Lopsided fish in the Snake River Basin — fluctuating asymmetry as a way of assessing impact of hatchery supplementation in chinook salmon, Oncorhynchus tshawytscha

Abstract

SynopsisThe use of developmental instability (an individual's failure to produce a consistent phenotype in a given environment) was evaluated to detect the effects of outplanting hatchery fish on wild salmon. Juvenile chinook salmon were collected in 1989, 1990, and 1991 from five drainages in the Snake River Basin. In each drainage we attempted to collect fish from streams with no hatchery supplementation (wild), naturally spawning fish from streams with hatchery supplementation (natural), and fish collected at a hatchery. Forty fish were collected per site and the number of elements in bilateral characters were counted on each side of the fish. Indices of fluctuating asymmetry (FA), a measure of minor, random deviations in perfect symmetry of bilateral counts, were calculated as an estimator of developmental instability. Analysis of character counts from seven paired characters revealed normal distributions. Only one of the characters displayed counts that were statistically larger on one side than the other, indicating that directional asymmetry (DA) or antisymmetry was not a major bias of FA. However, the means of all individual characters revealed a non-statistically significant left side bias. We analyzed our data using two indices of FA (FA1 and FA5) with different levels of sensitivity to DA. Differences in both FA indices were found among years, with collection sites in 1989 having significantly larger FA values than in 1991 (FA p < 0.01). Levels of FA among wild, natural, and hatchery fish were comparatively small (FA1 p = 0.17). This suggests developmental conditions were different in the first year of the study than in the last. The cause of these differences may be linked to either genetic or environmental variation or to gene-environment interactions, but the general population declines of salmon that occurred during this time obscures more specific conclusions.

Maladaptation and phenotypic mismatch in hatchery‐reared Atlantic salmon Salmo salar released in the wild

“…Consideration of FA as an index of development instability, i.e . the inability by an embryo to produce a consistent phenotype in a given environment (Johnson et al ., ), may shed some light on the relative importance of plasticity and selection. The development of bilateral structures on opposite sides of an organism (such as pectoral fins) is controlled by the same genes, and any deviations from perfect bilateral symmetry are thought to result from environmental and genetic stressors (Johnson et al ., ).…”

Outbreeding Depression after Two Generations of Hybridizing Southeast Alaska Coho Salmon Populations?

“…Several authors assessed different indices of FA and their utility as fitness measures (Moller 1997) with mixed results (Leary et al 1985;Campbell and Emlen 1996;Moran et al 1997;Johnson et al 2004). Such analyses have had mixed success in characterizing variation of fitness because (1) studies often do not adopt uniform methods for correlating developmental stability and FA, (2) the influence of genotype and environment on developmental stability as measured by FA is unknown, and (3) often the signal of a relationship between organismal stress and FA is weak (Lens et al 2002;Van Dongen 2006).…”

Fluctuating asymmetry and exogenous stress in fishes: a review

“…While no bilateral structure is perfectly symmetrical, the inference is that greater degrees of asymmetry arise when organisms are exposed to exogenous environmental stressors during development. While endogenous factors such as inbreeding may also contribute to asymmetry (e.g., Johnson et al 2004;Wedekind and Muller 2004;Iguchi et al 2005;Leamy and Klingenberg 2005), the focus of this review is specifically concerned with how FA can result from environmental stressors.…”