Biology subjects

Fordyce, J. A.

Publications and source records attributed to Fordyce, J. A..

8 recordsLinked to original sources

bioRxiv2025

Allochronic isolation between sympatric populations of an alpine butterfly

The role of isolation by distance in contributing to population structure across space is well understood, and the same principles should operate over time. Allochrony, the isolation of populations due to separation in time, can be a source of genetic differentiation, but remains infrequently documented between yearly asynchronous populations. In this study, we investigate divergence between two putative sympatric populations of the alpine butterfly Oeneis chryxus ivallda at Castle Peak, CA, USA. We find clear genetic differentiation between butterflies collected in odd and even years, with limited instances of admixture. The observed GST of 0.05 between the two populations is approximately equivalent to 26 km based on pairwise GST values observed between O. chryxus populations across space. These results demonstrate a potential source of population differentiation in systems that promote prolonged development, often found in high-elevation and high-latitude environments.

evolutionary biology↗

bioRxiv2025

Admixture in a butterfly species complex creates a genomic mosaic of ancestry with distinct histories for different chromosomes

Hybridization and admixture give rise to populations with mosaic genomes composed of ancestry segments with distinct origins and histories. Despite a growing number of documented cases of admixture in nature, relatively little is known about how mosaic patterns of ancestry vary simultaneously across the genome and among multiple populations or lineages of hybridizing species. Here, using pooled whole-genome sequence data from more than 20 populations representing three nominal species and multiple admixed or taxonomically ambiguous populations, we show that widespread admixture in Lycaeides butterflies has resulted in distinct evolutionary histories within and among chromosomes, with the most notable differences between the autosomes and the Z sex chromosome. Many populations exhibit substantial evidence of mixed ancestry on the autosomes, whereas the Z chromosome shows a more tree-like evolutionary history. In some cases, the predominant ancestry of the autosomes and the Z chromosome differ. We also find evidence of variation in ancestry within chromosomes, though this appears more idiosyncratic. We also show that differences in autosomal versus Z-chromosome ancestry have the potential to shape ecologically important trait variation. Specifically, using genome-wide association mapping, we demonstrate that wing-pattern elements--traits known to influence mate preference--are affected by genetic variants on both the autosomes and the Z chromosome. In sum, our results show that different chromosomes can exhibit distinct evolutionary histories, with the Z chromosome suggesting more discrete evolutionary lineages or species than the autosomes. These findings have implications both for our basic understanding of species and species boundaries and for how we view the sources of genetic and phenotypic variation that fuel ongoing evolutionary change.

evolutionary biology↗

bioRxiv2022

Lethal and sub-lethal concentrations of pesticides detected in milkweeds purchased from nurseries across the United States

The decline of monarch butterflies in both the eastern and western United States has garnered widespread public interest. Planting milkweeds, their larval host plants, has been promoted as one action individuals can take, but little is known with respect to potential pesticide contamination of store-bought milkweeds. In this study, we collected leaf samples from 235 milkweed plants purchased at 33 retail nurseries across the US to screen for pesticides. Across all samples, we detected 61 different pesticides with an average of 12.2 ({+/-}5.0) compounds per plant. While only 9 of these compounds have been experimentally tested on monarch caterpillars, 38% of samples contained a pesticide above a concentration shown to have a sub-lethal effect for monarchs. We detected only a modest predictive ability of retailer size and milkweed species; and plants with labels advertising their value for wildlife did not have fewer pesticides at concentrations known to have a negative effect on monarchs. These results demonstrate the extensiveness of pesticide exposure within nursery milkweeds and the potential impacts on monarchs and other insects exposed to store-bought plants. HighlightsO_LIMilkweeds were collected from stores in the United States and screened for pesticides. C_LIO_LIWe detected multiple pesticides in every milkweed plant sampled. C_LIO_LIOver one third of samples contained a pesticide at a known harmful concentration for monarchs. C_LIO_LIPlants labeled as wildlife-friendly did not have fewer potentially harmful compounds. C_LI

ecology↗

bioRxiv2022

Additive genetic effects in interacting species jointly determine the outcome of caterpillar herbivory

Plant-insect interactions are common and important in basic and applied biology. Trait and genetic variation can affect the outcome and evolution of these interactions, but the relative contributions of plant and insect genetic variation and how these interact remain unclear and are rarely subject to assessment in the same experimental context. Here we address this knowledge gap using a recent host range expansion onto alfalfa by the Melissa blue butterfly. Common garden rearing experiments and genomic data show that caterpillar performance depends on plant and insect genetic variation, with insect genetics contributing to performance earlier in development and plant genetics later. Our models of performance based on caterpillar genetics retained predictive power when applied to a second common garden. Much of the plant genetic effect could be explained by heritable variation in plant phytochemicals, especially saponins, peptides, and phosphatidyl cholines, providing a mechanistic understanding of variation in the species interaction. We find evidence of polygenic, mostly additive effects within and between species, with consistent effects of plant genotype on growth and development across multiple butterfly species. Our results inform theories of plant-insect coevolution and the evolution of diet breadth in herbivorous insects and other host-specific parasites. Teaser summaryThe combined, additive effects of plant and insect genetic variation explain Melissa blue caterpillar growth and development on alfalfa plants.

genomics↗

bioRxiv2020

Insects and recent climate change

Insects have diversified through 400 million years of Earths changeable climate, yet recent and ongoing shifts in patterns of temperature and precipitation pose novel challenges as they combine with decades of other anthropogenic stressors including the conversion and degradation of land. Here we consider how insects are responding to recent climate change, while summarizing the literature on long-term monitoring of insect populations in the context of climatic fluctuations. Results to date suggest that climate change impacts on insects have the potential to be considerable, even when compared to changes in land use. The importance of climate is illustrated with a case study from the butterflies of Northern California, where we find that population declines have been severe in high-elevation areas removed from the most immediate effects of habitat loss. These results shed light on the complexity of montane-adapted insects responding to changing abiotic conditions and raise questions about the utility of temperate mountains as refugia during the Anthropocene. We consider methodological issues that would improve syntheses of results across long-term insect datasets and highlight directions for future empirical work. Significance statementAnthropogenic climate change poses multiple threats to society and biodiversity, and challenges our understanding of the resilience of the natural world. We discuss recent ideas and evidence on this issue and conclude that the impacts of climate change on insects in particular have the potential to be more severe than might have been expected a decade ago. Finally, we suggest practical measures that include the protection of diverse portfolios of species, not just those inhabiting what are currently the most pristine areas.

ecology↗

bioRxiv2018

Caterpillars on a phytochemical landscape

Modern metabolomic approaches that generate more comprehensive phytochemical profiles than were previously available are providing new opportunities for understanding plant-animal interactions. Specifically, we can characterize the phytochemical landscape by asking how a larger number of individual compounds affect herbivores and how compounds covary among plants. Here we use the recent colonization of alfalfa (Medicago sativa) by the Melissa blue butterfly (Lycaeides melissa) to quantify plant metabolites and the performance of caterpillars as affected by both individual compounds and suites of covarying phytochemicals. We find that survival, development time and adult weight are all associated with variation in nutrition and toxicity, including biomolecules associated with plant cell function as well as putative anti-herbivore action. The plant-insect interface is complex, with clusters of covarying compounds in many cases encompassing divergent effects on different aspects of caterpillar performance. Individual compounds with the strongest associations are largely specialized metabolites, including alkaloids, phenolic glycosides and saponins. The saponins are represented in our data by more than 25 individual compounds with beneficial and detrimental effects on L. melissa caterpillars, which highlights the value of metabolomic data as opposed to approaches that rely on total concentrations within broad defensive classes.

ecology↗

bioRxiv2018

Impacts of a millennium drought on butterfly faunal dynamics

Climate change is challenging plants and animals not only with increasing temperatures, but also with shortened intervals between extreme weather events. Relatively little is known about diverse assemblages of organisms responding to extreme weather, and even less is known about landscape and life history properties that might mitigate effects of extreme weather. We find that northern California butterflies were impacted by a millennium-scale drought differentially at low and high elevations. At low elevations, phenological shifts facilitated persistence and even recovery during drought, while at higher elevations a shortened flight season was associated with decreases in species richness. Phenological and faunal dynamics are predicted by temperature and precipitation, thus advancing the possibility of understanding and forecasting biological responses to extreme weather.

ecology↗

bioRxiv2017

The predictability of genomic changes underlying a recent host shift in Melissa blue butterflies

Despite accumulating evidence that evolution can be predictable, studies quantifying the predictability of evolution remain rare. Here, we measured the predictability of genome-wide evolutionary changes associated with a recent host shift in the Melissa blue butterfly (Lycaeides melissa). We asked whether and to what extent genome-wide patterns of evolutionary change in nature could be predicted (1) by comparisons among instances of repeated evolution, and (2) from SNP x performance associations in a lab experiment. We delineated the genetic loci (SNPs) most strongly associated with host use in two L. melissa lineages that colonized alfalfa. Whereas most SNPs were strongly associated with host use in none or one of these lineages, we detected a ~two-fold excess of SNPs associated with host use in both lineages. Similarly, we found that host-associated SNPs in nature could also be partially predicted from SNP x performance (survival and weight) associations in a lab rearing experiment. But the extent of overlap, and thus degree of predictability, was somewhat reduced. Although we were able to predict (to a modest extent) the SNPs most strongly associated with host use in nature (in terms of parallelism and from the experiment), we had little to no ability to predict the direction of evolutionary change during the colonization of alfalfa. Our results show that different aspects of evolution associated with recent adaptation can be more or less predictable, and highlight how stochastic and deterministic processes interact to drive patterns of genome-wide evolutionary change.

evolutionary biology↗