Sources of assimilated protein in five species of New World frugivorous bats

Comparative study of endocrine pancreatic tissue in bats: Assessing variations among frugivorous, insectivorous, and nectarivorous diets

Whether the endocrine pancreas exhibits structural features to couple with dietary patterns is not fully explored. Considering the lack of data comparing endocrine pancreas and islet cell distribution among different bat species in the same study, we considered this an opportunity to explore the topic, including five species within three different predominant diets. For this, we applied morphometric techniques to compare the islets of frugivorous Artibeus lituratus and Carollia perspicillata, insectivorous Molossus molossus and Myotis nigricans, and nectarivorous Glossophaga soricina bats. Data for islet size, cellularity, and mass were equivalent between frugivorous A. lituratus and nectarivorous G. soricina, which differed from insectivorous bats. The frugivorous C. perspicillata bat exhibited morphometric islet values between A. lituratus and the insectivorous species. A. lituratus and G. soricina but not C. perspicillata bats had higher islet mass than insectivorous species due to larger size, instead of a higher number of islets per area. Insectivorous bats, on the other hand, had a higher proportion of α-cells per islet. These differences in the endocrine pancreas across species with different eating habits indicate the occurrence of species-specific adjustments along the years of evolution, with the demand for α-cells higher in bats with higher protein intake.

Nutrient balancing in a fruit-specialist primate, the black-and-white ruffed lemur (Varecia variegata)

Animals' foraging behavior and dietary choices are, in part, driven by their ultimate function: to meet nutritional demands. However, depending on their degree of dietary specialization and the availability and distribution of food resources in their environment, species may utilize different nutritional strategies. With shifting plant phenology, increasing unpredictability of fruiting, and declining food quality in response to anthropogenic climate change, existing nutritional constraints may become exacerbated. Such changes are especially concerning for Madagascar's endemic fruit specialists given the nutrient-limitation of the island's landscapes. In this study, we examined the nutritional strategy of one such fruit-specialist primate, the black-and-white ruffed lemur (Varecia variegata), over a 12-month period (January to December 2018) in Ranomafana National Park, Madagascar. We hypothesized that Varecia would balance nonprotein energy (NPE) to protein (AP) at a high ratio similar to other frugivorous primates, and that they would prioritize protein intake given their high degree of frugivory. We found that Varecia balance NPE:AP at a ratio of 11:1, higher than in any other primate studied to date; however, diets shifted such that nutrient balancing varied seasonally (12.6:1 abundant-9.6:1 lean). Varecia meet NRC suggested recommendations of 5-8% of calories from protein, despite having a diet mostly comprising fruits. However, seasonal shifts in NPE intakes result in significant energy shortfalls during fruit-lean seasons. Flowers provide an important source of NPE during these periods, with flower consumption best predicting lipid intake, suggesting this species' ability to shift resource use. Nevertheless, achieving adequate and balanced nutrient intakes may become precarious in the face of increasing unpredictability in plant phenology and other environmental stochasticities resulting from climate change.

You are more than what you eat: potentially adaptive enrichment of microbiome functions across bat dietary niches

BACKGROUND

Animals evolved in a microbial world, and their gut microbial symbionts have played a role in their ecological diversification. While many recent studies report patterns of phylosymbiosis between hosts and their gut bacteria, fewer studies examine the potentially adaptive functional contributions of these microbes to the dietary habits of their hosts. In this study, we examined predicted metabolic pathways in the gut bacteria of more than 500 individual bats belonging to 60 species and compare the enrichment of these functions across hosts with distinct dietary ecologies.

RESULTS

We found that predicted microbiome functions were differentially enriched across hosts with different diets. Using a machine-learning approach, we also found that inferred microbiome functions could be used to predict specialized host diets with reasonable accuracy. We detected a relationship between both host phylogeny and diet with respect to microbiome functional repertoires. Because many predicted functions could potentially fill nutritional gaps for bats with specialized diets, we considered pathways discriminating dietary niches as traits of the host and fit them to comparative phylogenetic models of evolution. Our results suggest that some, but not all, predicted microbiome functions may evolve toward adaptive optima and thus be visible to the forces of natural selection operating on hosts over evolutionary time.

CONCLUSIONS

Our results suggest that bats with specialized diets may partially rely on their gut microbes to fulfill or augment critical nutritional pathways, including essential amino acid synthesis, fatty acid biosynthesis, and the generation of cofactors and vitamins essential for proper nutrition. Our work adds to a growing body of literature suggesting that animal microbiomes are structured by a combination of ecological and evolutionary processes and sets the stage for future metagenomic and metabolic characterization of the bat microbiome to explore links between bacterial metabolism and host nutrition.

Molecular diet analysis of neotropical bats based on fecal DNA metabarcoding

Bat communities in the Neotropics are some of the most speciose assemblages of mammals on Earth, with regions supporting more than 100 sympatric species with diverse feeding ecologies. Because bats are small, nocturnal, and volant, it is difficult to directly observe their feeding habits, which has resulted in their classification into broadly defined dietary guilds (e.g., insectivores, carnivores, and frugivores). Apart from these broad guilds, we lack detailed dietary information for many species and therefore have only a limited understanding of interaction networks linking bats and their diet items. In this study, we used DNA metabarcoding of plants, arthropods, and vertebrates to investigate the diets of 25 bat species from the tropical dry forests of Lamanai, Belize. Our results report some of the first detection of diet items for the focal bat taxa, adding rich and novel natural history information to the field of bat ecology. This study represents a comprehensive first effort to apply DNA metabarcoding to bat diets at Lamanai and provides a useful methodological framework for future studies testing hypotheses about coexistence and niche differentiation in the context of modern high-throughput molecular data.

Dietary resource overlap among three species of frugivorous bat in Costa Rica

The maintenance of biodiversity in tropical forests is thought to be dependent on fine-scale mechanisms of niche partitioning that allow species to coexist. This study examined whether three species of short-tailed fruit bat that co-occur at a lowland tropical forest site in Costa Rica (Carollia castanea, C. perspicillata, C. sowelli) avoid inter- and intraspecific competition through dietary specialization on species in the genus Piper. First, dietary composition was examined using faecal samples (N = 210), which yielded three main findings: (1) bat species and sexes vary in overall reliance on fruits of Piper, with a higher percentage of seeds of Piper detected in the diets of C. castanea (98.2%) and females (91.5%); (2) adults and juveniles partition species of Piper by habitat, with a lower percentage of mid- to late-successional species of Piper detected in adults (20.8%); and (3) overall, there is a strong dietary overlap among and within the three species of Carollia. Second, controlled choice experiments were conducted with individual bats (N = 123) to examine preferences for different species of Piper. These results indicated few differences in Piper preference based on bat species, sex, age class or reproductive status, suggesting preference is not the primary mechanism shaping the observed differences in dietary composition. Overall, the dietary composition and preference similarities suggest there is strong competition both among and within the three species of Carollia for food resources.

Diverse RNA viruses of arthropod origin in the blood of fruit bats suggest a link between bat and arthropod viromes

Bats host diverse viruses due to their unique ecology, behavior, and immunology. However, the role of other organisms with which bats interact in nature is understudied as a contributor to bat viral diversity. We discovered five viruses in the blood of fruit bats (Hypsignathus monstrosus) from the Republic of Congo. Of these five viruses, four have phylogenetic and genomic features suggesting an arthropod origin (a dicistrovirus, a nodavirus, and two tombus-like viruses), while the fifth (a hepadnavirus) is clearly of mammalian origin. We also report the parallel discovery of related tombus-like viruses in fig wasps and primitive crane flies from bat habitats, as well as high infection rates of bats with haemosporidian parasites (Hepatocystis sp.). These findings suggest transmission between arthropods and bats, perhaps through ingestion or hyperparasitism (viral infection of bat parasites). Some "bat-associated" viruses may be epidemiologically linked to bats through their ecological associations with invertebrates.

Food restriction, but not seasonality, modulates the acute phase response of a Neotropical bat

Season and food intake are known to affect immune response of vertebrates yet their effects on metabolic rate have been rarely explored. We tested the effect of season and acute food restriction and their interaction on the energetic cost of immune response activation of a tropical vertebrate, the Seba's short-tailed fruit bat (Carollia perspicillata). We specifically stimulated the acute phase response (APR) with bacterial lipopolysaccharide (LPS) to measure metabolic changes along with changes in body temperature (T_b), body mass (M_b), white blood cell counts and the Neutrophil/Lymphocyte ratio (N/L). We found no effect of season on the different factors associated to the activation of the APR. In contrast to our expectations, unfed bats reached similar T_b increments and RMR peak values and had higher RMR scope values and higher caloric costs than fed bats after LPS injection. However, food deprivation led to delayed metabolic response indicated by longer time required to reach peak RMR values in unfed bats. Both food-deprived and fed bats did not present leukocytosis after APR activation and their WBC counts were similar, but unfed bats had a significant increase of N/L. APR activation represented a small fraction of the bat daily energy requirements which might explain why unfed bats were not limited to mount a metabolic response. Our study adds to recent evidence showing that activating the innate immune system is not an energetically expensive process for plant-eating bats.

Bacteria richness and antibiotic-resistance in bats from a protected area in the Atlantic Forest of Southeastern Brazil

Bats play key ecological roles, also hosting many zoonotic pathogens. Neotropical bat microbiota is still poorly known. We speculate that their dietary habits strongly influence their microbiota richness and antibiotic-resistance patterns, which represent growing and serious public health and environmental issue. Here we describe the aerobic microbiota richness of bats from an Atlantic Forest remnant in Southeastern Brazil, and the antibiotic-resistance patterns of bacteria of clinical importance. Oral and rectal cavities of 113 bats from Carlos Botelho State Park were swabbed. Samples were plated on 5% sheep blood and MacConkey agar and identified by the MALDI-TOF technique. Antibiotic susceptibility tests were performed using Kirby-Bauer’s antibiotic disc diffusion technique.We identified 596 isolates at the genus level and tentatively to the species level. Proteobacteria was the most abundant phylum in all the dietary guilds, representing 87% of the total identified samples. The most common bacteria within bat individuals were Escherichia coli, Klebsiella oxytoca and Serratia marcescens, and within bat species were Serratia marcescens, Pseudomonas sp. and Staphylococcus sp. Frugivores presented the most diverse microbiota. In general, the antibiogram results indicated a low occurrence of resistance on eigth potentially pathogenic bacteria species. The resistance to antibiotics found on our samples was related mostly to the intrinsic resistance of the tested species.The low occurrence of resistant bacteria in our samples could be related to the well preserved environment where bats were caught. Once the major causes of resistance-acquiring are related to anthropic activites, the controlled access of tourists on certain regions of the Park seems to be effectively protecting the environment.

Trophic position and dietary breadth of bats revealed by nitrogen isotopic composition of amino acids

Bats perform important ecosystem services, but it remains difficult to quantify their dietary strategies and trophic position (TP) in situ. We conducted measurements of nitrogen isotopes of individual amino acids (δ 15NAA) and bulk-tissue carbon (δ 13Cbulk) and nitrogen (δ 15Nbulk) isotopes for nine bat species from different feeding guilds (nectarivory, frugivory, sanguivory, piscivory, carnivory, and insectivory). Our objective was to assess the precision of δ 15NAA-based estimates of TP relative to other approaches. TPs calculated from δ 15N values of glutamic acid and phenylalanine, which range from 8.3-33.1‰ and 0.7-15.4‰ respectively, varied between 1.8 and 3.8 for individuals of each species and were generally within the ranges of those anticipated based on qualitative dietary information. The δ 15NAA approach reveals variation in TP within and among species that is not apparent from δ 15Nbulk data, and δ 15NAA data suggest that two insectivorous species (Lasiurus noctivagans and Lasiurus cinereus) are more omnivorous than previously thought. These results indicate that bats exhibit a trophic discrimination factor (TDF) similar to other terrestrial organisms and that δ 15NAA provides a reliable approach for addressing questions about variation in the TP of bats that have heretofore proven elusive.

Nutrient availability predicts frugivorous bat abundance in an urban environment

We used a mathematical model based on nutrient availability to predict

Trophic Niche Differentiation in Rodents and Marsupials Revealed by Stable Isotopes

Tropical rainforests support the greatest diversity of small mammals in the world, yet we have little understanding about the mechanisms that promote the coexistence of species. Diet partitioning can favor coexistence by lessening competition, and interspecific differences in body size and habitat use are usually proposed to be associated with trophic divergence. However, the use of classic dietary methods (e.g. stomach contents) is challenging in small mammals, particularly in community-level studies, thus we used stable isotopes (δ¹³C and δ¹⁵N) to infer about trophic niche. We investigated i) how trophic niche is partitioned among rodent and marsupial species in three Atlantic forest sites and ii) if interspecific body size and locomotor habit inequalities can constitute mechanisms underlying the isotopic niche partitioning. We found that rodents occupied a broad isotopic niche space with species distributed in different trophic levels and relying on diverse basal carbon sources (C3 and C4 plants). Surprisingly, on the other hand, marsupials showed a narrow isotopic niche, both in δ¹³C and δ¹⁵N dimensions, which is partially overlapped with rodents, contradicting their description as omnivores and generalists proposed classic dietary studies. Although body mass differences did not explained the divergence in isotopic values among species, groups of species with different locomotor habit presented clear differences in the position of the isotopic niche space, indicating that the use of different forest strata can favor trophic niche partitioning in small mammals communities. We suggest that anthropogenic impacts, such as habitat modification (logging, harvesting), can simplify the vertical structure of ecosystems and collapse the diversity of basal resources, which might affect negatively small mammals communities in Atlantic forests.

Molecular Evolution of the Nuclear Factor (Erythroid-Derived 2)-Like 2 Gene Nrf2 in Old World Fruit Bats (Chiroptera: Pteropodidae)

Mammals developed antioxidant systems to defend against oxidative damage in their daily life. Enzymatic antioxidants and low molecular weight antioxidants (LMWAs) constitute major parts of the antioxidant systems. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2, encoded by the Nrf2 gene) is a central transcriptional regulator, regulating transcription, of many antioxidant enzymes. Frugivorous bats eat large amounts of fruits that contain high levels of LMWAs such as vitamin C, thus, a reliance on LMWAs might greatly reduce the need for antioxidant enzymes in comparison to insectivorous bats. Therefore, it is possible that frugivorous bats have a reduced need for Nrf2 function due to their substantial intake of diet-antioxidants. To test whether the Nrf2 gene has undergone relaxed evolution in fruit-eating bats, we obtained Nrf2 sequences from 16 species of bats, including four Old World fruit bats (Pteropodidae) and one New World fruit bat (Phyllostomidae). Our molecular evolutionary analyses revealed changes in the selection pressure acting on Nrf2 gene and identified seven specific amino acid substitutions that occurred on the ancestral lineage leading to Old World fruit bats. Biochemical experiments were conducted to examine Nrf2 in Old World fruit bats and showed that the amount of catalase, which is regulated by Nrf2, was significantly lower in the brain, heart and liver of Old World fruit bats despite higher levels of Nrf2 protein in Old World fruit bats. Computational predictions suggest that three of these seven amino acid replacements might be deleterious to Nrf2 function. Therefore, the results suggest that Nrf2 gene might have experienced relaxed constraint in Old World fruit bats, however, we cannot rule out the possibility of positive selection. Our study provides the first data on the molecular adaptation of Nrf2 gene in frugivorous bats in compensation to the increased levels of LWMAs from their fruit-diet.

Bacterial diversity indicates dietary overlap among bats of different feeding habits

Bats are among the most conspicuous mammals with extraordinary adaptations. They play a key role in the ecosystem. Frugivorous bats are important seed dispersing agents that help in maintaining forest tree diversity, while insectivorous bats are natural insect pest control agents. Several previous reports suggest that bats are reservoir of viruses; nonetheless their bacterial counterparts are relatively less explored. The present study describes the microbial diversity associated with the intestine of bats from different regions of India. Our observations stipulate that there is substantial sharing of bacterial communities between the insectivorous and frugivorous bats, which signifies fairly large dietary overlap. We also observed the presence of higher abundance of Mycoplasma in Cynopterus species of bats, indicating possible Mycoplasma infection. Considering the scarcity of literature related to microbial communities of bat intestinal tract, this study can direct future microbial diversity studies in bats with reference to their dietary habits, host-bacteria interaction and zoonosis.

Food resource partitioning in syntopic nectarivorous bats on Puerto Rico

Understanding the dietary needs of syntopic species is essential for examining species coexistence and resource partitioning. We analysed stable isotopes of carbon (δ13C) and nitrogen (δ15N) to estimate the diet of two putative nectarivorous bats on Puerto Rico, the brown flower bat (Erophylla bombifrons) and the Greater Antillean long-tongued bat (Monophyllus redmani). Isotopic ratios of δ13C and δ15N were obtained from whole blood of both species of bat and tissues of available plant foods and insect prey over 15 wk at the same locality. We used a concentration-dependent Bayesian mixing model to determine probability distributions of feasible dietary contributions for major potential foods used by each species of bat. Additionally, separate dietary estimates were conducted for males and non-reproductive, pregnant and lactating females to determine differences due to reproductive condition. Insects were an important source of protein for M. redmani, whereas E. bombifrons obtained most of its protein from plants. In both species of bat, lactating females had lower assimilated nitrogen than males, suggesting more reliance on plants for protein. We observed no intraspecific differences in assimilated carbon among reproductive conditions. Flight and lactation are energetically expensive and may explain the increased consumption of high-energy foods, such as fruit or nectar, in lactating female bats. Comparison of isotopes between E. bombifrons and M. redmani illustrate the differential use of food resources by these insular syntopic species of bat.

Trophic niche differentiation and microhabitat utilization revealed by stable isotope analyses in a dry-forest bat assemblage at Ankarana, northern Madagascar

Bats are important components in tropical mammal assemblages. Unravelling the mechanisms allowing multiple syntopic bat species to coexist can provide insights into community ecology. However, dietary information on component species of these assemblages is often difficult to obtain. Here we measured stable carbon and nitrogen isotopes in hair samples clipped from the backs of 94 specimens to indirectly examine whether trophic niche differentiation and microhabitat segregation explain the coexistence of 16 bat species at Ankarana, northern Madagascar. The assemblage ranged over 4.4‰ in δ15N and was structured into two trophic levels with phytophagous Pteropodidae as primary consumers (c. 3‰ enriched over plants) and different insectivorous bats as secondary consumers (c. 4‰ enriched over primary consumers). Bat species utilizing different microhabitats formed distinct isotopic clusters (metric analyses of δ13C–δ15N bi-plots), but taxa foraging in the same microhabitat did not show more pronounced trophic differentiation than those occupying different microhabitats. As revealed by multivariate analyses, no discernible feeding competition was found in the local assemblage amongst congeneric species as compared with non-congeners. In contrast to ecological niche theory, but in accordance with studies on New and Old World bat assemblages, competitive interactions appear to be relaxed at Ankarana and not a prevailing structuring force.

Seasonal reliance on nectar by an insectivorous bat revealed by stable isotopes

Many animals have seasonally plastic diets to take advantage of seasonally abundant plant resources, such as fruit or nectar. Switches from insectivorous diets that are protein rich to fruits or nectar that are carbohydrate rich present physiological challenges, but are routinely done by insectivorous songbirds during migration. In contrast, insectivorous bat species are not known to switch diets to consume fruit or nectar. Here, we use carbon stable isotope ratios to establish the first known case of a temperate bat species consuming substantial quantities of nectar during spring. We show that pallid bats (Antrozous pallidus) switch from a diet indistinguishable from that of sympatric insectivorous bat species in winter (when no cactus nectar is present) to a diet intermediate between those of insectivorous bats and nectarivorous bats during the spring bloom of a bat-adapted cactus species. Combined with previous results that established that pallid bats are effective pollinators of the cardon cactus (Pachycereus pringlei), our results suggest that the interaction between pallid bats and cardon cacti represents the first-known plant-pollinator mutualism between a plant and a temperate bat. Diet plasticity in pallid bats raises questions about the degree of physiological adaptations of insectivorous bats for incorporation of carbohydrate-rich foods, such as nectar or fruit, into the diet.

Tropical secondary forest management influences frugivorous bat composition, abundance and fruit consumption in Chiapas, Mexico

Most studies on frugivorous bat assemblages in secondary forests have concentrated on differences among successional stages, and have disregarded the effect of forest management. Secondary forest management practices alter the vegetation structure and fruit availability, important factors associated with differences in frugivorous bat assemblage structure, and fruit consumption and can therefore modify forest succession. Our objective was to elucidate factors (forest structural variables and fruit availability) determining bat diversity, abundance, composition and species-specific abundance of bats in (i) secondary forests managed by Lacandon farmers dominated by Ochroma pyramidale, in (ii) secondary forests without management, and in (iii) mature rain forests in Chiapas, Southern Mexico. Frugivorous bat species diversity (Shannon H') was similar between forest types. However, bat abundance was highest in rain forest and O. pyramidale forests. Bat species composition was different among forest types with more Carollia sowelli and Sturnira lilium captures in O. pyramidale forests. Overall, bat fruit consumption was dominated by early-successional shrubs, highest late-successional fruit consumption was found in rain forests and more bats consumed early-successional shrub fruits in O. pyramidale forests. Ochroma pyramidale forests presented a higher canopy openness, tree height, lower tree density and diversity of fruit than secondary forests. Tree density and canopy openness were negatively correlated with bat species diversity and bat abundance, but bat abundance increased with fruit abundance and tree height. Hence, secondary forest management alters forests' structural characteristics and resource availability, and shapes the frugivorous bat community structure, and thereby the fruit consumption by bats.

Adaptive evolution of the myo6 gene in old world fruit bats (family: pteropodidae)

Myosin VI (encoded by the Myo6 gene) is highly expressed in the inner and outer hair cells of the ear, retina, and polarized epithelial cells such as kidney proximal tubule cells and intestinal enterocytes. The Myo6 gene is thought to be involved in a wide range of physiological functions such as hearing, vision, and clathrin-mediated endocytosis. Bats (Chiroptera) represent one of the most fascinating mammal groups for molecular evolutionary studies of the Myo6 gene. A diversity of specialized adaptations occur among different bat lineages, such as echolocation and associated high-frequency hearing in laryngeal echolocating bats, large eyes and a strong dependence on vision in Old World fruit bats (Pteropodidae), and specialized high-carbohydrate but low-nitrogen diets in both Old World and New World fruit bats (Phyllostomidae). To investigate what role(s) the Myo6 gene might fulfill in bats, we sequenced the coding region of the Myo6 gene in 15 bat species and used molecular evolutionary analyses to detect evidence of positive selection in different bat lineages. We also conducted real-time PCR assays to explore the expression levels of Myo6 in a range of tissues from three representative bat species. Molecular evolutionary analyses revealed that the Myo6 gene, which was widely considered as a hearing gene, has undergone adaptive evolution in the Old World fruit bats which lack laryngeal echolocation and associated high-frequency hearing. Real-time PCR showed the highest expression level of the Myo6 gene in the kidney among ten tissues examined in three bat species, indicating an important role for this gene in kidney function. We suggest that Myo6 has undergone adaptive evolution in Old World fruit bats in relation to receptor-mediated endocytosis for the preservation of protein and essential nutrients.

Insectivory in Fijian flying foxes (Pteropodidae)

We used scat and isotope analyses to assess insectivory in Fijian flying foxes (Pteropodidae), seeking insights into niche partitioning of co-occurring bat species with high plant diet overlap. Moth scales were most common in scats of Notopteris macdonaldi (87%; P. tonganus: 62%; Pteropus samoensis: 36%) and may indicate shared resources. The small and highly manoeuvrable N. macdonaldi exploited nectar-rich flowers also favoured by moths (e.g. Barringtonia spp.). Other invertebrate remains were most frequent in scats of P. tonganus (69%). On the basis of scat results and ecological observations, P. tonganus uses a combination of insectivory and a highly varied plant diet to obtain sufficient nutrients. Scats of P. samoensis contained few invertebrate remains, but abundant protein-rich plant species (including Freycinetia spp.), and juveniles seemed to consume moths frequently. Clustered δ15N and δ13C for N. macdonaldi and P. samoensis indicated a narrower dietary breadth than that of P. tonganus. P. tonganus juveniles appeared at a significantly higher trophic level than did adults, probably the result of milk consumption and/or higher rates of protein synthesis. The methods used detected little evidence that bats partitioned resources vertically. This study generates hypotheses for the further examination of flying-fox diets.

Sexual dimorphism in Sturnira lilium (Chiroptera, Phyllostomidae): can pregnancy and pup carrying be responsible for differences in wing shape?

Competition is one of the most cited mechanisms to explain secondary sexual dimorphism in animals. Nonetheless, it has been proposed that sexual dimorphism in bat wings is also a result of adaptive pressures to compensate additional weight caused by fetus or pup carrying during the reproductive period of females. The main objective of this study is to verify the existence of sexual dimorphism in Sturnira lilium wings. We employed geometric morphometrics techniques using anatomical landmarks superimposition to obtain size (Centroid Size) and shape variables of wings, which were reduced by Linear Discriminant Analysis (LDA). We also employed classical morphometrics using wing length measurements to compare efficiency between these two morphometric approaches and make comparisons using wing area measurements. LDA indicated significant differences between wing shapes of males and females, with 91% (stepwise classification) and 80% (leave-one-out cross validation) of correct classification. However, the size variable obtained did not contribute to such classifications. We have observed larger areas in female wings, but we found no differences in wing length measurements and no allometric effects in wing length, shape and area measurements. Interestingly, our study has provided evidences of morphological differences where classical morphometrics have failed. LDA and area measurements analyses revealed that females have a different area distribution in distinct portions of the wing, with wider dactylopatagia and plagiopatagia, and wingtips more triangular than males. No differences in body length or relative wing length were observed between the sexes, but pregnant females have more body weight than non-pregnant females and males. Our findings suggest that sexual dimorphism in the wing shape of S. lilium is probably related to the increase in flight efficiency of females during reproductive period. It decreases wing loading in specific portions of the wing and reduces energy cost to maintain a faster and maneuverable flight.

Scramble or contest competition over food in solitarily foraging mouse lemurs (Microcebus spp.): New insights from stable isotopes

The relationships between resource distribution, type of competition, and consequences for social organization have been formalized in the socioecological model (SEM) which predicts that ecological factors are the main determinants of female distribution. We tested this basic prediction in two solitary primates (Microcebus berthae and M. murinus) which differ in female association patterns. Using stable nitrogen and carbon isotope data of hair samples and food sources we quantified inter-specific differences in diet. delta(13)C in M. berthae reflected a diet composed mainly of insect secretions. Higher within-species as well as seasonal variation in delta(13)C of M. murinus indicated a wider trophic niche including plant and animal source food. Constantly elevated delta(15)N in M. murinus most likely reflected extended torpor during the lean season. This energy-saving strategy together with a wider, more opportunistic feeding niche might reduce female competition in this species, facilitating smaller female ranges, and a higher association potential. In contrast, delta(15)N fluctuated seasonally in M. berthae, most likely indicating varying amounts of arthropod food in the diet. Intense scramble competition over small and seasonally limited resources might lead to female spatial avoidance and a reduced association potential in M. berthae. Thus, differences in female association patterns between these two solitary foragers are due to different types of competition and overall intensities of intra-specific competition.

Drinking and flying: does alcohol consumption affect the flight and echolocation performance of phyllostomid bats?

Background

In the wild, frugivorous and nectarivorous bats often eat fermenting fruits and nectar, and thus may consume levels of ethanol that could induce inebriation. To understand if consumption of ethanol by bats alters their access to food and general survival requires examination of behavioural responses to its ingestion, as well as assessment of interspecific variation in those responses. We predicted that bats fed ethanol would show impaired flight and echolocation behaviour compared to bats fed control sugar water, and that there would be behavioural differences among species.

Methodology/Principal Findings

We fed wild caught Artibeus jamaicensis, A. lituratus, A. phaeotis, Carollia sowelli, Glossophaga soricina, and Sturnira lilium (Chiroptera, Phyllostomidae) sugar water (44 g of table sugar in 500 ml of water) or sugar water with ethanol before challenging them to fly through an obstacle course while we simultaneously recorded their echolocation calls. We used bat saliva, a non-invasive proxy, to measure blood ethanol concentrations ranging from 0 to >0.3% immediately before flight trials. Flight performance and echolocation behaviour were not significantly affected by consumption of ethanol, but species differed in their blood alcohol concentrations after consuming it.

Conclusions/Significance

The bats we studied display a tolerance for ethanol that could have ramifications for the adaptive radiation of frugivorous and nectarivorous bats by allowing them to use ephemeral food resources over a wide span of time. By sampling across phyllostomid genera, we show that patterns of apparent ethanol tolerance in New World bats are broad, and thus may have been an important early step in the evolution of frugivory and nectarivory in these animals.

The structure of a food web in a tropical rain forest in Malaysia based on carbon and nitrogen stable isotope ratios

Carbon and nitrogen stable isotope ratios (δ13C and δ15N) have been used to study the structure of food webs. However, few studies have examined how a terrestrial food web can be depicted by this technique. We measured δ13C and δ15N in various consumers of four trophic groups (detritivores, herbivores, omnivores and predators), including vertebrates and invertebrates (14 orders, ≥24 families), as well as canopy and understorey leaves in a tropical rain forest in Malaysia. We found that δ13C and δ15N of the consumers differed significantly among the trophic groups. The predators had significantly higher δ13C than the herbivores, and were similar in δ13C to the detritivores, suggesting that most predators examined depend largely on below-ground food webs. δ15N was higher in predators than detritivores by about 3‰. The comparison of δ13C in plant materials and herbivores suggests that most herbivores are dependent on C fixed in the canopy layers. The vertebrates had significantly higher δ15N and δ13C than the invertebrates of the same trophic group, likely reflecting differences in the physiological processes and/or feeding habits. This study indicates that stable isotope techniques can help better understanding of the terrestrial food webs in terms of both trophic level and the linkage of above- and below-ground systems.

Nutrient routing in omnivorous animals tracked by stable carbon isotopes in tissue and exhaled breath

Omnivorous animals feed on several food items that often differ in macronutrient and isotopic composition. Macronutrients can be used for either metabolism or body tissue synthesis and, therefore, stable C isotope ratios of exhaled breath (delta(13)C(breath)) and tissue may differ. To study nutrient routing in omnivorous animals, we measured delta(13)C(breath) in 20-g Carollia perspicillata that either ate an isotopically homogeneous carbohydrate diet or an isotopically heterogeneous protein-carbohydrate mixture. The delta(13)C(breath) converged to the delta(13)C of the ingested carbohydrates irrespective of whether proteins had been added or not. On average, delta(13)C(breath) was depleted in (13)C by only ca. -2 per thousand in relation to the delta(13)C of the dietary carbohydrates and was enriched by +8.2 per thousand in relation to the dietary proteins, suggesting that C. perspicillata may have routed most ingested proteins to body synthesis and not to metabolism. We next compared the delta(13)C(breath) with that of wing tissue (delta(13)C(tissue)) in 12 free-ranging, mostly omnivorous phyllostomid bat species. We predicted that species with a more insect biased diet--as indicated by the N isotope ratio in wing membrane tissue (delta(15)N(tissue))--should have higher delta(13)C(tissue) than delta(13)C(breath) values, since we expected body tissue to stem mostly from insect proteins and exhaled CO(2) to stem from the combustion of fruit carbohydrates. Accordingly, delta(13)C(tissue) and delta(13)C(breath) should be more similar in species that feed predominantly on plant products. The species-specific differences between delta(13)C(tissue) and delta(13)C(breath) increased with increasing delta(15)N(tissue), i.e. species with a plant-dominated diet had similar delta(13)C(tissue) and delta(13)C(breath) values, whereas species feeding at a higher trophic level had higher delta(13)C(tissue) than delta(13)C(breath) values. Our study shows that delta(13)C(breath) reflect the isotope ratio of ingested carbohydrates, whereas delta(13)C of body tissue reflect the isotope ratio of ingested proteins, namely insects, supporting the idea of isotopic routing in omnivorous animals.

Effect of forest use on trophic levels of small mammals: an analysis using stable isotopes

The degradation of tropical forests is progressing rapidly and its ecological effects on wild animals are a global concern. We evaluated the hypothesis that small mammals in highly degraded forest occupy higher trophic levels than those in somewhat degraded forests, as indicated by diets high in consumers such as insects, in a tropical rain forest in Sarawak, Malaysia. After correcting for differences in the δ15N values for primary production among the study sites, the δ15Ncorrected values for rats and mice (Muridae) differed significantly among forest types. Rats and mice in more degraded forest had higher δ15Ncorrected values than those in less degraded or primary forest; in contrast, treeshrews (Tupaiidae) and squirrels (Sciuridae) showed no significant differences in the δ15Ncorrected values among forest types. We found significant positive correlations between canopy openness and the δ15Ncorrected values for one species of squirrel and two species of rats. This hypothesis was supported for small mammals that have normal dietary preferences for plants, i.e., omnivorous rodents, but not for those that normally prefer insects, i.e., treeshrews. The δ15N values for omnivorous mammals may be useful as an indicator of changes in food-web structure in response to forest disturbance.

The influence of ambient temperature and the energy and protein content of food on nitrogenous excretion in the Egyptian fruit bat (Rousettus aegyptiacus)

The diets of frugivorous and nectarivorous vertebrates contain much water and generally have high energy but low protein contents. Therefore, we tested the prediction that to save energy under conditions of high energy demands and high water intake, frugivorous Egyptian fruit bats (Rousettus aegyptiacus) will increase both the absolute quantity and the proportion of ammonia in their urine. We also examined whether such changes occur when protein intake is low and water intake is high. We did three feeding trials. In trials 1 and 2, bats were fed one of four liquid diets containing constant soy protein concentrations but varying in sucrose concentration and were kept at ambient temperatures (T(a)) of 30 degrees Celsius and 12 degrees Celsius, respectively. In trial 3, bats were kept at Ta=12 degrees Celsius and fed one of four liquid diets with equal sucrose concentrations but varying protein concentrations. In trial 1, food intake at a sucrose concentration of 256 mmol/kg H(2)O was initially high but decreased to a constant rate with further increases in sucrose concentration, while in trial 2, food intake decreased exponentially with increasing sucrose concentration. As predicted, at 12 degrees Celsius with varying sucrose concentration, both the absolute quantity and the fraction of ammonia in the bats' urine increased significantly with food intake (P<0.02), while the absolute quantity of urea and the fraction of urea nitrogen excreted decreased significantly with food intake (P<0.03). Varying sucrose concentration had no significant effect on nitrogen excretion at Ta=30 degrees Celsius. Varying protein concentration had no significant effect on nitrogen excretion at Ta=12 degrees Celsius. We suggest that Egyptian fruit bats can increase ammonia excretion in response to increased energetic demands, and we calculate that they can save energy equal to approximately 2% of their daily metabolic rate by doing so.