Presentation Detail

Speciation

Muñoz, Martha [1], Crawford, Nicholas [2], McGreevy, Jr., Thomas [2], Schneider, Christopher [2].

Divergence in coloration and the evolution of reproductive isolation in the Anolis marmoratus species complex.

Adaptive divergence in coloration is expected to produce reproductive isolation in species that use colorful signals in mate choice and species recognition. Indeed, many adaptive radiations are characterized by differentiation in colorful signals, suggesting that divergent selection acting on coloration may be an important component of speciation. Populations in the Anolis marmoratus species complex from the Guadeloupean archipelago in the Caribbean display striking divergence in the color 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 on the island of Grande Terre in Guadeloupe. 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 extreme color variation in A. marmoratus 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 likely 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 while neutral portions are homogenized by gene flow and recombination. Our results suggest that the anoles on Grande Terre represent an early stage along the speciation continuum and that assortative mating is not complete. High gene flow among populations may inhibit further progress toward speciation, particularly if the loci affecting fitness in the two habitats are not the same as loci affecting traits involved in reproductive isolation; thus, these populations are likely at a stable endpoint that reflects a balance between divergent selection and gene flow. This migration– selection antagonism may explain the evolutionary species – area relationship, which suggests that in situ speciation is inhibited on islands below a threshold size, and also explain the fact that ecological speciation appears to have repeatedly stalled at different stages on topographically complex islands in the Lesser Antilles. We discuss the impact of these findings for studies of color evolution, ecological speciation, and the adaptive radiation of anoles.

1 - Harvard University, Organismic and Evolutionary Biology, 26 Oxford Street, Cambridge, MA, 02138, USA
2 - Boston University, Biology, 5 Cummington Mall, Boston, MA, 02215, USA

Keywords:
Speciation
adaptive radiation
Anolis
color evolution.

Presentation Type: Regular Oral Presentation
Session: 86
Location: Cotton C/Snowbird Center
Date: Sunday, June 23rd, 2013
Time: 4:15 PM
Number: 86004
Abstract ID:68
Candidate for Awards:W.D. Hamilton Award for Outstanding Student Presentation