Biology subjects

Wall, C. B.

Publications and source records attributed to Wall, C. B..

6 recordsLinked to original sources

bioRxiv2026

Does host diversity beget microbiome diversity? Effects of zooplankton diversity and composition on environmental and host-associated microbes

Microbiomes alter host health and are shaped by transmission within and among host taxa. Microbes can alter host communities, yet whether the diversity of hosts reciprocally shapes microbial communities remains poorly resolved. Diverse host communities may promote microbiome diversity through elevated cross-species microbial spillover or reduce it by diluting conspecific transmission. Here, we manipulated the composition and diversity of pond zooplankton communities to test how host diversity and density alter host-associated and environmental microbiomes. Host diversity had opposing effects on microbiome alpha diversity for different zooplankton host species, increasing microbiome diversity in calanoid copepods while reducing it in Daphnia, with no effect on environmental microbes. Host diversity amplified cross-species microbial spillover for subordinate competitors (calanoid copepods) and diluted conspecific transmission for the dominant competitor (Daphnia). These contrasting responses reflected shifts in indicator microbes associated with each host taxon. Increasing host turnover generated higher microbiome turnover, demonstrating that microbiome assembly depends on host community composition. Our results indicate that contact with both conspecifics and heterospecifics alters animal microbiomes, and that host diversity can either promote the spillover or dilute the transmission of microbes in different zooplankton with potential effects on host health and ecosystems.

ecology↗

bioRxiv2026

Coral Guard substrates accelerate growth and fragment fusion for coral restoration

Coral reefs are declining globally, creating an urgent need for scalable technologies that improve the efficiency and effectiveness of active reef restoration. Coral reef restoration is increasingly constrained by algal overgrowth, which suppresses coral growth, survival, and restoration efficiency. Building on the recently developed Coral Guard platform, we evaluate its restoration performance under long-term in situ coral nursery conditions and introduce Fusion Guard Tiles, a geometry-optimized Coral Guard design that accelerates microfragment fusion. We evaluated Coral Guard Plugs using the branching coral Stylophora pistillata under complementary ex situ conditions and Fusion Guard Tiles using the massive reef-building coral Porites evermanni in in situ coral nurseries. In P. evermanni, Fusion Guard Tiles increased lateral tissue growth 2.6-fold and three-dimensional tissue surface area growth by >2.7-fold after 6 months compared with conventional substrates. After 12 months, colony height and volume were approximately 4.0-fold and 2.2-fold greater, respectively, while complete fragment fusion occurred only on Fusion Guard Tiles. In S. pistillata, Coral Guard Plugs increased lateral tissue growth by [~]1.7-fold. Microcomputed tomography revealed 10-13% higher skeletal density in both species. In P. evermanni, Fusion Guard Tiles also increased symbiont density by 70% and tissue protein content by [~]2.5-fold relative to controls. Together, these findings demonstrate that Coral Guard substrates suppress algal competition while accelerating coral growth, skeletal development, and microfragment fusion, providing a scalable, low-maintenance technology to enhance coral nursery productivity and reef restoration.

bioengineering↗

bioRxiv2026

Consistent, scale-dependent differences in the biogeography of host-associated and free-living microbiomes across systems

Microbial communities are critical to the functioning of ecosystems and shape the ecology and evolution of host organisms. However, we have a limited understanding of how host-associated and free-living microbes differ in their structure and biogeography. Here, we test whether host-associated (fish gut) and free-living (lake bacterioplankton) microbes exhibit different metacommunity structure, spatial turnover, and consistency with neutral expectations using two independent lake systems. We characterized microbial communities in lake water (Vancouver Island and Sierra Nevada) and guts in two fish species (stickleback and brook trout) using 16S amplicon sequencing. We compared alpha and beta diversity within lakes, quantified spatial turnover (distance-decay), and tested for departure from neutral abundance-occurrence expectations between bacterioplankton and fish gut microbiomes. Fish microbiomes had lower alpha diversity compared to bacterioplankton, but higher beta diversity within lakes. Bacterioplankton were more similar across lakes yet showed stronger patterns of spatial turnover with distance than fish gut microbiomes. A neutral model explained a substantial proportion of abundance-occurrence relationships in bacterioplankton communities but performed poorly for fish-associated microbes. Our study indicates that host-associated and free-living microbes have disparate patterns of metacommunity structure and spatial turnover consistent with differences in the strength of neutral ecological processes. Fish microbiomes were less diverse at the local scale but more variable across space and time than bacterioplankton communities, suggestive of potentially strong local selection and/or reduced microbial exchange among hosts compared to environmental communities. Importantly, we observed highly consistent patterns across both lake systems despite differences in host species, sampling design, and region, demonstrating that differences in the distribution of host and environmental microbes are potentially widespread. This study demonstrates how host association fundamentally alters the diversity and spatial distribution of microbes, emphasizing the need to incorporate hosts into broader frameworks of microbial biogeography.

ecology↗

bioRxiv2020

Multiscale interactions between plant part and a steep environmental gradient determine plant microbial composition in a tropical watershed

Plant microbiomes are shaped by forces working at different spatial scales. Environmental factors determine a pool of potential symbionts while host physiochemical factors influence how those microbes associate with distinct plant tissues. Interactions between these scales, however, are seldom considered. Here we analyze epiphytic microbes from nine Hibiscus tiliaceus trees across a steep environmental gradient within a single Hawaiian watershed. At each location we sampled eight microhabitats: leaves, petioles, axils, stems, roots, and litter from the plant, as well as surrounding air and soil. While the composition of microbial communities is driven primarily by microhabitat, this variable predicted more than twice the compositional variance for bacteria compared to fungi. Fungal community compositional dissimilarity increased more rapidly along the gradient than did bacteria. Additionally, the spatial dynamics of fungal communities differed among plant parts, and these differences influenced the distribution patterns and range size of individual taxa. Within plants, microbes were compositionally nested such that aboveground communities contained a subset of the diversity found belowground. Our findings identify potential differences underlying the mechanisms shaping communities of fungi and bacteria associated with plants, and indicate an interaction between assembly mechanisms working simultaneously on different spatial scales.

microbiology↗

bioRxiv2020

Shifting Baselines: Repeat bleaching drives coral physiotypes through environmental legacy and cellular memory

O_LIGlobal climate change is altering coral reef ecosystems. Notably, marine heat waves are producing widespread coral bleaching events that are increasing in frequency, with projections for annual bleaching events on reefs worldwide by mid-century. C_LIO_LIThe response of corals to elevated seawater temperatures can be modulated by abiotic factors at site of origin and dominant endosymbiont type, which can result in a shift in multiple coral traits and drive physiological legacy effects that influence the trajectory of reef corals under subsequent thermal stress events. It is critical, therefore, to evaluate the potential for shifting physiological and cellular baselines driven by these factors in in situ bleaching (and recovery) events. Here, we use the back-to-back regional bleaching events of 2014 and 2015 in the Hawaiian Islands and subsequent recovery periods to test the hypothesis that coral multivariate trait space (here termed physiotype, sensu (Van Straalen, 2003) shift in multiple bleaching events, modulated by both environmental histories and symbiotic partnerships (Symbiodiniaceae). C_LIO_LIDespite fewer degree heating weeks in the first-bleaching event relative to the second (7 vs. 10), bleaching severity in a dominant reef building coral on Hawaiian reefs, Montipora capitata, was greater (~70% vs. 50% bleached cover) and differences due to environmental history (reef site) were more pronounced. Melanin, an immune cytotoxic response, provided an initial defense during the first event, potentially priming antioxidant activity, which peaked in the second-bleaching event (i.e., a legacy effect). While magnitude of bleaching differed, immune response patterns were shared among corals harboring heat-sensitive and heat-tolerant Symbiodiniaceae. This supports a pattern of increased constitutive immunity in corals resulting from repeat bleaching events, with greater specialized enzymes (catalase, peroxidase, superoxide dismutase) and attenuated melanin synthesis. C_LIO_LIThis study demonstrates bleaching events have implications for reef corals beyond shaping their ecological assemblages. These events can change the magnitude and/or identity of response variables contributing to physiotype, thus generating physiological legacies carried over into the future. Quantifying baseline coral physiotypes and tracking their shifts will be critical to understanding and forecasting the effects of increased bleaching frequency on coral biology and ecology in the Anthropocene. C_LI

ecology↗

bioRxiv2018

Spatial variation in the biochemical and isotopic composition of corals during bleaching and recovery

Ocean warming and the increased prevalence of coral bleaching events threaten coral reefs. However, the biology of corals during and following bleaching events under field conditions is poorly understood. We examined bleaching and post-bleaching recovery in Montipora capitata and Porites compressa corals that either bleached or did not bleach during a 2014 bleaching event at three reef locations in K[a]ne ohe Bay, O ahu. We measured changes in chlorophylls, biomass, and nutritional plasticity using stable isotopes ({delta}13C, {delta}15N). Coral traits showed significant variation among bleaching conditions, reef sites, time periods, and their interactions. Bleached colonies of both species had lower chlorophyll and total biomass. While M. capitata chlorophyll and biomass recovered three months later, P. compressa chlorophyll recovery was location-dependent and total biomass of previously bleached colonies remained low. Biomass energy reserves were not affected by bleaching, instead M. capitata proteins and P. compressa biomass energy declined over time, and P. compressa lipid biomass was site-specific. Stable isotope analyses of host and symbiont tissues did not indicate increased heterotrophic nutrition in bleached colonies of either species, during or after thermal stress. Instead, mass balance calculations revealed variance in {delta}13C values was best explained by augmented biomass composition, whereas {delta}15N values reflected spatial and temporal variability in nitrogen sources in addition to bleaching effects on symbiont nitrogen demand. These results emphasize total biomass quantity may change substantially during bleaching and recovery. Consequently, there is a need to consider the influence of biomass composition in the interpretation of isotopic values in corals.

physiology↗