The reproductive ecology of the European bitterling (Rhodeus sericeus)

Abstract

The European bitterling Rhodeus sericeus Pallas is a freshwater fish belonging to the Acheilognathinae, a subfamily that has an unusual spawning symbiosis with freshwater mussels. Female bitterling possess long ovipositors that they use to place their eggs onto the gills of a mussel through the mussels' exhalant siphon. Males fertilize the eggs by releasing sperm into the inhalant siphon of the mussel. The embryos develop inside the mussel for approximately a month, eventually leaving the mussel as actively swimming larvae. Because they use a discrete spawning site that can be readily manipulated they have recently been used in studies to understand oviposition choice with respect to mate and spawning site quality, host-parasite coevolution, alternative male mating tactics, and linking behavioural decisions with population dynamics. The current state of knowledge of bitterling reproductive ecology is reviewed and synthesized, and future directions for research on this species are proposed.

Cognitive ability is heritable and predicts the success of an alternative mating tactic

“…R. Soc. B 282: 20151046 their own territory, as well as those of their neighbours, examine the exhalant siphons of mussels and frequently ejaculate over them (termed pre-oviposition ejaculation) [14,15]. Nonterritorial males also engage in the same behaviour, which takes place even in the absence of females, though the presence of a female who is ready to mate significantly increases the rate of male inspection and ejaculation [17,37].…”

“…Dominant males aggressively defend territories to monopolize mussels and perform elaborate courtship towards females [14,15]. Females place their eggs into the gills of a mussel through its exhalant siphon.…”

“…The dominant 'guarder' and subordinate 'sneaker' mating tactics are not fixed, and male mating behaviour is opportunistic, with males capable of playing either role depending on environmental context [21,22], which is the typical situation in teleost fishes [15]. The sneaker tactic commonly involves pre-oviposition ejaculations [14,15,17], with male reproductive success determined by how males distribute their ejaculates among mussels in relation to the distribution of spawning females, the spatial distribution of mussels and the distribution of rival ejaculates [17], while minimizing the risk of sperm depletion [18].…”

An invasive species reverses the roles in a host–parasite relationship between bitterling fish and unionid mussels

“…Bitterling (Acheilognathinae) are cyprinid fishes that oviposit into the gills of live mussels where their embryos complete development. Hosting bitterling embryos is costly to mussels [6] and they have evolved adaptations to eject bitterling eggs and embryos, mirrored by counteradaptations in bitterling embryos to avoid ejection [6,7]. Bitterling are of east Asian origin, with more than 50 species distributed in east Asia and a single species in Europe [7].…”

“…Hosting bitterling embryos is costly to mussels [6] and they have evolved adaptations to eject bitterling eggs and embryos, mirrored by counteradaptations in bitterling embryos to avoid ejection [6,7]. Bitterling are of east Asian origin, with more than 50 species distributed in east Asia and a single species in Europe [7]. European R. amarus has expanded relatively recently (centuries to millennia before present) from the Black Sea region into central and west Europe [8,9] where it exploits evolutionarily naive mussel populations [10].…”