Spermathecal variation in temperate Opiliones

Area of Science:

• Arthropod reproductive biology
• Evolutionary morphology
• Sexual selection

Background:

• Internal fertilization in arachnids allows for diverse post-copulatory mechanisms.
• Female control over sperm fate is expected when gametic fusion is distant from oogenesis, syngamy is delayed, sperm are non-motile, or female morphology permits sperm selection.
• Opiliones (harvestmen) exhibit sexual antagonism, multiple mating, and delayed oviposition, meeting conditions for female control over sperm.

Purpose of the Study:

• To investigate the role of spermathecal morphology in controlling sperm fate in Opiliones.
• To test the hypothesis that species with traits associated with sexual antagonism have more complex spermathecae.
• To examine the correlation between spermathecal complexity and sexual conflict indicators in harvestmen.

Main Methods:

• Confocal laser scanning microscopy was used to image and analyze spermathecae in thirteen Leiobunum species and one Hadrobunus species.
• Phylogenetic multivariate comparative methods were applied to assess correlations between traits.
• Spermathecal morphology was categorized based on chamber structure and invaginations.

Main Results:

• Spermathecae varied from single-chambered to multi-lumina structures with 2-3 lumina.
• A trend towards cross-correlation between sexual conflict and spermathecal traits was estimated.
• Some species with more complex spermathecae also exhibited larger body size and thicker genital muscles, indicators of sexual conflict.

Conclusions:

• Spermathecal morphology plays a role in sperm control in Opiliones, potentially linked to sexual conflict.
• Confocal microscopy is a valuable tool for characterizing internal reproductive structures in arthropods.
• Further research is needed to fully elucidate spermathecal mechanisms and sperm precedence in these species.