Дисертації з теми "History of zoology"

Life-history research explores how environmental variation and physiological constraints shift the energy allocation decisions to competing functions of the body among individuals and populations. Variation in the energy available across the environmental landscape is of particular interest as it dictates the amount energy available for organisms to acquire and allocate to their life-history. Additionally, individuals vary in their ability to capture and assimilate energy from the environment. This dissertation seeks to understand how environmental variation in energy availability and physiological constraints of attaining this energy shape allocation decisions among individuals and populations. I examined diamond-backed watersnakes (Nerodia rhombifer) from five populations that differed in their access to energy resources of prey. I compared measures of reproduction and growth to detect the presence of differential allocation decisions. I tested whether differences in allocation among individuals and populations arose as a constraint of their ability to assimilate energy resources in the environment, or as a function of the variation in prey characteristics across the landscape. Lastly, I measured how variation in reproductive investment may limit energy acquisition among individuals.

Community ecology investigates questions related to the density, growth/decline and movements of species over time in given geographical regions. This study investigated similar questions regarding communities of endemic bat species in Connecticut. White-nose syndrome (WNS) has recently killed millions of bats in New England, yet few large-scale conservation efforts have occurred in Connecticut and few data have been published on the status of Connecticut bats post-WNS. This study aimed to: 1) survey bats persisting in WNS regions to document whether changes have occurred in species biodiversity, richness, distribution and habitat use; and 2) measure seasonality effects from summer through pre-hibernal months. Bat presence and activity were recorded using bat detectors set in grassland and forested habitats, near bodies of water and near anthropormorphic and geologic structures across Connecticut. Bioacoustics data have been analyzed by using Sonobat^© software. Combined, these data show that bat activity varies significantly across habitat type (p = 0.02) and over seasons (p = 0.05). Additionally, these data provide insight regarding relationships between individual species, and clumped species groups, with habitat types and across seasons. Ultimately, these data show how bat communities have changed over time in a post-WNS environment. Combined, these data can help drive future wildlife conservation, outreach, education and management practices.

Like many imperiled fishes, the endangered Pahrump Poolfish ( Empetrichthys latos latos) is managed in ex situ refuges. I investigated life history characteristics of females from two such populations at Lake Harriet and Shoshone Stock Pond. Lake Harriet is a relatively large lake with low fish densities located at relatively low elevation and low latitude, while Shoshone Stock is a small pond with high fish densities at a higher elevation and latitude. Females from the Lake Harriet population were larger, and had greater fat content, reproductive allocation, and ‘clutch’ size than females from the Shoshone Pond population. This divergence, which occurred in three decades, may result in a phenotypic mismatch if the fish are used as a source for restocking their native habitat or stocking new refuges.

Poolfish conservation may require establishing new populations; however, many sites are inhabited by non-native fish and/or other protected fish species. Thus, managers may wish to consider establishing multi-species refuges that may even already include undesirable species. I established experimental communities that included allopatric and sympatric communities of Poolfish, Amargosa Pupfish (Cyprinodon nevadensis), and invasive Western Mosquitofish (Gambusia affinis). Pupfish persisted in sympatry with both poolfish and mosquitofish, but had higher juvenile production when maintained in allopatry. By contrast, poolfish juvenile production was high in allopatry, but virtually absent in the presence of other species.

To evaluate the generality of these findings, I established experimental allopatric and sympatric communities of poolfish or pupfish with mosquitofish from two populations that differed in body size: Garrett mosquitofish were approximately twice the mass of Wabuska mosquitofish. Poolfish juveniles had high survival in allopatry, but produced virtually no juveniles when sympatric with either of the two mosquitofish populations. Pupfish juvenile survival was higher in allopatry than sympatric with Garrett mosquitofish, which in turn was higher than sympatric with Wabuska mosquitofish. These results were consistent with the earlier experiment suggesting that poolfish were functionally extirpated but pupfish maintained substantial production in the presence of mosquitofish. These findings suggest that poolfish should be maintained in single species refuges, but that multi-species refuges may protect imperiled pupfish species.

The integration of advances in computing technology with major innovations in sequence data collection and phylogenetic inference has revolutionized evolutionary biology in the 21^st century. In particular, the continual development of both theory and software that allow for more flexibility in utilizing molecular clock methods has radically transformed our understanding of the mode and tempo of diversification across the Tree of Life. Over the course of five chapters, this dissertation explores methodological challenges to phylogenetic inference with the aim of better understanding the evolutionary history of the Holocentridae (squirrelfishes and soldierfishes).

Chapter 1 begins by focusing on the problem of accommodating clade specific rate heterogeneity in molecular clock analyses. While various nucleotide substitution models have been developed to accommodate among lineage rate heterogeneity, recently developed "uncorrelated relaxed clock" and "random local clock" models are predicted to perform better in the presence of lineage specific rate heterogeneity as these models relax assumptions of inheritance of nucleotide substitution rates between descendant lineages. Using simulations and two cetacean (whale and dolphin) datasets as a case study, we demonstrate abrupt changes in rate isolated to one or a few lineages in the phylogeny can mislead rate and age estimation, even when the node of interest is calibrated; and provide suggestions for diagnosing extreme clade specific rate heterogeneity.

Homoplasy is another important, yet often overlooked, source of error in phylogenetic studies. Chapters 2 and 3 utilize phylogenetic informative approaches to screen nucleotide sequence data for homoplasious site patterns. Using phylogenetic informativeness profiles, chapter 2 reconciles two competing hypotheses of ray-finned fish divergence times by highlighting that mitogenomic based Jurassic and Triassic divergence time estimates for most major lineages of spiny-rayed (acanthomorph) fishes were an artifact of tree extension. Evolutionary relationships of early diverging acanthomorph fishes are also contentious, with molecular data supporting either holocentrids or a clade comprised of holocentrids and primarily deep-sea fishes as the sister lineage to the species-rich percomorpha. Chapter 3 reveals this conflict to also be largely driven by homoplasy and reconciles results based on previously published data with a 132 gene next-generation sequence dataset to identify the sister lineage of percomorph and the phylogenetic placement of holocentrid fishes.

Chapter 4 continues to explore holocentrid evolutionary relationships. Using a multi-locus dataset that includes all but one holocentrid genus, this chapter provides the first molecular phylogeny of the group. The systematics of holocentrid fishes has unstable for over 100 years. We demonstrate several of the key synapomorphies for holocentrid genera are in fact homoplasious. Likewise, several genera of holocentrine (squirrelfish) are rendered consistently paraphyletic by a series of maximum-likelihood and Bayesian analyses and we propose taxonomic revisions to reflect shared ancestry.

Chapter 5 further investigates the temporal history of holocentrid evolution. Contemporary holocentrid species richness is concentrated in the Indo-Australian Archipelago (IAA), yet these fishes also represent some of the most numerous fossil taxa in deposits of the Eocene West Tethyan biodiversity hotspot. Using likelihood-based methods integrated with a molecular timetree that incorporates fossils as tip taxa, we reconstruct the history of range evolution for these fishes. Following the collapse of the West Tethys, holocentrids exhibit a signature of increased range fragmentation, becoming isolated between the Atlantic and Indo-Pacific Ocean basins. However, rather than originating within the emerging IAA hotspot, the IAA appears to have acted as a reservoir for holocentrid diversity that originated in adjacent regions over deep evolutionary timescales. By integrating extinct lineages, these results provide a necessary historic perspective on the formation and maintenance of global marine biodiversity.

Amphidromous species migrate between fresh water and the sea for larval development. Many caridean shrimps, especially Macrobrachium spp., are amphidromous, and some populations are found far-upstream within continental river systems. This project tested the hypothesis that populations of Macrobrachium ohione from the Atchafalaya and Mississippi Rivers are amphidromous.

In the laboratory, I tested the hypothesis that upstream populations of M. ohione have freshwater larval development. My results indicated that saline habitats are essential for M. ohione development, and larval mortality increased after 3-4 days of freshwater drifting. This provides indirect evidence that upstream populations have extended marine larval development.

Due to their limited freshwater survival, M. ohione must deliver larvae to the sea. Spatial-temporal analysis in the Atchafalaya and Mississippi Rivers reported an influx of reproductive-sized shrimps and females with near-hatching broods into coastal sites. This suggests that females are migrating downstream to hatch larvae in downstream habitats.

Stable isotope analysis indicated that the upstream juvenile migration originates from saline habitats. Video surveillance revealed that juveniles migrate throughout the night at an average speed of ∼ 0.56 km hr ^-1, and swimming speeds were related to the water velocity they swam against. From these results, I estimated that juveniles are capable of migrating to far-upstream habitats within their life span (1-2 years).

Lastly, I investigated how dams affect the juvenile migration, and tested juvenile migrant climbing abilities. This study reported greater densities of juveniles downstream of dams than upstream of dams, indicating the dams impede the juvenile migration downstream of Old River Control. Shrimp climbing studies revealed that at various inclinations and water velocities, ~ 52% of the shrimps were climbing the shrimp ramp and ~ 12% completed the climb. These results demonstrated juveniles can climb bypass structures with detectable water flows.

My findings suggest that M. ohione populations within the Mississippi River System are amphidromous, because they require marine larval development and long-distance migrations are conducted to and from the sea. This study may serve as a general model for migrations of amphidromous shrimps in comparable large rivers, and potentially contribute to freshwater shrimp conservation.