Freshwater organisms are known to maintain hyperosmotic internal conditions despite outward diffusive loss of ions. The freshwater common pond snail Lymnaea stagnalis faces this challenge while additionally attaining the necessary ions for calcification. These are the first documented assessments of the time and mode of recovery for ions lost due to full-body withdrawal in adults of this species. Additionally, this document reports on the physiological and developmental onset of embryonic calcification and the commencement of active acquisition of shell-forming ions from the surrounding environment. The effect of water chemistry and lead (Pb) exposure on embryonic growth, development, and calcium (Ca2+) acquisition was also tested. Pharmacological and water chemistry manipulations were used to determine mechanisms for embryonic Ca2+ and HCO3-/CO32- acquisition and the sensitivity of those pathways. Lastly, L. stagnalis, was shown to have a lowest effective concentration of <1.5 µg Pb l-1 using net Ca2+ uptake, growth, and developmental endpoints in laboratory and natural waters. This is the lowest effective concentration observed for any organism to date. One of the most insightful findings reported here is the interconnectedness of the pathways for acquisition of Na+ and Ca2+ through endogenous production of H+ and HCO3- via carbonic anhydrase-catalyzed hydration of metabolic CO2. The combination of high demand for Ca2+ throughout early life stages and periodic acute demands for Na+ recovery following extracellular fluid loss apparently causes L. stagnalis to be highly sensitive to changes in water chemistry, including [Pb] in the embryos, and possibly pH. The findings reported here warn of the need to establish freshwater environmental indicators and consider raising awareness of the threat of freshwater acidification, which may be greater than that of ocean acidification.

Fast paced population growth in urban areas of southern Ontario is putting increased pressure on the surrounding aquatic environment. The City of Guelph uses the Speed River to assimilate its municipal wastewater effluent. With a projected 57% population increase in the watershed by 2031, the assimilative capacity of the river may be challenged in the coming years. The Guelph Wastewater Treatment Plant uses tertiary treatment methods greatly reducing ammonia, suspended solids and phosphate concentrations in the effluent. However there are still impacts detectable related to excessive nutrients released into this relatively small river (6th order) which promotes algae and aquatic macrophyte growth. There is also concern about a variety of emerging contaminants that may enter the river and impact the health of the ecosystem. The research in this thesis examined the seasonal and spatial variability and extent of the impacts of the wastewater effluent on the riffle fish communities in the Speed River. Stable isotope signatures (δ13C and δ15N) were used to understand the changes in the dominant benthic fish species, Rainbow Darters (Etheostoma caeruleum) and Greenside Darters (E. blennioides), relative to changes in invertebrate signatures and their abundance. Rainbow Darters were extremely abundant relative to Greenside Darters at the site immediately downstream of the effluent outfall, particularly in August. The benthic invertebrate community was distinctly different downstream of the effluent outfall, especially in the summer, with a reduced abundance of Elmidae beetle larvae and increased abundance of isopods (Caecidotea intermedius) compared to upstream. δ13C and δ15N of the two darters species were similar at all sites in May and July, but in August and October Rainbow Darter signatures were more enriched in the two heavier isotopes at sites downstream of the effluent outfall. The vast majority of invertebrate taxa sampled were also enriched at the downstream sites. An analysis of Rainbow and Greenside Darter stomach contents revealed that Rainbow Darters incorporated more isopods and other invertebrates in their diet, especially at the immediate downstream sites suggesting that they are more adaptable to the altered downstream environment. The feeding habits of Greenside Darters appear to change between July and August in response to changes in habitat and food availability. They are potentially consuming food organisms with less enriched isotopic signatures, which results in their isotopic signatures not rising during these months like most of the invertebrates and other fish. Alternatively, the Greenside Darters may move across the stream to feed on invertebrates that remain unexposed to the wastewater effluent. These impacts, although subtle, may be a reflection of the Speed River ecosystem being compromised by nutrient inputs from the wastewater effluent. With the impending increase in demand on the treatment plant (e.g., population growth), ongoing treatment and infrastructure improvements may be needed in the future to maintain the current ecosystem structure.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2001. / Includes bibliographical references.

Across bilaterian phyla, learning and memory allows animals to benefit from central-place foraging, return to ideal food sources, choose mates and avoid dangerous or harmful external stimuli. Although these behaviors are comparable in both vertebrate and invertebrate animals, it is unknown whether or not they are mediated by homologous brain structures. In insects, paired, lobate forebrain structures called mushroom bodies receive input from primary sensory neuropils and are necessary for learning and memory, whereas in crustaceans, this behavior is mediated by paired, compact forebrain structures called hemiellipsoid bodies. Mammalian learning and memory is mediated by the paired, horn-shaped hippocampi, which also receive sensory input and are likewise situated in the forebrain. Did these structures evolve independently along with the ability for animals to learn and remember associations and places? Alternatively, the hypothesis posited in this dissertation is that the last bilaterian ancestor already possessed the ability to learn and adapt to its environment, behavior mediated by paired forebrain structures that evolved divergently into the elaborated forms we observe in extant, crown-group taxa. This hypothesis is investigated and discussed in the following reports: 1) a review of insect brain anatomy and functional connectivity, including a description of mushroom bodies, in the context of arthropod evolution; 2) a comparison of neuroanatomy, circuitry, and protein expression between insect mushroom bodies and Malacostracan crustacean hemiellipsoid bodies, using cockroaches and Caribbean hermit crabs as representatives of their classes; 3) a deeper investigation of the fine structure of neuronal organization in the hemiellipsoid body of the Caribbean hermit crab, focusing on electron microscopical observations and comparisons to the ultrastructure of the fruit fly mushroom body; 4) a survey of four invertebrate Phyla, employing the strategy of comparing neuroanatomy and protein expression to investigate whether higher order forebrain structures in these animals were inherited from a common ancestor; 5) a comparison of neuroanatomy, connectivity, and protein expression in insect mushroom bodies and mammalian hippocampus, including a survey of PKA-Cα in these and corresponding structures across the Chordata. The total evidence suggests that a common Bilaterian ancestor possessed a center that evolved to become mushroom bodies in invertebrates and hippocampus in vertebrates.

Worldwide, finfish fisheries receive increasing assessment and regulation, slowly leading to more sustainable exploitation and rebuilding. In their wake, invertebrate fisheries are rapidly expanding with little scientific scrutiny despite increasing socio-economic importance. This thesis provides the first global analysis of the trends, drivers, and population and ecosystem consequences of invertebrate fisheries, in general, and sea cucumber fisheries, in particular, based on a global catch database in combination with taxa-specific reviews. Further, I developed new methods to quantify trends over space and time in resource status and fishery development. Since 1950, global invertebrate catches increased six-fold with 1.5 times more countries fishing and double the taxa reported. By 2004, 31% of fisheries were over-exploited, collapsed, or closed. New fisheries developed increasingly rapidly, with a decrease of six years (± three years) in time from start to peak from 1960 to 1990. Moreover, 71% of invertebrate taxa (53% of catches) are harvested with habitat-destructive gear, and many provide important ecosystem functions including habitat, filtration, and grazing. For sea cucumber fisheries, global catch and value has increased strongly over the past two to three decades, closely linked to increasing prices and demand on Asian markets. However, the catch of individual fisheries followed a boom-and-bust pattern, declining nearly as quickly as it expanded, and expanding approximately five times as quickly in 1990 compared to 1960. Also, new fisheries expanded increasingly far from their driving market in Asia, and encompassed a global fishery by the 1990s. One-third of sea cucumber fisheries experienced declines in average body size fished; half showed serial exploitation over space by moving further away from the coast; three-quarters showed serial exploitation from high- to low-value species; and two-thirds experienced population declines due to overexploitation with local extirpation in some cases. One-third of all sea cucumber fisheries remain unregulated. These findings suggest that the basis of marine food webs is increasingly exploited with limited stock and ecosystem-impact assessments, and a new management focus is needed to avoid negative consequences for ocean ecosystems and human well-being.

No description available.

Biological invasions pose a serious threat to biodiversity world-wide. Through various means, such as competition or predation, invaders can radically change species composition and the functioning of native ecosystems. Even though our understanding of the mechanisms underlying invasion success is improving, there is still a lack of knowledge on the response of native species under pressure from invasion. This study adds to existing knowledge on the responses of a native species to invasion by non-indigenous species. Pyura pachydermatina is a native ascidian in the southeast coast of New Zealand currently under pressure from increased urbanisation and invasion by other ascidian species. The reproductive strategies employed by P. pachydermatina are investigated and the role of these strategies to increase its resistance to invasion are assessed. A population study on the status of P. pachydermatina around the Banks Peninsula was carried out in Camp Bay, Pigeon Bay, and Wainui. Spawning experiments using P. pachydermatina and gonad histology were done regularly during the one year study period to assess its ability to self-fertilise and determine its reproductive period. In addition, predation experiments were carried out to assess the susceptibility of P. pachydermatina early life stages to two amphipod predators. The surveys indicated that the populations of P. pachydermatina in the three sites are different from one another. Wainui has on average the largest individuals of P. pachydermatina and Camp Bay, the smallest. Abundance of P. pachydermatina was highest in Pigeon Bay and lowest in Wainui. The three life stages of Pyura pachydermatina; recruits, juveniles, and adults, were present in all sites at all seasons. The spawning experiments confirmed the species’ ability to self-fertilise and that it has a year-round spawning period. The two amphipod predators, Jassa marmorata and Caprella mutica, were efficient in consuming the egg and larval stages of P. pachydermatina, but did not feed on the settlers. Year-round reproduction and the ability to self-fertilise potentially give P. pachydermatina increased resistance to the effects of urbanisation and invasion. This population study suggested that the species is thriving around the Banks Peninsula. This, combined with previous studies on the non-indigenous ascidian Styela clava that stated the static or declining populations of the potential invaders, gives a positive outlook for the native species for the future. I suggest the use of genetic techniques to assess, in more detail, the population structure and dispersal potential of this native species. I also suggest constant monitoring of native species is required to keep up to date with the current status of the species, which will in turn help management decisions should regional spread of the Lyttelton S. clava invasion occur in the future.

The conversion of natural forests to production land uses has led to huge losses of biodiversity and continues to threaten remaining terrestrial flora and fauna throughout the world. The global demand for wood products and energy, which was partly responsible for the loss of primary native habitat, is now one of the leading drivers of afforestation with significant new areas of plantation replacing former agricultural lands. While plantations do not support the same biodiversity values as natural forests they do provide significant habitat for a range of species. Saproxylic invertebrates (species that are dependent on deadwood) are strongly affected by the temporal and spatial availability of different deadwood resources. Previous research on saproxylic invertebrates has largely been restricted to natural or managed natural forests predominantly in the Northern Hemisphere, where forest management practices have been modified to conserve these species This thesis fills a distinct research gap in New Zealand and is the first large scale study to quantify the effects of deadwood age, wood species, and landscape composition on saproxylic invertebrates in our plantation forests by direct rearing. In this thesis I show that thinning residues, which are currently retained in many plantation forests, provide significant habitat for a range of native invertebrate taxonomic groups, including diverse assemblages of Coleoptera and Hymenoptera. Deadwood age is an important attribute determining taxonomic richness of saproxylic invertebrates. Richness of invertebrate orders/classes and Coleoptera species all increased in older deadwood material, and a stepwise multidimensional analysis procedure indicated that the age of deadwood was the most important factor structuring saproxylic invertebrate community composition in Pinus radiata thinning residues. Deadwood age was a stronger predictor of community composition in thinning residue than measures of landscape composition, such as the proportion of remnant native forest cover. The change in saproxylic invertebrate composition that occurs with deadwood age was related to changes in the feeding guilds, with a transition from primary wood feeding species to predators/parasitoids and fungal feeders with increasing dead wood age. Because thinning’s are carried out at prescribed times throughout the stand rotation, stand age could be adopted as a proxy for deadwood age in these systems allowing forest managers a simple method for monitoring saproxylic beetle habitat availability . My research provides strong empirical evidence that supports the existing conservation paradigm that forest managers should seek to create a mosaic of habitats at the landscape scale to enhance biodiversity opportunities in plantations. In addition to the habitat opportunities provided by P. radiata deadwood that is derived from silvicultural practices there are several sources of native wood in plantations. Native woody resources are found in either the embedded remnant areas of native forest or in the understory of stands as many native woody species colonise this habitat. As yet the importance of native understory deadwood resources for saproxylic species is unknown. In addition it is unclear how the importance of such understory resources is influenced by proximity to remnant native forest patches. I used experimental wood billets of four tree species (3 native and the exotic P. radiata) placed along replicated transects spanning native habitat and adjacent early stage regenerating plantation stands to assess the saproxylic invertebrate assemblages associated with different deadwood species as a function of proximity to native forest. I found that an interaction between wood host specificity (local scale) and proximity to interior native forest (landscape scale) was the most important factor regulating saproxylic invertebrate community structure. Deadwood of the native subcanopy trees Schefflera digitata, Melicytus ramiflorus, Aristotelia serrata and the exotic conifer P. radiata provided habitat for different subsets of the saproxylic fauna. The most pronounced differences in saproxylic community structure were between the native sub-canopy broadleaf species and the exotic P. radiata. Surprisingly the P. radiata supported a greater species richness and abundance of saproxylic Coleoptera in native remnants than the native wood species in the same habitat. In general, species richness was higher in native forest habitats and declined with increasing distance from native habitat. These results suggest that both the diversity of deadwood resources that are available and their proximity to native remnants are important for maintaining saproxylic communities in plantations. However, two of the native wood species (M. ramiflorus and A. serrata) exhibited steep declines in species richness at the plantation native forest boundary, suggesting that the contrasting stand types (native remnant and young regenerating plantation stands) with their different microclimate may have had a significant influence. Future research needs to compare the saproxylic fauna of dead wood in mature plantation stands with adjacent native remnants to ascertain if the effect of native habitat proximity is due to landscape composition or a reflection of microclimatic differences. The large diversity of saproxylic species observed during this study highlights the importance of plantations as habitat for saproxylic species, particularly in heavily fragmented landscapes that retain little original native forest. My research findings provide forest managers with options for improving forest management to enhance opportunities for the conservation of saproxylic invertebrates. In addition my thesis provides one of the most comprehensive multi-taxon data sets of saproxylic species associated with a variety of deadwood resources. This information will be invaluable to future researchers that continue to work on New Zealand’s saproxylic fauna.

Globally, stream invertebrate communities have been shown to respond to habitat degradation as a result of land use hanges. The effects of land use changes on stream communities have been well documented in temperate regions, however, their effects in the tropics are relatively unknown, particularly where land use activities can differ markedly (e.g., tea, maize and Eucalyptus plantations). To understand how land use affects tropical highland Nigerian stream communities, I surveyed 55 second and third order streams across four land use categories, ranging from continuous tropical montane forest to intensive crops/pasture. Streams were sampled in the dry season (October to March) for physico-chemical parameters (i.e., temperature, pH, conductivity, turbidity, current velocity, channel morphometry and riparian characteristics) and ecological characteristics (i.e., fine particulate organic matter [FPOM], coarse particulate organic matter [CPOM], algae and benthic invertebrates). Water temperature in all streams was high (up to 25oC) while levels of dissolved oxygen were frequently low (15–79 %). Physico-chemical conditions varied across land uses with continuous forested streams being cooler, with higher dissolved oxygen, larger bed substrate and more stable channels. Similarly, benthic invertebrate communities showed a strong response with the highest taxonomic diversity in forested streams and the lowest in streams within intensive crops (e.g., cabbage crops). Several of the taxa which occurred in forested streams (e.g., the mayflies Heptageniidae and Oligoneuridae and brachyuran crabs) were rare or absent in streams with more intensive land use. In contrast, damselflies and several true bugs (e.g., Notonectidae and Corixidae) were rare in forested streams but more common in other land uses. In order to test land use impacts on stream processes leaf litter decomposition experiments were carried out in nine streams, three in forest, three in tea plantations and three in maize fields. Leaf breakdown rates were slow compared with other reports for tropical streams, however leaves in forested streams broke down significantly faster (on a degree day basis) than in other land uses. This faster break down seemed to be driven by greater shredder densities in forested streams. Significantly lower densities of invertebrates were found in leaf bags incubated in streams draining tea plantation and maize fields than in forest streams. In the same nine streams food web components were sampled and analysed using gut content and stable isotope (N and C) analyses. Stream food webs in continuous forest were more complex than plantation and maize field streams. Stable isotope analysis indicated that primary consumers assimilated a mixture of autochthonous and allochthonous carbon resources, but the proportion varied among sites. Overall, my results suggest that in Nigerian highland tropical streams more intensive land use activities strongly affect the diversity and composition of benthic stream communities and ecosystem function, in similar ways to those reported in temperate streams.

Evidence is presented that Lymnaea contains homologues for mammalian Cav3 and NALCN 4-domain ion channels, which retain key amino acid sequence motifs that differentiate these channels from other 4-domain types. Molecular cloning and heterologous expression of the first invertebrate Cav3 channel cDNA from Lymnaea confirms that it indeed is a true homologue to mammalian Cav3 channels, retaining some hallmark biophysical and pharmacological features1. Interestingly, the Lymnaea Cav3 channel gene also exhibits alternative splicing that is conserved with mammalian Cav3.1 and Cav3.2 channels, with homologous exons 8b in the I-II linker (Cav3.1) and 25c in the III-IV linker (Cav3.1 and Cav3.2), that can selectively be included or omitted from the full length channel. We show that the developmental and spatial expression patterns of these splice variants are remarkably conserved, and that these splice variants produce analogous changes in membrane localization and biophysical properties when channels are expressed in HEK-293T cells. The Lymnaea Cav3 channel gene also undergoes alternative splicing in the domain II P-loop, with mutually exclusive exons 12A and 12B that code for a large portion of the P-loop just upstream of the selectivity filter. Such splicing is a novel discovery that is not conserved with vertebrates or any other deuterostome animal, all of which only contain 12A homologues of exon 12. However, protostome animals including Lymnaea stagnalis, Drosophila melanogaster, and C. elegans all have mutually exclusive 12A and 12B exons in their Cav3 channel genes. Evidence is presented that exon 12A is likely the ancestral exon for the domain II P-loop, and that alternate exon 12B evolved later. Furthermore, although the two Lymnaea variants possess the same selectivity filter motifs characteristic for Cav3 channels (i.e. EEDD), they exhibit dramatic differences in calcium vs. sodium selectivity, without significant differences in biophysical properties. This is the first account of alternative splicing used to modulate ion selectivity in a Cav3 channel homologue, and given that calcium is such an important electrogenic signaling molecule, these alterations are expected to have profound physiological implications. Amazingly, Lymnaea NALCN was also found to undergo alternative splicing in the domain II P-loop, but in this case, the entire P-loop is replaced by mutually exclusive exons 15a and 15b such that the selectivity filter is converted from the proposed non-selective sodium-permeable configuration (15b/EKEE; EEKE in mammals, nematodes and insects), to a calcium channel-like pore (15a/EEEE). Thorough phylogenetic analysis reveals that NALCN is extremely unconventional, in that alternative splicing has frequently and independently evolved to alter the selectivity filter in domains II or III, in multiple animal clades. Furthermore, the ancestral NALCN channel most likely contained an EEEE pore. This work brings into question NALCN???s proposed role as a major leak sodium conductance that depolarizes neurons to help set the resting membrane potential, since some species possess only an EEEE variant, and based on homology to other 4-domain ion channels, this should render the channel calcium-selective. Unfortunately, heterologous expression and electrophysiological characterization of the two Lymnaea NALCN isoforms was unsuccessful, corroborating with others the inability to record NALCN ionic currents in heterologous systems.