Abstract
Spotted spiny lobsters, Panulirus guttatus, are small,
obligate reef-dwellers that exhibit a highly sedentary lifestyle and a low
tendency to aggregate with conspecifics, and that reproduce asynchronously
year-round. Individual females can produce multiple clutches per year but
have a short receptivity per clutch. As in most spiny lobsters, females of
P. guttatus mate only once per clutch and resist
further mating attempts, features that may favour development of female mate
choice but limit the potential for sperm competition. We separately examined
mate choice by large and small mature females through laboratory experiments
that controlled for effects of male–male competition, quality of shelter,
and mere social attraction. Only large females expressed preference for
larger males relative to their own size, suggesting that only large females
that mate with small males risk sperm limitation on fecundity success. In
couples that mated, males deposited rather small, thinly spread
spermatophores on the sterna of females. Spermatophore area (considered as a
proxy measure of sperm content) increased with male size and showed no
relationship with female size, suggesting that males of P.
guttatus have a short sperm-recovery period or do not exhibit
strategic sperm allocation in a non-competitive context. A comparison of
average sperm allocation between P. guttatus and its
sympatric species, P. argus (a much larger, highly mobile,
and highly social species with more seasonal reproductive periods and a
longer receptivity of females per clutch), suggests that males of P.
guttatus allocate proportionally less sperm to females, on
average, than males of P. argus do. According to
predictions of across-species risk models, this result suggests that males
of P. guttatus perceive lower average levels of sperm
competition risk than males of P. argus do, implying that
different Panulirus species may exhibit different mating
strategies in accordance with their particular life-history and
sociobiological traits.
Sperm competition games: optimal sperm allocation in response to the size of competing ejaculates
