Maintenance of phenotypic variation: repeatability, heritability and size-dependent processes in a wild brook trout population.

Keith H. Nislow,Benjamin H. Letcher,Jason A. Coombs

doi:10.1111/j.1752-4571.2011.00184.x

Abstract

Phenotypic variation in body size can result from within-cohort variation in birth dates, among-individual growth variation and size-selective processes. We explore the relative effects of these processes on the maintenance of wide observed body size variation in stream-dwelling brook trout (Salvelinus fontinalis). Based on the analyses of multiple recaptures of individual fish, it appears that size distributions are largely determined by the maintenance of early size variation. We found no evidence for size-dependent compensatory growth (which would reduce size variation) and found no indication that size-dependent survival substantially influenced body size distributions. Depensatory growth (faster growth by larger individuals) reinforced early size variation, but was relatively strong only during the first sampling interval (age-0, fall). Maternal decisions on the timing and location of spawning could have a major influence on early, and as our results suggest, later (>age-0) size distributions. If this is the case, our estimates of heritability of body size (body length = 0.25) will be dominated by processes that generate and maintain early size differences. As a result, evolutionary responses to environmental change that are mediated by body size may be largely expressed via changes in the timing and location of reproduction.

Highlights

Forecasting effects of environmental change on population persistence, especially effects of climate change, can be improved by incorporating evolutionary processes into population models (Skelly et al 2007)
In an effort to move toward incorporation of evolutionary processes into population models and to understand the relative importance of sizedependent processes including growth and survival, we provide estimates of quantitative genetic variables for the key phenotypic traits of body size and growth from a wild population of brook trout (BKT) (Salvelinus fontinalis)
We focus on growth processes and ask three main questions: (i) To what extent do observed size distributions reflect repeatability of individual body size and growth rate? (ii) How are body sizes influenced by size-dependent growth and losses? (iii) Is heritability of body size and growth rate high enough that selection on size or growth could evoke an evolutionary response? Overall, we ask whether an evolutionary response to environmental change is likely to act through body size/growth processes, and to what extent early size differences, later growth rate variation, and size-selective mortality contribute to the generation of size distributions

Summary

Introduction

Forecasting effects of environmental change on population persistence, especially effects of climate change, can be improved by incorporating evolutionary processes into population models (Skelly et al 2007). Forecasts that ignore evolutionary processes may overestimate rates of extinction or population decline because they do not allow for adaptation to environmental change on contemporary time scales. In an effort to move toward incorporation of evolutionary processes into population models and to understand the relative importance of sizedependent processes including growth and survival, we provide estimates of quantitative genetic variables for the key phenotypic traits of body size and growth from a wild population of brook trout (BKT) (Salvelinus fontinalis). While BKT appear to adapt to isolation (Letcher et al 2007), it is not known whether local

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Conclusion