More about this project
If you'd like a little more information about this project, read on!
Background
Black widows have very poor vision, but they are extremely sensitive to vibratory and chemical information. Keen chemical senses allow essentially blind males to solve the problem of finding a mate in a large and complex environment. Females produce silk-borne pheromones that attract males at long range. These chemical messages act like scent-based personal ads, providing males with information about the female's mating status and feeding history, and allowing them to avoid potentially cannibalistic females. Once he arrives at a female's web and makes contact with the pheromone on the silk, he begins an elaborate courtship display. The web now becomes a dance floor that transmits vibrations to the female, with luck, sending the message that he is a male, not a meal.
We know from laboratory experiments that male widow spiders can detect airborne chemicals produced by nearby males and females. These cues about the local competitive environment and availability of females can affect the timing of a male’s development and thus his competitive ability. In nature, however, the number of rival males and available females changes over the mating season, and so will the traits that allow males to be most successful. For example, maturing quickly at a small size could allow a male to be the first to find a female at the beginning of the mating season, but make him a poor competitor later on when rival males are already abundant. Our field site is the ideal place to find out how western black widow males use social information during their development to maximize their chances of reproductive success in a fiercely competitive and changing environment.
Researchers in our lab were part of a team who recently discovered that males of closely related widow species are capable of mating with females before the females are sexually mature. Observations at our field site this past season suggest that immature mating is also common and advantageous in western black widows. However, as far as we know, only adult females produce the attractive chemical signal that allows males to locate them over long distances. So how do males detect valuable but chemically hidden immature females? To solve this mystery, we plan to test the hypothesis that nearby adult females and the silk left behind by rival males provide chemical cues that help males to locate immature females.
Significance (or, Why Anyone Should Care)
Black widows are popular research subjects, but much of what we know about their sexual behaviour and communication is based on carefully controlled laboratory experiments. Thus, despite decades of research on their mating behaviour, immature mating was reported for the first time only this year. This suggests there is much we still do not know, and field work is essential for uncovering more about how this fascinating mating system–a textbook example of sexual conflict–works. We spent the 2016 mating season carefully tracking the population of spiders at our field site. Because of this, we will be able to design and conduct experiments that are as naturalistic as possible in context and timing. This project will result in a much more complete understanding of how males assess and respond to competition and what makes them successful at finding and securing mates. It will also shed light on the largely overlooked role of male-produced chemical cues in spider communication systems.
More broadly, the results of this project will increase our understanding of chemical communication in spiders, some of which are invasive or considered pests in certain areas. Such an understanding in insects has been crucial to the development of pesticide-free control strategies for pest species. For example, once the chemical components of a naturally occurring female attractant are identified, they can be synthesized in the lab and used to trap and remove males from a insect pest population. Based on our previous work, we expect that this sort of control strategy has the potential to be very successful in spiders - in 2013, we were able to trap over 400 male black widows outside cages containing pheromone-laden female silk in less than 24 hours.
Related research by members of our team:
Baruffaldi L & Andrade MCB. (2015). Contact pheromones mediate male preference in black widow spiders: avoidance of hungry sexual cannibals? Animal Behaviour. 102: 25-32.
Biaggio MD, Sandomirsky I, Lubin Y, Harari AR, & Andrade MCB. (2016). Copulation with immature females increases male fitness in cannibalistic widow spiders. Biology Letters. 12(9): 20160516.
Kasumovic MM & Andrade MCB. (2004). Discrimination of airborne pheromones by mate-searching male western black widow spiders (Latrodectus hesperus): species-and population-specific responses. Canadian Journal of Zoology. 82(7): 1027-34.
Kasumovic MM & Andrade MCB. (2006) Male development tracks rapidly shifting sexual versus natural selection pressures. Current Biology. 16(7): R242-3.
MacLeod EC & Andrade MCB. (2014) Strong, convergent male mate choice along two preference axes in field populations of black widow spiders. Animal Behaviour. 89: 163-169.
Scott C, Kirk D, McCann S, & Gries G. (2015) Web reduction by courting male black widows renders pheromone-emitting females' webs less attractive to rival males. Animal Behaviour. 107:71-8. Summary
Scott C, McCann S, Gries R, Khaskin G, & Gries G. (2015) N-3-Methylbutanoyl-O-methylpropanoyl-L-serine Methyl Ester – Pheromone Component of Western Black Widow Females. Journal of Chemical Ecology. 41(5): 465-72. Summary
Vibert S, Scott C, & Gries G. (2014) A meal or a male: the ‘whispers’ of black widow males do not trigger a predatory response in females. Frontiers in Zoology. 11(4). Summary
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