No description available.

The Dungeness crab fishery is the most economically important on the West Coast; however, it has experienced dramatic fluctuations in annual catch. Previous research has shown the annual catch of megalopae is correlated with the commercial catch. The catch of megalopae is correlated with the phase of the Pacific Decadal Oscillation (PDO), the day of the year of the spring transition and the amount of upwelling following the spring transition. Further, the daily catch of megalopae is correlated with the internal tide. We developed individual based models of Dungeness crab dispersal, which we validated with results from a light trap. We demonstrated that the retention of larvae in the California Current is enhanced during negative phase PDOs. Further, we suggest that larvae migrate to or almost to the bottom each day. Specifically, megalopae exhibit a twilight vertical migration off of the continental shelf and remain in the neuston on the continental shelf. This concentrates megalopae at the continental shelf break. We also observed megalopae in situ and demonstrated that they swim in the neuston with the surface current at speeds of ~ 10 cm s-1. Using these results and data from a mooring, we demonstrated that this behavior would increase the distance internal waves would transport larvae. We analyzed mooring data and suggest that catch of megalopae is greater when the thermocline is deep and weak and there is less horizontal shear. We hypothesize this allows internal waves to remain coherent longer on the continental shelf. We show that the spring transition coincides with a shallowing of the thermocline, which would ultimately lead to the development of internal waves of depression rather than elevation. We hypothesize that the change in surface flow, based on whether the wave is one of elevation or depression, explains why most megalopae are caught following the spring transition. In general, these findings help us better understand the dispersal of Dungeness crabs. We suggest the dispersal patterns support Michael Sinclair’s member vagrant hypothesis. Further, we suggest these findings apply to many of the continental shelf species in the California Current. This dissertation includes both published and unpublished co-authored materials.

No description available.

Asymmetrical dispersal is when dispersal rates differ in opposite directions. This is expected to be common in natural populations. This work aims to study the symmetrical and asymmetrical dispersal through the use of a simulation program, simuPOP. The main questions were (i) "what are the differences between asymmetrical and symmetrical dispersal in relation to genetic differentiation and equilibrium?" and (ii) "Is it possible to identify asymmetrical dispersal structure from observed patterns of genetic differentiation between populations, and variation within populations?". To address these questions, simulations were conducted with two and three subpopulations subject by three different dispersal rate contrasts and several spatial patterns of dispersal. Variables were estimated at drift-dispersal equilibrium included genetic differentiation between subpopulations (θ) and heterozygosity. With pairwise θ for three subpopulations it was possible to determine whether the metapopulations were subject to symmetrical or asymmetrical dispersal and sometimes to identify the structure of dispersal. Equilibrium heterozygosities did not aid diagnosis of asymmetrical dispersal patterns. I also checked the applicability of two predictions originally made for symmetrical dispersal: Wright's expectations for θ at equilibrium, and Whitlock's expectations fro time to half of equilibrium θ. In most cases these expectations were not applicable. Study of asymmetrical dispersal on living organisms is strongly encouraged.

Orobanche ramosa L. is an annual, parasitic weed present in the western Murray-Mallee region of South Australia. A quarantine zone was established to encompass all known infestations, and has been adjusted over time as new infestations have been discovered. The movement of fodder, machinery, grain and straw, horticultural crops, livestock, and soil is controlled by strict quarantine procedures, to prevent further spread across the landscape. O. ramosa presents a unique situation for weed managers: plants are obligate parasites, relying entirely on broadleaved hosts for their water and nutrition; and seeds are tiny (0.3 mm), produced in large numbers (up to 100 000 seeds per plant), and are long-lived, persisting in the soil seed bank for up to 13 years. The dispersal vectors for O. ramosa in South Australia are the focus of this Master’s thesis. Two dispersal vectors were chosen for investigation: sheep and wind. Sheep were examined as possible vector for seeds, both via the gut (internal transport, or endozoochory) and via adhesion on the external surface of the animal (external transport, or epizoochory). Internal transport via sheep was investigated with a classic gut-passage experiment, which showed a peak in excretion of weed seeds at day 2, reducing to zero seeds excreted at day 8, and a half-life of 2 days. Two phases of external transport on sheep was studied: attachment and retention. Attachment was confirmed by finding seeds on the body wool and feet of sheep that had been kept for 7 days on soil with an O. ramosa seedbank. Seed retention was confirmed by placing seeds onto the body and still finding them in wool samples after 7 days. Wind was the other dispersal vector investigated for O. ramosa. A survey of natural wind dispersal was conducted, which confirmed wind as a vector and allowed trap design to be tested. Then a portable field-based wind tunnel was used to investigate the effects of ground cover (bare ground and cereal stubble) and wind speed (low, medium and high) on wind dispersal of O. ramosa seeds. For the stubble treatments, more seeds were trapped within the tunnel, and on bare ground more seeds were trapped exiting the tunnel. Importantly, the data showed that low wind speeds readily move O. ramosa seeds, and that the seeds are capable of aerodynamic lift in the wind profile. Results are discussed in the context of dispersal biology, quarantine procedures, and future work that would further refine knowledge of likely dispersal vectors for O. ramosa. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1459246 / Thesis (M.Sc.) -- University of Adelaide, School of Earth and Environmental Sciences, 2009

Asymmetrical dispersal is when dispersal rates differ in opposite directions. This is expected to be common in natural populations. This work aims to study the symmetrical and asymmetrical dispersal through the use of a simulation program, simuPOP. The main questions were (i) "what are the differences between asymmetrical and symmetrical dispersal in relation to genetic differentiation and equilibrium?" and (ii) "Is it possible to identify asymmetrical dispersal structure from observed patterns of genetic differentiation between populations, and variation within populations?". To address these questions, simulations were conducted with two and three subpopulations subject by three different dispersal rate contrasts and several spatial patterns of dispersal. Variables were estimated at drift-dispersal equilibrium included genetic differentiation between subpopulations (θ) and heterozygosity. With pairwise θ for three subpopulations it was possible to determine whether the metapopulations were subject to symmetrical or asymmetrical dispersal and sometimes to identify the structure of dispersal. Equilibrium heterozygosities did not aid diagnosis of asymmetrical dispersal patterns. I also checked the applicability of two predictions originally made for symmetrical dispersal: Wright's expectations for θ at equilibrium, and Whitlock's expectations fro time to half of equilibrium θ. In most cases these expectations were not applicable. Study of asymmetrical dispersal on living organisms is strongly encouraged.

Silicification of organisms in silica-depositing environments can impact both their ecology and their presence in the fossil record. Although microbes have been silicified under laboratory and environmental conditions, viruses had not been, prior to this work. Bacteriophage T4 was successfully silicified under laboratory conditions that closely simulated those found in silica-depositing hot springs. Virus morphology was maintained during the short period of silicification (48 hours), and a clear elemental signature of silicon and phosphorus was detected by energy-dispersive X-ray spectrophotometry (EDX). However, the EDX signature of silicified virus was not sufficiently distinct from that of cell membrane or phosphate minerals for that technique to be used to discover viral remains in hot spring mineral deposits. Having shown that bacteriophage T4 can be silicified, it was then determined that the impact of silica exposure on infectivity varied widely between different viruses. The effect on infectivity did not appear to be related to virus size or morphology. In addition, the impact on infectivity was at least partially reversible, indicating that it was caused, at least in part, by occluding infection-related structures on the virus, rather than destruction or denaturation of the virus. Those viruses which showed a decline in infectivity with silica exposure also showed increased resistance to desiccation after being exposed to silica, which has implication for long-range virus dispersal. The desiccation resistance was proportional to the degree that silicification reduced infectivity in that virus. Desiccation resistance also declined with prolonged exposure to drying, suggesting that the mechanism was due to the silica coating helping to retain water rather than replacing the hydrogen bonding of water. Virus dispersal is critical for both the spread of disease and the diverse roles that viruses play in Earth ecology. However, the mechanisms of host-independent virus dispersal are poorly understood and hotly debated. These experiments showed that, under mild conditions, diverse viruses can be coated in silica and that silica coating provides some, if not most, viruses with remarkable desiccation tolerance. Virus silicification thus provides a potential mechanism for global dispersal of viruses that could not otherwise tolerate the desiccation of wind-borne transportation.

No description available.

Although parasitoid wasps have shown promise as model systems for studying life history evolution, empirical studies of certain traits in these small insects have proven difficult. In this dissertation, two "black boxes" in the life histories of female parasitoids are examined: (1) oosorption, and (2) dispersal by flight.I first demonstrate that a short-lived species with high early reproductive investment (Eretmocerus eremicus) resorbs eggs, which runs counter to the notion that the time costs of oosorption are prohibitive to such wasps. Instead, it appears that the resorption mechanism in E. eremicus is capable of both decreasing costs and increasing nutritional benefits of oosorption relative to that of other parasitoid species. In addition, a literature review reveals four functional hypotheses for parasitoid oosorption: (1) age-related egg apoptosis, (2) conservation of ovarian capacity, and (3) nutrient allocation to either longevity or future oogenesis. As none of these can be rejected, I propose several avenues of future research: 1) refinement of physiological techniques to measure nutrient traffic into and out of eggs, 2) morphological phylogenetic studies of oosorption mechanisms, 3) development of lifetime nutrient budgets for parasitoids with different reproductive life histories, 4) examination of decay rates of oocytes with different yolk types, and 5) increased study of ovarian dynamics in pro-ovigenic parasitoids.Next, I describe results from a vertical flight chamber study designed to test hypotheses regarding the correlation between pre-oviposition dispersal and reproductive effort in parasitoid wasps. This experiment was conducted on 1-d-old female whitefly parasitoids from five species in two genera. The two Eretmocerus spp. showed a higher flight propensity than the three Encarsia spp. This may be, in part, due to a more time limited life history in the former. Within species, egg load did not correlate well with flight propensity for all species examined. Finally, among individuals of Er. eremicus, the relationship between effective flight distance and egg load appears to be context dependent, as data consistent with both positive and negative correlations were collected. Correlational changes between flight distance and egg load may be due to variation in biotic (female longevity) or abiotic (temperature, relative humidity) factors.

No description available.