Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
Browse
3 results
Search Results
Item RESPONSES OF THE COPEPOD ACARTIA TONSA TO HYPOXIA IN CHESAPEAKE BAY(2015) Barba, Allison Patricia; Roman, Michael R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chesapeake Bay experiences seasonal hypoxia each year and while studies have been done investigating how the copepod Acartia tonsa responds to hypoxia, few studies have focused on a comprehensive understanding of how its behavior and fitness are affected by low oxygen. The abundance, distribution, fitness and diel vertical migration patterns of A. tonsa were measured on series of six cruises in 2011 and 2012 in spring, summer and fall. I found that copepod abundance, distribution and vertical migration were significantly affected when hypoxic waters occurred below the pycnocline. I also found that males were less impacted by hypoxia than females, with a greater decrease in female abundance and vertical migration when there were hypoxic bottom waters.Item Physiological responses of Acartia and Eurytemora spp. to changes in the nitrogen:phosphorus quality of their food(2014) Bentley, Katherine Marie; Glibert, Patricia; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study addressed how copepods respond to varying nutrient content in their prey. Copepod physiological responses were measured along a gradient of prey nitrogen:phosphorus (N:P) ratios created by altering the P content in diatom prey grown at a constant rate. Acartia tonsa, a broadcast spawner, and Eurytemora carolleeae, a brood spawner, increased excretion of P as prey N:P declined (i.e. P increased). E. carolleeae had higher somatic tissue nutrient content, while A. tonsa had higher egg nutrient content overall and higher P in eggs as N:P decreased. E. carolleeae egg production was greatest when eating high N:P prey while A. tonsa showed the opposite. Egg viability declined at high N:P for both copepods, yet A. tonsa viability was always greater than E. carolleeae viability. Both copepods responded physiologically to food of varying quality, yet regulated their homeostasis differently. Prey nutrient content may be significant in the environmental selection of different copepods.Item CRYPTIC DIVERSITY, ECOLOGICAL DIFFERENTIATION AND POPULATION GENETICS OF AN ESTUARINE COPEPOD, ACARTIA TONSA DANA 1849 (COPEPODA: CALANOIDA)(2009) Chen, Gang; Hare, Matthew P; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Surprising genetic diversity has been discovered in marine holoplankton, organisms that "drift" in water currents throughout their life cycle. This discovery challenges our assumptions and suggests that holoplankton species may have limited dispersal and/or have adapted to small-scale oceanographic features. In this study, I investigated population genetics of Acartia tonsa, a holoplanktonic estuarine copepod containing deeply-diverged mitochondrial lineages, on the United States Atlantic coast. The study goals include: 1) assessing its cryptic species/genetic diversity; 2) inferring evolutionary and geographic origins of its cryptic lineages; 3) testing environmental associations of cryptic lineages; 4) inferring evolutionary and ecological processes/mechanisms underlying population diversification of A. tonsa. Phylogenetic analyses of DNA sequences from two gene loci, mitochondrial cytochrome c oxidase subunit I (mtCOI) and nuclear ribosomal internal transcribed spacer (nITS), resolved five morphologically cryptic, genetically diverged lineages that were reproductively isolated species based on genealogical concordance principle. Three co-distributed, deeply-diverged mtCOI lineages (X, S, F) showed significant population differentiation within lineages and contrasting phylogeographic patterns among lineages. Population structures and isolation by distance patterns detected for all lineages suggested that dispersal of Acartia lineages was more or less limited to adjacent estuaries; geographic isolation was a key mechanism underlying population diversification of A. tonsa. The highly diversified, relatively recent lineage F demonstrated a southern center of origin in Florida with northward stepwise diversification. Its distinct localized population structure and strong association with low-salinity environments suggested that environmental stressors (such as salinity) could act as physiological barriers to gene flow, facilitating diversification of Acartia populations. Co-existing Acartia lineages were parapatrically distributed along the estuarine gradient across systems on the US Atlantic coast. Genetic, morphological and ecological evidence indicated niche partitioning and ecological differentiation of A. tonsa within estuaries. Multiple factors may have contributed to the observed parapatric distribution and niche partitioning, including selection by salinity, biological competition, and/or local adaptation. These findings in one of the best known estuarine copepods reinforce the general conclusion that marine biodiversity is substantially underestimated, not only in terms of species numbers, but also with respect to niche partitioning and the potential importance of ecological divergence in marine holoplankton.