Body size evolution in otters distinguished from terrestrial mustelids

Area of Science:

• Evolutionary biology
• Mammalian evolution
• Comparative genomics

Background:

• Many mammal species have transitioned to aquatic life from terrestrial ancestors.
• The Mustelidae family includes terrestrial species and the aquatic subfamily Lutrinae (otters).
• Previous studies lacked phylogenetic evidence for distinct body size evolution in otters.

Purpose of the Study:

• To investigate the evolutionary patterns of body mass in mustelids.
• To determine if aquatic otters experienced different selection pressures on body size compared to terrestrial mustelids.
• To test hypotheses of directional selection versus relaxed constraints driving otter body size evolution.

Main Methods:

• Phylogenetic comparative methods were used to model body mass evolution.
• Lineage-specific directional selection models were applied to mustelid phylogeny.
• Simulation-based likelihood and approximate Bayesian computation approaches were employed.

Main Results:

• Evidence of lineage-specific directional selection for increased body mass in otters was found.
• No significant difference in selection strength for larger body mass between sea otters and other otters.
• No difference in the rate of body mass evolution in either direction between otters and other mustelids.

Conclusions:

• Otter body mass evolution is driven by selective advantages of larger size in aquatic environments.
• This contrasts with relaxed constraints as the primary driver, seen in other aquatic mammals.
• The findings provide insight into adaptive evolution in semi-aquatic and fully aquatic mammals.