Data from: Body size evolution in otters distinguished from terrestrial mustelids

Some taxa of mammals live in water, all of which evolved from
land-dwelling ancestors. In the family Mustelidae (Mammalia: Carnivora),
most species live on land, while otters, comprising the subfamily
Lutrinae, inhabit aquatic environments, which include the almost
exclusively aquatic sea otters (Enhydra lutris). Thus, the transition from
a terrestrial to an aquatic lifestyle has occurred within this family.
Despite potentially different selection pressures on body size in aquatic
and terrestrial habitats, no divergence in the evolutionary pattern of
body size between otters and other mustelids has previously been shown
using models of trait evolution on a phylogeny. We applied models that
explicitly incorporated lineage-specific directional selection to the
evolution of body mass in living mustelids. Using a simulation-based
likelihood and approximate Bayesian computation approach, we demonstrated
lineage-specific directional selection for larger body mass in otters,
which is distinct from other mustelids. There was no evidence of a
difference between sea otters and other otters in the strength of
directional selection for larger body mass. Additionally, our analyses
supported no difference in the rate at which body mass evolves in both
directions between otters and other mustelids. These findings suggest that
the evolution of body mass in otters is associated with selective
advantages of larger size rather than the relaxation of constraints on
body size in aquatic habitats, like other aquatic mammals such as
sirenians, cetaceans, and pinnipeds.