Biology subjects

Pelaez, J. N.

Publications and source records attributed to Pelaez, J. N..

5 recordsLinked to original sources

bioRxiv2025

Alternative Splicing in TRPA1 Drives Sensory Adaptation to Electrophiles in Drosophilids

Behaviors are among the first traits to evolve as animals enter new niches, but their molecular bases are poorly understood. To address this gap, we used the mustard-feeding drosophilid fly Scaptomyza flava, which feeds on toxic Brassicales plants like wasabi that produce noxious, electrophilic isothiocyanates (ITCs or mustard oils). We found that S. flava exhibits dramatically reduced behavioral sensitivity to allyl isothiocyanate (AITC) compared to its microbe-feeding relatives Scaptomyza pallida and Drosophila melanogaster. We hypothesized that molecular evolution of the "wasabi receptor" TRPA1, known to detect ITCs in flies, could explain this loss of aversion. Our experiments revealed three interconnected evolutionary genetic changes consistent with this hypothesis. First, TRPA1 was expressed in labellar tissues of S. flava at the lowest levels among the three species, at a nearly four-fold lower level than in D. melanogaster. Second, S. flava expressed a higher proportion of TRPA1 splice variants previously reported to be less sensitive to chemical stimulus. Third, we identified amino acid substitutions in S. flava that could influence the structure of intracellular domains of TRPA1. To test the functional salience of these mechanisms in vitro and in vivo, we validated TRPA1 splicing isoforms using Xenopus oocyte electrophysiology and the GAL4/UAS system in D. melanogaster. Single TRPA1 isoform electrophysiology in vitro revealed evolution of the channel in the S. flava lineage towards reduced electrophile sensitivity. Ectopic expression of S. flava TRPA1 in D. melanogaster also consistently conferred weaker AITC sensitivity in vivo than expression of its orthologues, although this did not fully recapitulate differences in wild-type phenotypes between species, suggesting other molecular mechanisms were involved. To address this, we explored the consequences of isoform co-expression using oocyte electrophysiology. We found that enrichment of electrophile-insensitive TRPA1 splicing isoforms as observed in the salient S. flava sensory organs additively reduced cellular responses to AITC, which could further contribute to reduced electrophile aversion. Our findings illuminate how expression differences, protein structural changes, and especially alternative splicing, together can drive sensory evolution as animals behaviorally adapt to toxic new niches.

evolutionary biology↗

bioRxiv2024

Taste evolution in an herbivorous drosophilid

Plant secondary metabolites pose a challenge for generalist herbivorous insects because they are not only potentially toxic, they also may trigger aversion. On the contrary, some highly specialized herbivorous insects evolved to use these same compounds as token stimuli for unambiguous determination of their host plants. Two questions that emerge from these observations are how recently derived herbivores evolve to overcome this aversion to plant secondary metabolites and the extent to which they evolve increased attraction to these same compounds. In this study, we addressed these questions by focusing on the evolution of bitter taste preferences in the herbivorous drosophilid Scaptomyza flava, which is phylogenetically nested deep in the paraphyletic Drosophila. We measured behavioral and neural responses of S. flava and a set of non-herbivorous species representing a phylogenetic gradient (S. pallida, S. hsui, and D. melanogaster) towards host- and non-host derived bitter plant compounds. We observed that S. flava evolved a shift in bitter detection, rather than a narrow shift towards glucosinolates, the precursors of mustard-specific defense compounds. In a dye-based consumption assay, S. flava exhibited shifts in aversion toward the non-mustard bitter, plant-produced alkaloids caffeine and lobeline, and reduced aversion towards glucosinolates, whereas the non-herbivorous species each showed strong aversion to all bitter compounds tested. We then examined whether these changes in bitter preferences of S. flava could be explained by changes in sensitivity in the peripheral nervous system and compared electrophysiological responses from the labellar sensilla of S. flava, S. pallida, and D. melanogaster. Using scanning electron microscopy, we also created a map of labellar sensilla in S. flava and S. pallida. We assigned each sensillum to a functional sensilla class based on their morphology and initial response profiles to bitter and sweet compounds. Despite a high degree of conservation in the morphology and spatial placement of sensilla between S. flava and S. pallida, electrophysiological studies revealed that S. flava had reduced sensitivity to glucosinolates to varying degrees. We found this reduction only in I type sensilla. Finally, we speculate on the potential role that evolutionary genetic changes in gustatory receptors between S. pallida and S. flava may play in driving these patterns. Specifically, we hypothesize that the evolution of bitter receptors expressed in I type sensilla may have driven the reduced sensitivity observed in S. flava, and ultimately, its reduced bitter aversion. The S. flava system showcases the importance of reduced aversion to bitter defense compounds in relatively young herbivorous lineages, and how this may be achieved at the molecular and physiological level.

evolutionary biology↗

bioRxiv2023

Evolution of chemosensory and detoxification gene families across herbivorous Drosophilidae

Herbivorous insects are exceptionally diverse, accounting for a quarter of all known eukaryotic species, but the genetic basis of adaptations that enabled this dietary transition remains poorly understood. Many studies have suggested that expansions and contractions of chemosensory and detoxification gene families - genes directly mediating interactions with plant chemical defenses - underlie successful plant colonization. However, this hypothesis has been challenging to test because the origins of herbivory in many lineages are ancient (>150 million years ago [mya]), obscuring genomic evolutionary patterns. Here, we characterized chemosensory and detoxification gene family evolution across Scaptomyza, a genus nested within Drosophila that includes a recently derived (<15 mya) herbivore lineage of mustard (Brassicales) specialists and carnation (Caryophyllaceae) specialists, and several non-herbivorous species. Comparative genomic analyses revealed that herbivorous Scaptomyza have among the smallest chemosensory and detoxification gene repertoires across 12 drosophilid species surveyed. Rates of gene turnover averaged across the herbivore clade were significantly higher than background rates in over half of the surveyed gene families. However, gene turnover was more limited along the ancestral herbivore branch, with only gustatory receptors and odorant binding proteins experiencing strong losses. The genes most significantly impacted by gene loss, duplication, or changes in selective constraint were those involved in detecting compounds associated with feeding on plants (bitter or electrophilic phytotoxins) or their ancestral diet (yeast and fruit volatiles). These results provide insight into the molecular and evolutionary mechanisms of plant-feeding adaptations and highlight strong gene candidates that have also been linked to other dietary transitions in Drosophila.

evolutionary biology↗

bioRxiv2021

Induction of autotetraploidy and microbiome associations mediate differential responses to pathogens

It has become increasingly clear that the microbiome plays a critical role in shaping the host organisms response to disease. There also exists mounting evidence that an organisms ploidy level is important in their response to pathogens and parasites. However, no study has determined if or how these two factors influence one another. We investigate the effect of whole-genome duplication in Arabidopsis thaliana on their above-ground (phyllosphere) microbiome, and determine the interacting impacts of ploidy and the microbiome on disease outcome. Using seven independently derived synthetic auto-tetraploid Arabidopsis accessions, a synthetic leaf-associated bacterial community, and the model pathogen Pseudomonas syringae pv. Tomato DC3000, we confirm that polyploids are generally more resistant to pathogens, but illustrate that this resistance may be in part due to a decrease in the reliance on beneficial bacteria. Polyploids fare better against the pathogen than diploids regardless of microbial inoculation, while we observed that diploids harboring an intact microbiome have lower pathogen densities than those without. We then use RNA sequencing to show that diploids have many more differentially expressed defense-related genes in the presence of their phyllosphere microbiota, while polyploids exhibit constitutively activated defenses regardless of exposure to the synthetic community. These results imply that whole-genome duplication can disrupt historical host-microbiome associations, and suggest that a potential cause or consequence of disruption is a heightened capacity for pathogen defense that is less impacted by the microbiome.

plant biology↗

bioRxiv2020

Evolution and genetic basis of the plant-penetrating ovipositor, a key adaptation in the transition to herbivory within the Drosophilidae

Herbivorous insects are extraordinarily diverse, yet are found in only one-third of insect orders. This skew may result from barriers to plant colonization, coupled with phylogenetic constraint on plant-colonizing adaptations. Physical barriers have been surmounted through the evolution of key morphological innovations, such as the plant-penetrating ovipositor. Despite their significance, the evolution and genetic basis of such innovations have not been well studied. Ovipositors densely lined with hard bristles have evolved repeatedly in herbivorous lineages within the Drosophilidae. Here, we focus on the evolution of this trait in Scaptomyza, an herbivorous radiation nested in a microbe-feeding clade, sister to Hawaiian Drosophila. Our phylogenetic approach revealed that ovipositor bristle number increased as herbivory evolved. We then dissected the genomic architecture of variation in ovipositor bristle number within S. flava through a genome wide association study. Top associated variants were enriched for transcriptional repressors, and the strongest associations included genes contributing to peripheral nervous system development. Genotyping individual flies replicated the association at a variant upstream of Gi, a neural development gene, contributing to a gain of 0.58 bristles/major allele. These results suggest that regulatory variation involving conserved developmental genes contributes to a key morphological adaptation required for plant colonization.

evolutionary biology↗