The evolution of sperm length in moths

Area of Science:

• Evolutionary biology
• Reproductive biology
• Zoology

Background:

• Sperm form and function are crucial but poorly understood biological aspects.
• Evolutionary associations between sperm traits and reproductive strategies offer insights.
• Moths (Lepidoptera) provide a model system due to significant variation in reproductive traits within a monophyletic group.

Purpose of the Study:

• To investigate the evolutionary associations between sperm lengths and male/female reproductive characters in moths.
• To explore the relationship between sperm dimensions, mating patterns, and female reproductive tract morphology.
• To examine potential coevolution between male investment in reproduction and female sperm storage capacity.

Main Methods:

• Comparative study across moth taxa (Lepidoptera).
• Analysis of eupyrene (fertilizing) and apyrene (non-fertilizing) sperm lengths.
• Correlation analysis with male reproductive traits (e.g., testis size) and female reproductive tract dimensions (e.g., spermathecal duct length).

Main Results:

• Positive correlation between eupyrene and apyrene sperm lengths across taxa.
• Both sperm types positively associate with residual testis size (mating pattern).
• Increased eupyrene sperm length correlates with longer female spermathecal ducts, suggesting female influence.
• Positive relationship between residual testis volume and spermathecal volume, indicating coevolution.
• Positive association between testes and accessory glands within males.

Conclusions:

• Sperm length evolution in moths is influenced by both male mating strategies and female reproductive tract morphology.
• Female reproductive tract length may select for longer eupyrene sperm.
• Male investment in spermatogenesis and female sperm storage capacity appear to coevolve.
• The study highlights complex interplays shaping sperm evolution in Lepidoptera.