EFFECTS OF ZEBRA MUSSEL INFESTATION ON GENETIC DIVERSITY OF NATIVE MUSSEL 
SPECIES.

Jason E. Granberg, Michael A. Romano, Richard V. Anderson.
Department of Biological Sciences, Western Illinois University, Macomb, IL 
61455.

Two species of native unionids, Amblema plicata and Pyganodon grandis, were 
collected to determine if variation in zebra mussel (Dreissena polymorpha) 
surface area infestation effects genetic structure among host populations found 
in Pool 19 of the Mississippi River. Foot muscle tissue taken from frozen 
samples was the source of soluble enzymes. From these tissue preparations, 
allozyme variation was quantified using starch gel electrophoresis to separate 
enzymes encoded by 11 presumptive structural loci. Deviations from Hardy-
Weinberg expectations, mean heterozygosity values and similarity phenograms were 
constructed using BIOSYS1 (Swofford and Selander 1981). Initial investigations 
into A. plicata suggest that low average zebra mussel infestation (.55 zebra 
mussels/host) results in heterozygote deficiency (-0.027). In other A. plicata 
populations where infestation is higher, ranging from 8.8 zm/host to 104.8 
zm/host, the heterozygote deficiency is smaller -.008 to +.005. This may be a 
result of the longer life expectancy of A. plicata where a pre-selection 
population (low zm) contrasts with a population that is currently undergoing 
selection. In P. grandis, the heterozygote deficiency ranges from -.054 in a 
population with 6.7 zm/host to a population with -.026 heterozygote deficiency 
with 177.7 zm/host. The variation in P. grandis may be the result of populations 
that occur at least one generation after initial infestation. However, because 
of the shorter life expectancy and subsequent generation time of P. grandis, it 
may be there is a completely different frequency of alleles in founder 
populations before infestation resulting in a different process from the other 
species. Further investigations will be required to determine the full genetic 
impact zebra mussels have on native unionid populations, both in areas where 
infestation has existed for several years versus areas where the zebra mussels 
have not yet invaded.


Keywords: Dreissena  polymorpha, mussels, Mississippi River, electrophoresis, 
parasitism.