Silver carp (Hypophthalmichthys molitrix). Photo credit: Department of Fisheries and Allied Aquacultures, Auburn University, Alabama, USA

Microsatellite DNA Markers for Assessing Phylogeographic and Population Structure in Three Invasive Asian Carp Species: Silver Carp (Hypophthalmichthys molitrix), Big Head Carp (Hypophthalmichthys nobilis), and Grass Carp (Ctenopharyngodon idella)

Invasive species costs to ecosystems and the human economy are staggering.  Control and eradication of exotic invasive species can be facilitated with detailed knowledge of population structure.  In somewhat of a paradigm shift, resource managers are realizing that the population and phylogeographic structure of invasive species, not unlike endangered species, must be understood before effective management (or eradication) programs can be implemented.  Leetown Science Center researchers have identified DNA markers for determining the existence and extent of hybridization among species of Asian carp in the Mississippi River drainages.  This research has shown not only that silver carp and bighead carp hybridize, but that female silver carp successfully mate with bighead males and that the reciprocal crosses also occur.  The same markers have also identified the presence of grass carp eggs in ichthyoplankton nets.  LSC has isolated and characterized microsatellite DNA markers in silver carp (Hypophthalmichthys molitrix), big head carp (Hypophthalmichthys nobilis), and grass carp (Ctenopharyngodon idella) for use in determining the population structure and effective population size of each invasive species.  Researchers are also investigating the utility of genetic engineering for use in controlling or eradicating these invasives.  LSC geneticists are considering the use of genetic manipulations that result in daughterless and under dominance inheritance.  A central strategy to the daughterless carp approach is the conversion of female embryos to males via RNAi knockdown of aromatase gene expression. Population modelling of daughterless technology has indicated that rate of reduction in population size is directly related to copy number of the daughterless gene construct in the recombinant males being released. How feasible is high copy number in fish is unclear. An increase in copy numbers has been suggested to cause silencing of transgenes in mammals. Whether or not this is also true in fish is unknown, as no systematic studies in fish have been performed to date.  LSC researchers also intend to investigate the potential for introgressing a desired engineered gene into a pest population by linking the desired gene to DNA constructs that exhibit underdominance properties. LSC geneticist’s deterministic model includes two independently segregating engineered constructs that both carry a lethal gene, but suppress each other. Only genotypes containing both or neither construct are viable.  

For more information contact Timothy L. King at the Leetown Science Center.