Academic literature on the topic 'Macropus Australia Reproduction'

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.

In the wet–dry tropics of northern Australia, temperatures are high and stable year-round but monsoonal rainfall is highly seasonal and variable both annually and spatially. Many features of reproduction in vertebrates of this region may be adaptations to dealing with this unpredictable variation in precipitation, notably by (i) using direct proximate (rainfall-affected) cues to synchronize the timing and extent of breeding with rainfall events, (ii) placing the eggs or offspring in conditions where they will be buffered from rainfall extremes, and (iii) evolving developmental plasticity, such that the timing and trajectory of embryonic differentiation flexibly respond to local conditions. For example, organisms as diverse as snakes ( Liasis fuscus , Acrochordus arafurae ), crocodiles ( Crocodylus porosus ), birds ( Anseranas semipalmata ) and wallabies ( Macropus agilis ) show extreme annual variation in reproductive rates, linked to stochastic variation in wet season rainfall. The seasonal timing of initiation and cessation of breeding in snakes ( Tropidonophis mairii ) and rats ( Rattus colletti ) also varies among years, depending upon precipitation. An alternative adaptive route is to buffer the effects of rainfall variability on offspring by parental care (including viviparity) or by judicious selection of nest sites in oviparous taxa without parental care. A third type of adaptive response involves flexible embryonic responses (including embryonic diapause, facultative hatching and temperature-dependent sex determination) to incubation conditions, as seen in squamates, crocodilians and turtles. Such flexibility fine-tunes developmental rates and trajectories to conditions–-especially, rainfall patterns–-that are not predictable at the time of oviposition.

Immunocontraception involves eliciting an immune response against eggs, sperm or hormones so that successful reproduction is prevented. Work in Australasia is aimed at European rabbits (Oryctolagus cuniculus), red foxes (Vulpes vulpes), house mice (Mus musculus), common brushtail possums (Trichosurus vulpecula), koalas (Phascolartcos cinereus) and kangaroos (Macropus spp.), with the vaccines involved all containing self antigens or their relatives. Two fundamental problems have been inadequately addressed in this research. The first problem is that it is difficult to obtain strong immune responses against self antigens and so the vaccines may be ineffective. Most published data on the effect of immunocontraceptives on reproduction involve the use of an adjuvant of which there are many kinds. The materials enhance the immune response greatly. The most frequently used is Freund?s adjuvant which can cause chronic suffering. Its use on wildlife will lead to very negative public perceptions. There has been no convincing demonstration that successful immunocontraception is possible with any method of vaccination likely to be used in the field, if success is defined as contraception of a proportion of the population high enough for management requirements. If it is assumed that success can be achieved, the second fundamental problem arises with two potential consequences. Even with adjuvant, a substantial minority of the vaccinated animals remains fertile. The first consequence is that since failure to be contracepted is likely to be in part genetic, there is likely to be rapid selection for these non-responders. The method will become ineffective in a few generations. The second problem is that the offspring of the animals which breed will have altered immune responses. Their capacities to respond to their own pathogens or to harbor pathogens of other species in the same ecosystem are likely to be changed. The presence of chlamydia in P. cinereus and bovine tuberculosis in New Zealand T. vulpecula means that responses to these pathogens would have to be studied in offspring of immunocontracepted parents to ensure that the offspring were not more susceptible to them. New Zealand intentions to put an immunocontraceptive into a T. vulpecula gut worm must be viewed with caution by Australia. The eggs of transgenic worms will be easily transplanted either accidentally or deliberately back into Australia, and so infect T. vulpecula in Australia.

The populations of western grey kangaroos (Macropus fuliginosus) and euros (M. robustus erubescens) in a 1196-ha area of native vegetation in the central wheatbelt of Western Australia were studied over six years (1985-91). The area was isolated from other remnants of native vegetation by at least 1.4 km. Captures were made periodically throughout each year and the animals weighed and measured. In all, 152 animals were captured (83 euros and 69 western grey kangaroos). The data for each sex and species were assigned to 'seasons' (February-July or August-January) and assessments made of body condition. The weights and tail circumstances, adjusted for individual size by regression on leg length, were higher for western grey kangaroos but not for euros in August-January. Euro males varied significantly in weight from year to year; euro females and grey males and females did not. Too few grey females were captured to analyse seasonality of reproduction. The estimated birth dates of 68 euro pouch young were distributed equally throughout the study period. There were approximately equal numbers of each species in an estimate made in 1988 from a helicopter survey, with a total (� s.e.) of 191�29 kangaroos. The mean faecal pellet counts on 42 Tied transects of 100 m2 did not differ significantly over the period 1985-88. These counts showed that the overall use of the different vegetation types varied by a factor of two. Heaths had the highest pellet counts and open mallee or woodland the least, with Allocasuarina-dominated shrublands being intermediate. Spotlight surveys around the reserve boundary showed a highly significant difference in distribution of the two species. This was confirmed by analysis of the home ranges of 13 radio-collared individuals. Euros showed a strong preference for areas of York gum-wandoo-jam woodland with a herbaceous ground layer and areas with tall Allocasuarina or dense heath. In contrast, the western grey kangaroos preferred the heathlands and open woodlands without a herbaceous ground cover. The sex ratios of the whole populations seen in spotlight searches was 0.72 : 1.00 (males: females) for western grey kangaroos and 0.81 : 1.00 for euros. Both differ significantly from parity. There was a higher proportion of female euros amongst the animals seen in the western part of the reserve than in the eastern part. These populations relied mainly on the resources of the reserve. The average number of kangaroos seen on adjacent farmland on any one night varied from 3.6 in 1986 to 13.5 in 1991. A significantly higher proportion of males of both species were seen on farmland.

Context Although road mortality has the potential to affect the fate of populations, it is often confounded with other forms of environmental change. Therefore determining its impact separately from other factors is difficult because it requires an understanding of how road mortalities affect age- and sex-specific survival rates. Aims We determined the impact of high numbers of road-kills and habitat modification on the growth and survival of the population of tammar wallabies (Macropus eugenii) on Garden Island, off the coast of Western Australia. The increased supply of food from large areas of fertilised and irrigated lawns on a naval base was expected to increase the population growth rate (λ) and the road-kills were expected to offset the population response. Methods We conducted a mark-and-recapture study over three years to estimate rates of survival, reproduction and population growth rates in areas of the island that were either heavily affected by the presence of a naval base that included a network of roads and buildings, close enough to the naval base that animals could be affected by the disturbance there, and completely unaffected and lacking major roads or buildings. All road-kills were collected to estimate the impact of road mortality on the survival and growth rates of the population. Key results The growth rate, λ, for the population on the naval base was 1.02 ± 0.083 (s.e.) per year, which was much higher than in an area of adjacent bushland at 0.92 ± 0.065 per year and in undisturbed bushland at 0.93 ± 0.100 per year. When the impact of road mortality was removed, λ increased to 1.15 ± 0.101 per year on the naval base and 0.96 ± 0.076 per year in the bushland adjacent to the naval base. On the naval base road mortality reduced survival rates of one-year-old and adult animals by 0.14 ± 0.087 and 0.12 ± 0.012 per year (mean ± s.e.). Conclusions Road mortality counteracted the increase in the size of the tammar population caused by the habitat modification on the naval base. The impact of road mortality on the adjacent bushland population may result in its long-term decline, as the population may not be able to recover from the reduction in survival rates. Implications Road mortality has the potential to threaten susceptible populations but its impact should be quantified so that mitigation measures can be implemented where they will achieve the greatest benefits.

We investigated timing of reproduction in a wild population of northern brown bandicoots (Isoodon macrourus) in the Australian Wet Tropics. Almost all births occurred during the late dry season and early wet season, and most adult females (78–96%) were carrying pouch young during those times. Litter sizes ranged from 1 to 6 pouch young (mean = 3.1) and was not influenced by season. Adult males had significantly larger testes in the late dry and early wet seasons, corresponding with the peak in births. Daylength was the only environmental factor that predicted the presence of a litter; when daylength exceeded 12 h, more than 70% of captured females were carrying pouch young, and most (94%) births were estimated to have occurred on days with >12 h of daylight. Various environmental factors have been proposed as a cue for breeding in I. macrourus, with daylength though to be the primary cue initiating breeding in temperate Australia, but temperature and rainfall thought to be more important in the tropics. Our data suggest that in the Australian Wet Tropics, increasing daylength in the late dry season acts as the primary cue for breeding.

Within Australia the northern short-nosed bandicoot, Isoodon macrourus, occurs in coastal areas from the Kimberleys to the monsoonal tropics of the Northern Territory and from Cape York Peninsula to the Hawkesbury River, New South Wales (Gordon 1983). The reproductive ecology of I. macrourus has been studied in two captive (Hall 1983; Gemmell 1988) and five natural populations (Gordon 1971, 1974; Gemmell 1982; Hall 1983; Friend 1990; Kem- per et al. 1990; Budiawan 1993). Three of the latter (Darwin, the Mitchell Plateau and Townsville) were in the tropics; breeding at these sites occurred dur- ing the wetter months of the year but not during the summer of 1982/3 in Darwin when the monsoon failed (Friend 1990) or during the relatively dry winter/spring of 1991 in Townsville (Budiawan 1993), suggesting a dependence on rainfall (Friend 1990; Budiawan 1993). We report on differences in the reproduction, growth and development of I. macrourus in Rockhampton, Queensland, from March - October 1993 at four adjacent sites which received different amounts of artificial watering.

Competing theories of sex allocation in mammals may best be reconciled in the light of data from diverse species. The tammar wallaby (Macropus eugenii) is potentially a particularly interesting study animal because females wean only one young per year, and exhibit extreme synchronicity in the annual onset of breeding. By contrast, reproduction in the closely related parma wallaby (M. parma) is almost asynchronous. These two Australian species are found sympatrically only on Kawau Island, New Zealand, where they were introduced in about 1870. We sampled wallabies on Kawau Island in April of 1996, when both species were breeding. Although the sex ratios in both species were not significantly different from unity, offspring of M. eugenii were very significantly more likely to be male with increasing maternal weight (logistic regression χ2 = 16.8, P < 0.0001), and the fewer M. parma data showed a non-significant trend in the same direction (χ2 = 1.9, P= 0.16). These data, at least for M. eugenii, are consistent with the Trivers–Willard hypothesis, and warrant further investigation in wild and captive populations under different measured or manipulated ecological conditions. We suggest an approach utilising the characteristics of M. eugenii which might help determine whether the sex bias is determined close to conception, or is effected later in the reproductive cycle by differential survival of the sexes.