AIM

Endothermic marine mammals face significant thermoregulatory challenges due to heat loss in highly conductive aquatic environments. While body size adaptations are well-studied, the role of appendage size across thermal gradients remains unclear in delphinids. Here, we aim to quantify how appendage size differs between warm- and cool-water delphinids in the Atlantic Ocean to explore how these species have adapted to different thermal regimes.

LOCATION

Atlantic Ocean.

TIME PERIOD

1973 – 2016.

MAJOR TAXA STUDIED

Dusky dolphins (Aethalodelphis obscurus), Commerson’s dolphins (Cephalorhynchus commersonii), white-sided dolphins (Leucopleurus acutus), common dolphins (Delphinus delphis), Atlantic spotted dolphins (Stenella frontalis), and bottlenose dolphins (Tursiops truncatus spp.).

METHODS

We combined morphometric data from stranded Atlantic delphinids with 3D modeling to generate 3D representations of individual animal body morphologies. From these models, we quantified surface area of the body cores and appendages and volume of the body cores, and constructed standardized major axis regressions to evaluate how the relationships between body core volume and surface area differ between cool- and warm-water species.

RESULTS

Cool-water dolphins had larger appendages overall relative to body volume than warm-water species, opposing predictions from Allen’s rule. However, we also find that total surface area (body core and appendages) relative to body volume is similar between cool- and warm-water species.

MAIN CONCLUSIONS

Our findings suggest that larger appendages may allow cool-water delphinids to dissipate excess heat when needed, while effective physiological insulation mechanisms likely allow for heat conservation in cool environments. Total surface area to volume ratio was tightly conserved across both cool- and warm-water dolphins, suggesting that factors other than temperature control overall body morphology for these species. This study highlights a potential decoupling between appendage size and heat conservation in cetaceans, and provides insights into thermal adaptations in marine mammals.