Female northern grass lizards judge mates by body shape to reinforce local adaptation

Abstract

Background: Identifying the factors that contribute to divergence among populations in mate preferences is important for understanding of the manner in which premating reproductive isolation might arise and how this isolation may in turn contribute to the evolutionary process of population divergence. Here, we offered female northern grass lizards (Takydromus septentrionalis) a choice of males between their own population and another four populations to test whether the preferences that females display in the mating trials correlate with phenotypic adaptation to local environments, or to the neutral genetic distance measured by divergence of mitochondrial DNA sequence loci.

Results: Females showed a strong preference for native over foreign males. Females that mated with native versus foreign males did not differ from each other in mating latency, or copulation duration. From results of the structural equation modelling we knew that: 1) geographical distance directly contributed to genetic differentiation and environmental dissimilarity; 2) genetic differentiation and environmental dissimilarity indirectly contributed to female mate preference, largely through their effects on morphological divergence; and 3) females judged mates by body shape (appearance) and discriminated more strongly against morphologically less familiar allopatric males.

Conclusions: Local adaptation rather than neutral genetic distance influences female mate preference in T. septentrionalis. The tendency to avoid mating with foreign males may indicate that, in T. septentrionalis, local adaptations are more valuable than genetic novelties. Our results highlight the importance of comprehensive studies integrating ecological, molecular and behavioral approaches to understand population divergence in female mate preferences as the consequence of local adaptations.

Keywords: Genetic differentiation; Geographical distance; Local adaptation; Mate preference; Morphology; Structural equation model.

Fig. 1

The body posture of heterospecific a, between male T. septentrionalis and female T. sexlineatus) and conspecific homosexual b, between males of T. septentrionalis) mating partners

Fig. 2

Locations of the five Takydromus septentrionalis populations from which we collected adult lizards. Three mainland populations are in Chang’an (CA), Chuzhou (CZ) and Lishui (LS); two island populations are in Liuheng (LH) and Xiushan (XS), Zhoushan Islands

Fig. 3

Frequency of matings in relation to geographical distance a, pairwise Fst (a measure of genetic differentiation between populations, b, environmental dissimilarity c and morphological difference d. Regression equations and coefficients are given in the figure. See Fig. 2 for abbreviations for sampling locations

Fig. 4

The most supported structural equation model for the roles of geographical distance, genetic differentiation, environmental dissimilarity and morphological difference in mate assessment by female T. septentrionalis. Numbers given in the figure represent the standard direct effects, and the symbol ** represents p < 0.01