Zoology - Theses
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ItemParental behaviour and mating system of the fairy martin, Hirundo Ariel(University of Melbourne, 1997)The birds are unique among the major animal taxa in that biparental care is common, occurring in about 90% of the 9000 or so extant species. Among these biparental species there is dramatic variation, both across and within taxa, in the extent to which males and females contribute to incubation and nestling care. However, despite considerable interest, the causes of this variation generally remain poorly understood. The aim of this thesis was to examine a range of factors that may contribute to variation in the participation of males and females within a population of the socially monogamous fairy martin, Hirundo ariel. Fairy martins are endemic to Australia and nest colonially in aggregations of enclosed mud nests. The sexes are morphologically similar, although only the female acquires a brood patch during the breeding season. In the Yarra Valley, where this study was conducted, colonies ranged in size from 8 to 29 nests. Over the three years from 1993 to 1996, birds arrived in the study area in September and usually commenced laying in October, although nesting activities were generally asynchronous both between and within colonies. Most colonies contained active nests until February. An average of at least 16% of adults and 5% of fledglings returned to the study area in the following year. Returning adults generally nested at the same colony site as the previous year (68%), while most first year birds nested at sites other than their natal colony (75%). Adult males were more likely to return than adult females. Similarly, fledgling males were more likely to return than fledgling females (assuming an equal sex ratio at fledging). Both sexes participated in building the mud nest, incubating the clutch and feeding the nestlings. Clutch size ranged from two to five (mean = 3.5) and declined during the course of the season. The clutch was attended for an average of 88% of the time during daylight hours, although attendance generally declined during the course of the day. Females were more attentive of the clutch than males (56%), resulting primarily from longer incubation bouts, but also shorter recess periods. Females almost invariably attended the clutch overnight, and were usually accompanied by the male. Total clutch attendance did not vary with clutch size, however, male attendance increased with clutch size while female attendance decreased. Total attendance increased with clutch age resulting from an increase in female but not male attentiveness. Both sexes were more attentive of the clutch on cooler days, especially in the early morning and late afternoon. The duration of the incubation period varied from 12 to 18 days (mean = 13.7), and was shorter if the clutch was attended for a greater proportion of the day. A mean of 1.8 chicks fledged per completed clutch, while 60% of these clutches produced at least one chick. The period from hatching to fledging varied from 17 to 32 days (mean = 22.1), and was longer for larger broods. Fledging success was highest during the middle of the breeding season (December). Adverse weather conditions, resulting in clutch and brood abandonment, were the most common cause of nest failure, and on several occasions also resulted in adult mortality. Pairs produced from zero to eight fledglings per season (mean = 2.8), with those that commenced nesting earlier in the season having higher annual productivity. Parents visited larger broods more frequently, although the visit rate per chick declined with brood size. Visit rate generally increased with brood age, reaching a plateau between days 8 and 16, before declining until the chicks fledged. The relative contribution of the sexes did not vary with brood size or brood age. Brood visit rate generally increased with ambient temperature and decreased during periods of rainfall. Male participation in incubation (both absolute and relative to his mate) declined with an increase in the proportion of fertile females in the colony. Males were most 'responsive' to the availability of fertile females in the early morning, when copulations are likely to occur most frequently. Furthermore, the decline in male contribution with the proportion of fertile females was greater among males with smaller than average clutches. Male contribution to brood visits also tended to decline with an increase in the proportion of fertile females over the most demanding days of the nestling period. These patterns, each demonstrated for the first time, provide strong support for the presence of a reproductive trade-off for males between parental and extra-pair copulation effort. This trade-off may be widespread among the 90% of bird species where males contribute to parental care. Microsatellite parentage analysis revealed that 14% (29/207) of young were not sired by the putative father, while 2% (4/207) appeared to be the result of conspecific brood parasitism. The frequency of extra-pair fertilizations was not influenced by nesting synchrony, but tended to increase with colony size. The genetic fathers of extra-pair young had larger tarsi, greater previous breeding experience, and were more attentive to their own clutch than both the male that they cuckolded and the other males in the colony. Moreover, males with previous breeding experience had greater paternity of their own brood than those without. These results are consistent with female extra-pair mate choice for 'good genes'. Male incubation attendance, both across and matched for bird, was lower for clutches with reduced paternity. Furthermore, males with reduced paternity took longer in returning to their clutch after a disturbance than males with complete paternity. Together, these results suggested that males may adjust their level of parental investment in relation to their confidence of paternity. However, these results were confounded by the relationship between male contribution to incubation and the availability of fertile females in the colony. Mean nestling mass was lower in broods with reduced paternity however there was no evidence that this resulted from a reduced rate of feeding by cuckolded males. Among the Hirundinidae, and birds in general, species with male incubation are usually sexually monomorphic and have relatively low frequencies of extra-pair paternity. This study indicates that the biparental fairy martin conforms to this pattern. The evolution/ maintenance of male incubation in fairy martins may, in part, relate to the small body size and high nesting density of this species.
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ItemMale germ cell transplantation(University of Melbourne, 1995)This thesis has explored the success of male germ cell transplantation in rats. Busulfan-treated black and white Long Evans rats were used as the germ cell-recipients, and white Sprague Dawley fetal and neonatal rats were used to provide donor germ cells which were transplanted by 2 different routes. Adult Long Evans male rats were injected intraperitoneally once or twice with busulfan, an alkylating agent, at a dose of 10 mg/kg body weight. Forty four days after the first busulfan treatment, their testes were essentially devoid of spermatogenic cells and therefore suitable as germ cell recipients. Following exposure to busulfan during intrauterine life on which primordial germ cells (PGCs) were exclusively destroyed, the rats at days 4 - 5 of age were devoid of germ cells and therefore used as newborn recipients. Donor fetal and newborn testes were excised and dissociated by trypsin-EDTA (fetal tissues) or collagenase/trypsin-EDTA (neonatal tissues) treatment. PGCs and gonocytes were purified by equilibrium centrifugation on a discontinuous Percoll gradient column. Alkaline phosphatase activity was used as a marker for both PGCs and gonocytes. Trypan blue exclusion was used to determine cellular viability. The donor germ cells were injected into the testes of the anaesthetised recipients by retrograde injection into the rete testis, or random multiple testicular injections. A total of 74 recipient rats were transplanted with either primordial germ cells or gonocytes. Forty eight of them were paternity tested with 563 fertile Sprague Dawley females, and they produced 2,280 progeny. However, none of the progeny was derived from the donor germ cells, as judged by coat colour. However, a detailed histological analysis of the recipient testes showed that the donor germ cells had apparently differentiated into mini-tubules or irregular segments of seminiferous epithelium within the lumen of the host�s seminiferous tubules, and exhibited qualitatively normal spermatogenesis in 13 out of 19 animals following rete testis injections. The stage of spermatogenesis of the donor intraluminal seminiferous epithelium was closely synchronised with that of the host�s epithelium, suggesting that the spermatogenic cycle is regulated locally by the intraluminal microenvironment. None of 15 neonatal or adult recipients given random multiple intratesticular injections showed any evidence of intraluminal spermatogenesis, suggesting that the donor germ cells were unable to migrate through the basement membrane of the host seminiferous tubules. In summary, this thesis has demonstrated that it is possible to transplant purified PGCs and gonocytes from one rat to another. Male germ cell transplantation therefore provides an interesting new tool for investigating the control of spermatogenesis, and if the success rate of the procedure can be improved, so that the donated germ cells all integrated with the host�s Sertoli cells, it could become an invaluable technique for manipulating the male germ cell line.
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ItemThe role of Customary Marine Tenure and local knowledge in fishery management at West Nggela, Solomon Islands( 1998-04)A proper understanding of the management of small-scale subsistence and artisanal fisheries requires not only detailed sociocultural study, but comprehensive analysis of the state of the fished population(s) using rigorous stock assessment and other fisheries biology tools. This study comprises such an interdisciplinary approach taken in an attempt to understand subsistence and artisanal fishing at West Nggela, with a particular focus on the management of the artisanal trochus fishery. The importance of an understanding of Customary Marine Tenure is dealt with in some detail. An analysis of the various categories of fishers’ ecological knowledge about marine fauna, with an emphasis on trochus, is also presented, and discussed with respect to the categories of biological and ecological information considered by most fisheries biologists as essential to the assessment and management of a fishery. The theoretical basis of my approach to the study of local knowledge, which could broadly be termed “rationalist”, is discussed and defended against “postmodernist” criticisms. Trochus are currently overfished at most of the reefs I studied at West Nggela. Densities measured using mark-recapture were apparently low compared to well-managed fisheries elsewhere in the Pacific. The current market demand, and the ease of capture, storage and marketing of the product, indicate that pressure on the fishery (which includes some poaching) is likely to remain high, and some improvement in management is required. Egg-per-recruit and yield-per-recruit modeling indicates that enforcement of a minimum size limit of 8cm basal diameter would bring about immediate improvement in yields and recruitment in the fishery. Such a measure would not only be practical and expedient but also more culturally sensitive than many of the alternatives. The system of customary marine tenure at West Nggela, which includes a system of serial prohibitions on harvesting, appears not to be adapted to the high levels of pressure currently being exerted on this valuable species. An analysis of the property tenure system at Nggela, including two case studies of formal disputes, outlines some of the reasons for this problem. Local ecological knowledge about marine fauna in general, and trochus in particular, appears to mostly concur with, and in some cases extend, scientific knowledge. However, there appear to be subject areas in which local knowledge is lacking, and these typically include parameters related to yield and recruitment, such as growth, natural mortality, lifespan and reproductive ecology. In particular, for broadcastspawning species such as trochus, the relationship between dwindling stock densities and recruitment failure is usually not recognised by most fishers at West Nggela. Customary manne tenure and local ecological knowledge thus appear to be insufficient for maximising and sustaining yields of trochus at current levels of fishing pressure. Nevertheless, any new management measures, or fisheries developments, should remain sensitive to the dynamic and competitive nature of the property tenure system. Collaboration between fishery biologists and local fishers is recommended wherever possible. Efforts by fishery biologists to extend, to rural fishers, their knowledge of reproductive biology and ecology of broadcast spawning organisms are encouraged. Outside knowledge is likely to be embraced by fishers only if it is communicated in a way that is compatible with the cognitive framework in which most local knowledge is situated. Such an input of expertise, when combined synergistically with the extensive local knowledge of rural fishers, cannot fail to result in improvements to strategies for community-based fishery management.
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ItemEcological effects of the introduced fanworm, Sabella spallanzanii, on hard substratum epifaunal assemblages( 1999)Observations on the impacts of introduced species abound, but little experimental work bears on the nature and mechanisms of these impacts. The recent invasion of the sabellid polychaete Sabella spallanzanii into several embayments on the south coast of Australia provides an opportunity to test hypotheses about the effects of this exotic species on the invaded assemblage. The large size (30 cm long) and high density S. spallanzanii results in a structurally complex canopy of feeding fans above the substratum. I investigated the effect of the canopy on various life history stages of co-occurring marine invertebrates in epifaunal assemblages on hard substrata. The effects of Sabella on recruitment of sessile taxa were complex, but a number of generalisations could be made. Recruitment of some barnacle, bryozoan, spirorbid and ascidian taxa to large experimentally cleared areas (pilings) was higher than on uncleared areas. On the scale of individual 20 by 20 cm settlement plates, where I controlled for the effect of physical structure using fanworm mimics, most of the effects were caused by the presence of physical structure on the plate. Barnacles responded negatively, and sponges and one bryozoan responded positively to structure in one experiment, while a spirorbid, a bryozoan and three ascidians all responded negatively in another. Recruitment on to tubes increased the abundance of several taxa on plates with fanworms, but not all taxa recruited to tubes. Effects were not consistent within taxonomic groups or between sites. Longer term experiments revealed fewer changes to the structure of the understorey assemblage. A two month experiment showed fewer effects of the fanworms on the smaller plate scale, and a six month experiment found few effects on either plate or piling scales. The apparent disappearance of canopy effects with time could be caused by processes associated with assemblage development such as overgrowth and senescence of early recruits. Alternatively it could simply be caused by differences in the composition of assemblages between experiments. Multivariate analyses showed that spatial variation in recruitment on the scale of 10’s of metres was important in determining the composition of the assemblage in both early and later stages. The planktonic abundances of larval solitary ascidians, spionid polychaetes and pooled larval taxa adjacent to the substratum were significantly reduced by the presence of a fanworm canopy, suggesting that larval flux to these areas may be lower. Little difference in overall recruitment between cleared and uncleared areas suggests that settlement rates may be enhanced or post-settlement mortality rates might be lower beneath canopies. Growth of the arborescent bryozoan Bugula stolonifera and an encrusting bryozoan, Watersipora subtorquata, were affected by the presence of a canopy, but these effects were not consistent between experiments. B. stolonifera growth increased beneath the canopy in one experiment and decreased in another, while W. subtorquata grew less in response to physical structure on the plates. Survivorship of B. stolonifera and a serpulid polychaete were lower beneath the canopy in one experiment each, but not in others, and survivorship of W. subtorquata was not affected. The variable results suggested that canopies may act in different ways at different times. The overall impact of Sabella spallanzanii on other species at the scales I looked at can be explained by its modification of the habitat. The use of tubes as settlement sites, and the predominance of small scale responses to physical structure support this idea. Traditional models of the ecological impacts of exotic species, which focus on competitive species replacement, may not be relevant in this system. Any impacts of Sabella spallanzanii must also be evaluated in the light of observations that the canopy was not constant through time, clue to population crashes that occurred a number of times and places.
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ItemEcological studies of barnacles in temperate mangrove forests( 1997)I have examined the horizontal distribution and abundance of Elminius covertus across three zones, landward, middle and seaward, of mangrove forests at Rhyll, Phillip Island, Victoria during 1995-1997. In the seaward zone of the forest, the vertical abundance of E. covertus between 0-15 cm from the bottom was also investigated. To determine what processes affect these horizontal and vertical patterns, presettlement, settlement and recruitment of E. covertus have been examined. The horizontal distribution of adults reflected the horizontal pattern of recruitment and settlement. The horizontal pattern of settlement was determined by larval supply and larval behaviour. Post-settlement factors had little influence on this pattern. Consequently, the horizontal pattern of adults were ultimately explained by patterns of larval supply and larval behaviour. The distribution of adults on pneumatophores reflected the vertical pattern of recruitment, but contrasted with the vertical pattern of settlement. Variability in the vertical distribution of settlers reflects larval settling behaviour not larval availability and the vertical pattern of recruits and adults is determined by post-settlement mortality. The patterns of settlement of E. covertus on seedlings of Avicennia marina in the seaward zone of the forest were also documented, with the greatest density of barnacles found on the stem, followed by the lower-leaf and upper-leaf surfaces. No further studies were undertaken to test what processes determine this pattern. The presence of E. covertus produced no negative effects on the survival and growth of seedlings of A. marina. Seedling survival appears to depend on other factors, such as, intermittent smothering by drift algae, seagrasses, and sediment as well as unfavourable climatic conditions, especially low temperatures and strong winds and currents.
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ItemThe nutritional biology of the black lip abalone, H.rubra( 1991)Nutritional factors affecting the growth of the black lip abalone H. rubra were investigated. To determine the growth value of various diets, abalone were fed single species of algae and a mixed diet, and their growth and feed intake were measured and compared. Such dietary trials have been used extensively by researchers to assess diet quality. However in this study, a critical analysis of this method revealed that previous diets and disturbance may affect results for the first 50 days or more, and that growth rates may change over long periods. Thus, dietary trials should be modified to standardise diets prior to the trials, and should extend over periods of greater than 100 days, with regular measurements of growth. The highest growth rate was achieved on a mixed diet, with little variability over time. The food preferences of abalone for the test algae were determined. The growth of H. rubra was significantly correlated with food preference, in accordance with the optimal foraging model, which predicts that animals should prefer to consume foods that maximise the intake of nutrients that are limiting in their diet, resulting in optimal growth. Abalone preferred and grew most rapidly on the perennial red alga Jeannerettia. However, abalone were selective within the reds, so that preference cannot be predicted on the basis of the divisions of algae, as has previously been supposed. The brown algae tested were least preferred, and the hierarchy of preference was related to the phenolic contents of these algae. Food intake did not correlate with preference or growth, supporting the observation made by other authors that intake is influenced by an array of factors other than the nutritional quality of the food. In the case of H. rubra, intake is most likely influenced by anti-nutritional factors, such as tannins, toxins, toughness and fibre. For herbivores, nitrogen has been identified as one of the nutrients most likely to be limiting, although energy is considered important also. The intakes of digestible nitrogen and energy on each of the test algae were determined by measuring the amounts ingested, and lost in the faeces. The nitrogen content of the algae and the intakes of digestible nitrogen were correlated with both preference and growth, indicating the important role it plays in influencing growth and setting preference. The energy contents of the algae were similar compared with the highly variable nitrogen contents. Consequently, it is likely that differences in energy availability between algae do not play a role in determining preference or intake. The importance of energy availability in determining growth was investigated by estimating the maintenance energy requirements of abalone, and the energy cost of growth. From this, a calculation was made of the amount of metabolisable energy that was available on the various diets after the demands for maintenance had been met. The high variability in food intake resulted in large differences in intakes of digestible energy. The amounts available for growth appear: to indicate that the growth performance of abalone on some of the diets tested is limited by energy availability.