Extreme reproducive conflict: sexual cannibalism, female deception and the evolution of male mate choice.

A project undertaken at the Department of Biological Sciences, Macquarie University, and supervised by Katherine Barry

This project addressed the intersection of two of the most enigmatic phenomena
in the evolution of reproductive strategies: sexual cannibalism and male mate
choice. Sexual cannibalism represents an extreme manifestation of sexual
conflict in many systems, and male mate choice in systems without paternal care
continues to challenge our understanding of gender roles within the framework
of sexual selection. Specifically, I investigated female-driven sexual conflict and
its effect on male mating strategies by studying three key sets of behavioural
adaptations in sexually cannibalistic praying mantids:

  1. deceptive signalling by
    females,
  2. precopulatory male mate choice and
  3. postcopulatory male mating
    strategies.

Together, these studies contribute significantly to our understanding
of the evolution of sex roles, sexual conflict and reproductive strategies.

1. Deceptive signaling by females

In many praying mantids, females attract males using a system of sex
pheromones, thus affording females a potential mechanism to exploit sexually
motivated males as easy prey. I examined the potential and extent of deception
among the subset of females most likely to benefit from cannibalism (i.e. poor
condition females).

Results
I found that female attractiveness increased with body condition (as
expected), except for the females in very poor condition, which were much more
attractive than any of the other groups. These results suggest that females in dire
straights deceptively signal to males in order to lure them in and obtain a meal.

Publication
Barry KL. 2015. Sexual deception in a cannibalistic mating system?
Testing the Femme Fatale hypothesis. Proceedings of the Royal Society of London
B
282: 20141428.

2. Precopulatory male mate choice

Male praying mantids are likely to encounter females of varying risk during
their lifetime. I investigated the capacity of males to assess variable levels of risk
imposed by their prospective mates.

Results
I found that female body condition and mating status were good
indicators of female propensity to cannibalise, but found no effect of those
factors on male mating behaviour (i.e. approach speed and distance to mount).

Publication
Jayaweera A, Rathnayake DN, Davis KS & Barry KL. 2015. The risk of
sexual cannibalism and its effect on male approach and mating behavior in a
praying mantid. Animal Behaviour 110: 113-119.

3. Postcopulatory male mating strategies

One of the biggest gaps in our understanding of male mate choice evolution is
the role of postcopulatory strategies, whereby males vary the quantity and/or
nature of the resources allocated to a particular mating. I explored the possibility
of increased ejaculate expenditure by cannibalised males to increase
reproductive output during their final mating, as well as the effect of any
increase on subsequent female attractiveness.

Results
As predicted, cannibalised males transferred a significantly higher
number of sperm to their mates than non-cannibalised males. These data suggest
that cannibalised males terminally invest their mating resources in the current
mating, as predicted by life history theory. I also found that mated females took 8
days on average to become chemically attractive again after their initial mating,
and that there was no significant difference in the period of unattractiveness
between cannibalistic (7.75 ± 0.95 days, N=4) and non-cannibalistic females
(8.25 ± 2.10 days, N=4). These data provide preliminary evidence that increased
ejaculate expenditure does not translate to a paternity advantage via a longer
female refractory period.

Publications
Jayaweera A. & Barry KL. The effect of sexual cannibalism on maleejaculatory expenditure in a praying mantid. Behavioral Ecology, in review.

Jayaweera A, Rathnayake DN, Dean B & Barry KL. Chemical signaling and
context-dependent polyandry in a sexually cannibalistic praying mantid. Austral
Entomology
, in review.

 
Figure 1. Large gravid female mantid

Figure 2. Dr Kate Barry releases an adult mantid at her field site in West Pymble, Sydney

Figure 3. A headless male mantid continues to mate with his female attacker