Effective number of breeders, Nb, effective population size, Ne, iteroparity, small population size, brook trout, age at maturation Abstract: The relationship between the effective number of breeders (Nb) and the generational effective size (Ne) has rarely been examined empirically in species with overlapping generations and iteroparity. Based on a suite of 11 microsatellite markers we examine the relationship between Nb, Ne, and census population size (Nc) in 14 brook trout (Salvelinus fontanels) populations inhabiting 12 small streams in Nova Scotia and sampled at least twice between 2009 and 2015. Unbiased estimates of Nb obtained with individuals of a single cohort, adjusted on the basis of age at first maturation (α) and adult life span (AL) were from 1.66 to 0.24 times the average estimates of Ne obtained with random samples of individuals of mixed ages [i.e., N ̂(b(adj2))/〖mean(N ̂ (e(mixed ages)))]. In turn, these differences led to adjusted Ne estimates that were from nearly 5 to 0.7 times the estimates derived from mixed aged individuals. These differences translate into the same range of variation in the ratio of effective to census population size (N ̂_(e(adj2))N ̂_c) within populations. Adopting N ̂(e(adj2)) as the more precise and unbiased estimates, we found that these brook trout populations differ markedly in their effective to census population sizes (range ~0.3 to ~0.001). Using AgeNe we then show that the variance in reproductive success or reproductive skew varied among populations by a factor of 40 from a Vk/k≈5 to 200. These results suggest wide differences in population dynamics likely resulting from differences in productivity affecting the intensity of competition for access to mates or redds and thus, reproductive skew. Understanding the relationship between Ne, Nb and Nc and how these relate to population dynamics and fluctuations in population size are important for the design of robust conservation strategies in small populations with overlapping generations and iteroparity.

Copy of Brook Trout Genotypes - December 17 2015excel file containing multilocus genotypes for 11 microsatellite loci in 1783 brook trout individuals from 14 locations in 12 streams