Tent Construction by the Short-nosed Fruit Bat Cynopterus sphinx (Chiroptera: Pteropodidae) in Southern India

Roost making in bats

Structures created by animals can serve many purposes. Spiders weave intricate webs to trap prey; beavers engineer complex networks of dams to alter waterways; male bower birds construct and decorate elaborate bowers to attract mates. Animal architecture ranges widely in function, but by far the most common use is shelter. Animals can spend a large amount of time in their shelters, and this is often where they both sleep and rear young, two of the most vulnerable states in animal lives. To optimize the safety and suitability of refuges available to them, many animals have become architects and create their own shelters, ranging from simple holes in the ground to the large complex nests of some social insects.

New architecture of leaf-tents in American oil palms (Elaeis oleifera) used by Pacific tent-making bat (Uroderma convexum) in Panama

In this study, we report for the first time the use of the American oil palm (Elaeis oleifera) as roost by the Neotropical Pacific tent-making bat (Uroderma convexum). Palms with tent roosts consisting of modified leaves were found within the semi-deciduous lowland rainforest in Panama. We present detailed information on a new style of leaf modifications and compare these to tent architectures in other palm species used by U. convexum.

Timing of emergence and cave return, and duration of nocturnal activity in an endemic Malagasy fruit bat

Bats emerge from their day roost after dusk and different factors can affect the timing of departure, return, and duration of nocturnal activities. This study provides information on the time of emergence and return of an endemic Malagasy fruit bat, Rousettus madagascariensis, in a cave located in the Réserve Spéciale d’Ankarana, northern Madagascar. Individuals were captured in a narrow passage between the roost and cave exit and capture time for each individual was noted. Variation according to sex, age, and body condition, as well as the influence of season, and the sunset and sunrise time were analyzed. During the dry season, individuals started to emerge at 1913 hours and returned to the cave generally by 0505 hours; the duration of time outside the cave during the dry season was higher in adult females (0952 hours) followed by subadult males (0937 hours), sub-adult females (0931 hours), and adult males (0910 hours). During the wet season, individuals exited at 1926 hours and returned at 0351 hours; as in the dry season, adult females spent more time outside the cave (0833 hours), than sub-adult females (0800 hours), and adult males (0752 hours). The period of emergence varied according to the age and sex classes, and time of predawn return associated with the previous nocturnal activity. The period of return was influenced by season, and age and sex classes. Such information is useful to quantify shifts in bat ecology, especially for endemic species with limited distribution or those playing an important role in ecosystem services.

Social grooming among Indian short-nosed fruit bats

Social grooming is conspicuous in group-living mammals. Bats are gregarious and may groom each other, but the motivation for such social behaviour remains unclear. Here, we describe patterns and infer function of social grooming in tent-making Indian short-nosed fruit bats. Combining field and captivity observations, we found that males and their harem of females mutually groom and apply bodily secretions to one another in tight clusters. Mutual grooming is more commonly initiated by females, before emergence flight at dusk, and during the non-mating season. The within-harem association pattern suggests males may recognize female reproductive status via social grooming. Chemical analysis of the secretions applied during grooming revealed volatile organic compounds that may be involved in chemosensory-mediated communication and/or mate choice. These fruit bat harems were previously seen as simple aggregations, with limited interactions among individuals. Our findings suggest social grooming is multi-functional, with potential implications for the bats’ social lives.

From resource to female defence: the impact of roosting ecology on a bat's mating strategy

With their extraordinary species richness and diversity in ecological traits and social systems, bats are a promising taxon for testing socio-ecological hypotheses in order to get new insights into the evolution of animal social systems. Regarding its roosting habits, proboscis bats form an extreme by occupying sites which are usually completely exposed to daylight (e.g. tree trunks, vines or rocks). This is accompanied by morphological and behavioural adaptations to remain cryptic in exposed day roosts. With long-term behavioural observations and genetic parentage analyses of individually marked proboscis bats, we assessed its social dispersion and male mating strategy during day and night. Our results reveal nocturnal male territoriality-a strategy which most closely resembles a resource-defence polygyny that is frequent also in other tropical bats. Its contrasting clumped social dispersion during the day is likely to be the result of strong selection for crypsis in exposed roosts and is accompanied by direct female defence in addition to male territoriality. To the best of our knowledge, such contrasting male mating strategies within a single day-night cycle have not been described in a vertebrate species so far and illustrate a possible evolutionary trajectory from resource-defence to female-defence strategy by small ecologically driven evolutionary steps.

Non-kin cooperation in bats

Many bats are extremely social. In some cases, individuals remain together for years or even decades and engage in mutually beneficial behaviours among non-related individuals. Here, we summarize ways in which unrelated bats cooperate while roosting, foraging, feeding or caring for offspring. For each situation, we ask if cooperation involves an investment, and if so, what mechanisms might ensure a return. While some cooperative outcomes are likely a by-product of selfish behaviour as they are in many other vertebrates, we explain how cooperative investments can occur in several situations and are particularly evident in food sharing among common vampire bats (Desmodus rotundus) and alloparental care by greater spear-nosed bats (Phyllostomus hastatus). Fieldwork and experiments on vampire bats indicate that sharing blood with non-kin expands the number of possible donors beyond kin and promotes reciprocal help by strengthening long-term social bonds. Similarly, more than 25 years of recapture data and field observations of greater spear-nosed bats reveal multiple cooperative investments occurring within stable groups of non-kin. These studies illustrate how bats can serve as models for understanding how cooperation is regulated in social vertebrates.

Human-modified habitats change patterns of population genetic structure and group relatedness in Peter's tent-roosting bats

Although coloniality is widespread among mammals, it is still not clear what factors influence composition of social groups. As animals need to adapt to multiple habitat and environmental conditions throughout their range, variation in group composition should be influenced by adaptive adjustment to different ecological factors. Relevant to anthropogenic disturbance, increased habitat modification by humans can alter species' presence, density, and population structure. Therefore, it is important to understand the consequences of changes to landscape composition, in particular how habitat modification affects social structure of group-forming organisms. Here, we combine information on roosting associations with genetic structure of Peter's tent-roosting bats, Uroderma bilobatum to address how different habitat characteristics at different scales affect structure of social groups. By dividing analyses by age and sex, we determined that genetic structure was greater for adult females than adult males or offspring. Habitat variables explained 80% of the variation in group relatedness (mainly influenced by female relatedness) with roost characteristics contributing the most explained variation. This suggests that females using roosts of specific characteristics exhibit higher relatedness and seem to be philopatric. These females mate with more males than do more labile female groups. Results describe ecological and microevolutionary processes, which affect relatedness and social structure; findings are highly relevant to species distributions in both natural and human-modified environments.

Energetics of tent roosting in bats: the case of Ectophylla alba and Uroderma bilobatum (Chiroptera: Phyllostomidae)

Roost selection in mammals is an important selective pressure, and many animals find shelter in previously existing structures. Furthermore, the microclimate of roosts is a crucial element for bat survival, and modified leaves are used for roosting (“tents”) by 22 species of bats. Our objective was to determine whether the inverted boat tents used by Ectophylla alba and pinnate tents used by Uroderma bilobatum provide energetic benefits. We measured the ambient temperature under modified and unmodified leaves (UMLs) of Heliconia imbricata and Cocos nucifera . We also measured temperature with (simulated bat presence) and without a heat source, and finally we measured bat energy expenditure at different temperatures. Our results show that when a heat source is present tents conserve heat better than a UML. The energy expenditure of E. alba and U. bilobatum increased up to 55% and 48%, respectively, with a decrease of temperature from 25°C to 20°C. We concluded that since the temperature at our study site drops below 25°C every night and remains that way until mid-morning, using a “tent” that maintains a temperature higher than ambient temperature, or close to 25°C degrees, provides an energetic advantage.

La selección del refugio en los mamíferos es una presión selectiva importante y muchos animales encuentran refugio en estructuras ya existentes. El microclima del refugio es un elemento crucial para la sobrevivencia de los murciélagos. Las hojas modificadas (tiendas) son utilizadas por 22 especies de murciélagos. Nuestro objetivo era determinar si la tienda de bote invertido utilizada por Ectophylla alba y tiendas pinnadas utilizadas por Uroderma bilobatum brindan un beneficio energético a los murciélagos. Se midió la temperatura bajo hojas modificadas y no modificadas de Heliconia imbricata y Cocos nucifera . Además se midió la temperatura con fuente (simulando la presencia de murciélagos) y sin fuente de calor, finalmente se midió el gasto energético de los murciélagos a diferentes temperaturas. Los resultados muestran que cuando hay una fuente de calor presente, la tienda conserva el calor mejor que una hoja no modificada. El gasto energético de E. alba y U. bilobatum puede incrementarse hasta 55% y 48%, respectivamente, cuando la temperatura decrece entre 25°C y 20°C. Concluimos que como la temperatura en este sitio de estudio baja de los 25°C cada noche y hasta media mañana, utilizar una tienda que mantiene la temperatura arriba o cerca de los 25°C, provee una ventaja energética.

Differences in foraging times between two feeding guilds within Old World fruit bats (Pteropodidae) in southern Thailand

Bats are important but understudied pollinators in the Palaeotropics, and much about their interactions with night-blooming, bat-pollinated plant species is still unknown. We compared visitation times to flowering and fruiting plant resources by nectarivorous bat species (obligate pollinators) and frugi-nectarivorous bat species (facultative pollinators) throughout the night to examine the temporal variability that occurs within Pteropodidae foraging. Timing of pollination is an important determinant of plant reproductive success and more temporally restrictive than fruit dispersal. We netted 179 nectarivorous bats and 209 frugi-nectarivorous bats across 367 total mist-net h at five plant species providing floral resources and six plant species providing fruit resources. We found that all three nectarivorous bat species in southern Thailand forage significantly earlier in the evening (20h30 versus 22h00), and over a significantly shorter time interval (1.73 h versus 3.33 h), than do the five most commonly netted frugi-nectarivorous species. These results indicate that the two feeding guilds may be imposing different selective pressures on bat-pollinated plant species and may comprise different functional groups. We propose that the observed differences in bat foraging times are due to temporal constraints imposed by the rewards of the plant species that they visit.

Promiscuous mating in the harem-roosting fruit bat, Cynopterus sphinx

Observations on mating behaviours and strategies guide our understanding of mating systems and variance in reproductive success. However, the presence of cryptic strategies often results in situations where social mating system is not reflective of genetic mating system. We present such a study of the genetic mating system of a harem-forming bat Cynopterus sphinx where harems may not be true indicators of male reproductive success. This temporal study using data from six seasons on paternity reveals that social harem assemblages do not play a role in the mating system, and variance in male reproductive success is lower than expected assuming polygynous mating. Further, simulations reveal that the genetic mating system is statistically indistinguishable from promiscuity. Our results are in contrast to an earlier study that demonstrated high variance in male reproductive success. Although an outcome of behavioural mating patterns, standardized variance in male reproductive success (I(m)) affects the opportunity for sexual selection. To gain a better understanding of the evolutionary implications of promiscuity for mammals in general, we compared our estimates of I(m) and total opportunity for sexual selection (I(m) /I(f), where I(f) is standardized variance in female reproductive success) with those of other known promiscuous species. We observed a broad range of I(m) /I(f) values across known promiscuous species, indicating our poor understanding of the evolutionary implications of promiscuous mating.

Characterization of the sleep architecture in two species of fruit bat

Bats (Chiroptera) are the second-most abundant mammalian order in the world, occupying a diverse range of habitats and exhibiting many different life history traits. In order to contribute to this highly underrepresented group we describe the sleep architecture of two species of frugivorous bat, the greater short-nosed fruit bat (Cynopterus sphinx) and the lesser dawn fruit bat (Eonycteris spelaea). Electroencephalogram (EEG) and electromyogram (EMG) data were recorded from multiple individuals (>or=5) by telemetry over a 72-h period in a laboratory setting with light/dark cycles equivalent to those found in the wild. Our results show that over a 24-h period both species spent more time asleep than awake (mean 15 h), less than previous reported for Chiroptera (20 h). C. sphinx spent significantly more of its non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM) quotas during the light phase, while E. spelaea divided its sleep-wake architecture equally between both light and dark phases. Comparing the sleep patterns of the two species found that C. sphinx had significantly fewer NREM and REM episodes than E. spelaea but each episode lasted for a significantly longer period of time. Potential hypotheses to explain the differences in the sleep architecture of C. sphinx with E. spelaea, including risk of predation and social interaction are discussed.

Genetic consequences of polygyny and social structure in an Indian fruit bat, Cynopterus sphinx. I. Inbreeding, outbreeding, and population subdivision

Population subdivision into behaviorally cohesive kin groups influences rates of inbreeding and genetic drift and has important implications for the evolution of social behavior. Here we report the results of a study designed to test the hypothesis that harem social structure promotes inbreeding and genetic subdivision in a population with overlapping generations. Genetic consequences of harem social structure were investigated in a natural population of a highly polygynous fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The partitioning of genetic variance within and among breeding groups was assessed using 10-locus microsatellite genotypes for 431 individually marked bats. Genetic analysis of the C. sphinx study population was integrated with field data on demography and social structure to determine the specific ways in which mating, dispersal, and new social group formation influenced population genetic structure. Microsatellite data revealed striking contrasts in genetic structure between consecutive offspring cohorts and between generations. Relative to the 1998 (dry-season) offspring cohort, the 1997 (wet-season) cohort was characterized by a more extensive degree of within-group heterozygote excess (F(IS) = -0.164 vs. -0.050), a greater degree of among-group subdivision (F(ST) = 0.123 vs. 0.008), and higher average within-group relatedness (r = 0.251 vs. 0.017). Differences in genetic structure between the two offspring cohorts were attributable to seasonal differences in the number and proportional representation of male parents. Relative to adult age-classes, offspring cohorts were characterized by more extensive departures from allelic and genotypic equilibria and a greater degree of genetic subdivision. Generational differences in F-statistics indicated that genetic structuring of offspring cohorts was randomized by natal dispersal prior to recruitment into the breeding population. Low relatedness among harem females (r = 0.002-0.005) was primarily attributable to high rates of natal dispersal and low rates of juvenile survivorship. Kin selection is therefore an unlikely explanation for the formation and maintenance of behaviorally cohesive breeding groups in this highly social mammal.