Experimental evidence for adaptive divergence in response to a warmed
habitat reveals roles for morphology, allometry, and parasite resistance
Abstract
Ectotherms are expected to be particularly vulnerable to climate change
driven increases in temperature. Understanding how populations adapt to
novel thermal environments will be key for informing mitigation plans.
We took advantage of threespine stickleback (Gasterosteus aculeatus)
populations inhabiting adjacent geothermal (warm) and ambient (cold)
habitats to test whether their evolutionary divergence was adaptive
using field reciprocal transplant experiment. We found evidence for
adaptive morphological divergence, as growth (length change) in the
non-native habitat was found to relate to head, posterior and total body
shape. Higher growth in fish transplanted to a non-native habitat was
found to be associated with shape profiles closer to that of the native
fish. The consequences of transplantation were asymmetric with cold
sourced fish transplanted to the warm habitat suffering from lower
survival rates and greater parasite prevalence than warm sourced fish
transplanted to the cold habitat. We also found evidence for divergent
shape allometries that related to growth. Our findings suggest that wild
populations can adapt quickly to thermal conditions. However, immediate
transitions to warmer conditions may be particularly difficult.