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Dyer, K.

Publications and source records attributed to Dyer, K..

9 recordsLinked to original sources
bioRxiv2026

Adapting flow cytometry for studying immune cell seasonality in wild migratory bats

Identifying the drivers of wildlife immunity is critical for assessing stressor impacts and zoonotic risks. However, such studies are limited by logistical challenges of wildlife research and lack of species-specific reagents. We adapt flow cytometry, typically confined to laboratory settings, to field settings to profile cellular immunity with small blood volumes and extended sample holding times. We apply these methods to analyze immune cell seasonality in migratory Mexican free-tailed bats (Tadarida brasiliensis). We confirmed four antibodies recognizing CD3, CD79a, MHCII, and CD11b that were originally validated in Egyptian fruit bats (Rousettus aegyptiacus), allowing us to quantify T and B cells, macrophages, and neutrophils, respectively. Flow cytometry outperformed hematology in quantifying leukocyte profiles and revealed pronounced immune cell seasonality. Adaptive cells steadily increased between spring and fall migration. Neutrophils were most abundant during the reproductive period and decreased during migrations, whereas B cells were most abundant after reproduction and before fall migration; granulocytes as a whole, macrophages, and T cells had no seasonality. Females had more B cells than males but did not differ in other cells. Our findings lay the groundwork for applying flow cytometry to field studies of wildlife and provide important insights into the seasonality of bat immunity.

ecology↗
bioRxiv2025

Habitat and seasonal drivers of leukocyte profiles within and across Neotropical bat species

Land conversion is a widespread form of environmental change that can alter infection dynamics in wildlife by modifying host immune defense. Such effects may be compounded by seasonal variation in resources and reproduction and differ among members of a host community, yet the combined effects of habitat, season, and species identity on wildlife immunity remain poorly understood. We tested within- and across-species effects of land conversion and seasonality on immunity in Neotropical bats by quantifying hematological markers of physiological stress and inflammation. We sampled seven species across a large forest preserve and smaller nearby forest fragment in northern Belize during the dry and wet seasons. Using phylogenetic generalized linear mixed models, we tested overall effects of habitat and season and quantified per-species impacts. Total leukocyte counts and neutrophil-to-lymphocyte ratios showed no overall habitat or seasonal effects but had strong species-specific responses to these predictors. In contrast, the systemic inflammation response index was higher across species in the dry season and in the smaller fragment, suggesting poor health in unfavorable conditions. Species-specific effects did not align with diet guilds, indicating potential roles for finer-scale ecological traits. Our results highlight the complex, species-dependent effects of environmental change on wildlife immunity.

ecology↗
bioRxiv2024

Geographically widespread and novel hemotropic mycoplasmas and bartonellae in Mexican free-tailed bats and sympatric North American bat species

Bacterial pathogens remain poorly characterized in bats, especially in North America. We describe novel (and in some cases panmictic) hemoplasmas (10.5% positivity) and bartonellae (25.5% positivity) across three colonies of Mexican free-tailed bats (Tadarida brasiliensis), a partially migratory species that can seasonally travel hundreds of kilometers. Molecular analyses identified three novel Candidatus hemoplasma species most similar to another novel Candidatus species in Neotropical molossid bats. We also detected novel hemoplasmas in sympatric cave myotis (Myotis velifer) and pallid bats (Antrozous pallidus), with sequences in the latter 96.5% related to C. Mycoplasma haemohominis. We identified nine Bartonella genogroups, including those in cave myotis with 96.7% similarity to C. Bartonella mayotimonensis. We also detected Bartonella rochalimae in migratory Mexican free-tailed bats, representing the first report of this human pathogen in the Chiroptera. The seasonality and diversity of these bacteria observed here suggest that additional longitudinal, genomic, and immunological studies in bats are warranted.

ecology↗
bioRxiv2023

Investigating the phylogenetic history of toxin tolerance in mushroom-feeding Drosophila

Understanding how and when key novel adaptations evolved is a central goal of evolutionary biology. Within the immigrans-tripunctata radiation of Drosophila, many mushroom-feeding species are tolerant of host toxins, such as cyclopeptides, that are lethal to nearly all other eukaryotes. In this study, we used phylogenetic and functional approaches to investigate the evolution of cyclopeptide tolerance in the immigrans-tripunctata radiation of Drosophila. We first inferred the evolutionary relationships among 48 species in this radiation using 978 single copy orthologs. Our results resolved previous incongruities within species groups across the phylogeny. Second, we expanded on previous studies of toxin tolerance by assaying 16 of these species for tolerance to -amanitin and found that six of these species could develop on diet with toxin. Third, we examined fly development on a diet containing a natural mix of toxins extracted from the Death Cap Amanita phalloides mushroom. Both tolerant and susceptible species developed on diet with this mix, though tolerant species survived at significantly higher concentrations. Finally, we asked how cyclopeptide tolerance might have evolved across the immigrans-tripunctata radiation and inferred that toxin tolerance was ancestral and subsequently lost multiple times. Our results suggest the evolutionary history of cyclopeptide tolerance is complex, and simply describing this trait as present or absent does not fully capture the occurrence or impact on this adaptive radiation. More broadly, the evolution of novelty can be more complex than previously thought, and that accurate descriptions of such novelties are critical in studies examining their evolution.

evolutionary biology↗
bioRxiv2023

Expanded diversity of hemoplasmas in rare and undersampled Neotropical bats

Hemotropic mycoplasmas are emerging as a model system for studying bacterial pathogens in bats, but taxonomic coverage of sampled host species remains biased. We leveraged a long-term field study in Belize to uncover novel hemoplasma diversity in bats by analyzing 80 samples from 19 species, most of which are infrequently encountered. PCR targeting the partial 16S rRNA gene found 41% of bats positive for hemoplasmas. Phylogenetic analyses found two novel host shifts of hemoplasmas, four entirely new hemoplasma genotypes, and the first hemoplasma detections in four bat species. One of these novel hemoplasmas (from Neoeptesicus furinalis) shared 97.6% identity in the partial 16S rRNA gene to a human hemoplasma (Candidatus Mycoplasma haemohominis). Additional analysis of the partial 23S rRNA gene allowed us to also designate two novel hemoplasma species, in Myotis elegans and Phyllostomus discolor, with the proposed names Candidatus Mycoplasma haematomyotis sp. nov. and Candidatus Mycoplasma haematophyllostomi sp. nov., respectively. Our analyses show that additional hemoplasma diversity in bats can be uncovered by targeting rare or undersampled host species.

microbiology↗
bioRxiv2021

Using embedded alginate microparticles to tune the properties of in situ forming poly(N-isopropylacrylamide)-graft-chondroitin sulfate bioadhesive hydrogels for replacement and repair of the nucleus pulposus of the intervertebral disc

Low back pain (LBP) is a major public health issue associated with degeneration of the intervertebral disc (IVD). The early stages of degeneration are characterized by the dehydration of the central, gelatinous portion of the IVD, the nucleus pulposus (NP). One possible treatment approach is to replace the NP in the early stages of IVD degeneration with a hydrogel that restores healthy biomechanics while supporting tissue regeneration. The present study evaluates a novel thermosensitive hydrogel based on poly(N-isopropylacrylamide-graft-chondroitin sulfate) (PNIPAAM-g-CS) for NP replacement. The hypothesis was tested that the addition of freeze-dried, calcium crosslinked alginate microparticles (MPs) to aqueous solutions of PNIPAAm-g-CS would enable tuning of the rheological properties of the injectable solution, as well as the bioadhesive and mechanical properties of the thermally precipitated composite gel. Further, we hypothesized that the composite would support encapsulated cell viability and differentiation. Structure-material property relationships were evaluated by varying MP concentration and diameter. The addition of high concentrations (50 mg/mL) of small MPs (20 {+/-} 6 {micro}m) resulted in the greatest improvement in injectability, compressive mechanical properties, and bioadhesive strength of PNIPAAm-g-CS. This combination of PNIPAAM-g-CS and alginate MPs supported the survival, proliferation, and differentiation of adipose derived mesenchymal stem cells (ADMSCs) towards an NP-like phenotype in the presence of soluble GDF-6. When implanted ex vivo into the intradiscal cavity of degenerated porcine IVDs, the formulation restored the compressive and neutral zone (NZ) stiffnesses to intact values and resisted expulsion under lateral bending. Overall, results indicate the potential of the hydrogel composite to serve as a scaffold for supporting NP regeneration. This work uniquely demonstrates that encapsulation of re-hydrating polysaccharide-based MPs may be an effective method for improving key functional properties of in situ forming hydrogels for orthopaedic tissue engineering applications.

bioengineering↗
bioRxiv2020

Gut microbial genes are associated with neurocognition and brain development in healthy children

The gastrointestinal tract, its resident microorganisms, and the central nervous system are connected by bio-chemical signaling, also known as the "microbiome-gut-brain-axis." Both the human brain and the gut microbiome have critical developmental windows in the first years of life, raising the possibility that their development is co-occurring and likely co-dependent. Emerging evidence implicates gut microorganisms and microbiota composition in cognitive outcomes and neurodevelopmental disorders (e.g., autism and anxiety), but the influence of gut microbial metabolism on typical neurodevelopment has not been explored in detail. We investigated the relationship of the microbiome with the neuroanatomy and cognitive function of 361 healthy children, demonstrating that differences in gut microbial taxa and gene functions are associated with overall cognitive function and with differences in the size of multiple brain regions. Using a combination of multivariate linear and machine learning (ML) models, we showed that many species, including Gordonibacter pamelae and Blautia wexlerae, were significantly associated with higher cognitive function, while some species such as Ruminococcus gnavus were more commonly found in children with low cognitive scores after controlling for sociodemographic factors. Microbial genes for enzymes involved in the metabolism of neuroactive compounds, particularly short-chain fatty acids such as acetate and propionate, were also associated with cognitive function. In addition, ML models were able to use microbial taxa to predict the volume of brain regions, and many taxa that were identified as important in predicting cognitive function also dominated the feature importance metric for individual brain regions. For example, B. wexlerae was the most important species in models predicting the size of the parahippocampal region in both the left and right hemispheres, while several species from the phylum Bacteroidetes, including GABA-producing B. ovatus, were important for predicting the size of the left accumbens area, but not the right. These findings provide potential biomarkers of neurocognition and brain development and may lead to the future development of targets for early detection and early intervention.

microbiology↗
bioRxiv2018

Broad geographic sampling reveals predictable and pervasive seasonal adaptation in Drosophila

To advance our understanding of adaptation to temporally varying selection pressures, we identified signatures of seasonal adaptation occurring in parallel among Drosophila melanogaster populations. Specifically, we estimated allele frequencies genome-wide from flies sampled early and late in the growing season from 20 widely dispersed populations. We identified parallel seasonal allele frequency shifts across North America and Europe, demonstrating that seasonal adaptation is a general phenomenon of temperate fly populations. Seasonally fluctuating polymorphisms are enriched in large chromosomal inversions and we find a broad concordance between seasonal and spatial allele frequency change. The direction of allele frequency change at seasonally variable polymorphisms can be predicted by weather conditions in the weeks prior to sampling, linking the environment and the genomic response to selection. Our results suggest that fluctuating selection is an important evolutionary force affecting patterns of genetic variation in Drosophila.

evolutionary biology↗