Biology subjects

Crossley, M. S.

Publications and source records attributed to Crossley, M. S..

4 recordsLinked to original sources

bioRxiv2023

Change in Monarch Butterfly Winter Abundance Over the Past Decade: A Red List Perspective

1. Assessing invertebrate species for the IUCN Red List under Criterion A requires fitting an appropriate statistical model to available abundance data and calculating a ten-year change (TYC) estimate from predicted abundances. When the rate of change has not been constant across the entire time series, models that accommodate variable change rates are strongly recommended. 2. The monarch butterfly (Danaus plexippus) was recently added to the IUCN Red List (A2ab Endangered) based on analysis of data on winter abundances in Mexico and the western USA between 1993 and 2020. TYC estimates in the monarch assessment came from models that assumed constant change rates. We conducted a Bayesian analysis of the same data using models that accommodated variable change rates and used those models to compute TYC estimates. 3. Our results suggested that monarch population change rates have not been constant. The analysis yielded a model averaged TYC estimate of +5.23%, which was not statistically distinguishable from 0% and was considerably different from values of -46% and -72% in the assessment. The Bayesian posterior probability of a TYC value below -30% (A2ab Vulnerable) was 0.15 and that of a TYC value below -50% (A2ab Endangered) was 0.03. 4. We suggest that a more thorough analysis of recent overwintering abundances will lead to an improved IUCN assessment for monarch butterflies. We recommend that other researchers evaluating monarch conservation status consider using models with variable change rates, as models with constant change rates may not accurately predict the trajectory of monarch abundances into the future.

ecology↗

bioRxiv2021

No broad decline of breeding monarch butterflies in North America: implications for conservation efforts

Many insects are in clear decline, with monarch butterflies (Danaus plexippus) drawing particular attention as a flagship species. Falling numbers of overwintering monarchs are well documented, but there has been debate regarding population trends of summer breeding populations. Here, we compile a series of long-term monarch monitoring datasets, some which are analyzed here for the first time, that reveal highly variable responses across the migratory geographic range, but no broad net decline in numbers of breeding monarchs. We also did not find evidence that sampling biased towards natural sites was masking declines at disturbed sites. Overall, our results suggest a robust resiliency in summer populations that thus far has allowed recovery from losses during the winter. Thus, monarchs may not require as much breeding habitat restoration as once thought, and focus should be on conserving the fall and spring migration.

ecology↗

bioRxiv2021

Genome resequencing reveals rapid, repeated evolution in the Colorado potato beetle, Leptinotarsa decemlineata

BackgroundInsecticide resistance and rapid pest evolution threatens food security and the development of sustainable agricultural practices. An improved understanding of the evolutionary mechanisms that allow pests to rapidly adapt to novel control tactics will help prevent economically damaging outbreaks. The Colorado potato beetle (CPB), Leptinotarsa decemlineata, is a global super-pest that rapidly evolves resistance to insecticides. Using whole genome resequencing and transcriptomic data focused on its ancestral and pest range in North America, we assess evidence for three, non-mutually exclusive models of rapid evolution: pervasive selection on novel mutations, rapid regulatory evolution, and repeated selection on standing genetic variation. ResultsPopulation genomic analysis demonstrates that CPB is geographically structured, even among recently established pest populations. Pest populations exhibit only modest reductions in nucleotide diversity, relative to non-pest ancestral populations, and show evidence of recent demographic expansion. Genome scans of selection provide clear signatures of repeated adaptation across different CPB populations, with especially strong evidence that insecticide resistance involves selection of different genes in different populations. Similarly, analyses of gene expression show that constitutive upregulation of candidate insecticide resistance genes drives distinctive population patterns. ConclusionCPB evolves insecticide resistance repeatedly across agricultural regions, and oftentimes at the same loci, supporting a prominent role of polygenic evolution from standing genetic variation. Despite expectations, we do not find support for strong selection on novel mutations, or rapid evolution from selection on regulatory genes. An important future goal will be to understand how polygenic resistance phenotypes spread among local pest populations, in order to refine integrated pest management practices to maintain the efficacy and sustainability of novel control techniques.

evolutionary biology↗

bioRxiv2019

Regional differences in gene regulation may underlie patterns of sensitivity to novel insecticides in Colorado potato beetle

Agricultural insect pests frequently exhibit geographic variation in levels of insecticide resistance, which are often presumed to be due to the intensity of insecticide use for pest management. However, regional differences in the evolution of resistance to novel insecticides suggests that other factors are influencing rates of adaptation. We examined LC50 bioassay data spanning 15 years and six insecticides (abamectin, imidacloprid, spinosad, cyantraniliprole, chlorantraniliprole, and metaflumizone) for evidence of regional differences in Colorado potato beetle (CPB) baseline sensitivity to insecticides as they became commercially available. We consistently found that CPB populations from the Western USA had the highest baseline sensitivity to novel insecticides, while populations from the Eastern USA had the lowest. Comparisons of gene expression between populations from these regions revealed constitutively elevated expression of an array of detoxification genes in the East, but no evidence of additional induction when exposed to imidacloprid. Our results suggest a mechanism for geographic variation in rates of adaptation to insecticides whereby baseline levels of gene expression determine a populations response to novel insecticides. These findings have implications for the regional development of insecticide resistance management strategies and for the fundamental question of what determines the rate of adaptation to insecticides.

evolutionary biology↗