Asymmetric dominance and asymmetric mate choice oppose premating isolation after allopatric divergence

Abstract

Assortative mating promotes reproductive isolation and allows allopatric speciation processes to continue in secondary contact. As mating patterns are determined by mate preferences and intrasexual competition, we investigated male–male competition and behavioral isolation in simulated secondary contact among allopatric populations. Three allopatric color morphs of the cichlid fish Tropheus were tested against each other. Dyadic male–male contests revealed dominance of red males over bluish and yellow-blotch males. Reproductive isolation in the presence of male–male competition was assessed from genetic parentage in experimental ponds and was highly asymmetric among pairs of color morphs. Red females mated only with red males, whereas the other females performed variable degrees of heteromorphic mating. Discrepancies between mating patterns in ponds and female preferences in a competition-free, two-way choice paradigm suggested that the dominance of red males interfered with positive assortative mating of females of the subordinate morphs and provoked asymmetric hybridization. Between the nonred morphs, a significant excess of negative assortative mating by yellow-blotch females with bluish males did not coincide with asymmetric dominance among males. Hence, both negative assortative mating preferences and interference of male–male competition with positive assortative preferences forestall premating isolation, the latter especially in environments unsupportive of competition-driven spatial segregation.

Past lake shore dynamics explain present pattern of unidirectional introgression across a habitat barrier

“…For instance, asymmetries in the direction of gene flow and among loci can elucidate various pre- and postzygotic processes that determine the evolutionary trajectories of the involved lineages. In animals, potential sources of asymmetric introgression include asymmetries in mate choice, driven, for example, by lineage-specific mating preferences and dominance relationships ( Rosenfield & Kodric-Brown, 2003 ; Sefc et al, 2015 ; While et al, 2015 ), geographic variation in the fitness of immigrants and hybrids ( Nosil et al, 2005 ; Carson et al, 2012 ), asymmetric range expansions ( Johannesen et al, 2006 ; but see Zhang, 2014 ), sex-specific dispersal ( Beysard et al, 2012 ), sex-specific hybrid mortality ( Johannesen et al, 2006 ), and cytonuclear incompatibilities ( Arntzen et al, 2009 ).…”

Shifting barriers and phenotypic diversification by hybridisation

“…Given that courtship among heterotypic Tropheus in two‐way choice experiments predicted interbreeding in experimental secondary contact (Sefc et al . ), the present results indicate that pre‐mating reproductive isolation between the yellow and its parental morphs has not yet evolved.…”

Weak link between dispersal and parasite community differentiation or immunogenetic divergence in two sympatric cichlid fishes

“…In T. moorii , hybridization upon secondary contact has been inferred with phylogenetic and population genetics methods, while partial prezygotic reproductive isolation by colour‐assortative mate choice has been observed in laboratory experiments or following anthropogenic translocations in the field (Sefc et al . , , in press; Sturmbauer et al . ; Salzburger et al .…”