POPULATION DYNAMICS AND GENETIC DIFFERENTIATION OF THE THREATENED FRESHWATER MUSSEL SPECIES FUSCONAIA ASKEWI, FUSCONAIA LANANENSIS, AND PLEUROBEMA RIDDELLII

North America has the most diverse freshwater mussel fauna in the world with approximately 300 species; unfortunately, extinction rates for freshwater mussels rivals the rates of many other groups of organisms. Population-level natural life history data is essential in the management of species of conservation concern, yet basic information about freshwater mussel life-history and demographic traits are unknown for many species. To further complicate matters, taxonomic uncertainty exists among some members of the group. The work detailed herein had two goals: to gain further understanding of the taxonomic relationship between Fusconaia lananensis and F. askewi by sequencing genes that had not been previously examined for these species, genes 16S and ITS1, and collect data on the population size, density, and structure for both F. askewi and F. lananensis, as well as for Pleurobema riddellii, all of which are classified as state threatened in Texas. The second goal was accomplished via qualitative analysis of data from 0.25 m2 quadrats and through mark-recapture studies at field sites where the highest densities of these species have been recorded. Specifically, quadrat surveys were conducted at seven mark-recapture sites in the Neches, Sabine, and Angelina Rivers during the summers of 2014 and 2015. In terms of my genetic analysis, data collected from the 16S gene has provided additional support that F. askewi and F. lananensis are one single species, as recently proposed by other researchers. Data collected from the ITS1 gene showed no genetic differentiation between F. askewi, F. lananensis, and F. flava, though recently published research indicates that there is low genetic variation within the ITS1 gene for several different species found in genus Fusconaia. Sites on the Neches and Angelina Rivers had significantly higher recapture rates between 2014 and 2015 than sites on the Sabine River, likely because of a flooding event that occurred in the Sabine River during that time. The largest population estimate for a F. askewi population was 302±26.72 in 2015 within the 25 m area while the largest population estimate for a P. riddellii population was 101±4.99 in 2015 within the 25 m area. Fewer juvenile P. riddellii were detected than F. askewi, leading to left-skewed size class distributions for P. riddellii. As conservation efforts for freshwater mussels increase, continued analysis of established freshwater mussel populations will be crucial