Physiological integration of coral colonies is correlated with bleaching resistance

Abstract

Inter-module physiological integration of colonial organisms can facilitate colony-wide coordinated responses to stimuli that strengthen colony fitness and stress resistance. In scleractinian corals, whose colonial integration ranges from isolated polyps to a seamless continuum of polyp structures and functions, this coordination improves re sponses to injury, predation, disease, and stress and may be one of the indications of an evolutionary origin of Symbiodinium symbiosis. However, observations of species-specific coral bleaching patterns suggest that highly integrated coral colonies may be more susceptible to thermal stress, and support the hypothesis that communication pathways between highly integrated polyps facilitate the dissemination of toxic byproducts created during the bleaching response. Here we reassess this hypothesis by parameterizing an integration index using 7 skeletal features that have been historically employed to infer physiological integration. We examine the relationship between this index and bleaching response across a phylogeny of 88 diverse coral species. Correcting for phylogenetic relationships among species in the analyses reveals significant patterns among species characters that could otherwise be obscured in simple crossspecies comparisons using standard statistics, whose assump tions of independence are violated by the shared evolutionary history among species. Similar to the observed benefits of in creased coloniality for other types of stressors, the results indicate a significantly reduced bleaching response among coral species with highly integrated colonies.KEY WORDS: Colony integration · Colony form · Coral bleaching · Phylogenetically corrected analysis Stylized representation of the phylogeny and morphologies that allowed detection of decreased thermal bleaching with greater polyp integration (coloniality).

Seeking Resistance in Coral Reef Ecosystems: The Interplay of Biophysical Factors and Bleaching Resistance under a Changing Climate

“…Directly underpinning the ability of corals to build reefs in nutrient‐poor tropical waters is the nutritional exchange of metabolites between coral host and endosymbiont . As colonial, marine cnidarians, corals are comprised of an interconnected network of polyps . The endosymbiont resides in cells beneath the oral ectoderm within the gastrodermal cell layer, in specialized organelles called symbiosomes (Box ).…”

Modularity is the mother of invention: a review of polymorphism in bryozoans

“…Despite this, these taxa can be highly polymorphic, possessing polyps specialized for reproduction, defence, feeding, colony structure, and asexual propagation (Table ) (Cartwright et al, ; Cartwright, ; Dunn, ; Dunn & Wagner, ; Williams et al, ; Sanders et al, ). By contrast, scleractinian corals have a wide range of modular dissociation: polyps may be completely separated by the skeleton, share an overlying tissue (cenosarc), or may possess gastrovascular connections (coelenteric canals) through voids in the skeleton (Swain et al, ). Despite this range in zooid compartmentalization, polymorphism is rare and poorly developed when present: apical polyps in Acropora colonies are sterile, possess fewer tentacles and have lower symbiont levels than gamete‐producing radial polyps (Hemond et al, ; Swain et al, ).…”

Revealing changes in the microbiome of Symbiodiniaceae under thermal stress

“…Global heat stress events are increasing in frequency and intensity (Hughes et al ., ), accelerating declines in coral reef health through unprecedented coral bleaching (Hughes et al ., ). Research efforts are increasingly focused on identifying core characteristics that maximize coral resilience to thermal stress (e.g., van de Water et al ., ; Chakravarti et al ., ; Swain et al ., ), for example, their bacterial associations (e.g. Reshef et al ., ; Grottoli et al ., ; Gardner et al ., ) and endosymbiotic algae, Symbiodiniaceae (e.g.…”