Molecular evidence for ecological speciation in tropical habitats

Abstract

Recent research on rainforest speciation has highlighted the importance of habitat variation in generating population diversification but lacks evidence of an associated reduction in gene flow. This paper describes a study in which molecular markers were used to examine the effects of allopatric divergence and habitat on levels of gene flow in the Caribbean lizard, Anolis roquet. Three study transects were constructed to compare variation in microsatellite allele frequencies and morphology across phylogenetic and habitat boundaries in northern Martinique. Results showed reductions in gene flow to be concordant with divergent selection for habitat type. No evidence could be found for divergence in allopatry influencing current gene flow. Morphological data match these findings, with multivariate analysis showing correlation with habitat type but no grouping by phylogenetic lineage. The results support the ecological speciation model of evolutionary divergence, indicating the importance of habitats in biodiversity generation.

Figure 1

Northern Martinique, showing the position of the three study transects with sampling localities (symbols), the phylogenetic lineage boundary (black line), and habitat structure for the region under study (shading).

Figure 2

Pairwise F_ST/(1 − F_ST) divided by pairwise geographic distance plotted against midpair distance for adjacent localities. Asterisk (*) indicates significant F_ST values (P < 0.05). (A) Lineage Transect shows no reduction in nuclear gene flow at lineage boundary. (B), Habitat Transect shows reduced gene flow at transitions from xeric coastal woodland to lower transitional woodland and from upper transitional woodland to montane rainforest. (C) Control Transect shows no sharp reduction in gene flow with geographic distance. Symbols and shading follow Fig. 1.

Figure 3

Plots of first canonical variate score (CV1) against transect distance showing variation in multivariate morphology among localities on each transect. (A), Lineage Transect and (C) Control Transect show no pattern in morphology with transect distance. (B) Habitat Transect shows a stepwise change in morphology at the rainforest boundary, significantly correlated with change in habitat, not transect distance (partial correlation, P < 0.05). Symbols follow Fig. 1.