Biology subjects

Conover, A. E.

Publications and source records attributed to Conover, A. E..

5 recordsLinked to original sources

bioRxiv2026

Connectivity and dispersal mode shape the landscape genetics of a carnivorous pitcher plant-arthropod metacommunity

Dispersal differences between hosts and their symbionts can generate mismatched population structure, potentially destabilizing beneficial interactions across space. We tested this possibility in the carnivorous pitcher plant Darlingtonia californica and its obligate arthropod associates, the midge Metriocnemus edwardsi and the mite Sarraceniopus darlingtoniae, sampled across sites spanning the hosts patchy range in Oregon and northern California, USA. Comparing nuclear and chloroplast genomic data from D. californica with mitochondrial COI data from both arthropods, we tested how range position, landscape connectivity, and dispersal mode influence population genetic structure across this mutualistic metacommunity. Host plant populations supported the central-marginal hypothesis: nuclear diversity declined toward the range margins, and marginal populations showed greater nuclear genetic differentiation. Chloroplast variation was more weakly structured, most clearly separating the northern Oregon Coast populations and revealing cytonuclear discordance consistent with historical seed-mediated movement or chloroplast capture near the boundary between neighboring regions. Landscape connectivity estimated from an ecological niche model was also associated with genetic exchange. Circuit-theoretic current flow was positively related to effective migration inferred independently from plant genotypes. Further, landscape resistance explained variation in plant and mite differentiation beyond geographic distance alone. Both arthropods showed significant spatial congruence with the host plant but not with one another, a pattern inconsistent with co-dispersal and suggesting that each associate tracks the shared landscape according to its own dispersal biology. These results show that regional genetic concordance among obligate ecological partners can coexist with substantial differences in the processes governing their movement and local connectivity.

ecology↗

bioRxiv2026

Global distribution of cultivated Trichodesmium subclades revealed by multi-omics

Trichodesmium is an important oceanic N2 fixing cyanobacterial genus that has been shown to provide up to 50% of new N to oligotrophic regimes. Despite its importance, we know relatively little about the genomic potential and functional diversity of the two major clades of Trichodesmium (Clade I and Clade III, hereafter Thieb and Tery, respectively). With the expanded collection of Trichodesmium isolates in the USCTCC (University of Southern California Trichodesmium Culture Collection), we sequenced genomes from seven cultivated strains to further characterize the genomic diversity within the genus. For example, sequencing the genome of the "gigantic", red Trichodesmium contortum surprisingly shows that they are closely related to the smallest Trichodesmium clade, TeryA. The high genomic identity between TeryA and T. contortum (>98.5% ANI) and lack of implicated auxiliary genes suggests their large biovolume differences might be transcriptional or epigenetic in origin. Furthermore, these data show that using Tery-subclades are a more accurate designation than the classical Trichodesmium species delineation. Finally, we placed the analysis of these genomes in an ecological context via read mapping with globally distributed RNA and DNA datasets. Our data show that Tery clades (A&B) are both lower in relative abundance compared to Thieb in global oceans, generally co-occur when detected in the field, and are highly linked to decreased salinity and increased temperatures, especially for sampling locations in the Bay of Bengal. Lastly, even though TeryA members are undersaturated with respect to current CO2 concentrations, our phenotypic and biogeography data suggests that salinity/ocean color could limit their predicted global impact as climate changes.

microbiology↗

bioRxiv2022

Importance of Mobile Genetic Element Immunity in Numerically Abundant Trichodesmium Clades

The colony-forming cyanobacteria Trichodesmium spp. are considered one of the most important nitrogen-fixing genera in the warm, low nutrient, open ocean. Despite this central biogeochemical role, many questions about their evolution, physiology, and trophic interactions remain unanswered. To address these questions, we describe the genetic potential of the genus via significantly improved genomic assemblies of strains Trichodesmium thiebautii H94, Trichodesmium erythraeum 2175, and 17 new Trichodesmium metagenome-assembled genomes (MAGs, >50% complete) from hand-picked, Trichodesmium colonies spanning the Atlantic Ocean. Phylogenomics identified [~]four N2 fixing clades of Trichodesmium across the transect, with T. thiebautii dominating the colony-specific reads. Pangenomic analyses showed that all T. thiebautii MAGs are enriched in defense mechanisms and encode a vertically inherited Type III-B Clustered Regularly Interspaced Short Palindromic Repeats and associated protein-based immunity system (CRISPR-Cas hereafter). Surprisingly, this CRISPR-Cas system was absent in all T. erythraeum genomes and MAGs, vertically inherited by T. thiebautii, and correlated with increased signatures of horizontal gene transfer. Multiple lines of evidence indicate that the CRISPR-Cas system is functional in situ: 1. Trichodesmium CRISPR spacer sequences with 100% identical hits to field-assembled, putative phage genome fragments were identified, 2. High Trichodesmium spacer sequence variability indicating rapid adaptation, and 3. metaproteomic and transcriptomic expression analyses detecting the CRISPR-Cas system components in Trichodesmium colonies from the Atlantic and Pacific Oceans. These data suggest that phage or mobile genetic element immunity in T. thiebautii could contribute to their success, gene diversity, and numerical dominance over T. erythraeum in the oceans, thus warranting further Trichodesmium virome investigations. Significance statementOur work identifies CRISPR-Cas immunity as a phylogenetically distinct, environmentally expressed factor in the speciation of closely related N2-fixing Trichodesmium clades. These findings suggest that differential phage predation and resistance could be a previously overlooked selective pressure in the genus, potentially leading to the current numerical dominance of T. thiebautii over T. erythraeum in the oceans. Furthermore, while the currently CO2-limited T. erythraeum is expected to be a winner of anthropogenic climate change, their predicted higher phage sensitivity than T. thiebautii could challenge this outcome.

microbiology↗

bioRxiv2021

Alphaproteobacteria facilitate Trichodesmium community trimethylamine utilization

In the surface waters of the warm oligotrophic ocean, filaments and aggregated colonies of the nitrogen (N)-fixing cyanobacterium Trichodesmium create microscale nutrient-rich oases. These hotspots fuel primary productivity and harbor a diverse consortium of heterotrophs. Interactions with associated microbiota can affect the physiology of Trichodesmium, often in ways that have been predicted to support its growth. Recently, it was found that trimethylamine (TMA), a globally-abundant organic N compound, inhibits N2 fixation in cultures of Trichodesmium without impairing growth rate, suggesting that Trichodesmium receives nitrogen from TMA. In this study, 15N-TMA DNA stable isotope probing (SIP) of a Trichodesmium enrichment was employed to further investigate TMA metabolism and determine if TMA-N is incorporated directly or secondarily via cross-feeding facilitated by microbial associates. Herein we identify two members of the marine Roseobacter clade (MRC) of Alphaproteobacteria as the likely metabolizers of TMA and provide genomic evidence that they converted TMA into a more readily available form of N, e.g., NH4+, which was subsequently used by Trichodesmium and the rest of the community. The results implicate microbiome-mediated carbon (C) and N transformations in modulating N2 fixation, and thus highlight the involvement of host-associated heterotrophs in global biogeochemical cycling.

microbiology↗

bioRxiv2019

Hydrothermal activity and water mass composition shape microbial eukaryote diversity and biogeography in the Okinawa Trough

Microbial eukaryotes (protists) contribute substantially to ecological functioning in marine ecosystems, but factors shaping protist diversity, such as dispersal barriers and environmental selection, remain difficult to parse. Deep-sea water masses, which form geographic barriers, and hydrothermal vents, which represent isolated productivity hotspots, are ideal opportunities for studying the effects of dispersal barriers and environmental selection on protist communities. The Okinawa Trough, a deep, back-arc spreading basin, contains distinct water masses in the bottom waters of northern and southern regions and at least twenty-five active hydrothermal vents. In this study, we used metabarcoding to characterize protist communities from fourteen stations spanning the length of the Okinawa Trough, including three hydrothermal vent sites. Significant differences in community structure reflecting regional oceanography and water mass composition were present, indicating the importance of geographic factors in shaping protist communities. Protist communities in bottom waters affected by hydrothermal activity were significantly different from communities in other bottom waters, suggesting that environmental factors can be especially important in shaping community composition under specific conditions. Amplicon sequence variants that were enriched in hydrothermally influenced bottom waters largely derived from cosmopolitan protists that were present, but rare, in other near-bottom samples, thus highlighting the importance of the rare biosphere.

ecology↗