Showing papers by "Jonathan B. Losos published in 2016"

Ecological Opportunity and Adaptive Radiation

Abstract: The process of adaptive radiation—the proliferation of species from a single ancestor and diversification into many ecologically different forms—has been of great interest to evolutionary biologists since Darwin. Since the middle of the last century, ecological opportunity has been invoked as a potential key to understanding when and how adaptive radiation occurs. Interest in the topic of ecological opportunity has accelerated as research on adaptive radiation has experienced a resurgence, fueled in part by advances in phylogenetic approaches to studying evolutionary diversification. Nonetheless, what the term actually means, much less how it mechanistically leads to adaptive diversification, is currently debated; whether the term has any predictive value or is a heuristic useful only for post hoc explanation also remains unclear. Recent recognition that evolutionary change can occur rapidly and on a timescale commensurate with ecological processes suggests that it is time to synthesize ecological and evo...

Determinants of spread in an urban landscape by an introduced lizard

Abstract: Urban landscapes are a mixture of built structures, human-altered vegetation, and remnant semi-natural areas. The spatial arrangement of abiotic and biotic conditions resulting from urbanization doubtless influences the establishment and spread of non-native species in a city. We investigated the effects of habitat structure, thermal microclimates, and species coexistence on the spread of a non-native lizard (Anolis cristatellus) in the Miami metropolitan area of South Florida (USA). We used transect surveys to estimate lizard occurrence and abundance on trees and to measure vegetation characteristics, and we assessed forest cover and impervious surface using GIS. We sampled lizard body temperatures, habitat use, and relative abundance at multiple sites. At least one of five Anolis species occupied 79 % of the 1035 trees surveyed in primarily residential areas, and non-native A. cristatellus occupied 25 % of trees. Presence and abundance of A. cristatellus were strongly associated with forest patches, dense vegetation, and high canopy cover, which produced cooler microclimates suitable for this species. Presence of A. cristatellus was negatively associated with the ecologically similar non-native A. sagrei, resulting in reduced abundance and a shift in perch use of A. cristatellus. The limited spread of A. cristatellus in Miami over 35 years is due to the patchy, low-density distribution of wooded habitat, which limits dispersal by diffusion. The presence of congeners may also limit spread. Open habitats—some parks, yards and roadsides—contain few if any A. cristatellus, and colonization of isolated forest habitat appears to depend on human-mediated dispersal.

Climate-mediated adaptation after mainland colonization of an ancestrally subtropical island lizard, Anolis carolinensis.

Abstract: Climate-mediated evolution plays an integral role in species migration and range expansion. Gaining a clearer understanding of how climate affects demographic history and adaptation provides fundamental insight into the generation of intra- and interspecific diversity. In this study, we used the natural colonization of the green anole (Anolis carolinensis) from the island of Cuba to mainland North America to investigate the role of evolution at the niche, phenotypic and genetic levels after long-term establishment in a novel environment. The North American green anole occupies a broader range of thermal habitats than its Cuban sister species. We documented niche expansion in the mainland green anole, mediated primarily through adaptation to winter temperatures. Common garden experiments strongly suggest a genetic component to differences in thermal performance found between populations in different temperature regimes. Analysis of geographic variation in population structure based on 53 486 single nucleotide variants from RAD loci revealed increased genetic isolation between populations in different vs. similar thermal environments. Selection scans for environment-allele correlations reveal 19 genomic loci of known function that may have played a role in the physiological adaptation of A. carolinensis to temperate environments on the mainland.

Proximate determinants of bite force in Anolis lizards.

Abstract: Performance measures associated with the vertebrate jaw system may provide important insights into vertebrate ecology and evolution because of their importance in many ecologically relevant tasks. Previous studies have shown that in many taxa, evolution toward higher bite force has gone hand in hand with the evolution of larger body size. However, independent of differences in overall body size, bite force may vary depending on head size and shape as well. Moreover, the underlying musculature may also drive variation in bite force. Here, we investigate the proximate determinants of bite force in lizards of the genus Anolis. We dissected the jaw muscles and quantified muscle mass, fibre length, and cross-sectional area. Data were analysed for both sexes independently given the sexual dimorphism detected in the dataset. Our results show that the traits that explain bite force are similar in both males and females with overall body size and muscle mass being the principal determinants. Among the different muscles examined, the adductor externus and the pseudotemporalis groups were the best determinants of bite force. However, models run for males predicted the variation in bite force better than models for females, suggesting that selection on morphology improving bite force may be stronger in males.

Geographical variation in morphology and its environmental correlates in a widespread North American lizard, Anolis carolinensis (Squamata: Dactyloidae)

Abstract: The green anole, Anolis carolinensis, has long been an important model organism for studies of physiology and behaviour, and recently became the first reptile to have its genome sequenced. With a large and environmentally heterogeneous distribution, especially in relation to well-studied Antillean relatives, A. carolinensis is also emerging as an important organism for novel studies of geographical differentiation and adaptation. In the present study, we quantify the degree of morphological variation in this species and test for environmental correlates of this variation. We also examine adherence to Bergmann's and Allen's rule, two eco-geographical principles that have been well studied over large species ranges. We sampled from 14 populations across the distribution of the species in North America and measured 28 distinct morphological traits. We also collected a suite of environmental variables for each site, including those related to temperature, precipitation, and vegetation. Ultimately, we found a large degree of geographical variation in morphology, with head traits contributing the most to differences among populations. Morphological variation was correlated with variation in temperature, precipitation, and latitude across sites. We found no support for reverse Bergmann's rule typical of squamates, although we did find a trend of reverse Allen's rule. Ultimately, the present study provides a novel look at A. carolinensis and establishes it as a strong candidate for further studies of variation and adaptation over a large range.

Comparative tests of the role of dewlap size in Anolis lizard speciation.

Abstract: Phenotypic traits may be linked to speciation in two distinct ways: character values may influence the rate of speciation or diversification in the trait may be associated with speciation events. Traits involved in signal transmission, such as the dewlap of Anolis lizards, are often involved in the speciation process. The dewlap is an important visual signal with roles in species recognition and sexual selection, and dewlaps vary among species in relative size as well as colour and pattern. We compile a dataset of relative dewlap size digitized from photographs of 184 anole species from across the genus' geographical range. We use phylogenetic comparative methods to test two hypotheses: that larger dewlaps are associated with higher speciation rates, and that relative dewlap area diversifies according to a speciational model of evolution. We find no evidence of trait-dependent speciation, indicating that larger signals do not enhance any role the dewlap has in promoting speciation. Instead, we find a signal of mixed speciational and gradual trait evolution, with a particularly strong signal of speciational change in the dewlaps of mainland lineages. This indicates that dewlap size diversifies in association with the speciation process, suggesting that divergent selection may play a role in the macroevolution of this signalling trait.

Discovery of a Giant Chameleon-Like Lizard (Anolis) on Hispaniola and Its Significance to Understanding Replicated Adaptive Radiations

Abstract: National Science Foundation [DEB-0918975, DEB-0808401]; Harvard University's David Rockefeller Center for Latin American Studies

Evolution of dorsal pattern variation in Greater Antillean Anolis lizards

Abstract: Dorsal patterning in animals can serve as an antipredator defence and may be involved in sexual selection, and is thus likely to be the target of multiple selective forces. Intraspecific variation in dorsal patterning is not rare, but the reasons behind it are poorly understood. Anolis lizards offer an ideal system to test for a role of ecological factors in driving variation in dorsal pattern. Anoles show a high degree of variation in dorsal pattern not only among species, but also between and within sexes. We use a comparative framework to explore whether ecological variables such as habitat use and perch height can explain the evolution of sexual dimorphism in dorsal pattern and the presence of female pattern polymorphism (FPP) in 36 Greater Antillean Anolis species. We provide evidence that anoles that perch closer to the ground are more likely to exhibit sexual dimorphism in dorsal pattern, and we suggest that habitat-use differences between sexes in ground-affiliated ecomorphs may drive the evolution of dorsal pattern dimorphism. In contrast, the ecological variables we investigated cannot explain the presence of FPP. Our results demonstrate that niche-associated diversification can generate phenotypic diversity within as well as among species, but the factors responsible for intrasexual polymorphism in some anole species remain cryptic. © 2016 The Linnean Society of London, Biological Journal of the Linnean Society, 2016, 00, 000–000.

Exotics exhibit more evolutionary history than natives: a comparison of the ecology and evolution of exotic and native anole lizards

Abstract: Long‐distance colonization was once rare causing species within regions to be closely related. Now, in the Anthropocene, biogeographic structure is being eroded by species introductions. Here, we contrast the ecology and evolution of native versus exotic Caribbean Anolis lizards and show that the once strong biogeographic structure in the clade has been altered by the introduction of 22 Anolis species. Anole introductions are more frequent and span greater distances than natural anole colonizations. As a result, exotic anole populations in the Anthropocene often contain more genetic diversity than native populations, and anole phylogenetic diversity on islands is rapidly increasing.