Simon J. Ward

The effects of habitat fragmentation via forestry plantation establishment on spatial genotypic structure in the small marsupial carnivore, Antechinus agilis

Dispersal is an important influence on species’ distributions, patch colonization and population persistence in fragmented habitat. We studied the impacts of habitat fragmentation resulting from establishment of an exotic pine plantation on dispersal of the marsupial carnivore, Antechinus agilis. We applied spatial analyses of individual multilocus microsatellite genotypes and mitochondrial haplotypes to study patterns of gene flow in fragmented habitat and natural habitat ‘control’ areas, and how this is affected by the spatial dispersion of habitat patches, the presence of corridors and a ‘mainland’ source of migrants. Spatial analysis of molecular variance and partial Mantel tests confirmed the absence of cryptic barriers to gene flow in continuous habitat, which if present would confound the comparison of genetic structures in fragmented vs. unfragmented habitats. Spatial genotypic structure suggested that although dispersal was male‐biased in both habitat types, fragmentation restricted dispersal of males more than that of females and the degree of restriction of male dispersal was dependent on the geographical isolation of the patch. The scale of positive genotypic structure in fragmented habitat was restricted to the two closest patches for females and the three closest patches for males. Our results provide evidence for significantly increased gene flow through habitat corridors relative to that across the matrix and for significantly lower gene flow between ‘mainland’ unfragmented habitat and habitat patches relative to that within either habitat type, suggesting a behavioural barrier to crossing habitat interfaces.

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

We describe the patterns of paternity success from laboratory mating experiments conducted in Antechinus agilis, a small size dimorphic carnivorous marsupial (males are larger than females). A previous study found last‐male sperm precedence in this species, but they were unable to sample complete litters, and did not take male size and relatedness into account. We tested whether last‐male sperm precedence regardless of male size still holds for complete litters. We explored the relationship between male mating order, male size, timing of mating and relatedness on paternity success. Females were mated with two males of different size with either the large or the small male first, with 1 day rest between the matings. Matings continued for 6 h. In these controlled conditions male size did not have a strong effect on paternity success, but mating order did. Males mating second sired 69.5% of the offspring. Within first mated males, males that mated closer to ovulation sired more offspring. To a lesser degree, variation appeared also to be caused by differences in genetic compatibility of the female and the male, where high levels of allele‐sharing resulted in lower paternity success.

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

Habitat fragmentation is one of the major contributors to the loss of biodiversity worldwide. However, relatively little is known about its more immediate impacts on within‐patch population processes such as social structure and mating systems, whose alteration may play an important role in extinction risk. We investigated the impacts of habitat fragmentation due to the establishment of an exotic softwood plantation on the social kin structure and breeding system of the Australian marsupial carnivore, Antechinus agilis. Restricted dispersal by males in fragmented habitat resulted in elevated relatedness among potential mates in populations in fragments, potentially increasing the risk of inbreeding. Antechinus agilis nests communally in tree hollows; these nests are important points for social contact between males and females in the mating season. In response to elevated relatedness among potential mates in fragmented habitat, A. agilis significantly avoided sharing nests with opposite‐sex relatives in large fragment sites (but not in small ones, possibly due to limited nest locations and small population sizes). Because opposite‐sex individuals shared nests randomly with respect to relatedness in unfragmented habitat, we interpreted the phenomenon in fragmented habitat as a precursor to inbreeding avoidance via mate choice. Despite evidence that female A. agilis at high inbreeding risk selected relatively unrelated mates, there was no overall increased avoidance of related mates by females in fragmented habitats compared to unfragmented habitats. Simulations indicated that only dispersal, and not nonrandom mating, contributed to inbreeding avoidance in either habitat context. However, habitat fragmentation did influence the mating system in that the degree of multiple paternity was reduced due to the reduction in population sizes and population connectivity. This, in turn, reduced the number of males available to females in the breeding season. This suggests that in addition to the obvious impacts of reduced recruitment, patch recolonization and increased genetic drift, the isolation of populations in habitat patches may cause changes in breeding behaviour that contribute to the negative impacts of habitat fragmentation.

Paternity success and the direction of sexual selection in a field population of a semelparous marsupial, Antechinus agilis

Antechinus agilis is a small sexually size dimorphic marsupial with a brief annual mating period of 2–3 weeks. All males die after this period, and females give birth to up to 10 young. Mating is thought to be promiscuous, however, there is no field data to confirm this. Using microsatellites, we investigated paternity patterns over two seasons in a wild population. Male weight was significantly positively related to the number of females fertilized and with the number of offspring sired, in both years. Furthermore, selection gradients indicated selection for larger males. Both results suggest that size dimorphism in A. agilis can be explained by sexual selection for larger males. The proportion of offspring sired within litters, did not relate to male size. Therefore, larger males are more successful through higher mating access, not through their sperm outcompeting that of smaller males. As expected from their known ranging behaviour, the number of offspring within litters left unassigned to a father did not depend on the grid location of the mother. Female size did not differ between successful reproducing and unsuccessful females. However, females that weaned offspring had larger heads than females that did not wean offspring. Males did not ‘prefer’ mating with larger females, nor did assortative mating occur. From our results, the mating system of A. agilis is clearly promiscuous. Selection for larger males occurred in both years, even though in one year the operational sex ratio was highly female biased, suggesting that the potential reproductive rate is a better predictor of the direction of sexual selection in A. agilis.

Are age‐related variations in breeding performance greatest when food availability is limited?

Age-related improvements in reproductive performance in seabirds have been well documented, and may be explained by improvements in foraging efficiency or increased experience and reproductive effort with age. The interactive effects of parental age and food supply on reproductive performance, however, remain poorly understood. A widespread mass mortality of pilchards Sardinops sagax in southern Australian waters in 1998 provided a unique opportunity to investigate the effects of a sudden reduction in the availability of amajor prey species on Australasian gannets Morus serrator, an important local marine predator. Age-related differences in the breeding performance of gannets were evident in 1 year of reduced pilchard availability; when food was not limited, both young and experienced parents were equally capable of rearing chicks and had similar levels of breeding success. These data clearly demonstrate the interactive effects of parental age and food supply on breeding performance and suggest that such differences only become apparent when conditions become more stressful.

Olfactory cues, genetic relatedness and female mate choice in the agile antechinus (Antechinus agilis)

Females show mate preferences for males that are genetically dissimilar to themselves in a variety of taxa, but how females choose these males is not clearly understood. In this study, we examined the effects of olfactory stimuli and genetic relatedness on female mate choice in a small carnivorous marsupial, the agile antechinus (Antechinus agilis), during two breeding seasons. Captive female antechinus in oestrus were provided with a combination of male urine and body scent from two novel males, one more genetically similar and one more dissimilar to the females, in a Y-maze olfactometer. Genetic relatedness between females and pairs of males was determined using highly polymorphic, species-specific, microsatellite markers. Females consistently chose to visit the scents of males that were genetically dissimilar to themselves first, spent significantly more time near the source of those scents and showed more sexual and non-exploratory behaviours near those scents. These data demonstrate that chemosensory cues are important in mate choice in the agile antechinus and that females prefer males that are genetically dissimilar to themselves.

Effects of drought on weight, survival and breeding success of agile antechinus (Antechinus agilis), dusky antechinus (A. swainsonii) and bush rats (Rattus fuscipes)

Extreme weather conditions, such as drought, significantly decrease the survival and breeding success of numerous species. Despite the frequent occurrence of such conditions in Australia, little is known about the effects of changing environmental conditions on the native small mammals. This study, conducted from 2002 to 2004, focussed on sympatric wild populations of the agile antechinus (Antechinus agilis), with more limited information on the dusky antechinus (A. swainsonii) and the bush rat (Rattus fuscipes). Bodyweights of agile antechinus before and during the breeding season were significantly lower in 2003 (drought) than in 2002 or 2004. Survival of female agile antechinus and the number of young per litter also decreased significantly during drought. In contrast, the dusky antechinus showed no difference in mean bodyweights between years, high survival rates of females and similar litter sizes in 2002 and 2003. There was also no difference in bodyweight of bush rats between years. Low rainfall was recorded during pregnancy and lactation in the agile antechinus, but rainfall was higher during pregnancy and lactation in the dusky antechinus. The survival and breeding success of the agile antechinus may have been adversely affected by a combination of interspecific competition, timing of the breeding season and severity of the drought.

Aspects of the ecology of swamp antechinus (Antechinus minimus maritimus) on a Bass Strait island

The swamp antechinus (Antechinus minimus maritimus) is a small insectivorous marsupial inhabiting closed heath and tussock grassland in south-eastern Australia. The species is considered ‘Near Threatened’ on the Australian mainland. Populations persist on coastal islands off Wilsons Promontory, but their current status is unknown. This study investigated the density, diet and reproduction of the swamp antechinus on Kanowna Island. Data were collected by live trapping in different vegetation types during four trips between August 2003 and January 2004. Higher animal densities (47–129 ha–1) were found for Kanowna Island than for previously studied mainland populations (1–18 ha–1). Examination of scats showed that this species eats a wide variety of prey types, with moth larvae a major dietary component, particularly during the breeding season. Births were estimated to have occurred between 28 June and 8 August, which is a longer period than reported for other populations of this species. Factors including reduced predation, restricted dispersal and increased food availability may be responsible for supporting this dense population.

Aspects of the breeding biology of antarctic petrels and southern fulmars in the rauer group, east Antarctica

Breeding phenology, success and nest attendance of Antarctic Petrels Thalassoica antarctica and Southem Fulmars Fulmarus glacialoides at the Rauer Group (68°51′S, 77°50′E), East Antarctica, are discussed. Most data were collected on Hop Island (68°50′S, 77°42′E) in January and February 1988, and from December 1988 to March 1989. Observations extended from the late stages of incubation to post-guard or fledging periods. Some annual breeding indices collected from 1983 onwards at census sites are compared with meteorological data and the extent of fast ice for the nearby Davis Station (68°35′E, 77°58′E). Both species had a restricted hatching period, reflecting a brief and synchronised egg-laying period, typical of other southem fulmarine petrels. Antarctic Petrel chicks hatched from 4 January (1989), and c. 90% appeared by 16 January (both years). Southern Fulmar hatching began on 21 January (1988) and almost all chicks appeared by 6 February (both years). Adult attendance at nests declined with increasing chick age. For Antarctic Petrels, this was most marked at about 11 days; no chicks had continuously attendant adults after 24 days, although adults returned to feed them. Incubation shifts in Southern Fulmars were longer than shifts following hatching and the post-guard period started, on average, 13 days after hatching. Egg and chick losses varied between years and sites. The South Polar Skua Catharacta maccormicki was apparently involved in the majority of losses. Nest sites of both species resemble those elsewhere: Southern Fulmars may require steeper sites, allowing a fall away from colonies. Antarctic Petrels are less affected by accumulation of snow or ice and shelter from katabatic winds may be important. Although weather may modify breeding success locally, annual success must depend on the ability of parents to produce eggs and feed chicks: this may be moderated by the extent and persistence of pack ice.

Multiple paternity and communal maternal care in the feathertail glider (Acrobates pygmaeus)

It has been predicted, on the basis of morphological and behavioural evidence, that female feathertail gliders (Acrobates pygmaeus) will mate with multiple males within a single oestrus and that multiple paternity may occur in their litters. To determine whether feathertail glider litters are sired by multiple males, DNA collected from 10 litters and their mothers was tested for hereditary polymorphisms. The techniques used to evaluate paternity included AFLP (amplified fragment length polymorphisms), RAPD (randomly amplified polymorphic DNA) and RAMP (randomly amplified microsatellite polymorphisms) analyses and microsatellite markers. Although most genetic techniques produced only monomorphic bands, analyses with AFLPs indicated that multiple paternity did occur in six of eight litters, confirming that multiple mating within a single oestrous period occurs in this species. Results further indicated that mothers care for young other than their own. On the basis of their high testes-to-bodyweight ratio, male-biased sexual size dimorphism and multiple paternity in litters, sperm competition is considered highly likely to occur in this species.