Ecological specialization in populations adapted to constant versus heterogeneous environments*

Abstract

Populations vary in their degree of ecological specialization. An intuitive, but often untested, hypothesis is that populations evolving under greater environmental heterogeneity will evolve to be less specialized. How important is environmental heterogeneity in explaining among‐population variation in specialization? We assessed juvenile viability of 20 Drosophila melanogaster populations evolving under one of four regimes: (1) a salt‐enriched environment, (2) a cadmium‐enriched environment, (3) a temporally varying environment, and (4) a spatially varying environment. Juvenile viability was tested in both the original selective environments and a set of novel environments. In both the original and novel environments, populations from the constant cadmium regime had the lowest average viability and the highest variance in viability across environments but populations from the other three regimes were similar. Our results suggest that variation in specialization among these populations is most simply explained as a pleiotropic by‐product of adaptation to specific environments rather than resulting from a history of exposure to environmental heterogeneity.

Morphological traits correlated with resource partitioning among small characin fish species coexisting in a Neotropical river

“…Specifically, we examined which morphological traits vary among species and whether such attributes are correlated with dietary patterns and trophic segregation among characins. Whereas heterogeneous and unstable conditions, such as those associated with plateau rivers, may not be appropriate conditions for subsequent ecological specialisation (González‐Bergonzoni et al, 2012; Wang, Singh, Huang, & Agrawal, 2019), it is expected that generalist species, that is those able to exploit any compartments, will take advantage and have their fitness favoured. From another perspective, niche theory (Chase & Leibold, 2003) emphasises that similar species can coexist only when they have traits that allow them to deal differently with environmental variability.…”

Digest: Unlocking the creative potential of specialization*

“…The results are surprising, but Wang et al (2019) explain that subtle and important differences between constant environments may be at work here. Since all populations demonstrated low survivability in the constant salt environment-even the salt-adapted population-this environment must have been intrinsically harsher than its cadmium counterpart.…”

“…In this issue, Wang et al. () investigate the link between environment and specialization in Drosophila melanogaster . They began by maintaining Drosophila populations under one of four regimes: (1) a constant cadmium‐enriched environment, (2) a constant salt‐enriched environment, (3) a temporally heterogeneous environment, alternating between cadmium‐enriched and salt‐enriched each generation, and (4) a spatially heterogeneous environment, with patches of cadmium‐enriched and salt‐enriched habitat.…”

“…In this issue, Wang et al (2019) in viability were considered to be more specialized because they survived well in some environments and poorly in others. Populations with lower variance were considered to be less specialized.…”

“…If the original assumption holds true, constant conditions should lead to the evolution of more specialized populations. But Wang et al (2019) found that this was only true of the constant cadmium environment, which gave rise to the most specialized populations. In contrast, populations from the constant salt regime had the "lowest" across-environment variance, suggesting they were the "least" specialized.…”