Biology subjects

Combs, M.

Publications and source records attributed to Combs, M..

4 recordsLinked to original sources

bioRxiv2025

The LAST mile: Evaluating genetic biocontrol as a supplemental tool for eradicating invasive rodents on islands

Invasive rodents cause severe ecosystem degradation on islands and can be challenging to eradicate. Current best-practices rely heavily on the application of toxic oral baits and have led to successful eradications and remarkable recoveries of native flora and fauna. Yet this single method is not universally applicable. Reliance on a single method limits further eradication success in situations where toxicants cannot be used or remnant populations persist after application. Genetic biocontrol offers a suite of new solutions to potentially improve outcomes in the critical "last mile" of eradication. These approaches involve the release of genetically modified individuals of the target species to reduce population fitness over time. These include self-limiting approaches which require multiple releases and self-sustaining mechanisms (i.e., select gene-drive systems) which could theoretically collapse populations after a single release. While gene drive systems have received significant attention, their development in vertebrates remains technically challenging, and their ecological and regulatory implications are still in active debate. In contrast, some non-drive genetic biocontrol approaches, such as Y-linked editors, fsRIDL, and Gravid Lethal, offer self-limiting alternatives that may be more immediately deployable. These approaches could be used to supplement toxicant-based methods and may also have reduced environmental risks and regulatory barriers. To evaluate the potential of these tools, we developed an individual-based model simulating the eradication of house mice (Mus musculus) on a 125ha island with an initial population of 11,000 individuals. We tested various combinations of genetic biocontrol release and effort strategies to understand tradeoffs between required effort and uncertainty for achieving successful eradication. Under certain effort strategies, we found that the Gravid Lethal approach performed the best, achieving eradication in less than 2.3 years with intensive release effort and monitoring. Our findings suggest that integrating non-drive genetic biocontrol into adaptive management frameworks could enhance the effectiveness and feasibility of rodent eradication programs. These tools are not replacements for toxicants but may serve as critical supplements--particularly in the "last mile" of eradication. Further stakeholder engagement is needed to assess the ecological, ethical, and logistical dimensions of deploying these technologies in real-world settings.

ecology↗

bioRxiv2025

Subways, zoning and social factors influence the dispersal and genetic connectivity of an iconic urban pest, the brown rat (Rattus norvegicus) across a complex cityscape

Cities present unique ecological challenges and opportunities for species that have adapted to human-dominated environments. To understand how urban landscape heterogeneity shapes the movements of an iconic urban animal, the brown rat (Rattus norvegicus), we investigated the factors influencing rat genetic connectivity across Manhattan, New York City. We generated genome-wide SNP data from rats sampled throughout Manhattan as well as paired surface-subway locations, created a habitat suitability model using systematic municipal rat survey data, and employed landscape genetic approaches to identify urban features influencing rat gene flow. Our models revealed that underground subway tunnels were the strongest facilitator of rat gene flow, with municipal zoning also strongly influencing connectivity, particularly through low / medium-density residential areas. Habitat suitability analysis showed that high human population density, old building ages, and lower median household income were the strongest predictors of rat presence. Subterranean sampling revealed that rats in subway stations exhibited greater genetic relatedness than surface rats at short distances but lower inbreeding coefficients, suggesting underground tunnels facilitate longer-distance dispersal while maintaining some connectivity to surface populations. These findings demonstrate that physical infrastructure, political, and socioeconomic factors shape urban rat ecology, with implications for more targeted approaches to pest management in complex urban environments. This study is the first comprehensive analysis of rat dispersal and genetic connectivity in relation to complex cityscape heterogeneity.

evolutionary biology↗

bioRxiv2020

Cellular and immunological mechanisms mediate reservoir host specialization by genotypically variable microparasites

Host specialization is an ecological and evolutionary process by which a pathogen becomes differentially adapted to a subset of hosts, restricting its host range. For parasites transmitted by generalist vectors, host specialization is not expected to evolve because of the decreased survival of those parasites in inadequate hosts. Thus, parasites may develop adaptation strategies, resulting in host specialization. The causative agents of Lyme disease are multiple species of bacteria, Borrelia burgdorferi sensu lato species complex (Bbsl), and are suitable for examining host specialization as birds and rodents were found to carry different species of these bacteria. Debate exists on whether host specialization occurs among these strains within a particular species of Bbsl, such as B. burgdorferi sensu stricto (Bbss). Current evidence supports some Bbss strains are widespread in white-footed mice but others are in non-rodent vertebrates, such as birds. To recapitulate specialization in the laboratory and define the mechanisms for host specialization, we introduced different genotypes of Bbss via tick transmission to American robins and white-footed mice, the Lyme disease reservoirs in North America. Among these strains, we found distinct levels of spirochete presence in the bloodstream and tissues and maintenance by these animals in a host-dependent fashion. We showed that the late stage persistence of these strains largely corresponds to bacterial survival at early infection onsets. We also demonstrated that those early survival phenotypes correspond to spirochete adhesiveness, evasion of complement-mediated killing in sera, and/or not triggering high levels of pro-inflammatory cytokines and antibodies. Our findings thus link host competence to Bbss with spirochete genotypic variation of adhesiveness and inducing/escaping host immune responses, illuminating the potential mechanisms that dictate host specialization. Such information will provide a foundation for further investigation into multi-disciplinary processes driving host specialization of microparasites. AUTHOR SUMMARYHost specialization arises when microparasites adapt to a subset of available hosts, restricting the host ranges they can infect. The mechanisms and selective pressures for the evolution of host specialization remain unclear. The causative agent of Lyme disease (LD), the bacteria species complex of Borrelia burgdorferi sensu lato, is adapted to different vertebrates. However, whether such a differential host adaption also applies to each genotype within the same species is under debate. Further, the mechanisms that drive such host specialization are unclear. We thus introduced three genotypes of one LD bacteria species (B. burgdorferi sensu stricto) individually via tick bite to American robins and white-footed mice, the most common LD reservoirs in North America. We found that these genotypes differed in the persistent maintenance by those reservoirs and occurred in a host-specific fashion. The ability of those bacteria for long-term maintenance was linked with their capability to attach to cells and a lack of induction of high levels of immune responses at early infection onsets. This work demonstrates the potential mechanisms that dictate host specialization of LD bacteria circulating in natural populations. Such information will pave the road to define the molecular, ecological, and evolutionary determinants that drive host-microparasite interactions.

microbiology↗

bioRxiv2020

Genetic Adaptation in New York City Rats

Brown rats (Rattus norvegicus) thrive in urban environments by navigating the anthropocentric environment and taking advantage of human resources and by-products. From the human perspective, rats are a chronic problem that causes billions of dollars in damage to agriculture, health and infrastructure. Did genetic adaptation play a role in the spread of rats in cities? To approach this question, we collected whole-genome sequences from 29 brown rats from New York City (NYC) and scanned for genetic signatures of adaptation. We tested for (i) high-frequency, extended haplotypes that could indicate selective sweeps and (ii) loci of extreme genetic differentiation between the NYC sample and a sample from the presumed ancestral range of brown rats in northeast China. We found candidate selective sweeps near or inside genes associated with metabolism, diet, the nervous system and locomotory behavior. Patterns of differentiation between NYC and Chinese rats at putative sweep loci suggests that many sweeps began after the split from the ancestral population. Together, our results suggest several hypotheses on adaptation in rats living in close proximity to humans.

evolutionary biology↗