Genetic diversity and cellulolytic activity among several species of unionid bivalves in Arkansas

Allozyme analysis was utilized to determine the genetic diversity of four s pecies of bivalves in the Subfamily Ambleminae (Amblema plicata, Plectomenu s dombeyanus, Quadrula pustulosa, and Q. quadrula) in the Cache and White r ivers of Arkansas. Bivalve populations of both rivers have been subjected t o frequent harvest, whereas White River populations have been exposed to pe riodic habitat destruction due to dredging. Nine enzyme systems representin g 16 loci were selected for analysis based upon their expression in adducto r muscle. Ranges of polymorphism (P) were from 0.572 for A. plicata to 0.36 0 for Q. quadrula; heterozygosity (H) values ranged from 0.049 for P. dombe yanus to 0.144 for Q. pustulosa. With the exception of low genetic diversit y (P, H, and number of alleles per locus) for Q. quadrula, genetic diversit y values were similar to previous studies involving Ambleminae of other wat er systems. Populations were characterized by heterozygote deficiencies at all loci. Several determinants of heterozygote deficiency were investigated , with selection posed as a viable hypothesis. Cellulolytic activity from b ivalves in both the Cache and White rivers was significantly reduced (propo rtional to 0.05) to as low as 12% and 28%, respectively, of upstream enzyme activities. This downsteam digestive enzyme difference was most apparent i n P. dombeyanus, whereas site reductions were not as apparent for other spe cies sampled. Evidence of genetic decline associated with bottlenecking was identified for Quadrula quadrula, and this loss of genetic diversity is de trimental to the stability of bivalve populations.