Biology subjects

Welch, K. C.

Publications and source records attributed to Welch, K. C..

7 recordsLinked to original sources

bioRxiv2026

Novel modifications to fructose metabolism are associated with adaptation to high-sugar diets in bats

High-sugar diets in mammals are associated with a number of metabolic diseases including diabetes and obesity. However, frugivorous and nectivorous bats specialize in consuming diets high in simple sugars while remaining healthy. To investigate the metabolic adaptations in bats with high-sugar diets, we conducted targeted metabolomics on blood samples collected during the first ten minutes after glucose or fructose feeding in five bat species whose natural diets vary in sugar content. By comparing changes in blood metabolite levels over time both between feeding treatments and across dietary guild, we have been able to identify shifts in sugar processing that likely support the healthy metabolism of simple sugars mammals with high-sugar diets. Notably, despite both sugars being readily absorbed, only fructose feeding induced significant changes in other metabolites within ten minutes after feeding. Species who naturally consume more sugar showed both faster production of metabolic intermediates and lowered production of common deleterious byproducts of fructose metabolism than species with comparatively lower-sugar diets. The prioritization and refinement of fructose metabolism is therefore likely a more key aspect of how bats with high-sugar diets are able to avoid the diseases typically associated with excessive sugar consumption than modifications to glucose metabolism.

physiology↗

bioRxiv2023

Learning when to learn: hummingbirds adjust their exploration behaviour to match the value of information

Exploration is a key part of an animals ability to learn. The exploration-exploitation dilemma predicts that individuals should adjust their exploration behaviour according to changes in the value of information. Here, we test this prediction by tracking ruby-throated hummingbirds as they foraged repeatedly from a large array of artificial flowers, wherein 25% of the flowers contained a sucrose reward. Similar to real-world floral dynamics, the reward locations were consistent in the short-term, but varied from day to day. Thus, the value of information about the flower contents would be greatest at the beginning of a daily foraging session, and decay toward the end of each session. We tracked five individual hummingbirds in repeated foraging sessions, comprising more than 3,400 floral probes. We analyzed two metrics of their exploration behaviour: (1) the probability that a bird would shift from probing one flower to another, and (2) the Shannon information entropy of a sequence of flowers probed. We show that initially, the hummingbirds increased their exploration behaviour as time elapsed within a session. As they performed more sessions and learned the rules of the environment, the hummingbirds switched to explore more diverse choices at the beginning of a foraging session, when the value of information was high, and less diverse choices toward the end of a session. Our results suggest that foraging hummingbirds can learn when to learn, highlighting the importance of plasticity in exploration behaviour. HighlightsO_LIExploration is a necessary part of learning C_LIO_LIForagers must balance sampling for information with the use of known rewards C_LIO_LIHummingbirds learned to explore more when the value of new information was high C_LIO_LIApparent mistakes may actually represent an information-seeking strategy C_LI

animal behavior and cognition↗

bioRxiv2022

Common insecticide affects spatial navigation in bats at environmentally-realistic doses

Bats are potentially exposed to pesticides via foraging in croplands. Common pesticides like organophosphates are neurotoxic for vertebrates and even low doses can impair essential processes such as locomotion and cognition. These sublethal effects are usually studied using molecular biomarkers with limited ecological relevance. Behavioral studies, in contrast, represent a more informative yet sensitive approach. Spatial navigation, for example, is an ecologically relevant behavior that is modulated by cellular pathways potentially targeted by neurotoxicants. We evaluated whether bats ability to memorize and navigate novel spaces was negatively affected by environmental relevant doses of chlorpyrifos, a common organophosphate insecticide. We also tested how the behavioral response correlated with molecular biomarkers. We orally dosed captive big brown bats (Eptesicus fuscus) with chlorpyrifos and studied exploratory behavior in two testing arenas. We evaluated similarity of stereotype flight trajectories in a flight tent, and associative memory in a Y-maze. We quantified brain cholinesterase (ChE) activity as a cellular biomarker and employed non-targeted proteomics as molecular biomarkers. Bats exposed to chlorpyrifos were less explorative and made more incorrect choices in the Y-maze, but the consistency of their flight trajectories was unaffected. Exposed bats had 30% lower ChE activity, showed down-regulation of proteins involved in memory (VP37D), learning and sound perception (NOX3). Other important nervous system processes such as synaptic function, plasticity, oxidative stress, and apoptosis were enriched in chlorpyrifos-exposed bats. These results support the sensitivity of behavior as a biomarker of toxicity and the importance of considering other levels of organization to help explain the mechanisms underlying altered behavior due to human activities.

pharmacology and toxicology↗

bioRxiv2022

Genomic insights into metabolic flux in ruby-throated hummingbirds

Hummingbirds are very well adapted to sustain efficient and rapid metabolic shifts. They oxidize ingested nectar to directly fuel flight when foraging but have to switch to oxidizing stored lipids derived from ingested sugars during the night or long-distance migratory flights. Understanding how this organism moderates energy turnover is hampered by a lack of information regarding how relevant enzymes differ in sequence, expression, and regulation. To explore these questions, we generated a chromosome level de novo genome assembly of the ruby-throated hummingbird (A. colubris) using a combination of long and short read sequencing and scaffolding using other existing assemblies. We then used hybrid long and short-read RNA-sequencing for a comprehensive transcriptome assembly and annotation. Our genomic and transcriptomic data found positive selection of key metabolic genes in nectivorous avian species and a deletion of critical genes (GLUT4, GCK) involved in glucostasis in other vertebrates. We found expression of fructose-specific GLUT5 putatively in place of insulin-sensitive GLUT4, with predicted protein models suggesting affinity for both fructose and glucose. Alternative isoforms may even act to sequester fructose to preclude limitations from transport in metabolism. Finally, we identified differentially expressed genes from fasted and fed hummingbirds suggesting key pathways for the rapid metabolic switch hummingbirds undergo.

genomics↗

bioRxiv2021

Reversal of the adipostat control of torpor during migration in hummingbirds

Many small endotherms use torpor to reduce metabolic rate and manage daily energy balance. However, the physiological "rules" that govern torpor use are unclear. We tracked torpor use and body composition in ruby-throated hummingbirds (Archilochus colubris), a long-distance migrant, throughout the summer using respirometry and quantitative magnetic resonance. During the mid-summer, birds entered torpor at consistently low fat stores ([~]5% of body mass), and torpor duration was negatively related to evening fat load. Remarkably, this energy-emergency strategy was abandoned in the late summer when birds accumulated fat for migration. Migrating birds were more likely to enter torpor on nights when they had higher fat stores, and fat gain was positively correlated with the amount of torpor used. These findings demonstrate the versatility of torpor throughout the annual cycle and suggest a fundamental change in physiological feedback between adiposity and torpor during migration. Moreover, this study highlights the underappreciated importance of facultative heterothermy in migratory ecology.

zoology↗

bioRxiv2021

Inter- and intra-specific variation in hair cortisol concentrations of Neotropical bats

Quantifying hair cortisol has become popular in wildlife ecology for its practical advantages for evaluating health. Before hair cortisol levels can be reliably interpreted however, it is key to first understand the intrinsic factors explaining intra- and interspecific variation. Bats are an ecologically diverse group of mammals that allow studying such variation. Given that many bat species are threatened or have declining populations in parts of their range, non-invasive tools for monitoring colony health and identifying cryptic stressors are needed to efficiently direct conservation efforts. Here we describe intra- and interspecific sources of variation in hair cortisol levels in 18 Neotropical bat species from Mexico and Belize. We found that fecundity is an important ecological trait explaining interspecific variation in bat hair cortisol. Other ecological variables such as colony size, roost durability, and basal metabolic rate did not explain hair cortisol variation among species. At the individual level, females exhibited higher hair cortisol levels than males, and the effect of body mass varied among species. Overall, our findings help validate and accurately apply hair cortisol as a monitoring tool in free-ranging bats.

ecology↗

bioRxiv2017

Single molecule, full-length transcript sequencing provides insight into the extreme metabolism of ruby-throated hummingbird Archilochus colubris

Hummingbirds can support their high metabolic rates exclusively by oxidizing ingested sugars, which is unsurprising given their sugar-rich nectar diet and use of energetically expensive hovering flight. However, they cannot rely on dietary sugars as a fuel during fasting periods, such as during the night, at first light, or when undertaking long-distance migratory flights, and must instead rely exclusively on onboard lipids. This metabolic flexibility is remarkable both in that the birds can switch between exclusive use of each fuel type within minutes and in that de novo lipogenesis from dietary sugar precursors is the principle way in which fat stores are built, sometimes at exceptionally high rates, such as during the few days prior to a migratory flight. The hummingbird hepatopancreas is the principle location of de novo lipogenesis and likely plays a key role in fuel selection, fuel switching, and glucose homeostasis. Yet understanding how this tissue, and the whole organism, achieves and moderates high rates of energy turnover is hampered by a fundamental lack of information regarding how genes coding for relevant enzymes differ in their sequence, expression, and regulation in these unique animals. To address this knowledge gap, we generated a de novo transcriptome of the hummingbird liver using PacBio full-length cDNA sequencing (Iso-Seq), yielding a total of 8.6Gb of sequencing data, or 2.6M reads from 4 different size fractions. We analyzed data using the SMRTAnalysis v3.1 Iso-Seq pipeline, including classification of reads and clustering of isoforms (ICE) followed by error-correction (Arrow). With COGENT, we clustered different isoforms into gene families to generate de novo gene contigs. We performed orthology analysis to identify closely related sequences between our transcriptome and other avian and human gene sets. We also aligned our transcriptome against the Calypte anna genome where possible. Finally, we closely examined homology of critical lipid metabolic genes between our transcriptome data and avian and human genomes. We confirmed high levels of sequence divergence within hummingbird lipogenic enzymes, suggesting a high probability of adaptive divergent function in the hepatic lipogenic pathways. Our results have leveraged cutting-edge technology and a novel bioinformatics pipeline to provide a compelling first direct look at the transcriptome of this incredible organism.

genomics↗