title: Effective number of breeders provides a link between interannual variation in stream flow and individual reproductive contribution in a stream salmonid.
abstract: The effective number of breeders that give rise to a cohort (N(b)) is a promising metric for genetic monitoring of species with overlapping generations; however, more work is needed to understand factors that contribute to variation in this measure in natural populations. We tested hypotheses related to interannual variation in N(b) in two long-term studies of brook trout populations. We found no supporting evidence for our initial hypothesis that N^(b) reflects N^(c) (defined as the number of adults in a population at the time of reproduction). N^(b) was stable relative to N^(C) and did not follow trends in abundance (one stream negative, the other positive). We used stream flow estimates to test the alternative hypothesis that environmental factors constrain N(b). We observed an intermediate optimum autumn stream flow for both N^(b) (R(2) = 0.73, P = 0.02) and full-sibling family evenness (R(2) = 0.77, P = 0.01) in one population and a negative correlation between autumn stream flow and full-sib family evenness in the other population (r = -0.95, P = 0.02). Evidence for greater reproductive skew at the lowest and highest autumn flow was consistent with suboptimal conditions at flow extremes. A series of additional tests provided no supporting evidence for a related hypothesis that density-dependent reproductive success was responsible for the lack of relationship between N(b) and N(C) (so-called genetic compensation). This work provides evidence that N(b) is a useful metric of population-specific individual reproductive contribution for genetic monitoring across populations and the link we provide between stream flow and N(b) could be used to help predict population resilience to environmental change.
authors.affiliation: Department of Environmental Conservation, University of Massachusetts, Amherst, MA, 01003, USA.|U.S. Forest Service, Northern Research Station, University of Massachusetts, Amherst, MA, 01003, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Whiteley
authors.affiliation: Department of Environmental Conservation, University of Massachusetts, Amherst, MA, 01003, USA.|U.S. Forest Service, Northern Research Station, University of Massachusetts, Amherst, MA, 01003, USA.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Coombs
authors.affiliation: Department of Environmental Conservation, University of Massachusetts, Amherst, MA, 01003, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Cembrola
authors.affiliation: U.S. Geological Survey, Leetown Science Center, S.O. Conte Anadromous Fish Research Center, Turners Falls, MA, 01376, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: O'Donnell
authors.affiliation: U.S. Geological Survey, Ecosystems, 12201 Sunrise Valley Drive, Reston, VA, 20192, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Hudy
authors.affiliation: U.S. Forest Service, Northern Research Station, University of Massachusetts, Amherst, MA, 01003, USA.
authors.forename: Keith H
authors.initials: KH
authors.lastname: Nislow
authors.affiliation: U.S. Geological Survey, Leetown Science Center, S.O. Conte Anadromous Fish Research Center, Turners Falls, MA, 01376, USA.
authors.forename: Benjamin H
authors.initials: BH
authors.lastname: Letcher
mesh_terms: D000818:Animals; D014644:Genetic Variation; D005828:Genetics, Population; D008404:Massachusetts; D018895:Microsatellite Repeats; D011156:Population Density; D012098:Reproduction / Q000235:genetics*; D045483:Rivers; D014337:Trout / Q000235:genetics*; D014768:Virginia; D014872:Water Movements
keywords: effective number of breeders; genetic monitoring; linkage disequilibrium; stream fishes; stream flow