Australian spiders court to avoid being eaten
If you think dating is tough, consider what some male spiders have to go through. Research from Professor Maydianne Andrade’s lab at the University of Toronto Scarborough suggests that in order to realize their copulatory dreams, male spiders have to know how to court, and must be able to do it for a long time. Australian redback spiders, Latrodectus hasselti, must engage in a courtship dance for at least 100 minutes to avoid being eaten by their partner.
Male Australian redback spiders court by “tapping” on a female’s web. Once a female has accepted the male as a mate, he climbs onto her abdomen and inseminates her. Immediately following insemination, the male voluntarily catapults himself into the female’s mouth. At this point, females make the decision to either consume the male, or feed on only part of his body and then release him. If released, the male will return to the female’s web and continue to court, repeating the entire process again (males that make it to a second insemination are usually consumed thereafter). However, males that courted for more than 100 minutes were less likely to be eaten after the first insemination. This somewhat peculiar sequence of events is best understood in the context of sexual selection.
Sexual selection supposes that individuals possessing traits that are attractive to the opposite sex will acquire more mates and therefore have more offspring than individuals without those traits. Generally, it is the males of a species that are “selected,” meaning females choose which males they prefer. To understand this, we can imagine that if female humans developed a preference for tall males, this preference would likely result in a mating bias (tall guys would get all the girls).
Male Australian redbacks stop eating once they embark on their journey to find a mate. Upon arrival at a female’s web, the only energy available to a male is that which he acquired during his development. Individuals that can acquire a lot of energy during development may possess good genes which can then be passed on to their offspring. PhD candidate and co-author of the study Jeff Stoltz argues that this is likely why female redbacks display a preference for males that can invest a lot of time and energy in courtship.
One interesting twist to this cannibalistic tale is the “sneaker male,” who does not invest energy into courtship, but instead benefits from the courting attempts of others. This behaviour has been well documented in ecological studies and is considered by many to be a type of mating strategy. In the Australian redback, sneaker males arrive at a female’s web after a courting male and copulate and inseminate the female. Why female spiders allow these sneaked copulations is unknown. According to Stoltz, the fact that “females appear unable to discriminate between rivals suggests that the costs may outweigh the benefits.” But he acknowledges that more research into these sneaky copulations is warranted.
The idea of sexual selection first proposed by Darwin has been illustrated in nature time and again. The Australian redback spider provides not just another example of sexual selection, but also a peek into how males may be circumventing female choice—a behaviour that may help explain why preferred “types” do not dominate a population. As the parallels between the world of invertebrates and humans continue to surface, we are provided with an opportunity to learn more about our own behaviour. Maybe it’s just me, but I know a few cannibalistic females and sneaker males.
