Sperm removal and ejaculate size correlate with chelae asymmetry in a freshwater crayfish species

Asymmetry in traits of sexual relevance may
impair copulation behaviour and sexual performance of
males, ultimately resulting in a fitness cost. Freshwater
crayfish males use chelae, a sexually selected trait, to secure
and position the female prior to and during mating. Thus, a
relatively large chelae asymmetry, resulting from accidental
loss and regeneration of one cheliped after autotomy, could
have great consequences for male sexual behaviour. We
studied copulatory behaviour and sperm expenditure of
males paired to a mated female in Austropotamobius
italicus, a freshwater crayfish species where both male
and female mate multiply and where last-mating males are
able to actively remove previously deposited sperm. We
aimed at assessing whether male sperm removal and
expenditure varied according to sperm allocated by firstmating
males, and according to copulation behaviour and
phenotypic traits (carapace length, chelae length and relative
chelae asymmetry) of second-mating males. Secondmating
males did not adjust their ejaculate size in relation to
first-mating male ejaculate, nor to the first-mating male’s
sperm removed. Moreover, the amount of sperm removed
by second-mating males increased with increasing firstmating
males ejaculate size, and first-mating male sperm
remaining after removal did not correlate with the original
first-mating male ejaculate size. Interestingly, the amount of
sperm removed by second-mating males decreased with
increasing relative chelae asymmetry, while increasing
with male body size. However, second-mating (but not
first-mating) asymmetric-clawed males produced larger
ejaculates than symmetric-clawed ones. Importantly, the
proportion of second-mating male sperm remaining after
the two matings did not vary with relative chelae asymmetry
nor with body size of second-mating males. Thus, small,
asymmetric-clawed crayfish males appear to adopt sperm
allocation tactics that allow them to fully compensate for
their inferior sperm removal ability.