Mating system does not predict permanent sperm depletion in black widow spiders

Area of Science:

• Evolutionary biology
• Animal reproductive strategies
• Arachnology

Background:

• Sperm production variation across species is linked to mating systems.
• Permanent sperm depletion (PSD) in male spiders, where spermatogenesis ceases before adulthood, has been theorized.
• PSD is hypothesized to correlate with mating systems where males have few mating opportunities, such as monogyny, genital mutilation, or sexual cannibalism.

Purpose of the Study:

• To test the hypothesis that permanent sperm depletion (PSD) in male spiders is associated with specific mating systems.
• To investigate the occurrence of PSD in two related spider species with differing mating systems and reproductive behaviors.

Main Methods:

• Comparative study of two related spider species: Latrodectus hasselti (monogynous, sexually cannibalistic) and Latrodectus hesperus (polygynous).
• Examination of sperm production and transfer in adult males of both species.
• Histological and observational analyses to determine the presence or absence of spermatogenesis post-molt and sperm transfer frequency.

Main Results:

• Permanent sperm depletion (PSD) was not observed in adult males of either Latrodectus hasselti or Latrodectus hesperus.
• Males of both species were observed to transfer sperm into their copulatory organs on multiple occasions as adults.
• The findings contradict the hypothesis linking PSD to monogyny, genital mutilation, or limited mating opportunities.

Conclusions:

• The evolutionary relationship between mating systems and male investment in sperm production is more intricate than previously assumed.
• The absence of PSD in these species suggests that males can maintain sperm production capabilities even with behaviors like genital mutilation or in monogynous systems.
• Further research is needed to fully understand the diverse reproductive strategies and sperm allocation patterns in spiders.