Biology subjects

Richards, L. A.

Publications and source records attributed to Richards, L. A..

5 recordsLinked to original sources

bioRxiv2025

Methanotrophic acetogenesis drives a novel pathway of arsenic mobilization in reducing groundwaters

Geogenic arsenic (As) contamination in groundwater, widely used as drinking water, poses a global health risk, yet the microbial pathways linking electron donor oxidation to the reduction of As-bearing Fe(III) oxyhydroxides remain poorly understood. Here, we deployed Fe(III) (oxyhydr)oxide-coated pumice stones in high-As, high-methane groundwater in Cambodia for 270 days to capture planktonic metal-reducing microbial communities in-situ. These were used to inoculate anaerobic microcosms with methane or volatile fatty acids (VFAs) as electron donors over 200 days. Genome-resolved metagenomics revealed that methane oxidation via reverse methanogenesis led to acetate production, which in turn provided the primary electrons for Fe(III) and As(V) reduction in the microcosms, resulting in As(III) release. Our findings highlight an indirect coupling between methane oxidation and arsenic mobilization, with acetate as the key intermediate. This study offers new insights into the role of methane in subsurface biogeochemical cycling and its implications for arsenic contamination in groundwater systems. SynopsisThe study uses a novel in situ sampling procedure, coupled with metagenomic analysis, to identify anaerobic methane oxidation producing acetate, as a potentially important pathway to generate electron donors for microbial Fe(III) and As(V) reduction in aquifer sediments. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=72 SRC="FIGDIR/small/696296v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@801222org.highwire.dtl.DTLVardef@268d01org.highwire.dtl.DTLVardef@f342e2org.highwire.dtl.DTLVardef@ac1f9d_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2025

Admixture and environment shape population genetic and phytochemical variation across a conifer hybrid zone

1Ancestry variation in hybrid zones can reflect the causes and genetic basis of reproductive isolation and result in novel phenotypic variation with the potential for extended ecological effects. Junipers (Juniperus) are foundational tree species in many semi-arid landscapes of western North America and often hybridize in zones of secondary contact. Such hybridization can be ecologically significant in foundational tree species, due to the strong genetic control and ecological consequences of plant chemistry. We generated genetic and phytochemical data to analyze hybridization among Juniperus grandis, J. occidentalis, and J. osteosperma in western Nevada and its impact on plant chemistry. We used population genomic data (9,125 SNPs; 326 individuals; 25 populations) to quantify patterns of genetic variation across populations and species and characterize ancestry variation in hybrids. While populations within species showed little genetic differentiation, the parental species formed distinct, monophyletic lineages with clear phenotypic and ecological differences. Hybrids occupied intermediate environments, contained ancestry from all three parents, and were mainly F1 or backcross hybrids. Phytochemical data (GC-MS; 163 terpenoid compounds) were likewise analyzed to understand the consequences of hybridization for plant chemistry. The parental species and hybrids displayed distinct phytochemical profiles, with hybrids often characterized by a combination of transgressive and intermediate chemical concentrations. Our results illustrate that geography and environment shape hybrid ancestry for a syngameon involving three Juniperus species, and that admixture generates novel phytochemical variation likely to have ecological consequences.

evolutionary biology↗

bioRxiv2023

Intra and interspecific diversity in a tropical plant clade alter herbivory and ecosystem resilience

Declines in biodiversity generated by anthropogenic stressors at both species and population levels can alter emergent processes instrumental to ecosystem function and resilience. As such, understanding the role of biodiversity in ecosystem function and its response to climate perturbation is increasingly important, especially in tropical systems where responses to changes in biodiversity are less predictable and more challenging to assess experimentally. Using large scale transplant experiments conducted at five neotropical sites, we documented the impacts of changes in intraspecific and interspecific plant richness in the genus Piper on insect herbivory, insect richness, and ecosystem resilience to perturbations in water availability. We found that reductions of both intraspecific and interspecific Piper diversity had measurable and site specific effects on herbivory, herbivorous insect richness, and plant mortality. The responses of these ecosystem-relevant processes to reduced intraspecific Piper richness were often similar in magnitude to the effects of reduced interspecific richness. Increased water availability reduced herbivory by 4.2% overall, and the response of herbivorous insect richness and herbivory to water availability were altered by both intra and interspecific richness in a site dependent manner. Our results underscore the role of intraspecific and interspecific richness as foundations of ecosystem function and the importance of community and location specific contingencies in controlling function in complex tropical systems.

ecology↗

bioRxiv2020

Evidence for both phylogenetic conservatism and lability in the evolution of secondary chemistry in a tropical angiosperm radiation

Over evolutionary timescales, shifts in plant secondary chemistry may be associated with patterns of diversification in associated arthropods. Although foundational hypotheses of plant-insect codiversification and plant defense theory posit closely related plants should have similar chemical profiles, numerous studies have documented variation in the degree of phylogenetic signal, suggesting phytochemical evolution is more nuanced than initially assumed. We utilize proton nuclear magnetic resonance (1H NMR) data, chemical classification, and genotyping-by-sequencing to resolve evolutionary relationships and characterize the evolution of secondary chemistry in the Neotropical plant clade Radula (Piper; Piperaceae). Sequencing data substantially improved phylogenetic resolution relative to past studies, and spectroscopic characterization revealed the presence of 35 metabolite classes. Broad metabolite classes displayed strong phylogenetic signal, whereas the crude 1H NMR spectra featured evolutionary lability in chemical resonances. Evolutionary correlations were detected in two pairs of compound classes (flavonoids with chalcones; p-alkenyl phenols with kavalactones), where the gain or loss of a class was dependent on the others state. Overall, the evolution of secondary chemistry in Radula is characterized by strong phylogenetic signal of broad compound classes and concomitant evolutionary lability of specialized chemical motifs, consistent with both classic evolutionary hypotheses and recent examinations of phytochemical evolution in young lineages.

evolutionary biology↗

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↗