Males of a sexually cannibalistic spider chemically assess relative female quality

Abstract

Background: Mate choice is a taxonomically widespread phenomenon, mostly exerted by females although male mate choice occurs as well. While costs and benefits of choosiness have been well studied, the underlying mechanisms are largely unclear. Different models exist, namely best-of-n or threshold rules, based on sequential or simultaneous sampling, which differ in the required cognitive demands. We applied an experimental approach to shed light on the underlying mechanisms of male mate choice in the sexually cannibalistic spider Argiope bruennichi. Males are limited to two copulations and preferentially monopolise large females, while they may leave smaller females after a single copulation and resume mate search. Here, we utilised significant size-differences between females from Northern and Southern populations and presented males with three different-sized females that were matched for origin: all three females originated either from the same Northern European population as the males or from Southern populations where the smallest female was about the same size as the largest Northern female. This allowed testing the hypothesis that males base their mating tactic on a fixed local size threshold. We predicted Northern males to be choosy among Northern females, but to accept all Southern females since they would all be above that threshold. Results: Males copulated with the first female they encountered, which was independent of her body size. Regardless of the females' origins, males chose a monogynous tactic with the largest female in the trio, while they left the smallest female after one copulation. The same pattern applied to Southern females even though the smallest females in the trio were of a similar size as monopolised Northern females. Since males have poor eyesight and did not actively sample all females, they likely have gained information about relative size differences between females based on volatile chemical cues only. Conclusions: Our findings suggest that male A. bruennichi can assess relative differences in mate quality and adjust their mating tactic to the prevailing conditions (Northern vs. Southern). We reject the presence of a locally-adapted fixed threshold and argue that our results are best explained by an adjustable threshold that was raised under Southern conditions.

Dragline silk reveals female developmental stage and mediates male vibratory courtship in the nuptial gift‐giving spider Pisaura mirabilis

“…As soon as a male P. mirabilis contacted silk of an adult female (unmated or mated), it emitted vibratory pulses at similar temporal patterns, dominant frequencies and pulse rates (Table 1). Thus, at the early stage of encounter as simulated in our experiments, when a male initiates courtship, male mate choice discriminates against immature and presumably also against heterospecific females, and male choice related to female condition and quality might take place later upon the physical encounter between the sexes or even after the first mating, as reported for Argiope bruennichi , where males exhibited choosiness only after the first copulation had taken place (Cory & Schneider, 2020).…”

Strategic pheromone signalling by mate searching females of the sexually cannibalistic spiderArgiope bruennichi

“…Behavioural studies have shown that males adjust their mating tactic, i.e. whether they invest maximally in one female or seek to obtain a second mating with another female, according to female condition [ 41 , 42 , 68 ]. In spiders, as in other arthropods, female body mass correlates with fecundity [ 69 ] and in female A. bruennichi , body mass is positively correlated with age.…”

“…Behavioural experiments with A. bruennichi revealed that males use chemical cues from female body surface and silk to both detect their presence and assess their mating status and body mass [39][40][41]. Moreover, field observations [42] and laboratory experiments [41] demonstrated that males are more likely to monopolize a female when she is relatively heavy and old, and older females attract more males than young ones in the field [43]. Although male mate choice has been well-studied in several spiders including A. bruennichi [20], the female perspective has rarely been looked at.…”

Spider diversity (Arachnida: Araneae) at Saurashtra University Campus, Rajkot, Gujarat during the monsoon

“…The proportion of the potential group (adults) to non-potential individuals was almost one and a half (1.5P:1NP). Age and sexual maturity of spiders may provide a broad range of mate choice decisions for males, as males of a sexually cannibalistic spider chemically assess relative female quality and mate with adaptive females (Cory & Schneider 2020).…”