Cold comfort: metabolic rate and tolerance to low temperatures predict latitudinal distribution in ants

Metabolic compensation has been proposed as a mean for ectotherms to cope
with colder climates. For example, under the metabolic cold adaptation and
the metabolic homeostasis hypotheses (MCA and MHH), it has been formulated
that cold-adapted ectotherms should display both higher (MCA) and more
thermally sensitive (MHH) metabolic rates (MRs) at lower temperatures.
However, whether such compensation can truly be associated with
distribution, and whether it interplays with cold-tolerance to support
species’ climatic niches, remains largely unclear despite broad ecological
implications thereof. Here, we teased apart the relationship between MRs,
cold-tolerance, and distribution, to test the MCA/MHH among 13 ant
species. We report clear metabolic compensation effects, consistent with
the MCA and MHH, where MR parameters strongly correlated with latitude and
climatic factors across species’ distributions. The combination of both
cold-tolerance and MR further upheld the best predictions of species’
climatic niches. To our knowledge, this is the first study showing that
the association of metabolic data with cold-tolerance supports better
predictive models of climatic temperature and distribution in social
insects than models including cold-tolerance alone. These results also
highlight that adaptation to higher latitudes in ants involved adjustments
of both cold-tolerance and MRs, to allow this extremely successful group
of insects to thrive under colder climates.