Biology subjects

Campbell, L. G.

Publications and source records attributed to Campbell, L. G..

5 recordsLinked to original sources

bioRxiv2025

Dissolved oxygen concentrations influence microbial diversity, abundance and dominant players in an oxygen minimum zone

Expansion of marine global oxygen minimum zones (OMZs) can have profound impacts on resident macrofauna. Less obvious is the influence OMZs will have on the diversity and abundance of planktonic microbes. This is particularly true in understudied OMZs such as the northern Benguela Upwelling System (nBUS). Here, we analyzed the influence of oxygen concentrations on the microbial community in the nBUS OMZ using 16S rRNA gene (iTag) sequence data. In the nBUS oxygen was a primary driver influencing microbial community structure and diversity. Diversity was highest in dysoxic samples and lowest in suboxic samples, which was primarily due to changes in community evenness in relationship to oxygen concentrations. For example, evenness decreased in suboxic samples due to oscillations in the abundance of microbial groups such as Thioglobaceae (SUP05), which was found to be the most abundant microbe in the nBUS OMZ and significantly increased in abundance as oxygen decreased. This finding prompted an analysis of 217 publicly available medium to high quality Thioglobaceae genomes, including cultured representatives, from the nBUS and other OMZs. Genome annotation of these Thioglobaceae indicated important roles in carbon cycling, sulfur oxidation and denitrification. Importantly, few Thioglobaceae possess the genetic potential to carry out complete denitrification, as most lack the gene that codes for nitrous oxide reductase (NosZ), which converts nitrous oxide (N2O), a potent greenhouse gas, to nitrogen gas. As OMZs expand in size and severity, decreasing microbial diversity and a concomitant increase in Thioglobaceae abundances, could lead to enhanced N2O production through incomplete denitrification. ImportanceHere, we found that microbial diversity decreased significantly with declining oxygen concentrations in the nBUS OMZ. However, one microbial group, the Thioglobaceae, was most abundant when oxygen was lowest. This group is able to support its growth through sulfur oxidation using either oxygen or nitrate (denitrification). A comprehensive genomic analysis of Thioglobaceae in the nBUS and in the global ocean revealed that few have the capacity to carry out complete denitrification, with the final step in this process often missing in these genomes. This incomplete pathway is consequential, as it can be an important source of nitrous oxide, particularly in marine OMZs such as the understudied nBUS. Collectively, this study provides new information on an OMZ, and definitively links an important microbial pathway, incomplete denitrification, to a particular and highly abundant group of microbes that appear to have a strong response to declining oxygen concentrations in the marine environment.

microbiology↗

bioRxiv2021

No Correlation Between Pollen Fertility and Viability: Differential Measures of Male Gametophytic Fitness in Cannabis sativa L.

Pollen grains are male gametophytes, an ephemeral haploid generation of plants, commonly engaging in competition for a limited supply of ovules. Since differential male fertility may influence the direction and pace of population evolution, the relative fitness of pollen is regularly estimated as either pollen viability, the proportion of pollen containing intact cytoplasms and regenerative nuclei, or pollen fertility, the frequency of pollen germinating under standardized conditions. Here, we estimated the relative fitness of pollen in a dioecious, wind-pollinated model system, Cannabis sativa, by characterizing pollen fertility and viability from multiple sires. Pollen fertility quickly declined within two weeks of anther dehiscence, and pollen stored under freezer conditions did not germinate regardless of storage time. In contrast, pollen viability declined slowly and persisted longer than the lifetime of a sporophyte plant under both room temperature and freezer conditions. Pollen samples that underwent both fertility and viability analysis displayed no significant correlation, implying researchers cannot predict pollen fertility from pollen viability, nor infer male gametophytic fitness from a single measure. Our work demonstrates two approaches to measure proxies of male fitness in C. sativa, and identifies new questions around what are valuable estimates of male fitness in plants.

plant biology↗

bioRxiv2021

A comparison of wild and captive Comal Springs riffle beetle (Heterelmis comalensis) microbiomes

The gut microbiome is affected by host intrinsic factors, diet, environment, and strongly linked to hosts health. Although fluctuations of microbiome composition are normal, some are due to changes in host environmental conditions. When species are moved into captive environments for conservation, education, or rehabilitation, these new conditions can influence a change in gut microbiome composition. Here, we compared the microbiomes of wild and captive Comal Springs riffle beetles (Heterelmis comalensis) by using amplicon sequencing of the 16S rRNA gene. We found that the microbiome of captive beetles was more diverse than wild beetle microbiomes. We identified 24 Amplicon Sequence Variants (ASVs) with relative abundances significantly different between the wild and captive beetles. Many of the ASVs overrepresented in captive beetle microbiomes belong to taxa linked to nitrogen-rich environments. This is one of the first studies comparing the effects of captivity on the microbiome of an endangered insect species. Our findings provide valuable information for future applications in the management of captive populations of H. comalensis.

microbiology↗

bioRxiv2019

Correlates of hybridization in plants

Hybridization is a biological phenomenon increasingly recognized as an important evolutionary process in both plants and animals, as it is linked to speciation, radiation, extinction, range expansion and invasion, and allows for increased trait diversity in agricultural and horticultural systems. Estimates of hybridization frequency vary across taxonomic groups, and previous work has demonstrated that some plant groups hybridize more frequently than others. Here, we ask on a global scale whether hybridization is linked to any of 11 traits related to plant life history, reproduction, genetic predisposition, and environment or opportunity. Given that hybridization is not evenly distributed across the plant tree of life, we use phylogenetic generalized least squares regression models and phylogenetic path analysis to detect statistical associations between hybridization and plant traits at both the family and genus levels. We find that perenniality and woodiness are each associated with an increased frequency of hybridization in univariate analyses, but path analysis suggests that the direct linkage is between perenniality and increased hybridization (with woodiness having only an indirect relationship with hybridization via perenniality). Associations between higher rates of hybridization and higher outcrossing rates, abiotic pollination syndromes, vegetative reproductive modes, larger genomes, and less variable genome sizes are detectable in some cases but not others. We argue that correlational evidence at the global scale, such as that presented here, provides a robust framework for forming hypotheses to examine and test drivers of hybridization at a more mechanistic level.\n\nIMPACT SUMMARYAlthough historically thought of as rare, inter-specific mating is increasingly recognized as an important evolutionary process. Hybridization can generate increased genetic and morphological variation and has been tied to increased diversification and other biological phenomena such as geographic range expansion and the success of invasive species. Here, we examine hybridization of plants on a global scale. Previous work has demonstrated that some plant groups hybridize more than others, but the reasons for this pattern remain unclear. We combine data from eight regional floras with trait data to test for associations between hybridization and different aspects of plant biology, such as life history, growth form, reproduction, and opportunity, all while accounting for the fact that plant lineages are related to each other.\n\nWe find that plant groups that are dominated by perennial species and species with woody growth forms tend to hybridize more than those dominated by annual or herbaceous species. We also find some evidence that frequent hybridization is found in plant families that are predominantly pollinated abiotically (such as by wind or water) or have higher rates of outcrossing, plant genera that have less variable genome sizes, and plant groups (both genera and families) that can reproduce asexually and have larger genome sizes. This study provides the first analysis of the global correlates of hybridization in plants. Although this correlational evidence does not provide any mechanistic explanations for these patterns, the trends we find are novel in terms of both geographic and taxonomic sale. The correlations detected provide robust hypotheses for understanding the conditions for hybridization and its contributions to evolution.

evolutionary biology↗

bioRxiv2018

Extent of the annual Gulf of Mexico hypoxic zone influences microbial community structure

Rich geochemical datasets generated over the past 30 years have provided fine-scale resolution on the northern Gulf of Mexico (nGOM) coastal hypoxic ([≤] 2 mg of O2 L-1) zone. In contrast, little is known about microbial community structure and activity in the hypoxic zone despite the implication that microbial respiration is responsible for forming low dissolved oxygen (DO) conditioXSns. Here, we hypothesized that the extent of the hypoxic zone is a driver in determining microbial community structure, and in particular, the abundance of ammonia-oxidizing archaea (AOA). Samples collected across the shelf for two consecutive hypoxic seasons in July 2013 and 2014 were analyzed using 16S rRNA gene sequencing, oligotyping, microbial co-occurrence analysis and quantification of thaumarchaeal 16S rRNA and archaeal ammonia-monooxygenase (amoA) genes. In 2014 Thaumarchaeota were enriched and inversely correlated with DO while Cyanobacteria, Acidimicrobiia and Proteobacteria where more abundant in oxic samples compared to hypoxic. Oligotyping analysis of Nitrosopumilus 16S rRNA gene sequences revealed that one oligotype was significantly inversely correlated with dissolved oxygen (DO) in both years and that low DO concentrations, and the high Thaumarchaeota abundances, influenced microbial co-occurrence patterns. Taken together, the data demonstrated that the extent of hypoxic conditions could potentially influence patterns in microbial community structure, with two years of data revealing that the annual nGOM hypoxic zone is emerging as a low DO adapted AOA hotspot.

microbiology↗