Male reproductive investment relative to age and flight behaviour in the monandrous butterfly Pararge aegeria |
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Authors: | Lesley Vande Velde Pauline Silvestre David Damiens Hans Van Dyck |
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Institution: | (1) Behavioural Ecology and Conservation Group, Biodiversity Research Centre, Earth and Life Institute, Universit? Catholique de Louvain (UCL), Croix du Sud 4, bte. 7.07.04, 1348 Louvain-la-Neuve, Belgium; |
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Abstract: | Male reproductive investment may signify a considerable cost to male insects that produce sperm packages or spermatophores.
Male butterflies allocate much of their active time budget to mate location, and they may adopt different behavioural strategies
to do so. In the speckled wood butterfly (Pararge aegeria L.), males adopt either a territorial wait-and-fight strategy (territorial perching) or a fly-and-search strategy in wider
areas (patrolling). In this study, we analysed the impact of male age, male size and male behaviour (i.e. behavioural strategies
and levels of activity) on spermatophore investment (i.e. spermatophore mass, number of eupyrene sperm bundles). As predicted,
reproductive investment increased with male age and size. Nevertheless, the increase of spermatophore mass with age and the
number of eupyrene sperm bundles (i.e. fertile sperm) was stronger in low-activity males compared to active flying males.
This suggests that flight activity has a negative impact on male reproductive investment. However, males that were forced
to fly in the laboratory produced more eupyrene sperm bundles than resting males. We discuss the potential effects of male–male
competition and predation risk on current versus future male reproduction. Males adopting different mate-locating strategies
(perching and patrolling) in outdoor cages did not differ in spermatophore traits as was predicted from their very different
flight performances. Copulations of territorial perching males took somewhat longer than copulations with non-perching males.
There was a significant family effect of spermatophore size and of the expression of male mate-locating strategies suggesting
heritable variation. Female traits (i.e. age and size) did not strongly affect spermatophore production. We discuss the results
relative to both ultimate and proximate explanations of the complex relationships between butterfly activity, behavioural
strategies, age and spermatophore production. |
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