Differences in male coloration are predicted by divergent sexual selection between populations of a cichlid fish

Abstract

Female mating preferences can influence both intraspecific sexual selection and interspecific reproductive isolation, and have therefore been proposed to play a central role in speciation. Here, we investigate experimentally in the African cichlid fish Pundamilia nyererei if differences in male coloration between three para-allopatric populations (i.e. island populations with gene flow) of P. nyererei are predicted by differences in sexual selection by female mate choice between populations. Second, we investigate if female mating preferences are based on the same components of male coloration and go in the same direction when females choose among males of their own population, their own and other conspecific populations and a closely related para-allopatric sister-species, P. igneopinnis Mate-choice experiments revealed that females of the three populations mated species-assortatively, that populations varied in their extent of population-assortative mating and that females chose among males of their own population based on different male colours. Females of different populations exerted directional intrapopulation sexual selection on different male colours, and these differences corresponded in two of the populations to the observed differences in male coloration between the populations. Our results suggest that differences in male coloration between populations of P. nyererei can be explained by divergent sexual selection and that population-assortative mating may directly result from intrapopulation sexual selection.

Keywords: assortative mating; cichlid; mate choice; reproductive isolation; sensory drive; sexual selection.

Figure 1.

Results of the tests if females from the three populations of P. nyererei exerted directional intrapopulation sexual selection on different male colours. Fitted lines show predicted probabilities to be a sire based on the colourscores from the most likely GLMM model for each population mate choice experiment (PNM (a–c), PNP (d–g), PNS (h–i)). p-values derive from the most likely GLMM model explaining female mate choice except for PNP, where the p-values are derived from models with ‘forced’ backward selection (see Material and methods, electronic supplementary material, table S1). •p < 0.1, *p < 0.05, **p < 0.05.

Figure 2.

Population-specific PCA bi-plots on all P. nyererei males from each of the three P. nyererei population female mate choice experiments (PNM (a), PNP (b), PNS (c)). Sires in each female mate choice experiment are highlighted with bold symbols. The black arrows represent the colour variables in PCA space. Below are the GLMM results from the three female mate choice experiments (PNM (d), PNP (e), PNS (f)). The plots of the predicted probability to be a sire show that either one PC axis or both PC axes explained the positive population assortative mating in PNM and PNP and the negative assortative mating in PNS. Representative photos of a homotypic male are given below the probability plots for the female mate choice experiments (PNM (d), PNP (e), PNS (f)). •p < 0.1, *p< 0.05, **p < 0.05.