Response to Hansen Wheat et al.: Additional analysis further supports the early emergence of cooperative communication in dogs compared to wolves raised with more human exposure.

Here, we address Hansen Wheat et al.'s commentary in this journal in response to Salomons et al. Current Biology, 31(14), 3137-3144.E11, (2021). We conduct additional analyses in response to Hansen Wheat et al.'s two main questions. First, we examine the claim that it was the move to a human home environment which enabled the dog puppies to outperform the wolf puppies in gesture comprehension tasks. We show that the youngest dog puppies who had not yet been individually placed in raisers' homes were still highly skilled, and outperformed similar-aged wolf puppies who had higher levels of human interaction. Second, we address the claim that willingness to approach a stranger can explain the difference between dog and wolf pups' ability to succeed in gesture comprehension tasks. We explain the various controls in the original study that render this explanation insufficient, and demonstrate via model comparison that the covariance of species and temperament also make this parsing impossible. Overall, our additional analyses and considerations support the domestication hypothesis as laid out by Salomons et al. Current Biology, 31(14), 3137-3144.E11, (2021).

Total energy expenditure of bottlenose dolphins (Tursiops truncatus) of different ages.

Marine mammals are thought to have an energetically expensive lifestyle because endothermy is costly in marine environments. However, measurements of total energy expenditure (TEE; kcal day-1) are available only for a limited number of marine mammals, because large body size and inaccessible habitats make TEE measurements expensive and difficult to obtain for many taxa. We measured TEE in 10 adult common bottlenose dolphins (Tursiops truncatus) living in natural seawater lagoons at two facilities (Dolphin Research Center and Dolphin Quest) using the doubly labeled water method. We assessed the relative effects of body mass, age and physical activity on TEE. We also examined whether TEE of bottlenose dolphins, and more generally of marine mammals, differs from that expected for their body mass compared with other eutherian mammals, using phylogenetic least squares (PGLS) regressions. There were no differences in body mass or TEE (unadjusted TEE and TEE adjusted for fat-free mass) between dolphins from the two facilities. Our results show that adjusted TEE decreased and fat mass increased with age. Different measures of activity were not related to age, body fat or adjusted TEE. Both PGLS and the non-phylogenetic linear regression indicate that marine mammals have an elevated TEE compared with that of terrestrial mammals. However, bottlenose dolphins expended 17.1% less energy than other marine mammals of similar body mass. The two oldest dolphins (>40 years) showed a lower TEE, similar to the decline in TEE seen in older humans. To our knowledge, this is the first study to show an age-related metabolic decline in a large non-human mammal.

Cooperative Communication with Humans Evolved to Emerge Early in Domestic Dogs.

Although we know that dogs evolved from wolves, it remains unclear how domestication affected dog cognition. One hypothesis suggests dog domestication altered social maturation by a process of selecting for an attraction to humans.1-3 Under this account, dogs became more flexible in using inherited skills to cooperatively communicate with a new social partner that was previously feared and expressed these unusual social skills early in development.4-6 Here, we comparedog (n = 44) and wolf (n = 37) puppies, 5-18 weeks old, on a battery of temperament and cognition tasks. We find that dog puppies are more attracted to humans, read human gestures more skillfully, and make more eye contact with humans than wolf puppies. The two species are similarly attracted to familiar objects and perform similarly on non-social measures of memory and inhibitory control. These results are consistent with the idea that domestication enhanced the cooperative-communicative abilities of dogs as selection for attraction to humans altered social maturation.