Four decades of opposing natural and human‐induced artificial selection acting on Windermere pike (Esox lucius)

Abstract

The ability of natural selection to drive local adaptation has been appreciated ever since Darwin. Whether human impacts can impede the adaptive process has received less attention. We tested this hypothesis by quantifying natural selection and harvest selection acting on a freshwater fish (pike) over four decades. Across the time series, directional natural selection tended to favour large individuals whereas the fishery targeted large individuals. Moreover, non-linear natural selection tended to favour intermediate sized fish whereas the fishery targeted intermediate sized fish because the smallest and largest individuals were often not captured. Thus, our results unequivocally demonstrate that natural selection and fishery selection often acted in opposite directions within this natural system. Moreover, the two selective factors combined to produce reduced fitness overall and stronger stabilizing selection relative to natural selection acting alone. The long-term ramifications of such human-induced modifications to adaptive landscapes are currently unknown and certainly warrant further investigation.

Fisheries-induced disruptive selection

“…In our model, such selection forces first give rise to a convergence stable mixed strategy, consistent with the argument by Carlson et al (2007) that natural selection and fisheries-induced selection often 340 act in opposite directions and hence produce strongly stabilizing selection. We have found that, however, with sufficiently strong tradeoffs in growth and fecundity, this convergence stable mixed strategy can become evolutionarily unstable, im- posite effect: disruptive selection is enhanced when this tradeoff is relaxed.…”

“…In particular, we assume limited energy availability only in the juvenile stage (which translates into density-dependent mortality due to resource competition), while no such limitations are present for the small and large be maintained, but also that such dimorphism may evolve de novo (Keller et al, 2013), thereby giving rise to a coexistence of maturation strategies (Gross, 1996). Several empirical studies have argued the possibility of disruptive selection in fish 334 populations through the interplay of natural selection and adaptive harvesting (Carlson et al, 2007;Edeline et al, 2007Edeline et al, , 2009): here we have systematically analyzed, for the first time, under which specific conditions such disruptive selection 336 may arise.…”

“…The interaction between adaptive harvest imposed by a fishery and biological evolution could possibly result in disruptive selection, as suggested by Carlson et al (2007) and Edeline et al (2007) and supported by statistical analysis 26 of field data by Edeline et al (2009). The objective of this study is to provide a first model-based investigation of this phenomenon.…”

“…Harvesting a stock's large individuals, as happens through many widely adopted fishing policies (Table 2), increases the directional selection pressure toward early maturation, as recurrently highlighted by earlier studies (e.g., Law 356 1979; Law and Grey 1989;Abrams and Rowe 1996). Moreover, when harvesting is adaptive, a fishery behaves similar to an optimally foraging predator that maximizes its intake rate (e.g., Egas et al 2005): this tends to increase the mortality of 358 large individuals, as these are more profitable to harvest (Fenberg and Roy, 2008;Darimont et al, 2009 has targeted large individuals of Northern pike for four decades (Carlson et al, 2007;Edeline et al, 2009). Size-selective 362 gill nets were also used for catching striped bass in Maryland during 1950s (Mansueti, 1961); size-selective harvesting of British Columbia pink salmon has been recorded since 1950 (McAllister andPeterman, 1992).…”

“…Therefore, adaptive harvesting under policies that allow the targeting of large individuals alters natural adaptive landscapes in a way that selects for increased reproductive investment early in life. This, in turn, reduces 368 somatic growth and fecundity later in life through life-history tradeoffs (Edeline et al, 2007), and thereby strengthens the mechanism that leads to disruptive selection. Poos et al (2011) andBodin et al (2012) have considered a rather similar 370…”