UU直播 study on redback spiders finds seemingly abhorrent mating strategy appears to benefit both males and females
![Photo of redback spider](/sites/default/files/styles/news_banner_370/public/2017-12-12-spider-resized.jpg?h=afdc3185&itok=KAsR_WNM)
Published: December 12, 2017
A mating strategy among redback spiders where males seek out immature females appears to benefit both sexes, a new UU直播 study has found.
鈥淭here鈥檚 no evidence to suggest this behaviour is costly to females in terms of survivorship and reproductive output,鈥 says Luciana Baruffaldi, post-doctoral researcher and director of the lab at UU直播 Scarborough and lead author of the research .
The research builds on past work by the Andrade lab that found some male redback spiders will avoid being cannibalized by mating with immature females that are not experienced in eating their partners. For this study, they wanted to determine whether males mating with immature females was a sign of 鈥渃oercion鈥 鈥 a male mating tactic that was costly to females.
At least superficially, the behaviour appeared to be against the female鈥檚 best interest. For one, males in this case mate with little investment in courtship, mating will sometimes injure females, while females will often attack potential mates, suggesting resistance.
But what they found was that being mated as an immature has no cost to females in terms of reproductive output or survival, and that females mating in this way do not signal for additional mates in the future.
鈥淭his early mating may be good for female redback spiders because in nature they鈥檙e at risk of not finding a mate at all,鈥 says Baruffaldi.
Luciana Baruffaldi, director of the Andrade lab at UU直播 Scarborough and lead author of the research published in Scientific Reports (photo by Ken Jones)
Any delays in mating are costly for female redbacks. Not only do they lose out on potential offspring, past research has shown that unmated females have shorter lifespans than mated females, likely the result of having eggs that have to be maintained that can be a drain on their resources.
Redbacks, a species of venomous widow spiders, are one of few arachnids that engage in sexual cannibalism while mating. In fact, males have been observed to actively assist in being cannibalized by doing summersaults to place their abdomen over the adult female鈥檚 mouth. In the majority of cases, females will continue to eat the male even while they mate. But this seemingly extreme form of mating also appears to have advantages in terms of reproductive success.
Professor Maydianne Andrade, co-author of the research and Baruffaldi鈥檚 thesis supervisor, says the behaviour needs to be considered in terms of its evolutionary consequences.
鈥淲hen you study evolutionary ecology, there鈥檚 a temptation to ascribe human characteristics or judgments on the behaviour being observed,鈥 says Andrade, a world-renowned expert on the mating habits of cannibalistic spiders.
鈥淲hat we鈥檙e seeing could have more than one evolutionary implication, and even if it looks abhorrent to us, the evolutionary consequence can be positive for the animal engaging in that behaviour.鈥
Andrade says if we want to think about why a particular set of behaviours has evolved, the underlying question is how it may affect the reproductive success of the animal doing it.
鈥淭hat鈥檚 the evolutionary currency 鈥 what鈥檚 playing out over time is the number of gene copies left behind in offspring,鈥 she says.
Read more about UU直播's Maydianne Andrade and her lab
鈥淚f there鈥檚 a behaviour that increases how many gene copies are left, this means more offspring showing the same traits as their parents, and that鈥檚 the behaviour we expect to see.鈥
The study received funding from the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation (CFI), and the Canada Research Chairs Program.