utilisa- tion de l'habitat. (Traduit par la Redaction)