No description available.

Aspects of the Pisaster-Tegula interaction are re-examined. Reproductive portions of T. funebrallis populations are shown to be immune to seastar predation through a combination of predator preference for larger snails and a withdrawal behavior that favors the escape of smaller snails after capture by a seastar . Experimental addition of p. ochraaceus in winter causes changes in the intertidal distribution of T. funebralis similar to those observed during the summer increase in seastar numbers. It is suggested that these results supplant the hypothesis that lowered prereproductive mortality influences formation and maintenance of vertical size gradients in the lower intertidal .

No description available.

No description available.

No description available.

The use of manure from animal feeding operations (AFOs) as fertilizer on agricultural land may introduce contaminants to aquatic environments that can negatively affect the health of aquatic organisms. This study utilized a landscape-scale regression-based design to assess the effects of AFOs on contaminant concentrations and resident populations of a pleurocerid snail, Leptoxis carinata, in streams within the Shenandoah River watershed (Virginia, USA). Individual characteristics of L. carinata were also evaluated to provide further understanding of observed population characteristics. In streambed sediment and mollusk tissue, concentrations of the trace element arsenic, used as an additive in poultry feed, were not directly related to watershed densities of AFOs. In-stream concentrations of dissolved nutrients and estrogenic compounds, measured as estrogenic activity, were directly related to watershed densities of AFOs. Population sex ratios of L. carinata varied across study sites, from balanced to female-biased, but were not related to concentrations of estrogenic compounds. However, the spatial variation in population sex ratios, coupled with little variation in site-specific sex ratios across seasons and generations, suggest an influence of site-specific environmental conditions. Individual-level studies of L. carinata revealed that there is an eight month lag between hatching and gametogenesis which could allow disruption of sexual differentiation by environmental contaminants, but further study of the effects of specific contaminants on sexual differentiation in this species is needed. Population densities of L. carinata were related to in-stream nutrient concentrations and landscape sources of nutrients, including AFOs, but none of these factors were directly related to the infection prevalence of digenetic trematodes in L. carinata populations. Although trematode infection rates in L. carinata populations do not appear to be viable indicators of the influence of eutrophic conditions on disease incidence in aquatic organisms, the identification of five types of trematodes in L. carinata populations highlights the utility of this snail species for further investigation of transmission dynamics of trematode parasites in lotic systems. / Ph. D.

published_or_final_version / Zoology / Master / Master of Philosophy

No description available.

The purpose of the present study is to examine the genetic and morphological variation found in narrow-range endemic terrestrial invertebrate species at different geographic scales, and the ramifications of this for their systematics, management and conservation. The listed endangered land snail Meridolum corneovirens and several related forms are restricted to the Sydney region, and were used to address the above issues. Morphological, anatomical, allozyme and DNA data were obtained for a total of 77 populations from across the known range of Meridolum. A particular emphasis was placed on the forms found across the Sydney region. The analysis of the different datasets, both individually and in combination indicate at least 35 taxa mostly parapatric and seven genera were represented. This includes several previously unrecognised taxa. The analysis supports the conclusion that Meridolum corneovirens belongs to a new genus. This includes several species found from eastern Sydney south along the coast to Nowra. A total of six new species and five new genera are described. The conservation and management of narrow-range endemics such as Meridolum corneovirens provide a number of challenges to conservation managers. The alternative of listing a gene pool rather than listing species separately is proposed and explore / Doctor of Philosophy (PhD)

The purpose of the present study is to examine the genetic and morphological variation found in narrow-range endemic terrestrial invertebrate species at different geographic scales, and the ramifications of this for their systematics, management and conservation. The listed endangered land snail Meridolum corneovirens and several related forms are restricted to the Sydney region, and were used to address the above issues. Morphological, anatomical, allozyme and DNA data were obtained for a total of 77 populations from across the known range of Meridolum. A particular emphasis was placed on the forms found across the Sydney region. The analysis of the different datasets, both individually and in combination indicate at least 35 taxa mostly parapatric and seven genera were represented. This includes several previously unrecognised taxa. The analysis supports the conclusion that Meridolum corneovirens belongs to a new genus. This includes several species found from eastern Sydney south along the coast to Nowra. A total of six new species and five new genera are described. The conservation and management of narrow-range endemics such as Meridolum corneovirens provide a number of challenges to conservation managers. The alternative of listing a gene pool rather than listing species separately is proposed and explore / Doctor of Philosophy (PhD)