Multi-generation selective landscapes and sub-lethal injuries in stickleback

The interaction between predation landscape and phenotypic variability within prey populations is of substantial significance in evolutionary biology. Extending from several decades of studies at a remote freshwater lake on Haida Gwaii, western Canada, we analyze the incidence of predator-induced sub-lethal injuries in 8,069 wild-captured threespine stickleback (Gasterosteus aculeatus) and using cohort analyses test whether the distribution of injuries informs the selective landscape influencing the bell-shaped frequency distribution of the traits. Our results indicate that (1) the incidence of injuries varies among phenotypes differing in the number and position of lateral plates, (2) these differences occur only among younger fish, (3) the incidence of injuries is inversely related to the estimated population frequencies of plate phenotypes, with the modal phenotype generally having the fewest injuries, (4) direct estimates of selective differentials and relative fitness based on analyses of 1,735 fish from 6 independent yearly cohorts indicates statistically informative elevated differentials in phenotypes with greater number of plates and elevated relative fitness of non-modal phenotypes, and (5) there are significant differences among yearly cohorts in strength and direction of selection, and an increased prevalence of diversifying versus stabilizing selection despite longer-term stasis (4 decades) in trait means. We conclude that the presence of multiple optimal phenotypes complements the renewed interests in quantifying short-term temporal or spatial variation in ecological processes in studies of fitness landscapes and intrapopulation variability.

Automated summary

The interaction between predation landscape and phenotypic variability within prey populations is a significant factor in evolutionary biology. Our study on wild-captured threespine stickleback in western Canada found that the incidence of injuries varied among different phenotypes and younger fish, and was inversely related to the population frequencies of plate phenotypes. The analysis of yearly cohorts revealed differences in strength and direction of selection, supporting the presence of multiple optimal phenotypes.