Ecological causes of morphological evolution in the three-spined stickleback

Abstract

The central assumption of evolutionary theory is that natural selection drives the adaptation of populations to local environmental conditions, resulting in the evolution of adaptive phenotypes. The three-spined stickleback (Gasterosteus aculeatus) displays remarkable phenotypic variation, offering an unusually tractable model for understanding the ecological mechanisms underpinning adaptive evolutionary change. Using populations on North Uist, Scotland we investigated the role of predation pressure and calcium limitation on the adaptive evolution of stickleback morphology and behavior. Dissolved calcium was a significant predictor of plate and spine morph, while predator abundance was not. Stickleback latency to emerge from a refuge varied with morph, with populations with highly reduced plates and spines and high predation risk less bold. Our findings support strong directional selection in three-spined stickleback evolution, driven by multiple selective agents.

Keywords: Adaptation; Gasterosteus aculeatus; calcium concentration; natural selection; nuptial coloration; phenotypic adaptation; selective predation.

Figure 1

The relationship between three-spined stickleback morph, dissolved calcium concentration (mg/L), and brown trout abundance for 33 lake populations on North Uist (Scotland). Circles denote minimal morph, triangles low morph three-spined sticklebacks.

Figure 2

Mean (±SE) time taken to emerge (s) from vegetation by minimal and low morph three-spined sticklebacks from North Uist (Scotland) lakes with low and high brown trout abundance.