Shooting darts: co-evolution and counter-adaptation in hermaphroditic snails

Area of Science:

• Evolutionary biology
• Animal behavior
• Genomics

Background:

• Sexual conflict is a key driver of evolution, leading to antagonistic traits and counter-adaptations.
• In simultaneous hermaphrodites, sexual conflict significantly influences mating systems and reproductive evolution.
• Land snail love-darts exemplify sexual conflict, benefiting the shooter (increased paternity) but manipulating sperm storage in the receiver.

Purpose of the Study:

• To investigate the evolutionary history of love-darts and associated reproductive structures in land snails.
• To determine if sexual conflict has driven co-evolutionary arms races in hermaphroditic mating systems.
• To provide the first comprehensive comparative analysis of reproductive organ evolution in simultaneous hermaphrodites.

Main Methods:

• Phylogenetic analysis of 28S ribosomal RNA gene sequences from dart-possessing land snail species.
• Statistical tests (Shimodaira-Hasegawa, Bayesian posterior probabilities) to assess the monophyly of reproductive structures.
• Phylogenetically independent contrasts, principal component, and correlation analyses to examine trait covariation.

Main Results:

• The study rejected a monophyletic origin for most reproductive structures, including the love-dart, indicating repeated evolution.
• Phylogenetic analyses revealed that reproductive traits, such as love-darts and spermatophore-receiving organs, covary.
• Correlated evolution of these traits was demonstrated, supporting the hypothesis of co-evolutionary arms races.

Conclusions:

• Co-evolutionary arms races driven by sexual conflict are significant in hermaphrodites.
• These arms races play a crucial role in shaping the evolution of simultaneous hermaphroditic mating systems.
• The findings offer novel insights into the dynamics of sexual conflict and reproductive trait evolution.