Reproductive ecology of wild tammar wallabies in natural and developed habitats on Garden Island, Western Australia

Abstract

Reproduction may be influenced by major environmental changes experienced by an entire population as well as variation within a population in maternal resource availability or quality. We examined relationships between body condition and reproductive traits in two wild populations of the seasonally breeding tammar wallaby (Macropus eugenii) on Garden Island, Western Australia, that differed in access to supplemental food resources. Body condition changed predictably over the year, with females losing condition over the dry summer and gaining condition over the winters, when lactation occurs and most annual precipitation falls. Body condition influenced reproduction, with females of greater body condition more likely to have a pouch young, and to have a larger pouch young, early in the reproductive season. This intrapopulation pattern was opposite to that seen across populations – females in a native bushland were in poorer condition yet were more likely to have pouch young, and had larger pouch young, in March than did females living in a water-supplemented habitat on a naval base. Body condition did not influence the probability of weaning a pouch young in a year, nor did reproductive success influence changes in body condition across seasons. Instead, annual variation in precipitation had a dramatic effect on population weaning success in the native bushland, but not on the naval base. In summary, individual variation in body condition as well as large climatic variation influenced the reproduction of tammar wallabies on Garden Island, but the nature of the effect depended on the different habitats experienced by the two study populations.

Artificial light at night desynchronizes strictly seasonal reproduction in a wild mammal

“…On the naval base, native vegetation persists in clumps, surrounded by lawns of introduced grasses ( primarily couch grass, Cynodon dactylon). Until recently, these irrigated grasses were a major part of the diet of the wallabies on the base [27,52] and we believe this access has to date buffered any negative effects [53]. However, the irrigation of these lawns was recently disconnected and the only irrigated area (the oval) has been fenced to exclude wallabies.…”

Sexual conflict in action: An antagonistic relationship between maternal and paternal sex allocation in the tammar wallaby, Notamacropus eugenii

“…Body condition of these females was measured at time of capture or death; this potentially being upwards of 12 months after the offspring was conceived (Tyndale‐Biscoe & Renfree, ). It is therefore unsurprising that maternal body condition was not related to offspring SR considering the variability in female condition across the season (Schwanz & Robert, ). The current study design did not allow for collection of body condition data at the point of conception, and further research would be required to determine whether this population conforms to the relationship predicted by Trivers and Willard ().…”

Costs of Rearing the Wrong Sex: Cross-Fostering to Manipulate Offspring Sex in Tammar Wallabies

“…We focused our cross-fostering experiment on wallabies found on the navy base (Fleet Base West, Australian Department of Defence), which occupies ~25% of the island. In this subpopulation, the wallabies live at high densities and have access to supplemental food and water (irrigated lawns and sports fields; see [ 55 ]).…”

“…Despite the energetic investment of lactation, most females gain body condition during the winter [ 13 , 55 ] and rely on current nutrition rather than stored reserves to meet lactational demands [ 36 ]. Body condition is lost over the summer when annual precipitation is at its minimum [ 55 ]. During this time, offspring are recently-weaned and reproductive females undergo a ~30-day gestation of the subsequent reactivated embryo ([ 56 ]; Fig 1 ).…”

“…Confusingly, although maintenance of body condition over the dry summer was associated with the production of daughters in both years of our study (consistent with LRC/LRI), higher body condition at the start of the summer (the time of embryonic reactivation; Fig 1 ) in one year (the second year) of our study was associated with producing sons (consistent with TW; [ 13 ]). This is because change in condition over the second summer was related to initial body condition–the highest-residual mothers in December had the greatest loss in condition by March [ 55 ]. With the goal of assessing whether LRC/LRI, TW or both operate in our study population, we performed a cross-fostering experiment to examine the direct fitness consequences of rearing the “wrong” sex.…”