Rachel A. Page

The acute phase response is a component of innate immunity that helps fight infections. Understanding variation in this response could be critical in bats, which can be asymptomatic hosts of pathogens that cause disease in other animals. Although bats are most famously tolerant of some viruses, research on the bat acute phase response has focused predominantly on bacterial antigens. To improve understanding of bat viral responses, we challenged wild Seba's short-tailed bats (Carollia perspicillata) with a viral mimic (polyinosinic:polycytidylic acid (polyI:C)). We injected nine bats subcutaneously with 2 mg kg−1 of polyI:C (n = 3), 5 mg kg−1 of polyI:C (n = 3) or phosphate buffered saline (n = 3). Over the next 24 hours, we measured body temperature hourly and collected body mass and blood smears for leucocyte counts every 4 hours. Regardless of dose, polyI:C-challenged bats had higher body temperatures compared to control bats but did not exhibit leucocytosis or reduced body mass. These preliminary findings improve understanding of how wild bats physiologically respond to viral challenges. Moreover, in showing that as little as 2 mg kg−1 of polyI:C can induce a febrile response, our study provides a framework to facilitate future investigations into causes and consequences of wild bat viral responses.

Telomeres are key biomarkers of cellular ageing, yet their dynamics remain poorly studied in tropical and short‐lived bat species. Here, we present the first investigation of telomere length across age in Molossus molossus , a tropical bat historically categorised as the shortest‐lived bat on record. Through a multi‐year mark‐recapture study in Gamboa, Panama, we sampled 492 individuals ( n = 317 females, 175 males) and documented a female M. molossus surviving to at least 13 years of age, more than doubling the previously reported maximum lifespan of 5.6 years. Relative telomere length (rTL) showed a negative association with age, although this association was not retained in sensitivity analyses. Males consistently exhibited longer telomeres than females in both robust and age‐matched analyses, while there was no evidence that age‐related telomere dynamics differed between the sexes. Overall, these findings challenge previous assumptions about the lifespan and ageing biology of M. molossus . They reveal a difference between the sexes in mean telomere length and reinforce the value of long‐term field studies for understanding ageing processes in the wild.

Aerial-hawking bats adjust their biosonar in the search, approach and capture phases of echolocation to guide aerial prey interception. Some bat species have secondarily evolved a gleaning strategy that relies on passive acoustic cues to detect and capture prey on vegetation. Here, we tested the hypothesis that such a gleaning specialist, the fringe-lipped bat, Trachops cirrhosus, must use stereotyped aerial-hunting echolocation phases, including a buzz when opportunistically capturing aerial prey. Using data from sound-recording tags on 8 individuals, we reject this hypothesis by showing that fringe-lipped bats can detect and intercept aerial prey by echolocation but do so with modest biosonar adjustments and without producing a high-resolution buzz. These findings challenge the notion that the stereotyped echolocation phases of hawking bats are required for aerial prey capture and show that echolocation is an extremely versatile sensory system that can be employed across otherwise specialized foraging niches.

In many group-living birds and mammals, the formation of affiliative relationships is hypothesized to cause vocal convergence (an increase in call similarity between individuals). However, testing this causal effect can be difficult, because it requires experimentally forming new relationships. Here, we demonstrate convergence in the contact calls of common vampire bats ( Desmodus rotundus ) that we introduced and experimentally housed together. To estimate and disentangle the roles of kinship, co-housing (familiarity), allogrooming and food sharing in predicting call similarity, we first measured call similarity using 35 features of 693 494 contact calls from 95 bats, then fitted a series of Bayesian generalized multi-membership models. We also measured changes in call similarity for a subset of individuals who were recorded before and after co-housing. We found that co-housing caused vocal convergence. Furthermore, food-sharing rates among familiar non-kin within the same co-housed group predicted contact call similarity. This finding suggests that the development of cooperative relationships causes further vocal convergence beyond the initial convergence caused by co-housing. Our findings have implications for the development of cooperative relationships and vocal learning.

Telomeres are key biomarkers of cellular ageing, yet their dynamics remain poorly studied in tropical and short-lived bat species. Here, we present the first investigation of telomere length across age in Molossus molossus , a tropical bat historically categorised as the shortest-lived bat on record. Through a multi-year mark-recapture study in Gamboa, Panama, we sampled 492 individuals ( n = 317 females, 175 males) and documented a female M. molossus surviving to at least 13 years of age, more than doubling the previously reported maximum lifespan of 5.6 years. Across the population, relative telomere length (rTL) showed no overall significant decline with age. No evidence was found for sex-specific rates of telomere attrition. Rather these results suggest that males and females follow parallel age-related telomere trajectories, with any sex differences primarily reflecting differences in mean telomere length rather than ageing dynamics. Overall, the findings here challenge previous assumptions about the lifespan and ageing biology of M. molossus . They demonstrate that telomere maintenance is not limited to temperate bats, show that sex differences in telomere biology are subtle and species-specific, and reinforce the value of long-term field studies for understanding ageing processes in the wild.

An animal's internal state can shift its behavior. Animals that would typically avoid dangerous foraging conditions may choose to forego safety when food is restricted. Furthermore, physiological demands such as gravidness can drive sex differences in foraging behavior among individuals of the same species. In bats, moonlight can impose risk: some bat species decrease or completely avoid foraging on full moon nights when visually oriented predators are most active. In this study, we tested the hypothesis that hunger increases risky foraging behavior. Previous work with the Jamaican fruit bat, Artibeus jamaicensis, demonstrated that this species shifts its foraging behavior in moonlight by increasing latency to land. In this experiment, bats trained to feed from a food platform were then observed landing in conditions of satiation and food-restriction, with and without the presence of artificial full moonlight. As predicted, we found that bats forage significantly more quickly when food-restricted than when satiated. We found that bats showed a nonsignificant trend to avoid moonlight via increased latencies to land on the food platform. Males—but not females—were significantly slower to land in the presence of moonlight when satiated but not when food-restricted. Our results demonstrate that internal state influences foraging decisions, with individuals landing faster when hungry than when satiated, but that the increased foraging risks associated with moonlight affect male bats more than females.

Sexual selection often favors the evolution of conspicuous mating displays. Emitting such overt displays carries the risk of interception by eavesdropping enemies, i.e. predators, parasitoids and parasites that exploit communication systems to find and attack their signaling victims. Yet, many signalers respond to variation in perceived eavesdropper risk, protecting themselves through risk-dependent inducible defenses to mitigate potential costs. Given that signalers are embedded in communication networks in which they interact with other signalers, target receivers and multiple eavesdropping enemies, here we investigated how variation in signaling and defensive strategies impacted by an eavesdropping enemy (frog-biting midges; Diptera: Corethrellidae) affects other receivers in a communication network. Ultimately, we aimed to determine whether and to what extent effects that cascade throughout the network shape relative fitness among chorusing males. Using female choice experiments with túngara frogs (Engystomops pustulosus) and predation experiments with eavesdropping, fringe-lipped bats (Trachops cirrhosus), we show that variation in the call elaboration and defensive strategies of competing males shapes their relative fitness. Defensive strategies targeting eavesdropping frog-biting midges indirectly shift a male's relative attractiveness to females and predatory bats, though the mechanisms and impacts are context and receiver specific. These findings showcase how the frequency-dependent effects of micropredation can dynamically shape variation in secondary sexual characteristics and thus influence the mechanisms driving sexual selection.

Across many taxa, males gather in leks to perform multisensory courtship displays for females. At a lek, changes in the sensory scene over the course of mate evaluation are inevitable. This dynamic nature makes a female’s ability to recall the location of individual signalers an important component of female mate choice. It is hypothesized that complex (especially multimodal) displays may improve a female’s ability to remember and thus discriminate amongst potential mates. To test this hypothesis, we presented female túngara frogs ( Physalaemus (= Engystomops ) pustulosus ) with male calls (auditory) and robotic frogs (visual) that could later be obstructed from view via the lowering of blinds. Specifically, we asked if the visual component of a multimodal display improves the ability of a receiver to remember a signaler. While our initial experiment did not find memory instantiation in female frogs, subsequent experiments with a longer presentation time and a brief period of silence successfully instantiated memories in females. Moreover, females continued to demonstrate significant preferences for calls associated with the visual cue even after 25 s following the obstruction of the visual stimulus (robotic frog). Thus, we propose that the duration of presentation and/or the silent period impact memory capability. Silence is common in choruses, and our data suggest that complex, multisensory stimuli may have evolved to help females remember their preferred mate even with such fluctuations in signal production. LAY SUMMARY: Multisensory signals function to stimulate one or more of a receiver’s senses, and in doing so, may make signalers more memorable to receivers. Multisensory signals are common in mating displays, including the advertisement of a male túngara frog: a call (acoustic) and a vocal sac inflation (visual). Here, we demonstrate that female túngara frogs were more likely to remember a multisensory male display over a unisensory display, but only after fluctuations in the signal’s intensity.

In many group-living birds and mammals, the formation of affiliative relationships is hypothesized to cause vocal convergence (an increase in call similarity between individuals). However, testing this causal effect can be difficult, because it requires experimentally forming new relationships. Here, we demonstrate convergence in the contact calls of common vampire bats ( Desmodus rotundus ) that we introduced and experimentally housed together. To estimate and disentangle the roles of kinship, co-housing (familiarity), allogrooming, and food sharing in predicting call similarity, we first measured call similarity using 35 features of 693,494 contact calls from 95 bats, then fit a series of Bayesian generalized multi-membership models. We also measured changes in call similarity for a subset of individuals that were recorded before and after co-housing. We found that co-housing caused vocal convergence. Furthermore, food-sharing rates among familiar nonkin within the same co-housed group predicted contact call similarity. This finding suggests that the development of cooperative relationships causes further vocal convergence beyond the initial convergence caused by co-housing. Our findings have implications for the development of cooperative relationships and vocal learning.