Asymmetric Reproductive Isolation between Two Sympatric Annual Killifish with Extremely Short Lifespans

Abstract

BackgroundInterspecific reproductive isolation is typically achieved by a combination of intrinsic and extrinsic barriers. Behavioural isolating barriers between sympatric, closely related species are often of primary importance and frequently aided by extrinsic factors causing spatial and temporal interspecific separation. Study systems with a severely limited role of extrinsic factors on reproductive isolation may provide valuable insights into how reproductive isolation between sympatric species is maintained. We used no-choice experimental set-up to study reproductive barriers between two closely related sympatric African killifish species, Nothobranchius furzeri and Nothobranchius orthonotus. These fish live in small temporary savannah pools and have complete spatial and temporal overlap in reproductive activities and share a similar ecology.Principal FindingsWe found that the two species display largely incomplete and asymmetric reproductive isolation. Mating between N. furzeri males and N. orthonotus females was absent under standard experimental conditions and eggs were not viable when fish were forced to mate in a modified experimental setup. In contrast, male N. orthonotus indiscriminately mated with N. furzeri females, the eggs were viable, and offspring successfully hatched. Most spawnings, however, were achieved by male coercion and egg production and embryo survival were low. Behavioural asymmetry was likely facilitated by mating coercion from larger males of N. orthonotus and at relatively low cost to females. Interestingly, the direction of asymmetry was positively associated with asymmetry in post-mating reproductive barriers.SignificanceWe showed that, in fish species with a promiscuous mating system and multiple matings each day, selection for strong mate preferences was relaxed. This effect was likely due to the small proportion of resources allocated to each single mating and the high potential cost to females from mating refusal. We highlight and discuss the fact that males of rarer species may often coercively mate with females of a related, more abundant species.

Parallel evolution of senescence in annual fishes in response to extrinsic mortality

“…orthonotus and N . kadleci ), can be crossed in the laboratory and give rise to viable offspring ([48], N’goma & Cellerino unpublished data). To test whether genetic markers generated for N .…”

Community assembly inNothobranchiusannual fishes: Nested patterns, environmental niche and biogeographic history

“…If post‐mating barriers are indeed fully developed in this species pair (Shidlovskiy et al., 2010), it remains to be investigated whether a lack of premating barriers or ecological exclusion interferes with the local co‐existence of the two species. Nothobranchius species are certainly a promising system in which to study prezygotic, postzygotic and ecological barriers to speciation (Ng'oma et al., 2014; Polačik & Reichard, 2011; Reichard & Polačik, 2010; Sedláček, Baciaková, & Kratochvíl, 2014; Valenzano et al., 2015). …”

Sexual selection against natural hybrids may contribute to reinforcement in a house mouse hybrid zone

“…Further, asymmetry in premating divergence between parental populations has been reported in many taxa [68][69][70][71][72] and can impact the dynamics of hybrid zones [73]. Here, asymmetric sexual selection against hybrids could have similar consequences.…”