Divergence in coloration and ecological speciation in the Anolis marmoratus species complex

Abstract

Adaptive divergence in coloration is expected to produce reproductive isolation in species that use colourful signals in mate choice and species recognition. Indeed, many adaptive radiations are characterized by differentiation in colourful signals, suggesting that divergent selection acting on coloration may be an important component of speciation. Populations in the Anolis marmoratus species complex from the Caribbean island of Guadeloupe display striking divergence in the colour and pattern of adult males that occurs over small geographic distances, suggesting strong divergent selection. Here we test the hypothesis that divergence in coloration results in reduced gene flow among populations. We quantify variation in adult male coloration across a habitat gradient between mesic and xeric habitats, use a multilocus coalescent approach to infer historical demographic parameters of divergence, and examine gene flow and population structure using microsatellite variation. We find that colour variation evolved without geographic isolation and in the face of gene flow, consistent with strong divergent selection and that both ecological and sexual selection are implicated. However, we find no significant differentiation at microsatellite loci across populations, suggesting little reproductive isolation and high levels of contemporary gene exchange. Strong divergent selection on loci affecting coloration probably maintains clinal phenotypic variation despite high gene flow at neutral loci, supporting the notion of a porous genome in which adaptive portions of the genome remain fixed whereas neutral portions are homogenized by gene flow and recombination. We discuss the impact of these findings for studies of colour evolution and ecological speciation.

Accumulation of transposable elements inHoxgene clusters during adaptive radiation ofAnolislizards

“…Although neutral processes cannot be completely ruled out as causes of the positive relationship between speciation rate and TE density in Hox clusters, the fact that microsatellite repeats located in the Hox clusters did not accumulate with the number of speciation nodes, and showed the expected pattern from neutral evolution, argues against this. In addition, low effective population sizes are unlikely to apply to Caribbean Anolis lizards as they are characterized by generally high abundances [24] and estimates of historical effective population sizes suggest this has been the case throughout the lineage's history [76]. Environmental factors such as temperature or humidity can potentially promote TE activity as demonstrated in model organisms exposed to biotic and abiotic stressors [77][78][79].…”

Phylogenetic relationships of Amazonian anole lizards (Dactyloa): Taxonomic implications, new insights about phenotypic evolution and the timing of diversification

“…Other studies have also found low genetic differentiation between distinct dewlap phenotypes (D'Angiolella et al, 2011;Lambert et al, 2013;Ng and Glor, 2011;Stapley et al, 2011). Within some anole taxa, divergence in sexual signals has not prevented high levels of contemporary gene flow between populations (Muñoz et al, 2013), which might also be the case of D. punctata and D. philopunctata.…”

“…The degree of dewlap dissimilarity that disrupts species recognition and mating in dactyloids is unclear (Ng and Glor, 2011;Stapley et al, 2011). In addition to the dewlap, anoles rely on a range of visual signals, including body coloration and stereotyped head bobbing displays (Jenssen and Gladson, 1984;Losos, 1985;Macedonia and Stamps, 1994;Muñoz et al, 2013). Other studies have also found low genetic differentiation between distinct dewlap phenotypes (D'Angiolella et al, 2011;Lambert et al, 2013;Ng and Glor, 2011;Stapley et al, 2011).…”

Conservation Genetics and Genomics of Amphibians and Reptiles

“…Environmental gradients are often viewed as one important driver of intraspecific adaptive variation that may allow species to persist through changing environments and be a source of variation for ecological speciation and intraspecific adaptive variation (51,79). In combination with environmental data layers from geographic information systems, genetic analyses of population structure and gene flow have provided insights into the role of ecological factors in promoting divergent selection and speciation in amphibians (77), phenotypic divergence in Anolis lizards (80), and convergent morphological evolution consistent with ecological speciation in three lizard species in the extreme White Sands desert of the southwestern United States (81). Morphologically similar but genetically distinct amphibian lineages sampled across climatic gradients have also shown that divergent selection maintains distinct lineage distributions in the salamander Aneides flavipunctatus/niger in western North America (82).…”