Differences in thermal tolerance between parental species could fuel thermal adaptation in hybrid wood ants

Genetic variability is essential for adaptation and could be acquired via
hybridization with a closely related lineage. We use ants to investigate
thermal adaptation and the link between temperature and genetic variation
arising from hybridization. We test for differences in cold and heat
tolerance between Finnish Formica polyctena and Formica aquilonia wood
ants and their naturally occurring hybrids. Using workers, we find the
parental individuals differ in both cold and heat tolerances and express
thermal limits which reflect their global distributions. Hybrids however
cannot combine thermal tolerance of parental species as they are equally
heat-tolerant to F. polyctena , but not equally cold-tolerant to F.
aquilonia . We then focus on a single hybrid population to investigate the
relationship between temperature variation and genetic variation across 16
years using reproductive individuals. Based on the thermal tolerance
results, we expected the frequency of putative F. polyctena alleles to
increase in warm years and F. aquilonia alleles to increase in cold years.
We find support for this in hybrid males but not in hybrid females. These
results contribute to understanding the outcomes of hybridization, that
may be sex-specific or depend on the environment. Furthermore, genetic
variability resulting from hybridization could help hybrid wood ants cope
with changing thermal conditions.