Predator life history and prey ontogeny limit natural selection on the major armour gene,Eda, in threespine stickleback

Abstract

Natural selection shapes the evolution of antipredator traits in prey. However, selection in the wild depends on ecological context, including features of predator and prey populations, making field studies of selection critical to understanding how predators shape selection on prey defences. Threespine stickleback (Gasterosteus aculeatus) is a classic system to study the effects of predators on the natural selection of prey.In lakes and rivers, fish predators have been shown to impose selection against low plated adult stickleback phenotypes and genotypes. We directly measured selection by predatory salmonids on the Ectodysplasin-A (Eda) gene in estuary stickleback from California. Despite previous studies showing a positive correlation between predator presence and frequency of the Eda "complete" allele in estuary populations, we found that Eda "low" genotypes were not significantly more frequent in salmonid predator diets. Further, we found no evidence of changes in Eda genotype frequencies across generations that would suggest directional selection driven by predators. Prior selection studies have examined the effects of large resident trout on adult stickleback. In contrast, predators in this study were juvenile anadromous salmonids, which only ate juvenile stickleback whose plate phenotypes had not fully developed. Thus, in this case, predator life history and stickleback ontogeny may preclude strong selection on stickleback armour. Our results underscore the importance of selection studies in the wild for understanding the context-dependent nature of selection in natural populations.

Applying empirical dynamic modeling to distinguish abiotic and biotic drivers of population fluctuations in sympatric fishes

“…Perhaps then, stickleback and gobies are responding similarly to an unmeasured environmental driver, such as the onset of spring productivity and availability of shared macroinvertebrate prey, but stickleback respond earlier or more quickly. The major reproductive period of the two species appear to be offset, so niche partitioning may be achieved across seasons (for data on annual cohort timing in nearby lagoons, see Swenson 1999 for gobies and Wasserman et al 2021 for stickleback). Such allochrony has been shown to help limit the potential for competition by offsetting peak resource use (Trivelpiece et al 1987; Spilseth and Simenstad 2011; Clewlow et al 2019).…”

Age-dependent genetic architecture across ontogeny of body size in sticklebacks

“…As such, age-specific genetic architecture would decrease the predictability of evolution by increasing the number of genomic regions available for selection to act on and, consequently, decreasing the probability of parallel evolution. In sticklebacks, population-specific age structure and age-specific selection is expected to occur in the wild [85–87] and more generally, temporal variation in selection at different ages should be pervasive in nature [41]. We thus propose that the age structure of natural populations constitutes a promising parameter to account for in studies of parallel evolution, and that future research on the pervasiveness of age-specific genetic architecture in the wild should prove particularly useful in our ability to predict evolution.…”

Morphological integration during postnatal ontogeny: implications for evolutionary biology

“…This sequential overlap leads to changes in the amount and distribution of morphological variation through time (Mitteroecker and Bookstein, 2009; Zelditch et al, 2006). Since natural selection is contingent on the availability and organization of morphological variation (Lande, 1979; Lande and Arnold, 1983), changes in this variation between life history stages can affect how selection operates, and how populations respond to selection in different life stages (Wasserman et al, 2021). Therefore, a broader comprehension of evolution involves understanding to what extent morphological variation changes during ontogeny.…”