Ecological ramifications of adaptation to size-selective mortality

Abstract

Size-selective mortality due to harvesting is a threat to numerous exploited species, but how it affects the ecosystem remains largely unexplored. Here, we used a pond mesocosm experiment to assess how evolutionary responses to opposite size-selective mortality interacted with the environment (fish density and light intensity used as a proxy of resource availability) to modulate fish populations, prey community composition and ecosystem functions. We used medaka ( Oryzias latipes ) previously selected over 10 generations for small size (harvest-like selection; small-breeder line) or large size (large-breeder line), which displayed slow somatic growth and early maturity or fast somatic growth and late maturity, respectively. Large-breeder medaka produced more juveniles, which seemed to grow faster than small-breeder ones but only under high fish density. Additionally, large-breeder medaka had an increased impact on some benthic prey, suggesting expanded diet breadth and/or enhanced foraging abilities. As a consequence, increased light stimulated benthic algae biomass only in presence of large-breeder medaka, which were presumably better at controlling benthic grazers. Aggregated effect sizes at the community and ecosystem levels revealed that the ecological effects of medaka evolution were of similar magnitude to those induced by the environment and fish introduction. These findings indicate the important environmental dependency of evolutionary response to opposite size-selective mortality on higher levels of biological organizations.

Within-species variation in the gut microbiome of medaka (Oryzias latipes) is driven by the interaction of light intensity and genetic background

“…The selection procedure consisted of mimicking either fishing mortality where only small-bodied individuals were allowed to reproduce (small-breeder SB line), or a more natural mortality regime rather favoring the reproduction of large-bodied individuals (large-breeder LB line) (Reneville et al 2020, Le Rouzic et al 2020). As we have previously reported, the LB and SB lines evolved opposite life-history traits and behaviors: small-breeder medaka grew slower, matured earlier and were less efficient foragers than the large-breeder medaka (Diaz Pauli et al 2019, Evangelista et al 2021.…”

“…Bacteria from the Aeromonas genus have been shown to be pathogenic for numerous fish species (Tomás 2012, Wang et al 2018). Our previous findings from the same pond experiment did not indicate any difference in survival probability and somatic growth rate among introduced adults of the LB and SB lines (although LB medaka produced more offspring that grew faster), but suggested that adult and juvenile LB medaka foraged more overall (Evangelista et al 2021). They were especially foraging more on benthic prey hidden in the sediments than the SB medaka (Evangelista et al 2021).…”

“…Our previous findings from the same pond experiment did not indicate any difference in survival probability and somatic growth rate among introduced adults of the LB and SB lines (although LB medaka produced more offspring that grew faster), but suggested that adult and juvenile LB medaka foraged more overall (Evangelista et al 2021). They were especially foraging more on benthic prey hidden in the sediments than the SB medaka (Evangelista et al 2021). Although further investigation is required to back-up this hypothesis, increased abundance of Aeromonadaceae in LB might reflect distinct foraging strategies between the two lines, rather than changes in health conditions as Aeromonadaceae are known to be facultative aerobes and are mainly found in anoxic sediments (Tomás 2012, Laviad and Halpern 2016).…”

“…We assessed how the genetic background of the two medaka lines interacted with light intensity and medaka population density to shape medaka’s gut microbiome composition and diversity. Based on life-history and foraging traits divergence between the two lines (Diaz Pauli et al 2019, Evangelista et al 2020, Evangelista et al 2021), and that these traits are key drivers of gut microbiome variations in teleost fish (Talwar et al 2018), we hypothesized that the gut microbial community would diverge between SB and LB medaka. We further hypothesized that gut microbiome differences between the two lines would be more pronounced under suboptimal conditions, i.e.…”

Determinants of survival and dispersal along the range expansion of a biological invasion

“…Culling-based containment might become even more efficient over the long term because, after several generations, selective removal of large-bodied individuals induces an evolutionary change towards smaller body sizes and earlier maturation, which would not only cause crayfish to disperse less, but are also traits generally associated with lower population growth rates (Evangelista et al, 2020(Evangelista et al, , 2021Heino et al, 2015;Hutchings, 2005). Such harvest-induced evolutionary changes are often considered as slowly reversible (Law, 2000), which is desirable from a long-term management perspective.…”