Tracking Maternal Influences in the Field: Does Selection on Maternal Phenotype Exist in a Pelagic Spawning Species?

Understanding the cause of recruitment variability remains a fundamental challenge for fishery scientists.  This is due in part to uncertainties in the characteristics of juvenile survivors, which prevents a full understanding of the factors governing recruitment through the first year of life.  In stochastic environments, survivors may simply be those produced during chance matching of reproductive activity to optimal environmental conditions.  However, survivors may also be those that possess exceptional phenotypes.  Furthermore, as shown in many laboratory studies, exceptional phenotypes may be produced by specific maternal phenotypes.  However, it is currently unknown whether maternal influences on offspring affect the distribution of survivors in nature.  Here a preliminary analysis was conducted in a Chesapeake Bay tributary to test the hypothesis that a few striped bass parents produce a disproportionate number of juvenile offspring.  We tested this hypothesis by evaluating whether the distribution of half-sibling group sizes in juveniles deviated from a null distribution generated by random mating and survival (i.e., Poisson).  We further hypothesized that the effective population size, N_e, would be orders of magnitude smaller than the estimated census population size, since increased variance in reproductive success causes reductions in N_e.  Our results provide preliminary evidence for higher than expected variance in reproductive success; however, methodological improvements will be necessary to confirm these results in the future.