Biology subjects

Simmonds, T. J.

Publications and source records attributed to Simmonds, T. J..

4 recordsLinked to original sources

bioRxiv2026

Multiple roads to swarming: divergent molecular machineries drive the repeated evolution of locusts

Locust swarming, one of nature's most spectacular examples of a repeated emergent polyphenism, has long been suspected to rely on conserved "swarming genes" or shared genomic features. By applying a model-clade approach comparing six species that vary in their degrees of plasticity and collective behavior, we show that the evolution of swarming locusts is not driven by shared genomic features or a universal set of swarming genes. In contrast, we find that this phenomenon evolved through flexible regulatory architectures, in which the degree of behavioral plasticity directly correlates with the total scale of density-responsive gene expression. While different locust species recruit largely non-overlapping gene sets to achieve the same syndrome, these divergent molecular machineries converge on similar higher-level biological functions. Thus, multiple molecular pathways achieve locust swarming, challenging the preconceived notion about the genetic prerequisites to transition from solitary to collective states. Further, we establish that a complex syndrome such as locust swarming emerges through modular regulatory systems that can be amplified, modified, or attenuated across the tree of life.

evolutionary biology↗

bioRxiv2026

Highly contiguous genomes of Rhodnius prolixus and Triatoma rubida reveal the molecular basis of haematophagy evolution in Triatominae

Insects of the subfamily Triatominae, commonly known as kissing bugs, are obligate blood-feeding vectors of Trypanosoma cruzi, the causative agent of Chagas disease. Rhodnius prolixus is among the most epidemiologically important vectors in Latin America, whereas Triatoma rubida frequently invades homes and is a potential vector in the southern United States and northern Mexico. Triatomines likely evolved from predatory reduviid assassin bugs through a transition from feeding on arthropods associated with vertebrate hosts to feeding directly on vertebrate blood. To investigate the genomic basis of this ecological and dietary shift, we generated highly contiguous, near chromosome-level genome assemblies and structural gene annotations for R. prolixus and T. rubida. The new R. prolixus assembly improves scaffold N50 more than 40-fold over the current reference genome, from 1.1 to 43.9 Mb, while reducing assembly gaps by several orders of magnitude. Both assemblies exceed 97% BUSCO completeness. Comparative analyses with representative hemipteran genomes revealed expansions of gene families associated with chemosensation and metabolism, including detoxification, protein degradation, and digestion, together with signatures of positive selection in genes involved in digestive and sensory functions. These assemblies represent the most contiguous and complete genomic resources available for Triatominae and provide a robust foundation for investigating vector biology, host adaptation, and the evolutionary origins of blood feeding within Reduviidae. Interpretive summaryKissing bugs are insects that are known for feeding on blood. They can spread a disease called Chagas disease because they transmit a parasite called Trypanosoma cruzi. To understand how kissing bugs evolved and which genes facilitate blood feeding of vertebrates, a collaboration between scientists at USDA-ARS, University of Georgia, and University of South Bohemia sequenced the genome of two kissing bugs: Rhodnius prolixus and Triatoma rubida. By comparing the genes with those of other insects in the order Hemiptera, scientists discovered that kissing bugs have more genes involved with detecting environmental chemical stimuli and metabolism as well as positive selection for genes involved with digestion and sensory-related proteins. These genome assemblies will help scientists learn more about how these insects evolved, and this research is important for understanding insect feeding biology which can be used to develop methods to control the kissing bugs and the spread of Chagas disease.

evolutionary biology↗

bioRxiv2025

An loss of independence: genomic insights into a pest fruit fly-bacterial mutualism

Obligate microbial symbioses are often characterized by streamlined biosynthetic pathways and reduced genomes. The evolutionary process of this reduction first involves an increase in the abundance of non-functional coding genes (pseudogenes) followed by their removal. The olive fruit fly (Bactrocera oleae) harbors an extracellular symbiotic gut bacterium Candidatus Erwinia dacicola, which is crucial to its usage of fruit from the olive genus Olea as a larval food source. In this study, we combined genomics and transcriptomics of Ca. E. dacicola to investigate pathways that facilitate this mutualism. Of 4,675 genes in the Ca. E. dacicola genome, 1,783 were classified as pseudogenes. Some biochemical pathways such as amino acid pathways, biofilm regulator BssS, and 6-phospho-{beta}-glucosidase which are implicated in hydrolyzing oleuropein were complete. However, pathways connected to baseline homeostasis, which would impact cellular functions needed for a bacterium to be free-living, were heavily pseudogenized. Gene selection analyses in Ca. E. dacicola, when compared to related organisms, indicated positive selection on genes related to amino acid metabolism, carbon utilization, transport, and energy production. Our results indicate that Ca. E. dacicola is likely producing amino acids and metabolizing plant phytochemicals. These results reveal that the Ca. E. dacicola genome is undergoing incipient genome erosion in support of an unculturable obligate mutualism. ImportanceMany beneficial bacteria that live inside insects have highly reduced genomes, but little is known about the transitional stages that occur as free-living microbes evolve into obligate symbionts. We show that the olive fruit fly symbiont, Candidatus Erwinia dacicola, retains hallmarks of its plant-associated ancestry while undergoing extensive genome degradation, including the accumulation of mobile DNA elements and inactive genes. At the same time, genes involved in nutrient production, environmental persistence, and host interactions remain functional and are evolving under selection, providing a rare snapshot of how bacterial genomes are reshaped during the evolution of an obligate mutualism. These findings have implications for how obligate gut symbioses are formed and maintained in insect herbivores.

genomics↗

bioRxiv2025

Genome Report: Improved chromosome-level genome assembly of the American cockroach, Periplaneta americana

1The American cockroach, Periplaneta americana, is a cosmopolitan insect notorious for thriving among humans undeterred by attempts to eliminate it. The traits that contribute to its ubiquity as an opportunistic pest, such as long lifespan, expansive neurosensory capacity, and nutritional flexibility, also make P. americana an excellent invertebrate model organism with a long history in neuroscience and physiological research. Current genetic resources available for P. americana highlight its large, complex genome and richly diverse transcriptional capabilities, but fall short of producing a complete, chromosome-level genome. Here, we present a high-quality de novo genome assembly of a laboratory-raised adult female P. americana using a combination of high fidelity PacBio long reads and Hi-C sequencing. The final 3.23 Gb genome was assembled with chromosomal resolution into 17 scaffolds, consistent with previous karyotype analysis, and has a scaffold N50 of 188.1 Mb and genome BUSCO score of 99.7%. This assembly includes a chromosome that was missing from the previous reference genome for this species. Protein prediction and annotation were performed via the NCBI Eukaryotic Genome Annotation Pipeline, which identified 16,780 protein-coding genes and generated an annotation BUSCO score of 97.8%. Ortholog comparisons with available Blattodea assemblies highlight the expanded chemosensory and immune capabilities of P. americana compared to termite relatives. This genome assembly is a valuable tool for facilitating future research on the biology and evolution of this remarkable insect.

genomics↗