Asymmetric reproductive isolation during simultaneous reciprocal mating in pulmonates

Area of Science:

• Evolutionary Biology
• Reproductive Isolation
• Speciation

Background:

• Asymmetric reproductive isolation is common, but reciprocal asymmetry in hermaphroditic animals is poorly understood.
• Hermaphroditic snails engage in simultaneous reciprocal copulation, complicating the study of premating isolation.
• Mate choice during prolonged copulation in snails may reveal asymmetric reproductive isolation.

Purpose of the Study:

• To investigate reciprocal asymmetry in reproductive isolation between two species of pulmonate snails.
• To determine if asymmetric hybridization success occurs during simultaneous reciprocal copulation in snails.
• To provide a clear example of reciprocal asymmetry in reproductive isolation in simultaneous hermaphroditic mating.

Main Methods:

• Examined hybridization success in simultaneous reciprocal copulations between Bradybaena pellucida (BP) and Bradybaena similaris (BS).
• Observed premating isolation and copulation behaviors during interspecific mating attempts.
• Assessed the roles of each species and sex in mate discrimination during copulation.

Main Results:

• A discrete difference in hybridization success was observed between reciprocal crosses of BP and BS.
• Interspecific copulation showed asymmetric roles: BS inseminated BP, while BP did not transfer spermatophores.
• 'Male' BP and 'female' BS rejected each other, whereas 'female' BP and 'male' BS accepted each other.
• This indicates opposing mate discrimination between the sexes of each species.

Conclusions:

• The study presents a clear case of reciprocal asymmetry in reproductive isolation during simultaneous reciprocal mating in hermaphroditic animals.
• Asymmetric mate discrimination by the two sexes within each species drives the observed reproductive isolation asymmetry.
• These findings contribute to understanding the evolution of isolation mechanisms in hermaphrodites.