Biology subjects

Mitchell, C.

Publications and source records attributed to Mitchell, C..

At least 19 recordsLinked to original sources

bioRxiv2026

Sperm length ornamentation associates with survival and sterility after heatwaves among Drosophila species

Whether sexual selection facilitates or hinders adaptation to novel environments is a question of fundamental importance due to current rapid environmental change. Using phylogenetic comparative analysis in 42 Drosophila species, we found that sperm length - a sexually selected ornament - positively associates with the ability of males to survive high temperatures. However, the ability to remain fertile does not increase with sperm length to the same extent, meaning that longer sperm species experience a larger gap between temperatures that kill and temperatures that sterilize males. The findings are consistent with the idea that strong sexual selection on condition-dependent exaggerated traits may facilitate somatic resilience to environmental stressors, but that susceptibility to heat-induced infertility may be a cost of extreme sperm ornamentation. Overall, the data suggests multifaceted links between postcopulatory sexual selection and climate change.

evolutionary biology↗

bioRxiv2026

Epigenetic and brain age across development: Performance and associations in the MIND consortium

Understanding how biological age measures perform across development lays the groundwork for investigations into lifespan trajectories of healthy aging. We provide the most comprehensive assessment of epigenetic and brain age models across development (birth to 24 years; [≤]20,917 observations across 15 cohorts), evaluating how these models associate with chronological age and with each other, and how these associations change across development. Chronological age-prediction accuracy of epigenetic and brain age models was modest and varied substantially. Accuracy improved with age and stabilized by middle childhood. Few brain and fewer epigenetic clocks performed stably and well across all developmental stages. Performance was better when age range and tissue corresponded between training and testing data. Associations between epigenetic-brain age residuals were small, and changed little across development, tissues or clock generation. Given this developmentally dynamic system of epigenetic-brain age performances and associations, we give key recommendations to improve developmental research in this field.

neuroscience↗

bioRxiv2026

Widespread occurrence of bovine-like and new viruses in wild deer across the United States

Over the past several decades, deer populations in North America have grown considerably, resulting in frequent contact with humans and livestock, and increased potential for pathogen spillover. Despite the importance of pathogen spillover among humans, wildlife, and livestock, the diversity of viruses present in deer remains largely unknown. Using a metagenomic high-throughput sequencing approach, we characterized viral communities in the upper respiratory tracts of live mule deer (Odocoileus hemionus) and white-tailed deer (Odocoileus virginianus) captured at fourteen study sites in nine states across the United States. We identified vertebrate-infecting viruses in both deer species at all but two of the study sites, located in Illinois and Utah. Viral richness did not vary among species or study sites. However, viral community composition was different across study sites but not among deer species. Amongst the detected viral sequences, several originate from or were closely related to viruses previously described in humans (e.g., severe acute respiratory syndrome coronavirus 2) and livestock (e.g., bovine-like coronavirus). We also documented viruses recently discovered in deer, such as CHeRI orbivirus 1. Finally, we identified several new putative viruses in the Picornaviridae, Rhabdoviridae and Tobaniviridae families, including a novel Aphthovirus related to bovine rhinitis A virus in both deer species, across seven states and nine study sites. Our findings expand the understanding of viral diversity in two deer species across the United States, providing important insights for managing pathogens at the wildlife, livestock, and human interface.

microbiology↗

bioRxiv2026

Rapid plastid isolation reveals the chloroplast proteome and structures of the chlororibosome large subunit and RuBisCO in Marchantia polymorpha

Plastids house the biology of eukaryotic photosynthesis. While 1000s of plastid genomes have been sequenced, the availability of less than ten proteomes and only two species with full 70S plastid ribosomal structures limit our understanding of plant evolution. We optimized a protocol for the rapid isolation of Marchantia polymorpha plastids that provides a highly enriched and intact organelle fraction from gradient volumes as little as 2 mL. The approach was successfully applied to six other species. Focusing on M. polymorpha, we determined the proteome of the plastid fraction, identifying 1337 nuclear-encoded proteins with a high confidence, where 83% belong to orthologs shared with angiosperms. We further isolated protein complexes by RNA affinity purification using poly-lysine and provide the high-resolution structures of the 50S subunit of the chloroplast ribosome and RuBisCO using cryogenic EM and image reconstruction to 2.23 and 2.12 [A] resolution, respectively. For plastids, our data show that the genome reduction event experienced by the bryophyte common ancestor has had little impact on the organelles complexity and they underscore a high level of structural conservation of key components. Our data provide novel resources to explore the functional evolution of plastid proteomes and major macromolecular complexes of cyanobacterial origin.

plant biology↗

bioRxiv2026

Structure determination and dual targeting of a plant TACO1 identifies its ancient role as an organelle translation regulator

Ribosome stalling caused by polyproline (PPs) motifs is common. Their translation is enhanced by accessory proteins such as YebC in bacteria, whose homolog, TRANSLATIONAL ACTIVATOR OF CYTOCHROME C OXIDASE 1 (TACO1), aids the translation of mitochondria-encoded proteins. The prevalence of PP motifs across plastid-encoded genes and their impact on the translation of photosynthesis-relevant proteins remains unexplored. Equally, a translation-enhancer of PP motifs equivalent to TACO1 for plastid ribosomes has not been reported. Here, we show that plastid genomes encode 24 proteins with a minimum of one PP motif on average, half of which are conserved in their cyanobacterial homologs, and that the vast majority of eukaryotes, including plants, encode a single TACO1 that we demonstrate to be dually targeted to mitochondria and plastids of Marchantia polymorpha. We resolved the MpTACO1 structure at 2.34 [A] by X-ray crystallography and the flexibility by small-angle X-ray scattering. Through modelling, we demonstrate that MpTACO1 can fit into the peptidyl transfer centre of plant chlororibosomes in a similar manner as human TACO1 in the mitoribosome. The identification and structure determination of the first plastid-targeted YebC/TACO1 allows us to sketch a unified model for the function and evolution of this ancient family of ribosomal accessory proteins, underscoring their indispensable role in the translation of bioenergetic membrane proteins reaching back almost 4 billion years. HighlightsO_LIDozens of GC-rich polyproline (PP) encoding regions are retained by AT-rich genomes C_LIO_LIPP motif conservation hints at regulatory mechanisms and required translation pauses C_LIO_LIChloroplast targeting of a (mitochondrial) translation enhancer of PP motifs C_LIO_LIMpTACO1 structure at 2.34 [A] resolution demonstrates its high level of conservation C_LI

plant biology↗

bioRxiv2026

An Observational Study of the Impact of Systemic B-cell Depletion on Cervicovaginal Mucosal Environment

ImportanceEmerging data show that B-cell depleting chemotherapies, which are increasingly used to treat autoimmune disorders and multiple sclerosis, can be associated with mucosal side effects such as inflammatory vaginitis. ObjectiveEvaluate the impact of rituximab treatment on vaginal mucosal immune markers, endocervical immune cell populations and vaginal microbiome. DesignCross-sectional observational study conducted between 2022 - 2024. SettingAcademic medical center, Boston Massachusetts. ParticipantsWe enrolled women aged >18 years who were either 1) receiving rituximab for autoimmune renal disease or were 2) healthy controls ExposureTreatment with rituximab, an anti CD20 monoclonal antibody. Main outcome and measureWe compared endocervical immune cell populations, vaginal fluid immune markers, vaginal fluid immunoglobulins and vaginal microbiome composition between individuals being treated with rituximab and healthy controls. ResultsWe enrolled 26 women treated with rituximab for autoimmune renal disease and 26 healthy controls. Median circulating and endocervical B-cell and plasma cell proportions were significantly lower in treated participants compared to controls. Median vaginal fluid IgA concentrations were significantly lower in participants treated with rituximab, while ILE, IgM, IgG1, IgG2, IgG3 and IgG4 were not different between groups. Total T cell frequencies were similar between groups, but the proportion of activated T cells (CD4+CD38+HLADR+) was significantly lower in people treated with rituximab. Concentrations of IL10, IL13, IL17, IL21, IL23, IL4, ITAC and TNFa were elevated in vaginal fluid from the rituximab group, while IL-8 was lower. A CST-IV-C, low-Lactobacillus pattern of vaginal microbiota was more common in the rituximab group. Conclusions and RelevanceSystemic B-cell depletion is associated with reduced vaginal fluid IgA, a more diverse microbiome composition, and increases in many vaginal fluid immune markers compared to healthy controls. The reduction in vaginal fluid IgA may provide opportunities for vaginal bacteria to induce inflammation. Key pointsO_ST_ABSQuestionC_ST_ABSHow does circulating B-cell depletion impact the vaginal microenvironment? FindingsIn this cross-sectional study of 52 women, B cell and plasma cell proportions were significantly lower in both blood and vaginal mucosa among rituximab-treated participants compared to healthy controls. Vaginal IgA concentrations, but not other immunoglobulins, were significantly lower in rituximab treated participants. In treated participants, vaginal cytokine concentrations were elevated, and microbiome composition shifted toward non-Lactobacillus-dominant communities. In six people with inflammatory vaginitis, both circulating and endocervical B cells were lowest in people with the most severe symptoms. MeaningSystemic B cell depletion is associated with alterations in vaginal mucosal immune markers and microbiome composition which increase local inflammation.

immunology↗

bioRxiv2026

Developmental Correlates of Epigenetic and Polygenic Indices of Cognition and Educational Attainment from Birth to Young Adulthood

Large-scale genomic studies have identified biomarkers of adult cognitive functioning and educational attainment, yet the developmental pathways connecting these biomarkers to adult outcomes remain unclear. Drawing on four cohorts, we examined the developmental correlates of an epigenetic index of adult cognitive function ( Epigenetic-g) alongside polygenic indices of cognition and education. Epigenetic-g and polygenic indices were uncorrelated and captured distinct variation in childrens cognitive and academic performance. Longitudinal analyses revealed that Epigenetic-g is plastic in early childhood, reaching moderate stability by adolescence, and, unlike polygenic indices, is not related to longitudinal cognitive growth. Twin models indicated that Epigenetic-g captures genetic and unique environmental variation relevant to cognitive and academic achievement that is not identified by current polygenic indices. Epigenetic indices relevant to psychological development can be generated from DNA methylation studies of adults, with most variation in these indices emerging early in life.

genomics↗

bioRxiv2026

Differential Methylation by Early Life Adversity in the Future of Families Child Wellbeing Study

Early life adversity (ELA) has a well-established link to mental health disorders later in life, yet the molecular mechanisms behind this relationship are incompletely understood. The Future of Families Child Wellbeing Study (FFCWS) provides an opportunity to examine experience encoding in the genome through functional changes in DNA methylation (DNAm) in a cohort enriched in subjects exposed to ELA. We investigated epigenome-wide differences in DNAm across thirteen early-life exposures in salivary samples from FFCWS participants. We calculated differential methylation associations with disease-linked genetic variants, evaluated tissue-specific gene expression, and assessed the persistence of DNAm changes from ages 9 to 15 years. Using data from the mSTARR-seq assay, we characterized methylation-dependent regulatory activity. Differential methylation in the FFCWS validated prior results and identified new genomic regions associated with child adversity. Differential methylation occurs in genomic regions likely to impact gene expression, and affected genes are expressed in disease-relevant tissues. We also identified association of genetic variants associated with downstream disorders near differential methylation, including depression, alcohol and substance use, and anxiety disorders. Overall, cumulative ELA is associated with specific DNAm changes, functional regulation, and persistence over time. Our findings indicate that ELA-associated differential methylation in the FFCWS does not simply occur at random, but in genomic regions that are functional. Our results support the conclusion that altered DNAm represents a biological link between early life experience and later health outcomes.

genomics↗

bioRxiv2026

Brain Age in Conduct Disorder: A Mega-Analysis of the ENIGMA Antisocial Behavior Working Group

Conduct disorder (CD) is the leading global cause of mental health burden in children and adolescents and has recently been hypothesized to be a neurodevelopmental disorder. Although prior research has identified neuroanatomical differences associated with CD, it remains unclear whether these differences reflect atypical brain development. Here, we investigated the difference between an individuals brain age and chronological age as a proxy for variations in brain maturation. Using a pretrained model, we estimated brain age from structural neuroimaging data obtained from 1,119 youth with CD and 1,183 typically developing controls across 14 international cohorts participating in the ENIGMA-Antisocial Behavior Working Group. Youth with CD exhibited a statistically robust but small acceleration in brain age compared to typically developing youth (around 0.50 years), which was restricted to the adolescence-onset subtype of the disorder. Our large-scale, coordinated analysis provides the first evidence of accelerated neurodevelopment as a potential mechanism underlying CD.

neuroscience↗

bioRxiv2025

Seasonal assembly of the phyllosphere fungal microbiome of a perennial grass is robust to nutrient addition

The leaf microbiome plays an important role in plant health and defense. Despite its importance, how the assembly of the leaf microbial community is modified by environmental conditions such as nutrient availability remains relatively uninvestigated. Soil nutrient availability may shift the outcome of microbial interactions within a host individual or influence the pool of microbes across the plant community. We hypothesized that leaf microbial diversity would increase across the season as leaves collect additional taxa, and that this seasonal assembly would be sensitive to nutrient addition. To assess this, we tracked the assembly of the fungal phyllosphere microbiome of the grass tall fescue (Lolium arundinaceum) in old-field vegetation over the growing season and experimentally tested whether the seasonality of the microbiome was modified by experimental addition of soil nutrients. Fungal diversity (Shannon diversity index, richness, and evenness) increased early in the season, with most metrics saturating before the end of the season. Community composition as measured by Bray-Curtis dissimilarity also shifted over the early and mid-growing season. Phylogeny-based machine-learning identified fungal lineages that were abundant in different seasons, linking seasonal community shifts to their evolutionary context. Nutrient addition was less important than time of season, but still significantly altered community composition and interacted with time to influence richness, with lowest richness in the low nutrient addition plots early in the season. The clear seasonality of the microbiome provides support for a dynamic phyllosphere microbiome, suggesting further studies manipulating fungal recruitment over the season. Furthermore, it highlights the robustness of seasonal assembly to variation in nutrient availability.

ecology↗

bioRxiv2025

Transmission Dynamics of Eastern Equine Encephalitis Infection Rates: The Role of Avian Host Stage and Differential Mosquito Exposure

Eastern equine encephalitis virus (EEEV) is a deadly arboviral pathogen with 30% severe case fatality. EEEV exhibits pronounced 2-3 year cyclical outbreak patterns in the northeastern United States, linked to shifts in mosquito feeding preferences between hatch-year and adult avians. We developed an age-structured vector-host model incorporating differential feeding patterns of Culiseta melanura mosquitoes on European Starlings and American Robins. Global sensitivity analysis revealed mosquito biting rate (a) as the dominant driver in transmission, with avian infectivity ({delta}) and exposure () playing secondary roles. Pairing tree-based machine learning algorithms with SHAP analysis on 100,000 parameter sets identified parameter hierarchies that govern cyclic transmission. Adult avian mortality ({micro}a) was identified as the key parameter underlying cyclic and stable transmission patterns. SHAP further revealed these patterns to be grounded on opposite sides of the same epidemiological mechanism. Stable endemics emerge from demographic stability paired with transmission optimization, while cyclic endemics emerge from demographic instability paired with minimal transmission optimization. Numerical simulations illustrated critical threshold dynamics at 0.2 [≤] [≤] 0.4, where heightened hatch-year exposure triggers demographic instability responsible for observed 2-3 year cycles, while balanced exposure ( {approx} 0.5) leads to stable endemics. These mechanisms provide a foundation for targeted surveillance and control interventions.

systems biology↗

bioRxiv2024

Current Reporting Practices in Human Neuroscience Research

Concerns for the replicability, reliability, and generalizability of human neuroimaging research have led to intense debates over sample size and open science practices, with more recent attention on the contributions of sampling and recruitment practices. Key to understanding the state of neuroscience research is an assessment of reporting practices that influence replicability, reliability, and generalizability. In this structured review, we evaluated reporting practice across three domains: (1) demographic (e.g., reporting participant race-ethnicity, age, any measure of socioeconomic position), (2) methodological (e.g., reporting recruitment methods, inclusion and exclusion criteria, why participants were excluded from analyses), and (3) open science and generalizability (e.g., analyses were preregistered, target population was stated). Included were 919 published MRI and fMRI studies from 2019 in nine top-ranked journals (N = 3,856 records screened). Reporting across domains was infrequent, with participant racial or ethnic identity (14.8%), reasons for missing imaging data (31.2%), and identification of a target population (19.4%) being particularly low/underreported. Reporting likelihood varied by study characteristics (e.g., participant age group) and was correlated across domains. The median sample size of studies was 55 participants. Study sample size, reporting frequency, was positively associated with two-year citation counts, providing some evidence that the complete reporting of demographic characteristics, methodological decisions, and open science and generalizability practices may not be as valued as study sample size. Recommendations for structural interventions at the journal level are proposed.

neuroscience↗

bioRxiv2024

Increased listening effort and cochlear neural degeneration underlie behavioral deficits in speech perception in noise in normal hearing middle-aged adults.

Middle age represents a critical period of accelerated brain changes and provides a window for early detection and intervention in age-related neurological decline. Hearing loss is a key early marker of such decline and is linked to numerous comorbidities in older adults. Yet, [~]10% of middle-aged individuals who report hearing difficulties show normal audiograms. Cochlear neural degeneration (CND) could contribute to these hidden hearing deficits, though its role remains unclear due to a lack of objective diagnostics and uncertainty regarding its perceptual outcomes. Here, we employed a cross-species design to examine neural and behavioral signatures of CND. We measured envelope following responses (EFRs) - neural ensemble responses to sound originating from the peripheral auditory pathway - in young and middle-aged adults with normal audiograms and compared these responses to young and middle-aged Mongolian gerbils, where CND was histologically confirmed. We observed near identical changes in EFRs across species that were associated with CND. Behavioral assessments revealed agerelated speech-in-noise deficits under challenging conditions, while pupil-indexed listening effort increased with age even when behavioral performance was matched. Together, these results demonstrate that CND contributes to speech perception difficulties and elevated listening effort in midlife, which may ultimately lead to listening fatigue and social withdrawal.

neuroscience↗

bioRxiv2024

Linked emergence of racial disparities in mental health and epigenetic biological aging across childhood and adolescence

Marginalization due to structural racism may confer an increased risk for aging-related diseases - in part - via effects on peoples mental health. Here we leverage a prospective birth cohort study to examine whether the emergence of racial disparities in mental health and DNA-methylation measures of biological aging (i.e., DunedinPACE, GrimAge Acceleration, PhenoAge Acceleration) are linked across childhood and adolescence. We further consider to what extent racial disparities are statistically accounted for by perinatal and postnatal factors in preregistered analyses of N=4,898 participants from the Future of Families & Child Wellbeing Study, of which N=2,039 had repeated saliva DNA methylation at ages 9 and 15 years. We find that racially marginalized children had higher levels of externalizing and internalizing behaviors and diverging longitudinal internalizing slopes. Black compared to White identifying children, children living in more racially segregated neighborhoods, and racially marginalized children more affected by colorism tended to have higher age-9 levels of biological aging and more biological age acceleration over adolescence. Notably, longitudinal increases in internalizing and externalizing behavior were correlated with longitudinal increases in biological aging. While racial and ethnic disparities in mental health were largely statistically accounted for by socioeconomic variables, racial differences in biological aging were often still visible beyond covariate controls. Our findings indicate that racial disparities in mental health and biological aging are linked and emerge early in life. Programs promoting racial health equity must address the psychological and physical impacts of structural racism in children. Comprehensive measures of racism are lacking in current population cohorts.

genomics↗

bioRxiv2024

Rapid and objective assessment of auditory temporal processing using dynamic amplitude-modulated stimuli

Auditory neural coding of speech-relevant temporal cues can be noninvasively probed using envelope following responses (EFRs), neural ensemble responses phase-locked to the stimulus amplitude envelope. EFRs emphasize different neural generators, such as the auditory brainstem or auditory cortex, by altering the temporal modulation rate of the stimulus. EFRs can be an important diagnostic tool to assess auditory neural coding deficits that go beyond traditional audiometric estimations. Existing approaches to measure EFRs use discrete amplitude modulated (AM) tones of varying modulation frequencies, which is time consuming and inefficient, impeding clinical translation. Here we present a faster and more efficient framework to measure EFRs across a range of AM frequencies using stimuli that dynamically vary in modulation rates, combined with spectrally specific analyses that offer optimal spectrotemporal resolution. EFRs obtained from several species (humans, Mongolian gerbils, Fischer-344 rats, and Cba/CaJ mice) showed robust, high-SNR tracking of dynamic AM trajectories (up to 800Hz in humans, and 1.4 kHz in rodents), with a fivefold decrease in recording time and thirtyfold increase in spectrotemporal resolution. EFR amplitudes between dynamic AM stimuli and traditional discrete AM tokens within the same subjects were highly correlated (94% variance explained) across species. Hence, we establish a time-efficient and spectrally specific approach to measure EFRs. These results could yield novel clinical diagnostics for precision audiology approaches by enabling rapid, objective assessment of temporal processing along the entire auditory neuraxis.

neuroscience↗

bioRxiv2023

Prot-SCL: State Of The Art Prediction Of Protein Subcellular Localization From Primary Sequence Using Contrastive Learning

Protein subcellular localization is a critically important parameter to consider when designing expression constructs and production strategies for industry scale protein production. In this study, we present Prot-SCL an innovative self-supervised machine learning approach to predict protein subcellular localization exclusively from primary sequence. The models herein were learned from a dataset of subcellular localizations derived by exhaustively analyzing the Uniprot database. The set of localization data was rigorously curated for machine learning by employing group sampling following clustering of the protein sequences. The novel component of this approach lies in the development of a triplet neural network architecture capable of generating meaningful embeddings for classification of protein subcellular localization. We observed a robust predictive power for our classical gradient boosted machine learning models trained on these triplet embeddings in both cross validation and in generalization to the testing set. Importantly, we have made this extensive dataset of protein subcellular localizations publicly accessible, facilitating future, need-based, localization studies. Finally, we provide the relevant codebase to encourage a wider adoption and expansion of this methodology. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=123 SRC="FIGDIR/small/555932v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1d9b205org.highwire.dtl.DTLVardef@1368c23org.highwire.dtl.DTLVardef@2a88edorg.highwire.dtl.DTLVardef@8380b7_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

bioRxiv2022

G Protein-Coupled Receptor Kinase-2 (GRK-2) regulates exploration through neuropeptide signaling in Caenorhabditis elegans

Animals alter their behavior in manners that depend on environmental conditions as well as their developmental and metabolic states. For example, C. elegans is quiescent during larval molts or during conditions of satiety. By contrast, worms enter an exploration state when removed from food. Sensory perception influences movement quiescence (defined as a lack of body movement), as well as the expression of additional locomotor states in C. elegans that are associated with increased or reduced locomotion activity, such as roaming (exploration behavior) and dwelling (local search). Here we find that movement quiescence is enhanced, and exploration behavior is reduced in G protein-coupled receptor kinase grk-2 mutant animals. grk-2 was previously shown to act in chemosensation, locomotion, and egg-laying behaviors. Using neuron-specific rescuing experiments, we show that GRK-2 acts in multiple ciliated chemosensory neurons to control exploration behavior. grk-2 acts in opposite ways from the cGMP-dependent protein kinase gene egl-4 to control movement quiescence and exploration behavior. Analysis of mutants with defects in ciliated sensory neurons indicates that grk-2 and the cilium-structure mutants act in the same pathway to control exploration behavior. We find that GRK-2 controls exploration behavior in an opposite manner from the neuropeptide receptor NPR-1 and the neuropeptides FLP-1 and FLP-18. Finally, we show that secretion of the FLP-1 neuropeptide is negatively regulated by GRK-2 and that overexpression of FLP-1 reduces exploration behavior. These results define neurons and molecular pathways that modulate movement quiescence and exploration behavior. Author summaryMany modulatory neurotransmitters affect behavior by binding to G protein-coupled receptors (GPCRs) and initiating signals that modify neuronal activity. GPCRs are regulated by G protein-coupled receptor kinases (GRKs). GRKs phosphorylate and promote the inactivation of GPCRs. Here we identify GRK-2 as a regulator of distinct locomotor states in C. elegans. We find that GRK-2 acts in olfactory sensory neurons to promote exploration and suppress movement quiescence. Additionally, we show that GRK-2 acts in opposition to a neuropeptide signaling pathway that acts in interneurons. Thus, this study demonstrates critical roles for GRK-2 in regulating neuromodulatory signaling and locomotor behavior.

genetics↗

bioRxiv2021

The price of defence: toxins, visual signals and oxidative state in an aposematic butterfly

In a variety of aposematic species, the conspicuousness of an individuals warning signal and the quantity of its chemical defence are positively correlated. This apparent honest signalling is predicted by resource competition models which assume that the production and maintenance of aposematic defences compete for access to antioxidant molecules that have dual functions as pigments and in protecting against oxidative damage. We raised monarch butterflies (Danaus plexippus) on their milkweed host-plants (Apocynaceae) with increasing quantities of cardenolides to test whether (1) the sequestration of secondary defences is associated with costs in the form of oxidative lipid damage and reduced antioxidant defences; and (2) that reduced oxidative state can decrease the capacity of individuals to produce aposematic displays. In male monarchs conspicuousness was explained by an interaction between oxidative damage and sequestration: males with high levels of oxidative damage become less conspicuous with increased sequestration of cardenolides, whereas those with low oxidative damage become more conspicuous with increased levels of cardenolides. There was no significant effect of oxidative damage or concentration of sequestered cardenolides on female conspicuousness. Our results demonstrate a physiological linkage between the production of coloration and protection from autotoxicity, and differential costs of signalling in monarch butterflies.

evolutionary biology↗