Mother species–father species: unidirectional hybridization in animals with female choice

Sexual selection by female choice prevents speciation reversal in a hybridizing trio of mormyrid fish in southern Africa: evidence from playback experiments of electric organ discharges

“…Whereas P. castelnaui and P. marianne clades must have separated 3.8-7.6 million years ago, those of P. marianne and P. cuandoensis are estimated to have separated about 2.1 million years ago (assuming a molecular clock of 0.58% distance equals 1 million years; obtained for freshwater fish, Burridge et al, 2008). The maternal cyt-b evidence shows that P. cuandoensis originated by unidirectional hybridization, with P. marianne the 'mother species' (as termed by Wirtz, 1999).…”

“…After P. marianne had differentiated from P. castelnaui in the Upper Zambezi, specimens of P. marianne that were swept into the Kwando by the Zambezi in flood represented the rarer species in the Kwando. Following the theory of Wirtz (1999), unidirectional hybridization occurs when females, that is, the more discriminating sex, of the rare species resist courting males of the more common species, but cannot find a mate of their own species. Eventually, the discriminating P. marianne females accepted the males of the common species as mates, and the hybrid offspring all carried their mothers' cyt-b gene.…”

“…Eventually, the discriminating P. marianne females accepted the males of the common species as mates, and the hybrid offspring all carried their mothers' cyt-b gene. Pollimyrus cuandoensis has thus originated as a phenotypically intermediate hybrid species, with P. marianne as the 'mother species' and P. castelnaui as the 'father species' (Wirtz, 1999). In many freshwater fish unidirectional hybridization has occurred whenever a translocated female, representing the rarer species, could not find a mate of its own species so that she eventually accepted an alien male as a mate (Wirtz, 1999).…”

“…Pollimyrus cuandoensis has thus originated as a phenotypically intermediate hybrid species, with P. marianne as the 'mother species' and P. castelnaui as the 'father species' (Wirtz, 1999). In many freshwater fish unidirectional hybridization has occurred whenever a translocated female, representing the rarer species, could not find a mate of its own species so that she eventually accepted an alien male as a mate (Wirtz, 1999). This situation may be fairly common in the Kwando at times of the Zambezi and Okavango in flood.…”

Mating with the wrong species can be right

“…In such areas, hybrid matings are usually between the females of a rare species and the males of a common species, but not vice versa. This is to be expected because the higher parental investment of females should make them more choosy than males, so that they only accept fertilizations by heterospecific males in the absence of conspecific males [12]. …”