Reproductive isolating mechanisms influencing the direction of Banded Killifish (Fundulus diaphanus) x Common Killifish (F. heteroclitus) hybridization in Porter’s Lake, Nova Scotia

Abstract

Hybridization events provide opportunities to examine the mechanisms influencing interspecific reproductive isolation. In Porter’s Lake, Nova Scotia, hybridization between two killifish species (<i>Fundulus heteroclitus</i> and <i>Fundulus diaphanus</i>) predominantly occurs with <i>F. diaphanus</i> mothers and <i>F. heteroclitus</i> fathers. To test if pre-zygotic isolating barriers contributes to this cross-direction bias, breeding behaviour was studied in the lab. <i>Fundulus heteroclitus</i> females preferred conspecific males while <i>F. diaphanus</i> females showed no preference. Additionally, all possible pairwise crosses were made <i>in vitro</i> and incubated at four salinities to test reproductive barriers related to fertilization and hybrid development. <i>Fundulus heteroclitus</i> x <i>F. diaphanus</i> (female x male) hybrids had lower fertilization and longer development times than other cross types. Together, these results suggest that both pre- and post-zygotic mechanisms contribute to the absence of <i>F. heteroclitus x F. diaphanus</i> hybrids in the wild, and that additional, un-measured reproductive isolating mechanisms are also likely to be quite important.