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

Oxidative Stress and Antioxidant Defense in the Heart, Liver, and Kidney of Bat Species with Different Feeding Habits

The aim of this study was to compare the oxidative metabolism of four neotropical bat species with different feeding habits and investigate the relationship between their feeding habits and oxidative status. In terms of oxidative damage, our findings revealed major differences among the four bat species. In particular, hematophagous bats had lower levels of oxidative damage in the heart but higher levels in the liver. Nectarivorous bats had lower levels of carbonyl groups in the kidneys compared to insectivorous and hematophagous bats. The activity of various antioxidant and non-antioxidant enzymes in the heart, liver, and kidney also showed significant differences among the bat species. H2O2 consumption was lower in the heart of hematophagous bats, while insectivorous bats exhibited the highest enzymatic activity in the kidney. SOD activity was lower in the heart of hematophagous bats and lower in nectarivorous bats in the liver. Fumarase activity was higher in the heart of frugivorous/insectivorous and lower in nectarivorous/hematophagous bats. GPx activity was higher in the heart of nectarivorous/insectivorous and higher in the kidney of insectivorous bats. GST activity was higher in the heart of nectarivorous and lower in hematophagous bats. The correlation analysis between oxidative markers and enzymatic/non-enzymatic antioxidants in the heart, liver, and kidney exhibited distinct patterns of correlations due to variations in antioxidant defense mechanisms and oxidative stress responses in different organs. The observed differences in oxidative damage, antioxidant enzyme activities, and correlations between oxidative markers and antioxidants highlight the adaptability and complexity of the antioxidant defense systems in these bats. Each organ appears to have specific demands and adaptations to cope with oxidative stress based on its physiological functions and exposure to dietary components. Our results have major significance for the conservation and management of bats, which are threatened species despite being crucial components of ecosystems. Our study's implications go beyond bat biology and offer valuable insights into comparative oxidative physiology.

Morphological specialization to nectarivory in Phyllostomus discolor (Wagner, 1843) (Chiroptera: Phyllostomidae)

Dedicated nectarivory is a derived feeding habit that requires specialized cranial and soft-tissue morphologies to extract nectar from flowers. Nectarivory has evolved many times in terrestrial vertebrates, and in four bat families (Pteropodidae, Phyllostomidae, Vespertilionidae, and Mystacinidae). Within phyllostomids, specializations to nectarivory have been well documented in two subfamilies, Glossophaginae and Lonchophyllinae. However, nectarivory has also evolved independently in the genus Phyllostomus (subfamily Phyllostominae). Since Phyllostomus species have an omnivorous diet with a high consumption of nectar, they can be used to explore the basic morphological modifications linked to evolving a nectarivorous habit. Here, we focused on describing and comparing the morphological features potentially associated with nectarivory in Phyllostomus discolor. We present the first detailed tongue and palate morphological descriptions for P. discolor and perform skull morphometric analysis including 10 species. We found hair-like papillae on the tongue of P. discolor, a convergent feature with Glossophaginae and nectarivorous Pteropodids; these papillae likely confer an advantage when feeding on nectar. P. discolor does not show skull morphological features characteristic of nectarivorous bats, such as a long and narrow snout. We pose that the consumption of a variety of food, such as hard insects and fruits, and the large size of P. discolor relative to specialized nectarivores may create trade-offs against morphological specialization of the skull towards nectarivory. In contrast, a long and mobile tongue with hair-like papillae may be an evolutionary solution for nectar extraction that does not have a major impact on this species' ability to feed on other resources.

Using eDNA metabarcoding to understand the effect of fire on the diet of small mammals in a woodland ecosystem

Food acquisition is a fundamental process that drives animal distribution and abundance, influencing how species respond to changing environments. Disturbances such as fire create significant shifts in available dietary resources, yet, for many species, we lack basic information about what they eat, let alone how they respond to a changing resource base. In order to create effective management strategies, faunal conservation in flammable landscapes requires a greater understanding of what animals eat and how this change following a fire. What animals eat in postfire environments has received little attention due to the time‐consuming methodologies and low‐resolution identification of food taxa. Recently, molecular techniques have been developed to identify food DNA in scats, making it possible to identify animal diets with enhanced resolution. The primary aim of this study was to utilize eDNA metabarcoding to obtain an improved understanding of the diet of three native Australian small mammal species: yellow‐footed antechinus (Antechinus flavipes), heath mouse (Pseudomys shortridgei), and bush rat (Rattus fuscipes). Specifically, we sought to understand the difference in the overall diet of the three species and how diet changed over time after fire. Yellow‐footed antechinus diets mostly consisted of moths, and plants belonging to myrtles and legume families while bush rats consumed legumes, myrtles, rushes, and beetles. Heath mouse diet was dominated by rushes. All three species shifted their diets over time after fire, with most pronounced shifts in the bush rats and least for heath mice. Identifying critical food resources for native animals will allow conservation managers to consider the effect of fire management actions on these resources and help conserve the species that use them.

Utility of carbon and nitrogen stable isotopes for inferring wild bee (Hymenoptera: Apoidea) use of adjacent foraging habitats

Isotope analysis has proven useful for understanding diets of animals that are difficult to track for extended periods. Bees are small yet highly mobile and often forage from multiple habitats. However, current methods of assessing diet are limited in scope. Efficient methods of tracking bee diets that integrate across life stages, distinguish habitat use, and are sensitive to taxonomic differences will inform conservation strategies. We evaluated the utility of stable isotope analysis for estimating contributions of adjacent habitats to bees’ diets. We also investigated taxonomic variation in bee and flower isotope composition. We measured natural abundance of carbon and nitrogen stable isotopes in two body regions from three wild bee genera, as well as in 25 species of flowers that likely comprised their diets. Bee ∂13C and ∂15N varied with habitat and taxonomic groups (conflated with month), but did not match spatial or seasonal trends in their food plants. Flower ∂13C was lowest in the forest and in April–June, as expected if driven by water availability. However, bee ∂13C was elevated in the spring, likely from overwintering nutritional stress or unpredictable food availability. Bumble bees (Bombus) were enriched in ∂15N compared to others, possibly reflecting differences in larval feeding. Bee diet mixing models had high variation and should be interpreted with caution. Models estimated similar habitat contributions to diets of spring Andrena and overwintered Bombus queens. Summer Bombus queens and workers were indistinguishable. Sweat bees (Halictus) were estimated to use comparatively more field flowers than others. Overall, taxon more strongly influenced isotope composition than either foraging habitat or month, likely because of associated differences in sociality and timing of annual activity. Future studies seeking to reveal bee diets by isotope analysis may gain better resolution in more isotopically distinct habitats, in conjunction with controlled feeding or isotope labeling experiments.

The Use of Intrinsic Markers for Studying the Migratory Movements of Bats

Mortality of migratory bat species at wind energy facilities is a well-documented phenomenon, and mitigation and management are partially constrained by the current limited knowledge of bat migratory movements. Analyses of biochemical signatures in bat tissues ("intrinsic markers") can provide information about the migratory origins of individual bats. Many tissue samples for intrinsic marker analysis may be collected from living and dead bats, including carcasses collected at wind energy facilities. In this paper, we review the full suite of available intrinsic marker analysis techniques that may be used to study bat migration, with the goal of summarizing the current literature and highlighting knowledge gaps and opportunities. We discuss applications of the stable isotopes of hydrogen, oxygen, nitrogen, carbon, sulfur; radiogenic strontium isotopes; trace elements and contaminants; and the combination of these markers with each other and with other extrinsic markers. We further discuss the tissue types that may be analyzed for each and provide a synthesis of the generalized workflow required to link bats to origins using intrinsic markers. While stable hydrogen isotope techniques have clearly been the leading approach to infer migratory bat movement patterns across the landscape, here we emphasize a variety of lesser used intrinsic markers (i.e., strontium, trace elements, contaminants) that may address new study areas or answer novel research questions.

Agave flower visitation by pallid bats, Antrozous pallidus, in the Chihuahuan Desert

Pallid bats, Antrozous pallidus, despite being primarily insectivorous gleaning predators, consume nectar of the cardón cactus, Pachycereus pringlei, in the Sonoran Desert. It is unknown whether nectar feeding occurs in the Chihuahuan Desert of Texas, where pallid bats covered in pollen have been captured. We collected pollen samples from 67 pallid bats in Brewster County, Texas, United States, between April and August 2018. Pollen-covered pallid bats were captured in every month sampled. Pollen densities were three times higher on wings than on the head or ventral body. In all samples collected, the pollen was homogeneous and identified as Agave pollen. Although two species of Agave, A. havardiana and A. lechuguilla, occur in this region of Texas, linear discriminant analysis classified 701 of 723 (97%) of pollen grains analyzed as A. lechuguilla. Additional evidence from infrared video footage collected in August 2018 indicated that pallid bats became covered in A. lechuguilla pollen while consuming nectar. Pallid bats might be engaging in facultative nectarivory across their range and could be important nocturnal pollinators.

Mesquite bugs, other insects, and a bat in the diet of pallid bats in southeastern Arizona

The pallid bat (Antrozous pallidus) is a species of western North America, inhabiting ecoregions ranging from desert to oak and pine forest. They are primarily insectivorous predators on large arthropods that occasionally take small vertebrate prey, and are at least seasonally omnivorous in certain parts of their geographic range where they take nectar from cactus flowers and eat cactus fruit pulp and seeds. Until recently, mesquite bugs were primarily tropical-subtropical inhabitants of Mexico and Central America but have since occupied the southwestern United States where mesquite trees occur. Using a noninvasive method, we investigated the bats' diet at the Cienega Creek Natural Preserve, Arizona, by collecting food parts discarded beneath three night roosts in soil-piping cavities in a mesquite bosque. We also made phenological and behavioral observations of mesquite bugs, Thasus neocalifornicus, and their interactions with the mesquite trees. We determined that the bats discarded inedible parts of 36 species in 8 orders of mainly large-bodied and nocturnal insects below the night-roosts. In addition, one partial bat wing represents probable predation upon a phyllostomid bat, Choeronycteris mexicana. About 17 of the insect taxa are newly reported as prey for pallid bats, as is the bat C. mexicana. The majority of culled insect parts (88%) were from adult mesquite bugs. Mesquite bug nymphs did not appear in the culled insect parts. After breeding in late summer, when nighttime low temperatures dropped below 21 °C, the adult bugs became immobile on the periphery of trees where they probably make easy prey for opportunistic foliage-gleaning pallid bats. Proximity of night-roosts to mesquite bug habitat probably also enhances the bats' exploitation of these insects in this location.

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.

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.