Researchers from the National University of Singapore (NUS) discovered that when male spiders are at risk of being cannibalized by their female mates, they make decisions to maximize their mating success. Despite the risk of being cannibalized by their mates, the evolved behavioral mating strategy increases their chances of mating.
Female Eats Male Spider After Mating
According to Scientific American, females of many spider species consume their mates after procreation in a gruesome practice known as sexual cannibalism, either for sustenance or to keep their reproductive options open. Female spiders are typically larger than male spiders, providing them with a significant physical advantage.
Male Spider Mating Syndrome
According to the male mating syndrome theory, male spiders are under sexual conflict pressure in sexually cannibalistic situations because they may only have one chance to mate. The researchers investigated whether male spiders use additional cannibalism countering strategies by focusing on two male mating tactics.
One of these is the better-charged palp hypothesis, which proposes that male spiders use one of their paired sexual organs, called pedipalps. On the other hand, the "fast sperm transfer" hypothesis predicts accelerated insemination when the risk of female cannibalism is high.
Research Findings Tested the Theory of Male Spider Mating Syndrome
To test the theory, the researchers compared five species of Singaporean orb-web spiders with varying degrees of female sexual cannibalism and sexual size dimorphism. Associate Professor Li Daiqin of the NUS Department of Biological Sciences led the study published in Communications Biology.
They discovered that male spiders choose the sperm-rich sexual organ for the first copulation with a cannibalistic female. Furthermore, when a female is cannibalistic or much larger, a male transfers significantly more sperm. Their findings support the faster sperm transfer and the better-charged palp hypotheses, lending credibility to the male mating syndrome.
The findings raise new research questions about a male spider's ability to differentiate sperm quantities between palps and the mechanisms involved in palp selection after assessing his cannibalistic partner.
The researchers discovered that sperm volume detection, rather than left-right palp dominance, plays a significant role in the selection of the male palp by further studying Nephilengys malabarensis.
Male Nephilengys malabarensis spiders of Southeast Asia and the southwestern Pacific region are thought to avoid sexual cannibalism through remote copulation, in which the male's copulatory organ detaches during mating and remains in the female, allowing for prolonged sperm transfer, according to Britannica.
Assoc Prof Li claims that the study clarifies how male mating syndrome relates to levels of sexual cannibalism and raises the possibility that there are evolutionary arms races and that sexual conflict significantly impacts animal biology and diversity.
ALSO READ: Male Spider Evades Sexual Cannibalism by Catapulting Itself Midair
Future Research Behind Male Spider Palp Choice
The researchers are considering future research to understand the reasoning behind male palp selection better. Assuming that volume detection is the primary mechanism for palp selection in orb-weaving spiders, the anatomical, neuronal, and hormonal aspects of male palp choice can be investigated to learn more about how a male spider distinguishes relatively minor differences in sperm volumes.
According to Assoc Prof Li, the large diversity of extant spiders worldwide suggests that these findings may not apply to all sexually dimorphic and cannibalistic spiders. Sexual selection can cause rapid changes in palpal anatomy, resulting in sperm transfer mechanisms that differ between species.
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