Mammal virus diversity estimates are unstable due to accelerating discovery effort

Host-virus association data underpin research into the distribution and eco-evolutionary correlates of viral diversity and zoonotic risk across host species. However, current knowledge of the wildlife virome is inherently constrained by historical discovery effort, and there are concerns that the reliability of ecological inference from host-virus data may be undermined by taxonomic and geographical sampling biases. Here, we evaluate whether current estimates of host-level viral diversity in wild mammals are stable enough to be considered biologically meaningful, by analysing a comprehensive dataset of discovery dates of 6571 unique mammal host-virus associations between 1930 and 2018. We show that virus discovery rates in mammal hosts are either constant or accelerating, with little evidence of declines towards viral richness asymptotes, even in highly sampled hosts. Consequently, inference of relative viral richness across host species has been unstable over time, particularly in bats, where intensified surveillance since the early 2000s caused a rapid rearrangement of species' ranked viral richness. Our results illustrate that comparative inference of host-level virus diversity across mammals is highly sensitive to even short-term changes in sampling effort. We advise caution to avoid overinterpreting patterns in current data, since it is feasible that an analysis conducted today could draw quite different conclusions than one conducted only a decade ago.

Should I stay or should I go? How activity synchronization affects fission decisions

Group-living animals need to deal with conflicting interests to maintain cohesion. When the costs of doing so outweigh the benefits, the group may (temporarily) split into two or more subgroups. Conflicting interests can concern what activity to pursue or the direction of travel. Temporary group separation is a common feature in species with a high degree of fission–fusion dynamics. We investigated the role activity synchronization played in fission decisions in a spider monkey group living in the Otoch Ma'ax Yetel Kooh Nature Reserve, Yucatan, Mexico. For 21 months, we recorded every fission event occurring in the followed subgroup, as well as the subgroup activity. We classified the activity as ‘synchronized’ when at least 75% of subgroup members performed the same activity (resting, foraging, socializing or travelling); otherwise, we classified it as ‘non-synchronized’. We found that fission events occurred more often when the activity was non-synchronized. In addition, when the activity was synchronized, fission events occurred more often when spider monkeys were travelling than when they were engaged in other subgroup activities. Our findings highlight the role of conflicting interests over the activity to pursue and travel direction in fission decisions.

Avoiding extinction under nonlinear environmental change: models of evolutionary rescue with plasticity

Rapid environmental changes are putting numerous species at risk of extinction. For migration-limited species, persistence depends on either phenotypic plasticity or evolutionary adaptation (evolutionary rescue). Current theory on evolutionary rescue typically assumes linear environmental change. Yet accelerating environmental change may pose a bigger threat. Here, we present a model of a species encountering an environment with accelerating or decelerating change, to which it can adapt through evolution or phenotypic plasticity (within-generational or transgenerational). We show that unless either form of plasticity is sufficiently strong or adaptive genetic variation is sufficiently plentiful, accelerating or decelerating environmental change increases extinction risk compared to linear environmental change for the same mean rate of environmental change.

Twist and chew: three-dimensional tongue kinematics during chewing in macaque primates

Three-dimensional (3D) tongue movements are central to performance of feeding functions by mammals and other tetrapods, but 3D tongue kinematics during feeding are poorly understood. Tongue kinematics were recorded during grape chewing by macaque primates using biplanar videoradiography. Complex shape changes in the tongue during chewing are dominated by a combination of flexion in the tongue's sagittal planes and roll about its long axis. As hypothesized for humans, in macaques during tongue retraction, the middle (molar region) of the tongue rolls to the chewing (working) side simultaneous with sagittal flexion, while the tongue tip flexes to the other (balancing) side. Twisting and flexion reach their maxima early in the fast close phase of chewing cycles, positioning the food bolus between the approaching teeth prior to the power stroke. Although 3D tongue kinematics undoubtedly vary with food type, the mechanical role of this movement—placing the food bolus on the post-canine teeth for breakdown—is likely to be a powerful constraint on tongue kinematics during this phase of the chewing cycle. The muscular drivers of these movements are likely to include a combination of intrinsic and extrinsic tongue muscles.

Dogs' looking times and pupil dilation response reveal expectations about contact causality

Contact causality is one of the fundamental principles allowing us to make sense of our physical environment. From an early age, humans perceive spatio-temporally contiguous launching events as causal. Surprisingly little is known about causal perception in non-human animals, particularly outside the primate order. Violation-of-expectation paradigms in combination with eye-tracking and pupillometry have been used to study physical expectations in human infants. In the current study, we establish this approach for dogs ( Canis familiaris ). We presented dogs with realistic three-dimensional animations of launching events with contact (regular launching event) or without contact between the involved objects. In both conditions, the objects moved with the same timing and kinematic properties. The dogs tracked the object movements closely throughout the study but their pupils were larger in the no-contact condition and they looked longer at the object initiating the launch after the no-contact event compared to the contact event. We conclude that dogs have implicit expectations about contact causality.

No evidence for future planning in Canada jays ( Perisoreus canadensis )

In the past 20 years, research in animal cognition has challenged the belief that complex cognitive processes are uniquely human. At the forefront of these challenges has been research on mental time travel and future planning in jays. We tested whether Canada jays ( Perisoreus canadensis ) demonstrated future planning, using a procedure that has produced evidence of future planning in California scrub-jays. Future planning in this procedure is caching in locations where the bird will predictably experience a lack of food in the future. Canada jays showed no evidence of future planning in this sense and instead cached in the location where food was usually available, opposite to the behaviour described for California scrub-jays. We provide potential explanations for these differing results adding to the recent debates about the role of complex cognition in corvid caching strategies.

The lose-to-win strategy of the weak: intraspecific parasitism via egg abduction in a termite

Predation by larger conspecifics poses a major threat to small juveniles in many animal species. However, in social insects, raids perpetrated by large colonies may provide smaller colonies with opportunities for parasitization. Herein, in the termite Reticulitermes speratus , we demonstrate that small incipient colonies parasitize large mature colonies through egg abduction when attacked by raiding conspecifics. We observed that the eggs of incipient colonies were brought into raiding colonies while their parents were killed during the attack. In this species, unmated females found new colonies with female–female (FF) cooperation, in addition to the typical monogamous colony foundation. Interestingly, the abducted eggs of FF pairs developed into nymphs (reproductive caste) in the raiding colonies, whereas the eggs of male–female (MF) pairs developed into workers (non-reproductive caste). Parthenogenetic eggs are known to be developmentally predisposed to becoming female reproductives owing to genomic imprinting in termites. This study demonstrates that the plundering of small colonies by larger conspecific colonies not only results in the extinction of the weaker colonies, but also serves as a strategy that incipient colonies use to obtain the reproductive position in large colonies by stealth. The results elucidate the diversity and complexity of inter-colonial interactions in social insects.

Maternal responses to pup calls in a high-cost lactation species

Bonding between mothers and their young is fundamental to mammalian reproductive behaviour and individual fitness. In social systems where the risk of confusing filial and non-filial offspring is high, mothers should demonstrate early, strong and consistent responses to their kin throughout the period of offspring dependence, irrespective of maternal traits. We tested this hypothesis through playback experiments in the northern elephant seal Mirounga angustirostris , a phocid species that breeds in high-density colonies. We found that mothers recognized their offspring throughout lactation and as early as 1–2 days after parturition. Measures of experience (age) and temperament (aggressivity) did not predict their response strength to filial playback treatments, nor did pup age or sex. Some mothers showed great consistency in behavioural responses throughout the lactation period, while others were less predictable. The strength of a female's response did not influence her pup's weaning weight; however, more consistent females weaned pups of higher mass. This is a rare demonstration of individual recognition among phocid mothers and their offspring, and suggests that consistency in maternal responsiveness may be an important social factor influencing the pup's growth and survival.

Annual precipitation predicts the phylogenetic signal in bat–fruit interaction networks across the Neotropics

Closely related species tend to be more similar than randomly selected species from the same phylogenetic tree. This pattern, known as a phylogenetic signal, has been extensively studied for intrinsic (e.g. morphology), as well as extrinsic (e.g. climatic preferences), properties but less so for ecological interactions. Phylogenetic signals of species interactions (i.e. resource use) can vary across time and space, but the causes behind such variations across broader spatial extents remain elusive. Here, we evaluated how current and historical climates influence phylogenetic signals of bat–fruit interaction networks across the Neotropics. We performed a model selection relating the phylogenetic signals of each trophic level (bats and plants) with a set of current and historical climatic factors deemed ecologically important in shaping biotic interactions. Bat and plant phylogenetic signals in bat–fruit interaction networks varied little with climatic factors, although bat phylogenetic signals positively covaried with annual precipitation. These findings indicated that water availability could increase resource availability, favouring higher niche partitioning of trophic resources among bat species and hence bat phylogenetic signals across bat–fruit interaction networks. Overall, our study advances our understanding of the spatial dynamics of bat–fruit interactions by highlighting the association of current climatic factors with phylogenetic patterns of biotic interactions.