Biology subjects

Aardema, M. L.

Publications and source records attributed to Aardema, M. L..

3 recordsLinked to original sources

bioRxiv2021

A gene-based capture assay for surveying patterns of genetic diversity and insecticide resistance in a worldwide group of invasive mosquitoes

Understanding patterns of diversification, genetic exchange, and pesticide resistance in insect species of human health concern is necessary for effective population reduction and management. With the broad availability of next-generation sequencing technologies, one of the best approaches for surveying such patterns involves the simultaneous genotyping of many samples for large numbers of genetic markers from across the known genome. To this end, the targeting of gene sequences of known function or inheritance can be a cost-effective strategy. One insect group of substantial health concern are the mosquito taxa that make up the Culex pipiens complex. Members of this complex transmit damaging arboviruses and filariae worms to humans, as well as other pathogens that are detrimental to endangered vertebrate species such as bird malaria. Here we describe our development of a targeted gene-based assay for surveying genetic diversity and population structure in this mosquito complex. To test the utility of this assay, we examined taxonomic divergence among samples from several members of the complex, as well as distinct populations of the relatively under-studied Culex quinquefasciatus, an urban pantropical species. We also examined the presence of known insecticide-resistance conferring alleles. Broadly, our developed gene-based assay proved effective for examining patterns of taxonomic and geographic clustering within the species complex, as well as for surveying genetic variants that have been associated with insecticide resistance. This assay will be useful for future studies that aim to understand the genetic mechanisms underlying the evolution of ubiquitous and increasingly damaging disease vectors.

genomics↗

bioRxiv2021

Persistence and expansion of cryptic endangered red wolf genomic ancestry along the American Gulf coast

Admixture and introgression play a critical role in adaptation and genetic rescue that has only recently gained a deeper appreciation. Here, we explored the geographic and genomic landscape of cryptic ancestry of the endangered red wolf that persists within the genome of a ubiquitous sister taxon, the coyote, all the while the red wolf has been extinct in the wild since the early 1980s. We assessed admixture across 102,621 SNP loci genotyped in 293 canid genomes. We found support for increased red wolf ancestry along an east-to-west gradient across the southern United States that was associated with historical admixture in the past 100 years. Southwestern Louisiana and southeastern Texas, the geographic zone where the last red wolves were known prior to their extinction in the wild, contained the highest and oldest levels of red wolf ancestry. X-linked regions of low recombination rates were depleted of introgression, relative to the autosomes, suggestive of the large X effect and enrichment with loci involved in maintaining reproductive isolation. Recombination rate was positively correlated with red wolf ancestry across coyote genomes, consistent with theoretical predictions. The geographic and genomic extent of cryptic red wolf ancestry can provide novel and variable genomic resources for the survival of the endangered red wolf.

evolutionary biology↗

bioRxiv2020

The urban-adapted underground mosquito, Culex molestus, maintains exogenously influenced circadian rhythms despite an absence of photoperiodically induced dormancy

In temperate climates, the mosquito Culex molestus lives almost exclusively in urban underground locations such as flooded basements, sewer systems and subway tunnels. Unlike most other mosquito taxa found at higher latitudes, Cx. molestus remains active and continues to breed throughout the winter. This is attributable to year-round above freezing temperatures in its preferred underground habitats combined with an inability to enter a state of arrested development ( diapause) in response to shortening photoperiods in autumn. Prior studies have shown that the genes associated with circadian rhythms (i.e. clock genes) also influence the photoperiodic induction of diapause in the closely related mosquito, Cx. pipiens. These results suggest that molecular changes in one or more clock genes could contribute to the absence of photoperiodically induced diapause in Cx. molestus. As Cx. molestus predominantly inhabits underground locations generally devoid of a predictable photoperiod, such mutations may not be removed by purifying selection as they would have minimal fitness consequences. To examine the possibility that Cx. molestus- specific genetic changes in one or more clock genes correlate with its inability to enter a photoperiodically induced dormant state, we first used genomic data to search for inactivating mutations or other structural variants in genes known to influence circadian rhythms in Diptera ( flies). We further investigated non-synonymous, derived genetic divergence in this same class of genes. Next, we generated transcriptome data from multiple life-stages of Cx. molestus to survey binary expression of annotated clock genes throughout this mosquitos lifecycle. Finally, we carried out experimental studies to assess the extent to which Cx. molestus retains exogenously influenced circadian rhythms, and whether it harbors any tendencies towards dormancy when exposed to a shortened photoperiod. Our results indicate that the gene Helicase domino (dom) has a nine-nucleotide, in-frame deletion specific to Cx. molestus. Previous work has shown that splice variants in this gene influence circadian behavior in Drosophila melanogaster. We also find derived, non-synonymous single nucleotide polymorphisms (SNPs) in eight genes that may also affect circadian rhythms and/or diapause induction in Cx. molestus. Four other circadian genes were found to have no quantifiable expression during any examined life stage, suggesting potential regulatory variation. Our experimental results confirm that Cx. molestus retains exogenously-influenced circadian rhythms but is not induced to enter a dormant state by a shortened photoperiod. Collectively, these findings show that the distinct, but potentially molecularly interconnected life-history traits of diapause induction and circadian rhythms are decoupled in Cx. molestus and suggest that this taxon may be a valuable tool for exploring exogenously influenced phenotypes in mosquitoes more broadly.

evolutionary biology↗