Hybridization between pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon Scaphirhynchus platorynchus.

This study found that introgressive hybridization of the pallid sturgeon Scaphirhynchus albus with the common shovelnose sturgeon Scaphirhynchus platorynchus has probably occurred across the range of S. albus. Bayesian clustering found evidence of hybridization in all management units of S. albus. Some individuals were intermediate at both genetic and morphological characters, and some had discordant results. The results support introgressive hybridization throughout much of the range of S. albus, yet individuals consistent with being pure members of each species were detected in all management units. Simulations demonstrated that it would be very difficult to distinguish introgressed individuals from pure specimens after multiple generations of backcrossing with these microsatellite markers. Using hybrid or backcross fish as broodstock could artificially accelerate the loss of unique genetic variation in S. albus. Additional microsatellite loci or additional genetic markers, along with morphological data may be required to ensure that hybrid or backcross fish are not used. Introgressive hybridization requires at least two generations and generation lengths of S. albus are long, perhaps as long as 30 years. The proportion of individuals consistent with introgressive hybrid origins indicates that hybridization between S. albus and S. platorynchus probably has occurred for several generations and is not a recent phenomenon.

Modulation of host response by Trichinella pseudospiralis.

Measurement of myeloperoxidase activity in the muscles of mice infected with Trichinella pseudospiralis, T. spiralis or both helminths allowed quantitation of host inflammatory response to the parasite. Infection of the host with T. pseudospiralis alone was accompanied by less inflammation in host diaphragm muscle than was the case in hosts infected with T. spiralis alone. A dramatic reduction in inflammation around s.c. implanted cotton string was observed in mice infected with T. pseudospiralis alone below that seen in uninfected mice. Concurrent infection of the host with T. spiralis and T. pseudospiralis resulted in a lowering of myositis below that seen in the diaphragm muscles of mice infected with T. spiralis alone.