A physiological perspective on nectar-feeding adaptation in phyllostomid bats

Evaluation of Octopus maya enzyme activity of the digestive gland and gastric juice

As the demand for Octopus maya grows, sustainable farming practices become essential to prevent overexploitation, so that farming can be developed as a sustainable alternative to traditional fishing. Understanding the digestive dynamics of the octopus is essential for devising optimal dietary formulations in aquaculture. Despite the progress in understanding cephalopod digestion, little is known about the specific functioning of the digestive enzymes responsible for breaking down protein substrates. This knowledge gap underscores the need for further research to support sustainable O. maya population management. In this paper, dietary formulations are identified for cephalopods by characterizing O. maya digestive enzymes present in the digestive gland and gastric juice. The investigation revealed that acidic proteases showed a peak activity at higher temperatures than alkaline proteases. Inhibitors confirmed the presence of H, L, and D cathepsins. The lower activation energy of alkaline enzymes compared to acidic ones observed highlights an intriguing aspect of O. maya's digestive physiology. This research provides valuable insights into O. maya digestive enzyme functions, representing a significant advancement in formulating diets crucial for successful octopus farming that may help to fully understand its physiology.

Dying of thirst: Osmoregulation by a hawkmoth pollinator in response to variability in ambient humidity and nectar availability

Climate-induced shifts in flowering phenology can disrupt pollinator-floral resource synchrony, especially in desert ecosystems where rainfall dictates both. However, baseline metrics to gauge pollinator health in the wild amidst rapid climate change are lacking. Our laboratory-based study establishes a baseline for pollinator physiological state by exploring how osmotic conditions influence survivorship in a desert hawkmoth pollinator, Manduca sexta. We sampled hemolymph osmolality from over 1000 lab-grown moths at 20 %, 50 %, and 80 % ambient humidity levels. Starved moths maintained healthy osmolality of 350-400 mmol/kg for 1-3 days after eclosion regardless of ambient humidity, but it sharply rose to 550 mmol/kg after 4-5 days in low and moderate humidity, and after 5 days in high humidity. Starved moths in low humidity conditions perished within 5 days, while those in high humidity survived twice as long. Moths fed synthetic Datura wrightii nectar, synthetic Agave palmeri nectar, or water, maintained osmolality within a healthy range of 350-400mmol/kg. The same was true for moths fed authentic floral nectars from Datura and Agave plants, although moths consumed more synthetic than authentic nectars, possibly due to non-sugar constituents. Simulating a 4-day mismatch between pollinator emergence and nectar availability, a single nectar meal osmotically rescued moths under dry ambient conditions. Our findings highlight hemolymph osmolality as a rapid and accurate biomarker distinguishing dehydrated from hydrated states in insect pollinators.

Large-scale genome sampling reveals unique immunity and metabolic adaptations in bats

Comprising more than 1,400 species, bats possess adaptations unique among mammals including powered flight, unexpected longevity, and extraordinary immunity. Some of the molecular mechanisms underlying these unique adaptations includes DNA repair, metabolism and immunity. However, analyses have been limited to a few divergent lineages, reducing the scope of inferences on gene family evolution across the Order Chiroptera. We conducted an exhaustive comparative genomic study of 37 bat species, one generated in this study, encompassing a large number of lineages, with a particular emphasis on multi-gene family evolution across immune and metabolic genes. In agreement with previous analyses, we found lineage-specific expansions of the APOBEC3 and MHC-I gene families, and loss of the proinflammatory PYHIN gene family. We inferred more than 1,000 gene losses unique to bats, including genes involved in the regulation of inflammasome pathways such as epithelial defence receptors, the natural killer gene complex and the interferon-gamma induced pathway. Gene set enrichment analyses revealed genes lost in bats are involved in defence response against pathogen-associated molecular patterns and damage-associated molecular patterns. Gene family evolution and selection analyses indicate bats have evolved fundamental functional differences compared to other mammals in both innate and adaptive immune system, with the potential to enhance antiviral immune response while dampening inflammatory signalling. In addition, metabolic genes have experienced repeated expansions related to convergent shifts to plant-based diets. Our analyses support the hypothesis that, in tandem with flight, ancestral bats had evolved a unique set of immune adaptations whose functional implications remain to be explored.

Discrimination of small sugar concentration differences helps the nectar-feeding bat Leptonycteris yerbabuenae cover energetic demands

Every day nectar-feeding animals face an energetic challenge during foraging: they must locate and select flowers that provide nectar with adequate amounts of sugar to cover their very high energy needs. To understand this decision-making process, it is crucial to know how accurately sugar concentration differences can be discriminated. In a controlled laboratory setting, we offered the nectar-specialist bat Leptonycteris yerbabuenae the choice between different sugar solutions covering the entire concentration range of bat-pollinated plants (3-33%). When feeding on solutions below 10% sugar concentration, L. yerbabuenae were unable to cover their energetic demands because of physiological constraints. Their ability to discriminate sugar concentrations was better than that of any other nectar-feeding animal studied to date. At sugar concentrations below 15%, L. yerbabuenae can discriminate solutions differing by only 0.5%. The bats may utilize this fine-tuned ability to select nectar from flowers with reward qualities that provide them with the necessary amount of energy to survive.

Gut reaction! Neotropical nectar-feeding bats responses to direct and indirect costs of extreme environmental temperatures

One of the consequences of anthropogenic climate change is an increase in the frequency and intensity of extreme weather events. These events have caused mass mortality of different species of wildlife, including bats. In this study, we exposed two species of neotropical nectar-feeding bats that live in contrasting environmental conditions (A. geoffroyi and L. yerbabuenae) to extreme high and low temperatures while offering them diets with different energy content. This experimental approach allowed us to determine their thermal and behavioral responses, and to identify environmental conditions that impose high physiologic costs to these species. To determine how bats' responded, we monitored both changes in their body masses and skin temperatures. Both bat species responded differently, with L. yerbabuenae spending more time in normothermia at high temperatures than A. geoffroyi. While both species presented torpor, they used it differently. Torpor allowed A. geoffroyi to maintain and increase body mass at intermediate and low ambient temperatures. At the same time, L. yerbabuenae used torpor only when facing cold ambient temperatures and low-quality food. Understanding the mechanisms that allow species to face changes in their environment is essential given the current climate trends and the fact that the loss of these species could have significant negative consequences in tropical and subtropical ecosystems.

Genomic consequences of dietary diversification and parallel evolution due to nectarivory in leaf-nosed bats

BACKGROUND

The New World leaf-nosed bats (Phyllostomids) exhibit a diverse spectrum of feeding habits and innovations in their nutrient acquisition and foraging mechanisms. However, the genomic signatures associated with their distinct diets are unknown.

RESULTS

We conducted a genomic comparative analysis to study the evolutionary dynamics related to dietary diversification and specialization. We sequenced, assembled, and annotated the genomes of five Phyllostomid species: one insect feeder (Macrotus waterhousii), one fruit feeder (Artibeus jamaicensis), and three nectar feeders from the Glossophaginae subfamily (Leptonycteris yerbabuenae, Leptonycteris nivalis, and Musonycteris harrisoni), also including the previously sequenced vampire Desmodus rotundus. Our phylogenomic analysis based on 22,388 gene families displayed differences in expansion and contraction events across the Phyllostomid lineages. Independently of diet, genes relevant for feeding strategies and food intake experienced multiple expansions and signatures of positive selection. We also found adaptation signatures associated with specialized diets: the vampire exhibited traits associated with a blood diet (i.e., coagulation mechanisms), whereas the nectarivore clade shares a group of positively selected genes involved in sugar, lipid, and iron metabolism. Interestingly, in fruit-nectar-feeding Phyllostomid and Pteropodids bats, we detected positive selection in two genes: AACS and ALKBH7, which are crucial in sugar and fat metabolism. Moreover, in these two proteins we found parallel amino acid substitutions in conserved positions exclusive to the tribe Glossophagini and to Pteropodids.

CONCLUSIONS

Our findings illuminate the genomic and molecular shifts associated with the evolution of nectarivory and shed light on how nectar-feeding bats can avoid the adverse effects of diets with high glucose content.

Salt has contrasting effects on the digestive processing of dilute nectar by two Neotropical nectarivorous bats

Nectarivorous vertebrates might include sugar-dilute nectar in their diet and they are expected to undergo compensatory feeding. However, physiological constraints might limit the intake of sugar-dilute nectar, affecting energy budgets. Among other physiological processes, the limiting role of osmoregulation is supported by enhanced intake rate of dilute sugar solutions by avian nectarivores when salt is added. We tested if the Greater Antillean Long-tongued bat (Monophyllus redmani) and the Brown flower bat (Erophylla sezekorni) compensated energy intake when fed dilute-sugar solutions (2.5 and 5% sucrose), and if salt content (11, 20 and 40 mM NaCl l^-1) modulated the intake rate of these solutions. Both species were unable to compensate intake of solutions with varying sugar densities, and energy intake on the 2.5 and 5% diets was lower than on the most concentrated diets (10, 20 and 30% sucrose). Both species responded differently to the addition of salt. Salt addition did not affect the intake of 2.5% sugar solutions by the Greater Antillean Long-tongued bat, and it decreased the intake of 5% sugar solutions. In contrast, the Brown flower bat increased the intake of 2.5 and 5% sugar solutions when salt was added. Intake responses to varying sugar densities of our two focal species and that of other bat species previously studied indicate that they are not uniform and that they might be modulated by digestive and osmoregulatory physiological traits.

Fecal microbiota of different reproductive stages of the central population of the lesser-long nosed bat, Leptonycteris yerbabuenae

In this study we analyzed the microbiota composition of fecal samples from the lesser-long nosed bat Leptonycteris yerbabuenae in different reproductive stages (juveniles and adult bats of both sexes as well as pregnant and lactating females). The V4 region of the 16s rRNA gene from 33 individuals was analyzed using alpha and beta diversity metrics. We found that microbiota diversity (expressed in Amplicon Sequence Variants) is higher in pregnant and lactating females. The microbiota of the juveniles and non-reproductive adults was dominated by Gammaproteobacteria and Firmicutes. Reproductive females had a much more diverse microbiota, with a significant increase in phyla such as Bacteroidetes and Alphaproteobacteria. There was no difference in fecal microbiota diversity between pregnant and lactating females and juveniles and non-reproductive adults. Results suggest that differences in microbiota diversity are related to reproduction. We infer that males maintain stable microbiota composition because they do not undergo the large physiological changes that females do during reproduction and maintain a more specialized diet throughout all life stages.

Effect of diet quality and ambient temperature on the use of torpor by two species of neotropical nectar-feeding bats

Neotropical bats use torpor as a strategy to save energy when they experience a low energy intake and/or low ambient temperature (T_a). Digestive physiology limits the energy intake of several glossophaginid bats, and could play an important role in the onset of torpor in these tropical animals. We measured the effect that diet quality and T_a had on the use of torpor by the nectar-feeding bats Glossophaga soricina and Leptonycteris yerbabuenae Captive bats were fed with 5% (low) or 35% (high) sucrose solutions while exposed to two different T_a (17.7 and 23.2°C; low T_a and high T_a) in four different treatments: (1) high sucrose:high T_a, (2) high sucrose:low T_a, (3) low sucrose:high T_a and (4) low sucrose:low T_a We measured their energy intake, changes in body mass (ΔM_b) and skin temperature (T_skin) as response variables. Energy intake (in 10 h) was limited when both species fed on 5% sucrose, but body mass gain was only affected in G. soricina. Energy intake and T_a had a negative effect on the minimum T_skin of both species, and ΔM_b affected the time that G. soricina used torpor. Both species remained normothermic on the high sucrose:high T_a treatment, but used torpor on the other three treatments. Bats used torpor during their resting and activity periods. Leptonycteris yerbabuenae spent more time in torpor in the low sucrose:high T_a treatment, while G. soricina used this strategy for longer periods of time in the high sucrose:low T_a treatment. We found that diet quality and T_a played an important role in the use of torpor by nectar-feeding bats.

Bayesian hierarchical models suggest oldest known plant-visiting bat was omnivorous

The earliest record of plant visiting in bats dates to the Middle Miocene of La Venta, the world's most diverse tropical palaeocommunity. Palynephyllum antimaster is known from molars that indicate nectarivory. Skull length, an important indicator of key traits such as body size, bite force and trophic specialization, remains unknown. We developed Bayesian models to infer skull length based on dental measurements. These models account for variation within and between species, variation between clades, and phylogenetic error structure. Models relating skull length to trophic level for nectarivorous bats were then used to infer the diet of the fossil. The skull length estimate for Palynephyllum places it among the larger lonchophylline bats. The inferred diet suggests Palynephyllum fed on nectar and insects, similar to its living relatives. Omnivory has persisted since the mid-Miocene. This is the first study to corroborate with fossil data that highly specialized nectarivory in bats requires an omnivorous transition.

Digestive capacity predicts diet diversity in Neotropical frugivorous bats

1. Predicting the diet diversity of animals is important to basic and applied ecology. Knowledge of diet diversity in animals helps us understand niche partitioning, functional diversity and ecosystem services such as pollination, pest control and seed dispersal. 2. There is a negative relationship between the length of the digestive tract and diet diversity in animals; however, the role of digestive physiology in determining diet diversity has been ignored. This is especially important in vertebrates with powered flight because, unlike non-flying vertebrates, they have limitations that may constrain gut size. 3. Here, we evaluate the relationship between digestive capacity and diet diversity in Carollinae and Stenodermatinae frugivorous bats. These bats disperse the seeds of plants that are key to Neotropical forest regeneration. 4. Our results show that digestive capacity is a good predictor of diet diversity in Carollinae and Stenodermatinae frugivorous bats (R(2) = 0·77). 5. Surprisingly, the most phylogenetically closely related species were not similar in their digestive capacity or diet diversity. The lack of a phylogenetic signal for the traits evaluated implies differences in digestive physiology and diet in closely related species. 6. Our results highlight the predictive usefulness of digestive physiology for understanding the feeding ecology of animals.

Digestive capacities allow the Mexican long-nosed bat (Leptonycteris nivalis) to live in cold environments

Digestive capabilities of nectar-feeding vertebrates to assimilate sugars affect their ability to acquire and store energy and could determine the minimal temperatures at which these animals can survive. Here, we described the sugar digestive capability of Leptonycteris nivalis and related it with its capacity to live in cold environments. We measured the enzymatic activity, food intake rate and changes in body mass of bats feeding at four different sucrose concentrations (from 5 to 35% wt./vol.). Additionally, we used a mathematical model to predict food intake and compared it with the food intake of bats. L. nivalis was able to obtain ~111.3kJ of energy regardless of the sugar concentration of their food. Also, bats gained ~2.57g of mass during the experimental trials and this gain was independent of sugar concentration. The affinity (1/Km) of sucrase (EC 3.2.1.48) was one order of magnitude higher relative to that reported for its sister species Leptonycteris yerbabuenae (0.250 and 0.0189mmol(-1)L, respectively), allowing this species to have a higher energy intake rate. We propose that the high ability to acquire energy conferred L. nivalis the faculty to invade cold environments, avoiding in this way the ecological competition with its sympatric species L. yerbabuenae.