Against the Odds: Hybrid Zones between Mangrove Killifish Species with Different Mating Systems.

Waldir M Berbel-Filho,Carlos M Rodríguez-López,John C Avise,Sergio M Q Lima,Sofia Consuegra,Mateus G Lira,Carlos Garcia De Leaniz,Andrey Tatarenkov,Helder M V Espírito-Santo,George Pacheco

doi:10.3390/genes12101486

Abstract

Different mating systems are expected to affect the extent and direction of hybridization. Due to the different levels of sexual conflict, the weak inbreeder/strong outbreeder (WISO) hypothesis predicts that gametes from self-incompatible (SI) species should outcompete gametes from self-compatible (SC) ones. However, other factors such as timing of selfing and unilateral incompatibilities may also play a role on the direction of hybridization. In addition, differential mating opportunities provided by different mating systems are also expected to affect the direction of introgression in hybrid zones involving outcrossers and selfers. Here, we explored these hypotheses with a unique case of recent hybridization between two mangrove killifish species with different mating systems, Kryptolebias ocellatus (obligately outcrossing) and K. hermaphroditus (predominantly self-fertilizing) in two hybrid zones in southeast Brazil. Hybridization rates were relatively high (~20%), representing the first example of natural hybridization between species with different mating systems in vertebrates. All F1 individuals were sired by the selfing species. Backcrossing was small, but mostly asymmetrical with the SI parental species, suggesting pattern commonly observed in plant hybrid zones with different mating systems. Our findings shed light on how contrasting mating systems may affect the direction and extent of gene flow between sympatric species, ultimately affecting the evolution and maintenance of hybrid zones.

Highlights

Hybridization is a major source of evolutionary innovation, with important implications for phenotypic diversification, adaptation and speciation [1,2]
We ran NEWHYBRIDS v.1.1 with the same parameters described for the microsatellites to investigate the posterior probability of each individual to belong to one of the six hybrid classes. Both microsatellite genotypes and SNPs confirmed the hybridization between the outcrossing and SI K. ocellatus and the predominantly selfing SC K. hermaphroditus in two hybrid zones (FUN and GUA in Figure 2) in Southeast Brazil (Figure 3)
At K = 3 indicated that all K. ocellatus were assigned with nearly 100% probability to one cluster, while K. hermaphroditus individuals were assigned with nearly 100% probability to another cluster, apart from the subset of the divergent FUN and GUA fish, with admixed genetic backgrounds of both species

Summary

Introduction

Hybridization is a major source of evolutionary innovation, with important implications for phenotypic diversification, adaptation and speciation [1,2]. Natural crosses between self-compatible (SC) and self-incompatible (SI) plants generally produce viable embryos only when SI pollen (male parent) fertilizes SC styles (female parent), but not vice-versa. This pattern of unilateral incompatibility (UI) is known as the ‘SI × SC rule’ [9,10]. The opposite pattern was observed in Caenorhabditis interspecific crosses involving other species [21], where more progeny was generated in crosses involving selfer males and outcrossing hermaphrodites than the ones in the opposite direction These mixed results call for further research into the generality of the ‘SI × SC rule’ in animals, under natural conditions

Methods

Results

Discussion

Conclusion