Dollo meets Bergmann: morphological evolution in secondary aquatic mammals

Area of Science:

• Evolutionary Biology
• Macroevolutionary Studies
• Vertebrate Adaptations

Background:

• Secondary transitions to aquatic environments are common in vertebrates.
• Previous studies often overlook freshwater and semi-aquatic transitions, focusing mainly on marine realms.
• Aquatic adaptations may lead to irreversible evolutionary changes.

Purpose of the Study:

• To investigate the reversibility of aquatic adaptations in mammals.
• To explore the relationship between aquatic transitions and changes in relative body mass.
• To analyze dietary shifts associated with aquatic adaptations in mammals.

Main Methods:

• Phylogenetic comparative methods were employed across extant mammals.
• The study tested hypotheses regarding the irreversibility of aquatic adaptations (Dollo's Law).
• Correlations between aquatic transitions, body mass, and diet were examined.

Main Results:

• Irreversible aquatic adaptations were observed in highly aquatic lineages.
• Reversible adaptations were found in semi-aquatic lineages allowing terrestrial movement.
• A consistent trend of increased relative body mass and carnivorous diets was identified in transitioning lineages.

Conclusions:

• Dollo's Law applies to irreversible aquatic adaptations in fully aquatic mammals.
• Semi-aquatic adaptations remain reversible, allowing for terrestrial excursions.
• Increased body mass and carnivorous diets in aquatic mammals are linked to thermoregulation and nutritional needs.