| dc.description.abstract | Sex-biased predation occurs when one sex of a prey species is consumed more than the other,
irrespective of their relative availability (sex-ratio). Some of the potential factors leading to sex-
biased predation are sex differences in morphology and/or behaviour of prey species. In the
context of mate-finding, we often see sex-specific behavioural strategies, such as signalling and
searching. The relative risk of predation on the two sexes during mate-finding depends on who
signals, who searches, the risks associated with these behaviours, and the degree of
involvement in these activities. Prey wing remains found in the roosts of a bat predator,
Megaderma spasma, reveal interesting patterns for two katydid genera, Mecopoda and
Onomarchus. Mecopoda sp. wing remains are male-biased in the breeding season and female-
biased in the non-breeding season, while Onomarchus uninotatus wing remains are female-
biased year-round. These two katydids differ in their mate-finding strategies: in Mecopoda sp.,
which are found close to the ground, males signal acoustically and females search silently to
locate them. Onomarchus uninotatus is an arboreal katydid, that uses an acoustic-vibratory
multimodal duet for mate-finding within trees, with both sexes signalling and searching to
find mates.
To explore the factors driving the sex-biased predation by M. spasma on Mecopoda sp., I used a
combination of field observations and enclosure experiments with wild-caught live animals.
The males and females of Mecopoda sp. were compared with respect to (i) their availability,
i.e., natural sex-ratio across the seasons, (ii) the predation risks associated with different
behaviours, and (iii) the prevalence of their risky behaviours in the wild. The results show that
the relative availability of the sexes does not explain the male-biased predation on Mecopoda in
the breeding season; whereas in the non-breeding season, very few males are available, which
could lead to the female-biased predation. Males perform high-risk mate-finding behaviours,
such as calling and flight, with a high prevalence in the wild. Although flight is equally risky
for both sexes, females rarely fly.
To understand bat predation risk on male and female O. uninotatus and its possible role as a
selection pressure driving the evolution of multimodal duetting, outdoor enclosure
experiments were performed with live bats and katydids. Bat predation risks were compared
(i) between the signalling and searching strategies of each sex, and (ii) between male and
female signalling. The findings indicate that bat predation risk fails to explain the evolution
of vibrational signalling in O. uninotatus females, as searching by walking is as safe as
signalling, leading to an overall low predation risk on females within a tree. However, their
duetting behaviour lowers the risk on males, who can shift from high-risk signalling to low-
risk searching by walking, once females start signalling.
Finally, I focused on bat predation risk of searching behaviour in O. uninotatus, which
potentially takes flights across trees. Comparisons were made between males and females for
(i) bat predation risk of flight using enclosure experiments and (ii) across-tree movement
patterns using radio-telemetry. I found that flight is equally risky for both sexes, but females
move across trees 1.6 times more often and 1.8 times greater distances, which could make
them more vulnerable to predation, offering a possible explanation for the female-biased prey
remains found in M. spasma roosts.
Overall, this thesis provides a comprehensive examination of the predation risks associated
with signalling and searching behaviours of katydids. The interplay between sex-specific
behaviours and ecological factors can explain sex-biased predation patterns | en_US |
