Trait changes in a harvested population are driven by a dynamic tug-of-war between natural and harvest selection

Abstract

Selective harvest of large individuals should alter natural adaptive landscapes and drive evolution toward reduced somatic growth and increased reproductive investment. However, few studies have simultaneously considered the relative importance of artificial and natural selection in driving trait changes in wild populations. Using 50 years of individual-based data on Windermere pike (Esox lucius), we show that trait changes tracked the adaptive peak, which moved in the direction imposed by the dominating selective force. Individual lifetime somatic growth decreased at the start of the time series because harvest selection was strong and natural selection was too weak to override the strength of harvest selection. However, natural selection favoring fast somatic growth strengthened across the time series in parallel with the increase in pike abundance and, presumably, cannibalism. Harvest selection was overridden by natural selection when the fishing effort dwindled, triggering a rapid increase in pike somatic growth. The two selective forces appear to have acted in concert during only one short period of prey collapse that favored slow-growing pike. Moreover, increased somatic growth occurred concurrently with a reduction in reproductive investment in young and small female pike, indicating a tradeoff between growth and reproduction. The age-specific amplitude of this change paralleled the age-specific strength of harvest pressure, suggesting that reduced investment was also a response to increased life expectancy. This is the first study to demonstrate that a consideration of both natural selection and artificial selection is needed to fully explain time-varying trait dynamics in harvested populations.adaptive landscapes ͉ conservation ͉ contemporary evolution ͉ fisheries ͉ top predators

Human predators outpace other agents of trait change in the wild

“…We therefore used all available data, which was comprised of 40 systems from 34 studies on 29 species (21 fish, 4 intertidal invertebrates, 2 ungulates, 2 plants). We used entire study intervals, but excluded periods of fishing moratoria and a period in one study during which natural selection overrode harvest selection (18). Data for different sexes, ages, management areas, and traits within each system generated 475 estimates of phenotypic change (see supporting information (SI) Dataset S1).…”

Size‐selective fishing and the potential for fisheries‐induced evolution in lake whitefish

“…Thus, fishing mortality, which can target a large range of ages and sizes, is expected to be an important selection factor on life histories in exploited fish populations, leading to evolutionary changes in growth rate, size and age thresholds for maturation, and fecundity (Dunlop, Enberg, Jørgensen, & Heino, 2009; Heino, Pauli, & Dieckmann, 2015; Jørgensen et al., 2007; Kuparinen & Merilä, 2007). Indeed, evidence has emerged that fishing mortality of stocks, both marine and freshwater, can be sufficiently high for evolutionary changes in life history traits to occur at trackable, ecological timescales (Edeline et al., 2007; Heino et al., 2015; Jørgensen et al., 2007; Nusslé, Bornand, & Wedekind, 2009; Olsen et al., 2004). Further, the direction and intensity of fisheries‐induced selection are expected to depend on which sizes are targeted, either through size or gear restrictions (Dunlop, Heino, & Dieckmann, 2009; Hutchings, 2009; Jørgensen, Ernande, & Fiksen, 2009; Wang & Höök, 2009).…”

Human-induced evolution caused by unnatural selection through harvest of wild animals

“…In their long-term study of Windermere pike (Esox lucius) in England, Edeline et al (50) contrasted temporal patterns of natural and fishing selection on this species; it was the first study to relate these patterns to long-term trends in life-history characteristics of wild fish (12). They estimated a substantial, fishing-induced negative selection differential on the reaction norm describing variation in gonad weight/body length, a measure of reproductive investment, in age-3 females.…”