Comparison Study of Fecundity and Size Between Urban and Rural Black Nosed Dace (Rhinichthys atratulus) Populations
Erika Monee’ Mc Afee and Dr. Joel Snodgrass
Evolutionary theory suggest that when faced with decreased adult survival rates organisms may adapt by allocating more energy to reproduction at an earlier age. Organisms persisting in urban environments are expected to have higher adult mortality rates and it has been reported that black nosed dace (Rhinichthys atratulus) from urbanized watersheds tend to have decreased age and size at maturity when compared to populations in more rural watersheds (Franker, et al. 2002). Based on these results we investigated the relationship between size and fecundity among dace from urbanized and rural watersheds. Histograms of egg diameter indicated that a single clutch of eggs could be identified in each female examined. An ANCOVA model indicated a significant difference (P = 0.002) in the intercepts of lines relating clutch size to standard length between females from urbanized and rural watersheds. There was no difference in slope for these lines (P = 0.257). Our results suggest that dace from urbanized watersheds allocate more energy to reproduction. However, because other studies have found increased growth among dace from urbanized watersheds, it remains unclear whether dace in urbanized watersheds have adapted to increased adult mortality or are just responding to increased resources levels in the urban environment.
black nosed dace population