Life History Variation, Genetic Diversity and Extinction Risk in Tidewater Goby

The fitness consequences of low genetic diversity are of great concern to species conservation. The federally endangered tidewater goby, Eucyclogobius newberryi, occurs in discrete and reproductively isolated populations along the California coast that exhibit tremendous variation in genetic diversity. To evaluate relationship between demographics and genetic diversity in tidewater goby, a detailed otolith microstructural analysis was conducted in two focal populations exhibiting high and low genetic diversity (H_O = 0.58 versus 0.08). Daily increment deposition in sagittal otolith of tidewater goby was validated and a predominantly annual life cycle (annual survivorship, M, < 3%) was observed in both populations. Year-round reproductive activity was detected in the population with high genetic diversity.  In contrast, the genetically depauperate population was characterized by a very narrow, single annual reproductive period . Analysis of eleven additional populations shows that the duration of the reproductive period within isolated populations of tidewater goby is highly variable and correlated with genetic diversity levels (p = 0.009, R²=0.52). Theory predicts that reproductive periods of long duration may serve as a safeguard against environmental stochasticity.  Our analyses support this assertion as the focal population exhibiting a narrow reproductive period went extinct, presumably as result of a drastic increase in salinity shortly after the temporally constricted, single annual reproductive period, whereas the population exhibiting year-round reproductive activity persisted through similar salinity fluxes.