Sperm fertility and skewed paternity during sperm competition in the Australian long‐eared bat Nyctophilus geoffroyi (Chiroptera: Vespertilionidae)

Abstract

Prolonged sperm storage, rare among mammals, is widespread among bats and may promote sperm competition, assuming stored sperm are fertile. However, while sperm storage has been documented in many bat species, there have been few investigations of the fertility of stored sperm. Related to this, and a fundamental question in the study of competition at the gametic level, is the effect of mating order on success during sperm competition. For mammals there are no clear mating order effects, in part because females do not store sperm for prolonged periods, but there have been no investigations of mating order effects during sperm competition in sperm-storing bats. I report here on a study designed to investigate the fertility of stored sperm and the effects of mating order on success during sperm competition in a captive colony of Australian long-eared bats Nyctophilus geoffroyi (Chiroptera: Vespertilionidae). Bats were housed in outdoor¯ight-cages, under natural light and temperature regimes. Females were housed serially with two males and were separated from them at intervals throughout the year. Blood plasma progesterone concentrations, measured using double antibody radioimmunoassay, were monitored to assess the duration of sperm storage. Paternity of offspring was assessed using genetic markers identi®ed using gel electrophoresis of blood enzymes.Blood plasma progesterone concentrations were basal from early autumn till mid-late winter, increased markedly during pregnancy, and generally fell back to basal 5±6 weeks post-partum. Data indicated that females could store fertile sperm for more than 90 days, while sperm stored by males were fertile after 4±5 months' storage. Paternity was signi®cantly biased toward one male which fathered all offspring. Results are discussed in the context of sperm competition.

Population size, catchment area, and sex-influenced differences in autumn and spring swarming of the brown long-eared bat (Plecotus auritus)

“…Spring swarming could also occur if there are advantages for males in late matings through sperm competition (Fenton 1984;Watt and Fenton 1995;Hosken 1998) or by increased fertilization success in females. Hosken (1998) found out superior males of the less long-eared bat (Nyctophilus geoffroyi Leach, 1821) during sperm competition.…”

“…Hosken (1998) found out superior males of the less long-eared bat (Nyctophilus geoffroyi Leach, 1821) during sperm competition. Senior et al (2005) demonstrated mating to be skewed towards males that roost with females in summer and Watt and Fenton (1995) found reproductive success to be skewed in swarming M. lucifugus.…”

Determinants and Patterns of Reproductive Success in the Greater Horseshoe Bat during a Population Recovery

“…Where males compete with each other for access to females, large body size often confers an advantage and thus correlates positively with individual paternity success [1] . High variance in breeding success among individuals leads to reproductive skew at the population level, which has been shown in a range of mammalian groups including ungulates [2] , primates [3] , pinnipeds [4] , carnivores [5] and bats [6] . In addition to size, other sources of variation (some correlated with size) may also influence a male's access to females, such as whether he holds a high quality territory [7] , his age [8] and his level of heterozygosity [9] .…”