Genetic assessment of Macrobrachium species in Texas coastal streams

Freshwater shrimps in the genus Macrobrachium are ecologically and economically important as they provide essential services in habitats through a range in ecological roles such as detritus removal and predation as well as being prey items for large fish. Economically, Macrobrachium species have been exploited for aquaculture as well as commercial and recreation fisheries. Despite their importance, species distributions in Macrobrachium are poorly understood as the species exhibit similar morphologies making delineation difficult. The amphidromous lifestyle exhibited in many Macrobrachium species, including all that are native to the US, limits the dispersal capabilities potentially separating populations and allowing for localized adaptations. This lifestyle opens Macrobrachium species to multiple vulnerabilities such as habitat degradation and loss due to damming, land-use alterations, and pollution as well as past exploitation which have resulted in striking population declines of Macrobrachium species occurring in the United States. This study developed a robust phylogenetic hypothesis for M. carcinus throughout the species known distribution, including other North American species of Macrobrachium as outgroups using mitochondrial genes and made a preliminary assessment of M. ohione population structure between individuals occurring in different bay systems using mitochondrial cytochrome oxidase subunit I (COI). Phylogenetic trees created in BEAST and MEGA showed monophyly in the group as well as three genetically distinct clades of M. carcinus Puerto Rico, Central/South America, and Texas. Net p-distances of between these three clades were among species level divergences. Preliminary population assessment on M. ohione showed low levels of genetic diversity, which could be due to marker choice, but did show recent population expansion into Texas coastal streams.