Density Estimates of Unmarked Large Mammals at Camera Traps Vary among Models, Species, and Years, Signalling Importance of Model Assumptions

Density estimation is a key goal in ecology but accurate estimates remain elusive, especially for unmarked animals. Data from camera-trap networks combined with new density estimation models can bridge this gap but recent research has shown marked variability in accuracy, precision, and concordance among estimators. We extend this work by comparing estimates from two different classes of models: unmarked spatial capture-recapture (spatial count, SC) models, and Time In Front of Camera (TIFC) models, a class of random encounter model. We estimated density for four large mammal species with different movement rates, behaviours, and sociality, as these traits directly relate to model assumptions. TIFC density estimates were typically higher than SC model estimates for all species. Black bear TIFC estimates were ~ 10-fold greater than SC estimates. Caribou TIFC estimates were 2-10 fold greater than SC estimates. White-tailed deer TIFC estimates were up to 100-fold greater than SC estimates. Differences of 2-5 fold were common for other species in other years. SC estimates were annually stable except for one social species; TIFC estimates were highly annually variable in some cases and consistent in others. Tests against densities obtained from DNA surveys and aerial surveys also showed variable concordance and divergence. For gregarious animals TIFC may outperform SC due to the latter model’s assumption of independent activity centres. For curious animals likely to investigate camera traps, SC may outperform TIFC, which assumes animal behavior is unaffected by cameras. Unmarked models offer great possibilities, but a pragmatic approach employs multiple estimators where possible, considers the ecological plausibility of assumptions, and uses an informed multi-inference approach to seek estimates from models with assumptions best fitting a species’ biology.

Naked mole-rat brown fat thermogenesis is diminished during hypoxia through a rapid decrease in UCP1

Naked mole-rats are among the most hypoxia-tolerant mammals. During hypoxia, their body temperature (Tb) decreases via unknown mechanisms to conserve energy. In small mammals, non-shivering thermogenesis in brown adipose tissue (BAT) is critical to Tb regulation; therefore, we hypothesize that hypoxia decreases naked mole-rat BAT thermogenesis. To test this, we measure changes in Tb during normoxia and hypoxia (7% O2; 1–3 h). We report that interscapular thermogenesis is high in normoxia but ceases during hypoxia, and Tb decreases. Furthermore, in BAT from animals treated in hypoxia, UCP1 and mitochondrial complexes I-V protein expression rapidly decrease, while mitochondria undergo fission, and apoptosis and mitophagy are inhibited. Finally, UCP1 expression decreases in hypoxia in three other social African mole-rat species, but not a solitary species. These findings suggest that the ability to rapidly down-regulate thermogenesis to conserve oxygen in hypoxia may have evolved preferentially in social species.

Behavioral Attributes of Social Groups Determine the Strength and Direction of Selection on Neural Investment

The evolution of social systems can place novel selective forces on investment in expensive neural tissue by changing cognitive demands. Previous hypotheses about the impact of sociality on neural investment have received equivocal support when tested across diverse taxonomic groups and social structures. We suggest previous models for social behavior-brain relationships have overlooked important variation in social groups. Social groups vary significantly in structure and function, and the specific attributes of a social group may be more relevant to setting cognitive demands than sociality in general. We have identified intragroup competition, relationship differentiation, information sharing, dominance hierarchies, and task specialization and redundancy as attributes of social behavior which may impact selection for neural investment, and outline how variation in these attributes can result in increased or decreased neural investment with transitions to sociality in different taxa. Finally, we test some of the predictions generated using this framework in a phylogenetic comparison of neural tissue investment in Anelosimus social spiders. Social Anelosimus spiders engage in cooperative prey capture and brood care, which allows for individual redundancy in the completion of these tasks. We hypothesized that in social spider species, the presence of redundancy would reduce selection for individual neural investment relative to subsocial species. We found that social species had significantly decreased investment in the arcuate body, the cognitive center of the spider brain, supporting our predictions. Future comparative tests of brain evolution in social species should account for the special behavioral characteristics that accompany social groups in the subject taxa.

Are Humans More Like Wolves or Dogs?

What makes humans a unique species? How did ancient humans evolve to live together and cooperate with each other? Research on the evolution of prehistoric humans shows that we have some characteristics in common with domesticated animals, like dogs, cows, and pigs. These similarities led researchers to propose that the human species has also undergone a type of domestication, which decreased our aggression and increased our social nature. In this article, we examine this idea and present an alternative: that the human species did not become domesticated like pets or farm animals, but instead evolved the ability to control its emotions, similar to other highly social species, like wolves. Emotional control allows us to restrain our aggression or promote it, depending on the situation. We think that emotional control is what allowed the human species to develop unique ways of communication in the animal kingdom.

Environmental quality mediates the ecological dominance of cooperatively breeding birds

Species as diverse as humans and ants are among the most abundant organisms on Earth, partly because of their ability to form cooperative societies1-3. Yet, animals form groups for many reasons4,5, and how these differences affect their ‘social conquests’2 remains unknown. Here we use a theoretical model to demonstrate that the different fitness benefits that animals receive by forming groups4,6 depend on the quality of their environment, which in turn impacts their ecological dominance and resilience to global change. Our model predicts species that group because of environmental hardships will have wider ecological niches, larger geographic ranges, and higher abundances than non-social species, whereas those that group because of intraspecific resource competition will not. As predicted, an analysis of >1500 avian species finds that cooperative breeders occurring in harsh and fluctuating environments have larger ranges and higher abundances than non-cooperative breeders, whereas cooperative breeders occurring in benign and stable environments do not. These results are consistent with our model predictions showing that species cooperating in harsh or fluctuating environments will be less vulnerable to climate change than non-social species and those cooperating against intra-specific competitors in benign or stable environments. Ultimately, by combining macroecological and sociobiological perspectives, our study helps understand and predict the past, present, and future state of social species, including our own.

Social convergence of gut microbiomes in vampire bats

The ‘social microbiome’ can fundamentally shape the costs and benefits of group-living, but understanding social transmission of microbes in free-living animals is challenging due to confounding effects of kinship and shared environments (e.g. highly associated individuals often share the same spaces, food and water). Here, we report evidence for convergence towards a social microbiome among introduced common vampire bats, Desmodus rotundus , a highly social species in which adults feed only on blood, and engage in both mouth-to-body allogrooming and mouth-to-mouth regurgitated food sharing. Shotgun sequencing of samples from six zoos in the USA, 15 wild-caught bats from a colony in Belize and 31 bats from three colonies in Panama showed that faecal microbiomes were more similar within colonies than between colonies. To assess microbial transmission, we created an experimentally merged group of the Panama bats from the three distant sites by housing these bats together for four months. In this merged colony, we found evidence that dyadic gut microbiome similarity increased with both clustering and oral contact, leading to microbiome convergence among introduced bats. Our findings demonstrate that social interactions shape microbiome similarity even when controlling for past social history, kinship, environment and diet.

The Relational Dimension

The damaging consequences of solitary confinement in prison indicate the importance of relationships for human flourishing. Loneliness affects a high proportion of people, especially as they get older. The health consequences of loneliness can be severe. Our early relationships within our family and with others are crucial for our well-being. There are many species where the parents effectively abandon their offspring early in life but humans don’t normally do that. As a species we produce few offspring and parents can invest in them heavily. We are a social species. At the same time, the more people we know, the more difficult it becomes to maintain social relationships with them. Married people are generally happier than unmarried people. Helping is at the heart of most positive relationships. Human relationships need not be restricted to other humans.

Cues of Social Status: Associations Between Attractiveness, Dominance, and Status

Hierarchies naturally emerge in social species, and judgments of status in these hierarchies have consequences for social relationships and health. Although judgments of social status are shaped by appearance, the physical cues that inform judgments of status remain unclear. The transition to college presents an opportunity to examine judgments of social status in a newly developing social hierarchy. We examined whether appearances—as measured by raters’ judgments of photographs and videos—provide information about undergraduate students’ social status at their university and in society in Study 1. Exploratory analyses investigated whether associations differed by participants’ sex. Eighty-one first-year undergraduate students ( Mage = 18.20, SD = 0.50; 64.2% female) provided photographs and videos and reported their social status relative to university peers and relative to other people in society. As hypothesized, when participants were judged to be more attractive and dominant they were also judged to have higher status. These associations were replicated in two additional samples of raters who evaluated smiling and neutral photographs from the Chicago Faces Database in Study 2. Multilevel models also revealed that college students with higher self-reported university social status were judged to have higher status, attractiveness, and dominance, although judgments were not related to self-reported society social status. Findings highlight that there is agreement between self-reports of university status and observer-perceptions of status based solely on photographs and videos, and suggest that appearance may shape newly developing social hierarchies, such as those that emerge during the transition to college.

Matriphagy in five species of the genus Anelosimus (Araneae: Theridiidae)

Parental care has evolved numerous times in many taxonomic groups of animals. Matriphagy, as an extreme example of parental care, is present in many social species, subsocial species, and even in solitary spiders. Here, we describe matriphagy in five species of Anelosimus of different levels of sociality: social (A. dubiosus), intermediate social (A. jabaquara), subsocial (A. vierae, A. baeza), and solitary (A. nigrescens). Each group contained a female and its brood, maintained under standardized laboratory conditions. All species showed matriphagy, regardless of their social level. Further studies are necessary to clarify whether matriphagy is a necessary precondition for the evolution of sociality in spiders, or if it is phylogenetically conserved in some families.