Multiple paternity and precocial breeding in wild Tasmanian devils, Sarcophilus harrisii (Marsupialia: Dasyuridae)

Polyandry, a common reproductive strategy in various animal species, has potential female benefits, which include enhanced offspring fitness. Benefits can be direct, such as reduced risk of male infanticide of offspring, or indirect, such as increased genetic diversity of offspring and the acquisition of ‘good genes’. Multiple paternity of litters has been recorded in numerous marsupial species but has not been reported in Tasmanian devils, Sarcophilus harrisii (Boitard). We investigated whether multiple paternity occurred in litters within a wild population of Tasmanian devils. Using major histocompatibility complex-linked and neutral microsatellite markers, the paternity of nine litters was analysed. We found multiple paternity in four out of nine litters and that yearling (> 1, < 2 years old) male devils were siring offspring. This is the first record of multiple paternity and of male precocial breeding in wild Tasmanian devils. To date, there are no data relating to the subsequent survival of devils from single- vs. multiple-sired litters; therefore, we do not know whether multiple paternity increases offspring survival in the wild. These results have implications for the Tasmanian devil captive insurance programme, because group housing can lead to multiple-sired litters, making the maintenance of genetic diversity over time difficult to manage.

Eimeria taggarti N. Sp., a Novel Coccidian (Apicomplexa: Eimeriorina) in the Prostate of an Antechinus flavipes

A novel coccidian species was discovered in the prostate of an Antechinus flavipes (yellow-footed antechinus) in South Australia during the period of postmating male antechinus immunosuppression and mortality. This novel coccidian is unusual because it develops extraintestinally and sporulates endogenously within the prostate gland of its mammalian host. Histological examination of prostatic tissue revealed dense aggregations of spherical and thin-walled tetrasporocystic, dizoic, sporulated coccidian oocysts within tubular lumina, with unsporulated oocysts and gamogonic stages within the cytoplasm of glandular epithelial cells. This coccidian was observed occurring concurrently with dasyurid gammaherpesvirus 1 infection of the antechinus' prostate. Eimeria-specific 18S small-subunit ribosomal (r)DNA polymerase chain reaction amplification was used to obtain a partial 18S rDNA nucleotide sequence from the antechinus coccidian. Bayesian phylogenetic analysis based on 18S rDNA gene sequences revealed that the novel coccidian clusters with reptile-host coccidians, forming an ancestral basal lineage of the eimeriid clade. The species has been named Eimeria taggarti n. sp. on the basis of both sporulated oocyst morphology and molecular characterization. It is suspected that E. taggarti is sexually transmitted via excretion of sporulated oocysts or free sporocysts with prostatic secretions in semen.

Females Choose Mates Based on Genetic Relatedness in a Small Dasyurid Marsupial, the Agile Antechinus (Antechinus agilis)

Females in a variety of taxa mate with more than one male during a single oestrus and exhibit mate preferences for genetically compatible males, but the influence of female mate choice on siring success is not clearly understood. Whether females choose to mate with more than one male or endure forced copulations is also often unknown. Here, we examined the effects of genetic relatedness on female mate choice and siring success in a small semelparous carnivorous marsupial, the agile antechinus (Antechinus agilis), during two consecutive breeding seasons. Experimental trials were conducted in captivity over periods of 72 hours using interconnected enclosures in which female antechinus could choose to access any of four separated males, but males were only able to access females that entered their quarters. Females had access to two genetically similar and two genetically dissimilar males simultaneously and all behavioural interactions were observed and scored from continuous video recordings. Genetic similarity between mates and paternity of young was determined by microsatellite analyses. Some females chose to enter and mate with more than one male during a single oestrus period. Although females investigated all males, they spent significantly more time visiting, and mated more times with, genetically dissimilar males. Males that were genetically dissimilar to the female sired 88% of subsequent offspring. Whilst males mated readily with most females, they rejected the advances of some receptive females, indicating a previously unexpected level of male mate choice. The results show that genetic relatedness between mates has a significant influence on mate choice, breeding and siring success in the agile antechinus.

Multiple paternity in the swamp antechinus (Antechinus minimus)

Multiple paternity within litters or broods occurs across a variety of taxa. In the present study, paternity patterns in the swamp antechinus (Antechinus minimus), a small carnivorous marsupial, were investigated using genetic analyses. Microsatellite data confirmed that, of 10 litters sampled from two habitats, a minimum of eight litters were sired by more than one male. Mating with multiple males may enable female swamp antechinuses to increase offspring viability and to ensure fertilisation.

Observation of reproductive strategies of captive kultarrs (Antechinomys laniger)

Captive kultarrs (Antechinomys laniger) were bred from June to February. Their gestation period was longer than 12 days, as suggested by previous research. Pouches were observed to determine whether births occurred. Individuals were capable of producing offspring in their second and third year of life, which has been suspected previously, but never demonstrated in other published studies.

Size breeds success: multiple paternity, multivariate selection and male semelparity in a small marsupial, Antechinus stuartii

Mating in the marsupial genus Antechinus is a synchronous annual event that is characterized by monoestry in females and abrupt postmating mortality in males. Male semelparity (multiple copulations during a single breeding season per lifetime) is often assumed to occur as a consequence of the intense mating effort expended by males in the rut, but the forces selecting for this remain elusive. Here, we investigate selection in male brown antechinus, Antechinus stuartii, and test two hypotheses for the evolution of semelparity: intermale competition and sperm competition. If intermale competition drives semelparity, we predicted that males would be under strong selection for large body size. If sperm competition is important, we predicted that selection would be strongest on scrotal size, a surrogate for testes volume. Using microsatellite markers, we found that 92% of females in free-living conditions mated with multiple males, producing litters of eight that had up to four fathers. These observations confirm the potential for sperm competition. Using selection analysis, we then found paternity success in 119 males to be related most strongly to body mass and scrotal size, thus providing support for both hypotheses. Large males presumably experience increased paternity success by gaining more matings or prolonged copulations via mate guarding, while large testes may allow increased sperm investment per copulation. Increased levels of free corticosteroid hormones in males facilitate the extreme mating effort during the short period of rut, but lead to immune suppression and consequently to the phenomenon of postmating mortality.

Genetic similarity, not male size, influences female mate choice in the agile antechinus (Antechinus agilis)

Our research investigates the effects of genetic relatedness between mates and male size on female mate choice in the agile antechinus (Antechinus agilis). Females were provided with a simultaneous choice between one large and one small male, with a minimum 5 g (~20% of male weight) difference between males, in specially designed mate-choice enclosures. Genetic relatedness between males and females was determined using highly polymorphic, species-specific, microsatellite markers. Male size did not influence mate choice, with approximately equal numbers of large and small males chosen. Females chose males that were more genetically dissimilar to themselves significantly more times and showed significantly more sexual and non-exploratory behaviours near the genetically dissimilar males. The results show that, when free female mate choice is possible, female agile antechinus choose males on the basis of genetic relatedness, rather than male size.

Population density and presence of the mother are related to natal dispersal in male and female Antechinus stuartii

In common with most mammals, the frequency of natal dispersal in antechinuses is strongly male-biased. Inbreeding avoidance has been put forward as the most likely explanation, with juvenile dispersal being driven by the mother. Dispersal distances and factors affecting emigration and immigration of each sex have not previously been studied in antechinuses, because of the difficulty of following the fates of individual dispersers. I studied a dense population of brown antechinuses (Antechinus stuartii) of known parentage in linear habitat that could be comprehensively trapped, and determined the fate of 27 females and 14 males that survived to dispersal age. Juvenile males dispersed not only more frequently than females (71% v. 11%), but also much further (maximum known distance: 1230 m v. 270 m). Males dispersed further if they had been raised in an area of low population density, and were more likely to immigrate into an area with a higher density of females than the natal site. Death of the mother disrupted normal home-range establishment, resulting in frequent philopatry of sons and dispersal of some daughters. Some females emigrated after young were weaned, and this also prompted dispersal of daughters. There was no evidence that daughters with surviving, philopatric mothers were more likely to survive to breed. I conclude that male-biased dispersal appears to result not only from costs of inbreeding, but also partly by the benefits of finding a site with more mating opportunities.

Seasonal changes in the physiology of male Virginia opossums (Didelphis virginiana): signs of the Dasyurid semelparity syndrome?

Semelparity, which is multiplying once in a lifetime, is a rare reproductive strategy among mammals. Several species of the marsupial family Dasyuridae experience 100% male mortality following an intense mating period. We investigated seasonal physiological changes that may be associated with early mortality in the male Virginia opossum (Didelphis virginiana; Didelphidae) and compared these changes with those of semelparous, male dasyurids. Free-ranging male Virginia opossums (n=36) were collected during 2001 at the Oklahoma State University Cross Timbers Experimental Range. Seasonal data were collected on hematological, morphological, and helminth parameters of these individuals. We used one-way ANOVA to determine whether there were seasonal differences among means for each parameter. It appeared that male Virginia opossums experienced some physiological changes similar to those of male dasyurids exhibiting semelparity. All males collected in summer (August) were juveniles of the year. Lack of adult males in August suggests high mortality of this cohort during the breeding season. Opossum characteristics exhibiting the dasyurid semelparity syndrome included packed cell volume, adrenal mass, and helminth numbers. Minor lymphocytopenia, neutrophilia, and testosterone concentrations also were similar to semelparous dasyurids. However, a lack of change in serum cortisol concentration and body mass and dynamics in immunoglobulin protein, serum protein, and testes mass were not consistent with previous reports of semelparous dasyurid physiology. Evolutionary divergence and differences in breeding behavior between dasyurids and didelphids may be responsible for the lack of consistency between the taxa.