Sperm competition and genetic diversity in the agile antechinus (Dasyuridae: Antechinus agilis)

Abstract

The mouse-like marsupial Antechinus agilis is common to south-eastern Australia with breeding and lifehistory traits being highly synchronous. Mating activity is con®ned to a 10-to 15-day period in August, at the end of which all males die as a result of a stress-induced suppression of the immune system. Ovulation occurs at this time and females rely on stored sperm from specialized crypts in the lower isthmus of the oviduct for successful fertilization. Here we report a high incidence of mixed paternity litters, which can be attributed to sperm from multiple males being stored in the isthmic crypts. Data from this study also suggest a possible second male siring advantage in controlled ex situ sperm competition mating trials, irrespective of the delay between the two males being given mating access to the female or of the mating time relative to ovulation. In determining paternity through DNA pro®ling, population genetic data were obtained that showed signi®cant differences in the genetic heterozygosity between unrelated adults, half siblings and full siblings. We suggest that the isthmic crypts, in addition to storing viable sperm, are capable of releasing a mix of sperm that increases the likelihood of mixed paternity litters. This allows all mating males the opportunity to sire young, increases female reproductive ®tness and overall maintains high levels of population genetic heterozygosity in the face of total male mortality annually.

Gender and parental influences on the growth of a sexually dimorphic carnivorous marsupial

“…As males die before the young are born, paternal investment is limited to their genetic contribution. These male semelparous species tend to mate promiscuously, with factors such as genetic similarity (Parrott, Ward & Temple‐Smith, 2006), male genetic quality (Fisher et al ., 2006), mating order (Shimmin, Taggart & Temple‐Smith, 2000; Kraaijeveld‐Smit et al ., 2002) and male body size (Kraaijeveld‐Smit, Ward & Temple‐Smith, 2003) observed to affect siring success.…”

The effects of habitat fragmentation on the social kin structure and mating system of the agile antechinus, Antechinus agilis

“…Mating in A. agilis is promiscuous and occurs in August. Multiple males usually contribute to the litters of 6 to 10 offspring, and male siring success is negatively associated with the genetic similarity between mates (Shimmin et al . 2000; Kraaijeveld‐Smit et al .…”

Factors influencing paternity success in Antechinus agilis: last-male sperm precedence, timing of mating and genetic compatibility

“…Previous work on sperm competition in A. agilis in captivity concluded that last‐male sperm precedence occurs, with the last male siring 64% of the offspring (Shimmin et al ., 2000). Last‐male precedence was strongest when both matings occurred early in the oestrous period, with the last male siring 72% (Shimmin et al ., 2000). Male size was not taken into account in this study, and the molecular technique used required that pouch young remain with the mothers until they were large enough to obtain sufficient DNA.…”

“…Male size was not taken into account in this study, and the molecular technique used required that pouch young remain with the mothers until they were large enough to obtain sufficient DNA. This resulted in reduced numbers of offspring, because when under stress, females may consume their own pouch young (Shimmin et al ., 2000). With current microsatellite typing techniques, only a small amount of tissue is needed for paternity analysis (Queller et al ., 1993), and paternity results can be obtained on complete litters, sampled immediately after birth.…”