Microtubular systems are an integral and essential element of eukaryotic cells. Many of these systems display linkages between the microtubules. The aim of this study was to investigate one such system, the cytostomal apparatus of Tetramitus rostratus. It was hoped that some insight could be gained into the nature of inter-microtubule linkages as well as investigating conditions for possible isolation via differential solubilization. The cytostomal apparatus consists of two sheaves of microtubules that originate at the basal bodies and extend through two-thirds of the length of the cell, apparently supporting the gullet. These microtubules are extremely stable: they are cold stable, calcium stable and griseofulvin/colchicine stable. They are highly cross-linked by fine filaments. These "linkers" have an average length of 107 nm. Linker width varies from the mid-portion (6 nm) to the ends (12 nm). In this and other respects they are similar to the highly contested microtrabecular lattice. The linkers were observed in positively stained samples and in thin-sections. Glutaraldehyde was found to have a very destructive effect on the linkers. A combination of paraformaldehyde and glutaraldehyde (2.25\/0.5\) was found not to have this effect over times that are normally used for primary fixation. Another component of the cytostomal apparatus is the system of longitudinal filaments that is especially wellrevealed with high salt (0.25M NaCl or KCl) extraction. Since this extraction solubilizes the microtubules, it may allow the longitudinal filaments to be isolated. These filaments may be related to the tektin filaments found in flagellar microtubules. In addition, a novel set of crossfibres is found to originate at the juncture of the two sheaves of microtubules and fan out across two-thirds of the width of the apparatus. These fibres were found to be especially stable in urea which may, again, allow for their isolation and characterization. The linkers have been investigated for motility. Linker length was measured after treatment with ATP (which successfully reactivated the flagellar dynein) and after treatment with ATP followed by treatment with calcium (which efficiently halted all reactivated movement of the flagella). The length of the ATP treated linkers was very close (5 nm) to the control linkers and their morphology was indistinguishable. The length of the calcium treated linkers was considerable shorter (20 nm) but the morphology suggested that this was artifactual rather than due to a physiological cause. / Thesis / Master of Science (MSc)

The honey possum Tarsipes rostratus is a tiny (7 - 12 g) highly specialised flower-feeding marsupial endemic to the south-western corner of Australia. The impact of fire on this small mammal was studied, over a 19-year period, in the Fitzgerald River National Park, a large (330,000 ha) area of relatively undisturbed heathland/shrubland, rich in the proteaceous and myrtaceous plants upon which the honey possum appears to rely for food. The honey possum is the most abundant and widespread mammal in this Park. Capture rates of honey possums were significantly related to the years since the vegetation was last burnt, annual rainfall in the preceding (but not the current) year, the season when trapping occurred, and the trapping grid operated. Capture rates declined markedly after fire and remained low (less than one third of those in long unburnt vegetation) for about 4 - 5 years following a fire. Rates of capture then increased steadily over the next 20 - 25 years, with maximal abundance recorded about 30 years after fire. Thereafter, there appeared to be a slight decline in capture rates, but even in the vegetation unburnt for longest (> 50 years since fire), honey possum abundance was substantial and relatively stable. In contrast to these changes in abundance, the structure of the honey possum population, with 79 % adults and 57 % males, appeared little influenced by fire history, annual rainfall, season or grid. The increase in the rates of capture of honey possums following fire paralleled the pattern of availability of cover in the vertical and, to a lesser extent, horizontal plane. Indeed, projective foliage cover took around 20 years after fire to reach levels similar to those available in areas unburnt for even longer. The trend in capture rates was also congruent with the maturation of the most frequently visited foodplants of honey possums, particularly Banksia nutans (summer flowering) and B. baueri (winter flowering). Areas long unburnt still contained shelter and foodplants adequate for honey possums even 50 years or more after fire, with only slight evidence of senescence. Pollen loads indicated that honey possums caught in burnt areas, where their preferred foodplants were absent, continued to feed on these favoured foodplants (Banksia and Dryandra spp.) at nearby unburnt areas. In addition, they also fed, in both burnt and long unburnt areas, upon a suite of other plant species that regenerated more rapidly from lignotubers and epicormic buds, as well as from seeds (e.g. Eucalyptus and Calothamnus spp.). Thus, honey possums appeared to persist with their preferences for feeding from a limited number of flowering plants despite some of these species not being available in recently burnt areas for many years. Nearby patches of unburnt vegetation can clearly be important refuges, feeding grounds and shelter for the few honey possums that visit recently burnt areas, and appear to be the source of honey possum colonists in the years following a fire. Capture rates were also greater following years when rainfall was higher than average. Indeed, rainfall had as great an influence upon capture rates as time since fire. Capture rates were also consistently higher over winter, and to a lesser extent over summer, than in either autumn or spring. Individual grids, even those close together in apparently similar vegetation with a similar fire history, still differed significantly overall in their capture rates of honey possums. This last finding has implications for the use of chronosequences in the study of post-fire changes in biota. Although not the primary focus of the study, data on the limited suite of other, far less abundant, small mammals present indicated that house mouse Mus musculus domesticus numbers peak soon after fire (about two years after fire), grey-bellied dunnart Sminthopsis griseoventer numbers somewhat later (about eight years after fire) and that southern bush rats Rattus fuscipes fiuscipes, like honey possums, are later successional species. Most species were present in vegetation over a range of post-fire ages, with data consistent with models based on sequential changes in relative abundance. Like many Australian mammals, the range of the honey possum has contracted substantially over the last 200 years and the coastal heathlands of the south-west are its last stronghold. In terms of its conservation, this study indicates that, if possible, management burns in these heathlands should be separated by intervals of at least 20 years between successive burns, and preferably even longer. If burns are required more frequently to meet other management priorities, it is highly preferable that they are small and patchy, rather than large scale. Such practices may help ensure the long-term survival of this unique, highly specialised and endemic marsupial.

The honey possum Tarsipes rostratus, a marsupial endemic to South-Western Australia, feeds exclusively upon nectar and pollen. It is one of the smallest marsupials, with adult females (8-12g) significantly larger than adult males (6-9g). Honey possum males have the longest sperm (356µm) recorded for any mammaland the testes represent 4.2% body weight, amongst the largest recorded formammal species. These features suggest that sperm competition is an importantpart of the mating system. This study used a combination of field based studies,DNA analysis and histological examination of the female reproductive tract toinvestigate the life history, multiple paternity and reproduction of the honey possum innatural populations in the Fitzgerald River National Park (FRNP), on the south coastof Western Australia. This study drew upon earlier work on the honey possum in the FRNP in order to describe its life-history. The honey possum is short-lived (1-2 years), and attains sexual maturity whilst still growing. All four teats are occupied after birth, but the litter is reduced to 2 or 3 young during pouch life. The young have a relatively slow rate of growth. Breeding occurs continuously throughout the year, but is affected by the flowering phenologies of its foodplants. The greatest proportion of females with pouch-young occurs in winter; there are fewest pouch-young in autumn, a time of year when there is a dearth of flowers. Honey possums are essentially solitary animals, with no structured social unit, and male and female home ranges overlap. In captivity they are largely tolerant of one another, but larger females are behaviorally dominant to smaller females and to males. The densities and structure of the honey possum populations in the FRNP were analyzed from trapping data collected over 19 years. Population densities fluctuated significantly from season to season throughout the year, with changes in the flowering food resources available. There were also year-to-year differences in the intensity of those fluctuations, and these were significantly associated with rainfall in the previous year, and probably mediated through a lag effect in the flowering of the honey possum’s foodplants. The greatest densities of animals occurred over winter. In years following high rainfall, mean winter densities reached 88 individuals per hectare. The lowest densities occurred in spring, and in years following low rainfall mean spring densities fell to 8 individuals per hectare. Even at these lowest densities, there is still the potential for interaction between males and females. A succession from high to low, then back to high densities was seen during the three years of the present study (2000-2002) and this shadowed a similar succession of changes in rainfall. The proportion of females with pouch-young was significantly affected by the season, and by rainfall in the previous year. Years following low rainfall had a lower proportion of females in a condition to breed. The autumn dip in breeding that occurred in all years was exacerbated following dry years. Of those females that did breed in 2001, a time of low resources, there was no difference in the size of the litter compared to 2000 and 2002, times of higher resource availability. The sex-ratio of pouch young was at parity, but there was a slight bias towards males among both juveniles (56%) and adults (58%). This was probably due to the greater movements shown by males. Sex ratios were not affected by changes in rainfall and density. Male-biased dispersal was detected using genetic data and the movement patterns of males showed that they moved greater distances than females during their normal activity. Analysis of four microsatellite loci revealed extremely high levels of variation, with 28 to 50 alleles per locus and a mean expected heterozygosity of 0.95. These are amongst the highest seen in any microsatellite study of vertebrates. There was multiple paternity in 86% litters, using a minimum number of sires per litter method, and in 95% litters, using an estimated number of sires method based upon the relatedness of litter males. This indicates that multiple mating is frequent in female honey possums and is evidence for sperm competition. The estimated number of sires in a litter was often three or four. In 41% of cases, the number of sires was less than the number of young in the litter, indicating that some males were more successful at siring offspring than others. Nevertheless, no more than two offspring in a litter were known to have been sired by the same male. Despite marked fluctuations in density from high in 2000, to low in 2001, then high again in 2002, the level of multiple paternity remained equally high in all years. Embryonic diapause and female reproduction was investigated in the honey possum. All adult females examined, both with and without pouch-young, were either close to oestrus, had ovulated or were carrying conceptuses. The honey possum has a postpartum oestrus and it was evident that this occurs approximately 2-4 days after birth. Cleavage and formation of the unilaminar blastocyst appears to occur rapidly over approximately 5 days. Embryonic diapause proceeded in a two phase manner similar to other small possum species. The unilaminar blastocyst expanded rapidly at first; and then, from about 18-20 days after birth, the diameter of the blastocyst remained constant at approximately 1.2-1.8mm. No growth or development beyond the unilaminar stage was observed during pouch-life. The first signs of reactivation occurred during lactation, after pouch exit, and expansion of the blastocyst only occurred in one post-lactational female. The development of the corpus luteum appeared different to patterns described for other marsupials, but its formation coincided with the formation of the unilaminar blastocyst. The diameter of the corpus luteum remained constant throughout diapause. The histology of the reproductive tract was generally similar to other marsupials. There were no sperm storage crypts in the female reproductive tract. The length of pouch-life in the honey possum was 55-65 days, and the interval between litters of the same size varied between 65 and 100 days. Embryonic diapause may reduce the time between production of successive litters in the honey possum, but lifetime reproductive potential is reasonably low. Females had up to four litters over the period that they were captured. Thus, each litter represents a substantial proportion (25%) of a female’s lifetime reproductive output. Reproductive amortization occurred, with 61% loss overall, due to overproduction of ova, loss of conceptuses and reduction of the litter during lactation. The behavioural dominance of females suggests that multiple mating is an active strategy, and this presumably allows the genetic quality of their offspring to be maximized. Males that succeed in sperm competition may be of better intrinsic quality. Overproduction of conceptuses by females presents the opportunity for them to select those fertilized by intrinsically viable males or genetically compatible males. Sexually active males are present all year round. Females were not synchronous in their sexual receptivity, and this would lead to a skewed operational sex ratio, with more reproductive males than oestrous females. Since adult males are significantly smaller than adult females and possess no ornaments or armaments, it is unlikely that males overtly fight for access to females. Rather, males appear to monitor the reproductive status of females through smell, and probably compete in their ability to locate oestrous females. The risk and intensity of sperm competition is high, sexual selection for a large investment in spermatogenesis is evident and competition after copulation is probably an important factor in the mating system. It is likely that males, as well as females mate multiply, and the mating system is promiscuous.