Comparisons between closely related radiations in different environments provide a unique window into understanding how abiotic and biotic factors shape evolutionary pathways. Anolis lizards have radiated extensively in the West Indies, as well as mainland Central and South America. In the Caribbean, similar communities of anole species specialized for different habitats (ecomorphs) have evolved independently on each Greater Antillean island. We examined ecological and morphological data on 49 Anolis species (33 Caribbean, 16 mainland) to investigate whether the same set of ecomorphs has arisen in mainland regions. More generally, we investigated whether the relationship between ecology and morphology was similar among anoles in the two regions.Radiations in the two regions are very different. The majority of mainland anole species exhibit morphological characteristics unlike any Caribbean ecomorph. Furthermore, relationships between ecology and morphology are very different between the two sets of anole species. Among mainland anole species, toepad size is positively correlated with perch height, whereas tail length is negatively related to perch diameter. In contrast, among Caribbean anole species, both forelimb length and body mass are positively associated with perch diameter, and both tail length and hindlimb length are negatively related to perch diameter. Biomechanical considerations provide a functional basis for some of these correlations, but much variation remains to be explained. These findings demonstrate that factors that caused anole species to converge repeatedly in the West Indies are not present in mainland regions, and that environmental factors can strongly influence the shape of evolutionary radiations.

We compared morphology of two geographically close populations of the tropical lizard Tropidurus hispidus to test the hypothesis that habitat structure inf luences the evolution of morphology and ecology at the population level. T. hispidus isolated on a rock outcrop surrounded by tropical forest use rock crevices for refuge and appear dorsoventrally compressed compared with those in open savanna. A principal components analysis revealed that the populations were differentially distributed along an axis representing primarily three components of shape: body width, body height, and hind-leg length. Morphological divergence was supported by a principal components analysis of size-free morphological variables. Mitochondrial DNA sequences of ATPase 6 indicate that these populations are closely related relative to other T. hispidus, the rock outcrop morphology and ecology are derived within T. hispidus, and morphological and ecological divergence has occurred more rapidly than genetic divergence. This suggests that natural selection can rapidly adjust morphology and ecology in response to a recent history of exposure to habitats differing in structure, a result heretofore implied from comparative studies among lizard species.There has been a recent upsurge of interest in innovative techniques to account for evolutionary relationships in comparative analyses (1-4). Phylogenetic analyses provide the opportunity to polarize the direction of character change and to estimate the time over which divergence has occurred. With respect to lizards, numerous techniques have been used to compare ecology and morphology among closely related species (5, 6). These studies and others (7-13) suggest that morphology can be adjusted by adaptation to differing structural characteristics of habitats. However, there have been few ecomorphological studies comparing populations within species (14, 15) and none directly integrating morphological change at the population level with recent change in structural habitat in lizards.One underlying assumption of the ecomorphology paradigm (16) is that morphology differs among species as a result of competition (17, 18) or habitat shift (6). We demonstrate that morphological evolution has occurred at the population level as an adaptation to rock dwelling in South American lizards in the genus Tropidurus (19,20), a clade that is much less speciose than Caribbean and Central American Anolis lizards in which most ecomorphology studies have been done (7-9, 21).Species of Tropidurus occur in savanna, cerrado, caatinga, and lowland forest habitats of South America (20). All are insectivores (22-26) with a tendency toward ant specialization in arboreal species (23,25). A recent study (26) found that species that inhabited isolated rock outcrops in the southern Amazon region and used narrow crevices for escape were more compressed dorsoventrally than a widespread species (Tropidurus hispidus) that used a diversity of habitats and microhabitats. However, because a phylogeny for those populations did ...

Only model organisms live in a world of endless summer. Fitness at temperate latitudes reflects the ability of organisms in nature to exploit the favorable season, to mitigate the effects of the unfavorable season, and to make the timely switch from one life style to the other. Herein, we define fitness as Ry, the year-long cohort replacement rate across all four seasons, of the mosquito, Wyeomyia smithii, reared in its natural microhabitat in processor-controlled environment rooms. First, we exposed cohorts of W. smithii, from southern, midlatitude, and northern populations (30-50 degrees N) to southern and northern thermal years during which we factored out evolved differences in photoperiodic response. We found clear evidence of evolved differences in heat and cold tolerance among populations. Relative cold tolerance of northern populations became apparent when populations were stressed to the brink of extinction; relative heat tolerance of southern populations became apparent when the adverse effects of heat could accumulate over several generations. Second, we exposed southern, midlatitude, and northern populations to natural, midlatitude day lengths in a thermally benign midlatitude thermal year. We found that evolved differences in photoperiodic response (1) prevented the timely entry of southern populations into diapause resulting in a 74% decline in fitness, and (2) forced northern populations to endure a warm-season diapause resulting in an 88% decline in fitness. We argue that reciprocal transplants across latitudes in nature always confound the effects of the thermal and photic environment on fitness. Yet, to our knowledge, no one has previously held the thermal year constant while varying the photic year. This distinction is crucial in evaluating the potential impact of climate change. Because global warming in the Northern Hemisphere is proceeding faster at northern than at southern latitudes and because this change represents an amelioration of the thermal environment and a concomitant increase in the duration of the growing season, we conclude that there should be more rapid evolution of photoperiodic response than of thermal tolerance as a consequence of global warming among northern, temperate ectotherms.

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