Biology subjects

Byers, K. J. R. P.

Publications and source records attributed to Byers, K. J. R. P..

11 recordsLinked to original sources

bioRxiv2025

In-depth phenotyping reveals unexpected floral trait variation in Mimulus cardinalis across a range-wide latitudinal gradient

Background & AimsPollinators play a crucial role in the evolution and diversification of flowering plants. Intraspecific variation in floral traits occurs frequently and likely reflects variable biotic and abiotic selection pressures. The hummingbird-pollinated monkeyflower Mimulus cardinalis occurs across western North America, where geographic mosaics of selection have likely influenced its natural history, due to this wide species range. Processes driving early stages of divergence and speciation remain poorly understood, though theory predicts that trait divergence will be most likely at range edges. Within M. cardinalis, which is usually red-flowered and hummingbird-pollinated, two independent shifts to yellow flowers have occurred at the northern and southern range edges, including a population found on Cedros Island, off the coast of Baja California, Mexico. MethodsThis study characterises the local climatic variables of five accessions of M. cardinalis derived from locations across a latitudinal geographic gradient. Highly integrative methods in metabolomics and morphological analyses were used to characterise a suite of pollinator-relevant floral traits across the range of M. cardinalis species variation. We use transcriptomics and whole genome sequencing to study underlying genetic variation in two yellow-coloured, range-edge accessions. Key ResultsThis study uncovers high levels of variation in morphology, nectar properties, pigmentation and scent profile across geographically diverse Mimulus cardinalis accessions, in addition to profiling how these accessions are perceived by potential pollinators. We find high levels of phenotypic variation across M. cardinalis, particularly in the biochemistry of pigment and scent, where inflorescences that appear to be the same shade of red have completely different anthocyanin profiles. Floral trait-underlying genetic differences between different M. cardinalis lines were also investigated, revealing potential mechanisms underlying floral diversification. ConclusionsThis work highlights the importance of interplay between floral trait diversification, pollinator perception and climate. This work also highlights the importance of considering suites of floral traits in a quantitative fashion when studying intraspecific variation in relation to species range. This study also provides genetic insight into changes in these traits and provides many future directions to study the early stages of pollinator-mediated trait differentiation across a species range.

plant biology↗

bioRxiv2025

Redesigning petal shape, size, and color in soybean reveals unexpected phenotypes for floral organ development

Soybean (Glycine max) has not yet benefited from large-scale hybrid breeding efforts due to its small, self-fertilizing flowers that are difficult to emasculate, and limited attractiveness to pollinators. This study explores targeted floral trait engineering to enhance pollinator attraction, aiming to overcome barriers to soybean hybridization. We generated a high-resolution floral organ expression atlas and H3K4 trimethylation ChIP-Seq dataset to identify candidate genes involved in petal development, nectar sugar content, and petal pigmentation. Using CRISPR-based activation and repression systems, we modified the expression of AINTEGUMENTA (GmANT), BIGPETAL (GmBPE), and SUCROSE TRANSPORTER2 (GmSUC2). Contrary to expectations based on Arabidopsis homologs, transcriptional activation of GmANT_B and repression of GmBPE led to reduced, rather than increased, petal size, highlighting divergent regulatory mechanisms in soybean. Complementation of the W1 gene that controls petal pigmentation successfully converted white petals to purple, with preliminary evidence indicating that this color conversion may increase pollinator visitation. These results underscore the complexity of floral development in soybean and provide foundational tools and resources for future efforts to engineer reproductive traits for hybrid seed production.

plant biology↗

bioRxiv2025

Pollinator-relevant floral traits underlie bidirectional hybridisation in the orchid genus Gymnadenia

Reproductive isolation is mediated by ecological, phenotypic, and genetic barriers. Where such barriers are not upheld, hybridisation can occur, revealing insight about the formation of species. Here, we provide an integrative investigation of hybrid formation between the orchids Gymnadenia conopsea and G. rhellicani and potential isolating barriers in zones of overlap in the European Alps. We examine opportunities for hybridisation by quantifying hybrid frequency and pollinator assemblages of parent species. Next, we characterise floral phenotypes and genetic parentage of hybrids to examine how genetic inheritance of traits shapes ecological interactions, and thus fitness, of hybrids. We find that pollinator assemblages of parents overlap partially, consistent with observed rare hybrids (<1% of the population). Phenotypically, hybrids were intermediate across floral traits, consistent with all hybrids being identified as F1s, resulting from a primary hybridisation event between G. conopsea and G. rhellicani. No evidence of backcrossing or introgression was found, but direction of pollen transfer varied across sites. Additionally, hybrids were heterozygous for parental alleles at two loci impacting anthocyanin production, suggesting hybrids intermediate floral colour reflects inheritance of these alleles. Finally, we find little support that ploidy variation or hybrid seed infertility explains the absence of advanced generations of hybrids. Thus, we suggest that floral isolation represents an important isolating mechanism between G. conopsea and G. rhellicani in limiting the formation of uncommon, unfit hybrids and shaping species boundaries.

plant biology↗

bioRxiv2024

Quantitative analysis of gas chromatography-coupled electroantennographic detection (GC-EAD) of plant volatiles by insects

PremisePlant-interacting insects receive plant volatile signals through their antennae, and voltage changes across an antenna exposed to volatile stimuli can be measured to determine if insects can perceive them, often by coupling gas chromatography to electroantennographic detection (GC-EAD). Current methods for analysing GC-EAD data rely on qualitative observation, rather than using quantitative analysis, and are thus prone to bias. Methods and ResultsWe developed a novel quantitative methodology for analysis of GC-EAD data using a signal processing technique on EAD data to compare responses of hawkmoths and bumble bees to a library of common floral volatiles. Responses varied between species and sexes and these responses were in some cases affected by compound type or modification. Our method also works with existing, published GC-EAD datasets. ConclusionsOur novel GC-EAD analysis technique is robust to baseline drift and low signal:noise ratios commonly found in GC-EAD data, and provides a way forward for quantitative studies of plant volatile- mediated plant-insect interactions.

plant biology↗

bioRxiv2023

Do color polymorphisms reflect pollinator shifts?: Integrating floral traits as signals to a novel pollinator to understand species divergence

Understanding how evolution proceeds from molecules to organisms to interactions is critical for evolutionary biology and requires integrative studies that span biological levels. By linking phenotypic changes with associated genes and fitness implications, we gain insight on the repeatability of evolution and how adaptive walks move organisms between fitness peaks, which remains poorly understood at intermediate stages, e.g. potential fitness valleys. Floral trait evolution can proceed rapidly, confer reproductive isolation, and provides numerous examples of convergent evolution associated with pollinator guilds. Within the monkeyflowers (Mimulus sect. Erythranthe), intraspecific shifts to yellow flowers within red hummingbird-pollinated species have arisen at least twice and may represent incipient shifts between optima of pollinator adaptation. Here, we compare two natural yellow-flowered forms of M. cardinalis and M. verbenaceus to their red conspecifics in floral phenotypes, biochemistry, transcriptomic and genomic variation, and interactions with pollinators. We find convergent evolution in the adaptive walks of yellow morphs in both species, with consistent changes in traits of large effect (floral pigments and associated gene expression), which result in strong preference for yellow flowers by bumblebees. Shifts in additional traits (scent emissions and floral opening size) are also consistent with bee pollination, which may represent smaller-effect steps in an ongoing walk from hummingbird to bee pollination. By examining intraspecific variation representing incipient pollinator shifts in two related species, this work elucidates how adaptive walks proceed at early stages by highlighting how convergent large effect mutations (floral color) may drive pollinator attraction, preceding smaller effect changes controlling pollinator fit and reward access. This work integrates phenotypic, biochemical, genomic, and behavioral evidence to shed light on how repeated steps in adaptive walks to new fitness optima may impact reproductive isolation and incipient speciation via convergent evolution.

evolutionary biology↗

bioRxiv2020

Clustering of loci controlling species differences in chemical bouquets of sympatric Heliconius butterflies

The degree to which loci promoting reproductive isolation cluster in the genome - i.e. the genetic architecture of reproductive isolation - can influence the tempo and mode of speciation. Tight linkage between these loci can facilitate speciation in the face of gene flow. Pheromones play a role in reproductive isolation in many Lepidoptera species, and the role of endogenously-produced compounds as secondary metabolites decreases the likelihood of pleiotropy associated with many barrier loci. Heliconius butterflies use male sex pheromones to both court females (aphrodisiac wing pheromones) and ward off male courtship (male-transferred anti-aphrodisiac genital pheromones), and it is likely that these compounds play a role in reproductive isolation between Heliconius species. Using a set of backcross hybrids between H. melpomene and H. cydno, we investigated the genetic architecture of putative male pheromone compound production. We found a set of 40 significant quantitative trait loci (QTL) representing 33 potential pheromone compounds. QTL clustered significantly on two chromosomes, chromosome 8 for genital compounds and chromosome 20 for wing compounds, and chromosome 20 was enriched for potential pheromone biosynthesis genes. There was minimal overlap between pheromone QTL and known QTL for mate choice and color pattern. Nonetheless, we did detect linkage between a QTL for wing androconial area and optix, a color pattern locus known to play a role in reproductive isolation in these species. This tight clustering of putative pheromone loci might contribute to coincident reproductive isolating barriers, facilitating speciation despite ongoing gene flow.

evolutionary biology↗

bioRxiv2019

A novel terpene synthase produces an anti-aphrodisiac pheromone in the butterfly Heliconius melpomene

Terpenes, a group of structurally diverse compounds, are the biggest class of secondary metabolites. While the biosynthesis of terpenes by enzymes known as terpene synthases (TPSs) has been described in plants and microorganisms, few TPSs have been identified in insects, despite the presence of terpenes in multiple insect species. Indeed, in many insect species, it remains unclear whether terpenes are sequestered from plants or biosynthesised de novo. No homologs of plant TPSs have been found in insect genomes, though insect TPSs with an independent evolutionary origin have been found in Hemiptera and Coleoptera. In the butterfly Heliconius melpomene, the monoterpene (E)-{beta}-ocimene acts as an anti-aphrodisiac pheromone, where it is transferred during mating from males to females to avoid re-mating by deterring males. To date only one insect monoterpene synthase has been described, in Ips pini (Coleoptera), and is a multifunctional TPS and isoprenyl diphosphate synthase (IDS). Here, we combine linkage mapping and expression studies to identify candidate genes involved in the biosynthesis of (E)-{beta}-ocimene. We confirm that H. melpomene has two enzymes that exhibit TPS activity, and one of these, HMEL037106g1 is able to synthesise (E)-{beta}-ocimene in vitro. Unlike the enzyme in Ips pini, these enzymes only exhibit residual IDS activity, suggesting they are more specialised TPSs, akin to those found in plants. Phylogenetic analysis shows that these enzymes are unrelated to previously described plant and insect TPSs. The distinct evolutionary origin of TPSs in Lepidoptera suggests that they have evolved multiple times in insects.\n\nSignificance statementTerpenes are a diverse class of natural compounds, used by both plants and animals for a variety of functions, including chemical communication. In insects it is often unclear whether they are synthesised de novo or sequestered from plants. Some plants and insects have converged to use the same compounds. For instance, (E)-{beta}-ocimene is a common component of floral scent and is also used by the butterfly Heliconius melpomene as an anti-aphrodisiac pheromone. We describe two novel terpene synthases, one of which synthesises (E)-{beta}-ocimene in H. melpomene, unrelated not only to plant enzymes but also other recently identified insect terpene synthases. This provides the first evidence that the ability to synthesise terpenes has arisen multiple times independently within the insects.

biochemistry↗

bioRxiv2019

A major locus controls a biologically active pheromone component in Heliconius melpomene

Understanding the production, response, and genetics of signals used in mate choice can inform our understanding of the evolution of both intraspecific mate choice and reproductive isolation. Sex pheromones are important for courtship and mate choice in many insects, but we know relatively little of their role in butterflies. The butterfly Heliconius melpomene uses a complex blend of wing androconial compounds during courtship. Electroantennography in H. melpomene and its close relative H. cydno showed that responses to androconial extracts were not species-specific. Females of both species responded equally strongly to extracts of both species, suggesting conservation of peripheral nervous system elements across the two species. Individual blend components provoked little to no response, with the exception of octadecanal, a major component of the H. melpomene blend. Supplementing octadecanal on the wings of octadecanal-rich H. melpomene males led to an increase in the time until mating, demonstrating the bioactivity of octadecanal in Heliconius. Using quantitative trait locus (QTL) mapping, we identified a single locus on chromosome 20 responsible for 41% of the parental species difference in octadecanal production. This QTL does not overlap with any of the major wing color or mate choice loci, nor does it overlap with known regions of elevated or reduced FST. A set of 16 candidate fatty acid biosynthesis genes lies underneath the QTL. Pheromones in Heliconius carry information relevant for mate choice and are under simple genetic control, suggesting they could be important during speciation.

evolutionary biology↗

bioRxiv2019

Species specificity and intraspecific variation in the chemical profiles of Heliconius butterflies across a large geographic range

In many animals, mate choice is important for the maintenance of reproductive isolation between species. Traits important for mate choice and behavioural isolation are predicted to be under strong stabilising selection within species, however such traits can also exhibit variation at the population level driven by neutral and adaptive evolutionary processes. Here, we describe patterns of divergence among androconial and genital chemical profiles at inter- and intra-specific levels in mimetic Heliconius butterflies. Most variation in chemical bouquets was found between species, but there were also quantitative differences at the population level. We found a strong correlation between interspecific chemical and genetic divergence, however, this correlation varied in intraspecific comparisons. We identified indicator compounds characteristic of particular species that included known biologically active compounds, suggesting an approach for identification of candidate compounds for future behavioural studies in novel systems. Overall, the strong signal of species identity suggests a role for these compounds in species recognition, but with additional potentially neutral variation at the population level.

evolutionary biology↗

bioRxiv2018

Male pheromone composition depends on larval but not adult diet in Heliconius melpomene

Condition-dependent traits can act as honest signals of mate quality, with fitter individuals able to display preferred phenotypes. Nutrition is known to be an important determinant of individual condition, with diet known to affect many secondary sexual traits. In Heliconius butterflies, male chemical signalling plays an important role in female mate choice. Heliconius pheromones are sexually dimorphic, found only in mature males, but it is unclear what information they convey to the female. Here, we manipulate both the larval and adult diet of male Heliconius melpomene rosina to test for environmental effects on wing and genital pheromone production. We find no evidence that adult pollen consumption affects pheromone production in the first ten days after eclosion. We also find strong overlap in the chemical profiles of individuals reared on different larval host plants. However, individual compounds were found in different amounts between host plant treatments. Further electrophysiological and behavioural experiments will be needed to determine the biological significance of these differences.

ecology↗

bioRxiv2017

Rational Design Of A Novel Pollinator Interaction

Diversification of the ca. 250,000 extant flowering plant species has been driven in large part by coevolution with animal pollinators. A recurring pattern of pollinator shifts from hummingbird to hawkmoth pollination has characterized plant speciation in many western North American plant taxa, but in the genus Mimulus (monkeyflowers) section Erythranthe the evolution of hawkmoth pollination from hummingbird-pollinated ancestors has not occurred. We manipulated two flower color loci and tested the attractiveness of the resulting four color phenotypes (red, yellow, pink, white) to naive hawkmoths. Hawkmoths strongly prefer derived colors (yellow, pink, white) over the ancestral red, and prefer the two-locus change (white) to either of the single-locus changes (yellow, pink). The simple flower color genetics underlying this innate pollinator preference suggests a potential path for speciation into an unfilled hawkmoth-pollinated niche, and the deliberate design of a hawkmoth-pollinated flower demonstrates a new, predictive method for studying pollination syndrome evolution.

evolutionary biology↗