Biology subjects

Huzar, A. K.

Publications and source records attributed to Huzar, A. K..

5 recordsLinked to original sources

bioRxiv2025

The microbial fingerprint: fine-scale environmental, genetic, and temporal factors drive the reef metagenome during coral spawning

Understanding the stability of microbial community assembly on coral reefs is crucial for determining their response to changing environments. Here, we evaluate how the marine sediment, water column, and mountainous star coral (Orbicella faveolata) metagenomic communities shift over temporal, spatial, and genetic gradients, centered on the annual coral spawning event on St. Croix, USVI. Using low-coverage shotgun sequencing and a reference-free approach, we characterized metagenomic communities and additionally report 15 metagenome-assembled genomes from environmental samples. We show that diel time can be as important as kilometer-scale distance in structuring the coral-associated and marine sediment community structure, albeit with other highly local factors (genotype, within-reef location) driving most variation. Through multivariate machine learning methods, we find several taxa and metabolic pathways enriched over time, where broad metagenomic community shifts may be linked with concurrent temperature increase or the annual coral spawning event. As understanding the coral microbiome in the context of its environment becomes increasingly important, our research underscores the importance of small-scale variation, both spatially and temporally, in structuring coral reef metagenomic communities.

ecology↗

bioRxiv2024

Outside your shell: how temperature shapes genetic variation in two species of congeneric marine snails

Intertidal organisms withstand extreme temperature fluctuations, and their ability to cope with this variation may affect their distributions across the seascape. Genetic variation and local environments likely interact to determine variation in thermal performance across intertidal species ranges, so characterizing the relationship between temperature variation and population structure is key to understanding the biology of marine invertebrates. Here, we use 2bRAD-sequencing to examine population genetic structure in two congeneric intertidal marine gastropods (Crepidula fornicata, C. plana), sampled from locations along a natural temperature gradient on the Northeast shores of the United States. These two species share similar life histories, yet C. plana exhibits a narrower distribution than C. fornicata. Our results demonstrate that both species show patterns of genetic divergence consistent with isolation by distance, though this pattern was only significant in C. fornicata. Both putatively selected and neutral loci displayed significant spatial structuring in C. fornicata; however, only putatively selected loci showed significant clustering in C. plana. When exploring whether temperature differences explained genetic differentiation, we found that 9-12% of genetic differentiation was explained by temperature variation in each species even when controlling for latitude and neutral population structure. Our results suggest that temperature shapes adaptive variation across the seascape in both Crepidula species and encourages further research to differentiate our results from models of neutral evolutionary drift.

evolutionary biology↗

bioRxiv2024

Distinct modes of holobiont specialization among cryptic coral lineages

As ocean warming threatens reefs worldwide, identifying corals with adaptations to higher temperatures is critical for conservation. Genetically distinct but morphologically similar (i.e., cryptic) coral populations can be specialized to extreme habitats and thrive under stressful conditions. These corals often associate with locally beneficial microbiota (Symbiodiniaceae photobionts and bacteria), clouding interpretation of the drivers of thermal tolerance. Here, we leverage a holobiont (massive Porites) with high host-partner fidelity to investigate adaptive variation across classic ("typical" conditions) and extreme reefs characterized by higher temperatures and light attenuation. We uncovered three cryptic lineages that exhibit limited micro-morphological variation; one lineage dominated classic reefs (L1), one had more even distributions (L2), and a third was restricted to extreme reefs (L3). Two lineages were more closely related to populations [~]4300 km away, suggesting that these lineages are widespread. All corals harbored Cladocopium C15 photobionts, but strain-level compositions differed among lineages and reef types. L1 associated with distinct photobionts and bacteria in each reef type, whereas L2 had relatively stable associations. L3 hosted unique photobiont strains, signaling high host-photobiont fidelity. Analysis of light harvesting capacity and thermal tolerance revealed key adaptive variation underpinning survival in distinct habitats. L1 had the highest light absorption efficiency and lowest thermal tolerance, suggesting it is a classic reef specialist. L3 had the lowest light absorption efficiency and the highest thermal tolerance, showing that it is an extreme reef specialist. L2 had intermediate light absorption efficiency and thermal tolerance, signaling habitat generalism, potentially explaining how it survives well in both habitat types. These findings reveal diverging holobiont strategies to cope with extreme conditions. Resolving coral lineages is key to understanding variation in thermal tolerance among coral populations; uncovering thermally-tolerant holobionts can strengthen our understanding of coral evolution and symbiosis, and support global conservation and restoration efforts.

ecology↗

bioRxiv2023

Symbiosis modulates gene expression of symbionts, but not hosts, under thermal challenge

Increasing ocean temperatures are causing dysbiosis between coral hosts and their symbionts. Previous work suggests that coral host gene expression responds more strongly to environmental stress compared to their intracellular symbionts; however, the causes and consequences of this phenomenon remain untested. We hypothesized that symbionts are less responsive because hosts modulate symbiont environments to buffer stress. To test this hypothesis, we leveraged the facultative symbiosis between the scleractinian coral Oculina arbuscula and its symbiont Breviolum psygmophilum to characterize gene expression responses of both symbiotic partners in and ex hospite under thermal challenges. To characterize host and in hospite symbiont responses, symbiotic and aposymbiotic O. arbuscula were exposed to three treatments: 1) control (18{degrees}C), 2) heat (32{degrees}C), and 3) cold (6{degrees}C). This experiment was replicated with B. psygmophilum cultured from O. arbuscula to characterize ex hospite symbiont responses. Both thermal challenges elicited classic environmental stress responses (ESRs) in O. arbuscula regardless of symbiotic state, with hosts responding more strongly to cold challenge. Hosts also exhibited stronger responses than in hospite symbionts. In and ex hospite B. psygmophilum both downregulated genes associated with photosynthesis under thermal challenge; however, ex hospite symbionts exhibited greater gene expression plasticity and differential expression of genes associated with ESRs. Taken together, these findings suggest that O. arbuscula hosts may buffer environments of B. psygmophilum symbionts; however, we outline the future work needed to confirm this hypothesis.

molecular biology↗

bioRxiv2022

Exposure to global change and microplastics elicits an immune response in an endangered coral

Global change is increasing seawater temperatures and decreasing oceanic pH, driving declines of coral reefs globally. Coral ecosystems are also impacted by local stressors, including microplastics, which are ubiquitous on reefs. While the independent effects of these global and local stressors are well-documented, their interactions remain less explored. Here, we examine the independent and combined effects of global change (ocean warming and acidification) and microplastics exposures on gene expression (GE) and microbial community composition in the endangered coral Acropora cervicornis. Nine genotypes were fragmented and maintained in one of four experimental treatments: 1) ambient conditions (ambient seawater, no microplastics; AMB); 2) microplastics treatment (ambient seawater, microplastics; MP); 3) global change conditions (warm and acidic conditions, no microplastics; OAW); and 4) multistressor treatment (warm and acidic conditions with microplastics; OAW+MP) for 22 days, after which corals were sampled for genome-wide GE profiling and ITS and 16S metabarcoding. Overall A. cervicornis GE responses to all treatments were subtle; however, corals in the multistressor treatment exhibited the strongest GE responses, and genes associated with innate immunity were overrepresented in this treatment, according to gene ontology enrichment analyses. 16S analyses revealed stable microbiomes dominated by the bacterial associate Aquarickettsia, suggesting that these A. cervicornis fragments exhibited remarkably low variability in bacterial community composition. Future work should focus on functional differences across microbiomes, especially Aquarickettsia and viruses, in these responses. Overall, results suggest that local stressors present a unique challenge to endangered coral species under global change.

ecology↗