Crappie Hybridization in Southern Minnesota Lakes and Its Effects on Growth Estimates

Abstract

Species-specific microsatellite DNA markers were used to identify hybrids of black crappies Pomoxis nigromaculatus and white crappies P. annularis and to determine the effect of hybridization on crappie growth. Specifically, we determined the contribution of hybrids to the skew in length frequency distributions that is frequently observed within year-classes of sympatric crappie populations and the resulting upward bias on growth estimates for the two species. Hybridization was found throughout most southern Minnesota lakes that contained both species, but the frequency of hybrids was low in our length-stratified subsamples (mean frequency of first-generation [F 1 ] hybrids among all lakes and year-classes ¼ 3.2%; mean frequency of advanced-generation [F x ] hybrids ¼ 1.4%). Among the 22 study lakes, only 2 contained no hybrids (based on polymerase chain reaction amplification of microsatellite loci). The F 1 hybrids were disproportionately classified as black crappies under a Minnesota Department of Natural Resources (MNDNR) classification system that only allowed assignment of crappies to the two parental species. In one lake sampled over multiple years, we found F 1 hybrids in only 5 of 14 year-classes of MNDNR-classified black crappies and in 4 of 11 year-classes of MNDNR-classified white crappies, indicating annual variation in the prevalence of hybridization. Consistent with their faster growth and tendency to be classified as black crappies, F 1 hybrids accounted for 82% of all statistical outliers in length distributions of MNDNR-classified black crappie age-classes and 33% of the infrequent outliers in MNDNR-classified white crappie age-classes. The presence of F 1 hybrids in our subsamples produced an upward bias in back-calculated length estimates for black crappies but had nonsignificant effects on white crappie length estimates. The effects of hybridization should be taken into account when estimating growth in crappie species from sympatric populations.

Seasonal Patterns in White Crappies' Consumption and Growth: Influences of Varying Water Temperatures and Prey Availability

“…Potential causes for this slow growth include overcrowding, heredity, quantity and quality of food resources, and excessively high summer water temperatures (Ellison 1984;Mitzner 1984;Hayward and Arnold 1996;Michaletz 1998a). Overcrowding can occur in crappies from 682 MICHALETZ ET AL. their hybrids (e.g., Travnichek et al 1996;Miller et al 2008). The most common causes of slow growth in crappies appear to be related to inadequate prey resources and unfavorable thermal conditions, but the relative importance of each of these variables is poorly understood.…”