Ancestral ecological regime shapes reaction to food limitation in the Least Killifish,Heterandria formosa

Abstract

In populations with contrasting densities of conspecifics, we often see genetically-based differences in life histories. The divergent life histories could be driven by several distinct agents of selection, including, amongst other factors, variation in per-capita food levels, the intensity of crowding-induced stress, rates of pathogen transmission, mate encounter rates, and the rates with which waste products accumulate. Understanding which selective agents act in a particular population is important as the type of agents can affect both population dynamics and evolutionary responses to density-dependent selection. Here we used a full-factorial laboratory experiment to examine whether two populations of a small live-bearing freshwater fish, characterised by high-density/low-predation or low-density/high-predation conditions, are adapted to different per-capita food levels. As expected, fish from the higher density regime handled food limitation better than those from the lower density regime. Although the lower food level resulted in slower growth, smaller body size, delayed maturation and reduced survival in both populations, especially survival to maturity showed a highly significant population x food-level interaction. At low food, 75% of fish from the low-density population died, compared to only 15% of fish from the high-density population. This difference was much smaller at high food (15% vs. 0% mortality), and was mediated, at least partly, through a larger size at birth of fish from the high-density regime. While we cannot preclude other agents of selection from operating differently in the study populations, we demonstrate that selection at higher density confers a greater ability to cope with low per-capita food availability.

Life histories as mosaics: Plastic and genetic components differ among traits that underpin life‐history strategies

“…The prevalence of plasticity in response to food availability (seen in 69% of traits) emphasizes the pervasive effects of resources on life histories and corroborates our understanding of life histories as complex, emergent properties of interactions between the phenotype and its (resource) environment (Van Noordwijk and De Jong 1986;Coulson et al 2006;Coulson 2020). This finding tallies with life-history studies of food effects in other fishes (e.g., Riesch et al 2016;Felmy et al 2021). However, 10 traits measured after the start of food treatments were largely unaffected by food levels, including interbirth intervals, most offspring weights, the percentage fat in both females and offspring, and the reproductive allotment.…”

“…2016; Felmy et al. 2021). However, 10 traits measured after the start of food treatments were largely unaffected by food levels, including interbirth intervals, most offspring weights, the percentage fat in both females and offspring, and the reproductive allotment.…”