Density‐dependent natural selection mediates harvest‐induced trait changes

International audienceHarvesting has been demonstrated to cause rapid, yield-decreasing trait change towards slower somatic growth and earlier maturation in wild populations. These changes are largely considered to result from direct, density-independent harvest selection on traits. Here, we show that exact same trait changes may also indirectly result from a harvest-induced relaxation of density-dependent (K) natural selection for faster growth and delayed maturation. We exposed 12 pond populations of medaka fish (Oryzias latipes) to contrasted size-selective harvesting during 5 years, and show that harvesting effectively changed juvenile natural mortality from density-dependent to density-independent. We then laboratory-reared medaka progeny under contrasted food levels mimicking the environmental effects of a harvest-induced density gradient. Interaction between past harvest regime and present food environment on progeny traits revealed that harvest-induced trait changes in medaka resulted from selection in a low-food environment only, i.e., were driven by relaxed K-selection only, not by direct harvest selection. Feeding trials further demonstrated that trait changes were associated with reorganizations in rates of food acquisition, assimilation and allocation that were contingent upon the food environments. This is the first study to demonstrate that harvesting can induce undesirable distortions of natural selection that impair productivity traits. We conclude that sustaining harvesting yields over extended time scales requires a preservation of high population densities

Some like it dry: Water restriction overrides heterogametic sex determination in two reptiles

The evolution of sex determination is complex and yet crucial in our understanding of population stability. In ectotherms, sex determination involves a variety of mechanisms including genetic determination (GSD), environment determination (ESD), but also interactions between the two via sex reversal. In this study, we investigated whether water deprivation during pregnancy could override GSD in two heterogametic squamate reptiles. We demonstrated that water restriction in early gestation induced a male-biased secondary sex ratio in both species, which could be explained by water sex reversal as the more likely mechanism. We further monitored some long-term fitness estimates of offspring, which suggested that water sex determination (WSD) represented a compensatory strategy producing the rarest sex according to Fisher's assumptions of frequency-dependent selection models. This study provides new insights into sex determination modes and calls for a general investigation of mechanisms behind WSD and to examine the evolutionary implications

Pollination and the city: a collaborative study to measure pollination function in a range of European cities

International audienc

Pollination and the city: a collaborative study to measure pollination function in a range of European cities

International audienc

Pollination and the city: a collaborative study to measure pollination function in a range of European cities

International audienc

Pollination and the city: a collaborative study to measure pollination function in a range of European cities

International audienc