Bursts in species diversification are well documented among animals and plants, yet few studies have assessed recent adaptive radiations of eukaryotic microbes. Consequently, we examined the radiation of the most ecologically dominant group of endosymbiotic dinoflagellates found in reef-building corals, Symbiodinium Clade C, using nuclear ribosomal (ITS2), chloroplast (psbA(ncr)), and multilocus microsatellite genotyping. Through a hierarchical analysis of high-resolution genetic data, we assessed whether ecologically distinct Symbiodinium, differentiated by seemingly equivocal rDNA sequence differences, are independent species lineages. We also considered the role of host specificity in Symbiodinium speciation and the correspondence between endosymbiont diversification and Caribbean paleo-history. According to phylogenetic, biological, and ecological species concepts, Symbiodinium Clade C comprises many distinct species. Although regional factors contributed to population-genetic structuring of these lineages, Symbiodinium diversification was mainly driven by host specialization. By combining patterns of the endosymbiont's host specificity, water depth distribution, and phylogeography with paleo-historical signals of climate change, we inferred that present-day species diversity on Atlantic coral reefs stemmed mostly from a post-Miocene adaptive radiation. Host-generalist progenitors spread, specialized, and diversified during the ensuing epochs of prolonged global cooling and change in reef-faunal assemblages. Our evolutionary reconstruction thus suggests that Symbiodinium undergoes "boom and bust" phases in diversification and extinction during major climate shifts.

High sea surface temperatures often lead to coral bleaching wherein reef-building corals lose significant numbers of their endosymbiotic dinoflagellates (Symbiodiniaceae). These increasingly frequent bleaching events often result in large scale coral mortality, thereby devasting reef systems throughout the world. The reef habitats surrounding Palau are ideal for investigating coral responses to climate perturbation, where many inshore bays are subject to higher water temperature as compared with offshore barrier reefs. We examined fourteen physiological traits in response to high temperature across various symbiotic dinoflagellates in four common Pacific coral species, Acropora muricata , Coelastrea aspera , Cyphastrea chalcidicum and Pachyseris rugosa found in both offshore and inshore habitats. Inshore corals were dominated by a single homogenous population of the stress tolerant symbiont Durusdinium trenchii , yet symbiont thermal response and physiology differed significantly across coral species. In contrast, offshore corals harbored specific species of Cladocopium spp. (ITS2 rDNA type-C) yet all experienced similar patterns of photoinactivation and symbiont loss when heated. Additionally, cell volume and light absorption properties increased in heated Cladocopium spp., leading to a greater loss in photo-regulation. While inshore coral temperature response was consistently muted relative to their offshore counterparts, high physiological variability in D . trenchii across inshore corals suggests that bleaching resilience among even the most stress tolerant symbionts is still heavily influenced by their host environment.

The treatment of castration‐resistant prostate cancer (CRPC) remains palliative. Immunotherapy offers a potentially effective therapy for CRPC; however, its advancement into the clinic has been slow, in part because of the lack of representative in vitro tumor models that resemble the in vivo tumor microenvironment for studying interactions of CRPC cells with immune cells and other potential therapeutics. This study evaluates the use of 3D porous chitosan–alginate (CA) scaffolds for culturing human prostate cancer (PCa) cells and studying tumor cell interaction with human peripheral blood lymphocytes (PBLs) ex vivo. CA scaffolds and Matrigel matrix samples support in vitro tumor spheroid formation over 15 d of culture, and CA scaffolds support live‐cell fluorescence imaging with confocal microscopy using stably transfected PCa cells for 55 d. PCa cells grown in Matrigel matrix and CA scaffolds for 15 d are co‐cultured with PBLs for 2 and 6 d in vitro and evaluated with scanning electron microscopy (SEM), immunohistochemistry (IHC), and flow cytometry. Both the Matrigel matrix and CA scaffolds support interaction of PBLs with PCa tumors, with CA scaffolds providing a more robust platform for subsequent analyses. This study demonstrates the use of 3D natural polymer scaffolds as a tissue culture model for supporting long‐term analysis of interaction of prostate cancer tumor cells with immune cells, providing an in vitro platform for rapid immunotherapy development.

Symbiotic dinoflagellates in the genus Breviolum (formerly Symbiodinium Clade B) dominate coral communities in shallow waters across the Greater Caribbean. While some formally described species exist, mounting genetic, and ecological evidence indicate that numerous more comprise this genus, many of which are closely related. To test this, colonies of common reef‐building corals were sampled across a large geographical range. Phylogenetic and population genetic markers then used to examine evolutionary divergence and delineate boundaries of genetic recombination. Three new candidate species were distinguished by fixed differences in nucleotide sequences from nuclear and chloroplast DNA. Population connectivity was evident within each lineage over thousands of kilometers, however, substantial genetic structure persisted between lineages co‐occurring within sampling locations, signifying reproductive isolation. While geographically widespread with overlapping distributions, each species is ecologically distinct, exhibiting specific mutualisms with phylogenetically distinct coral hosts. Moreover, significant differences in mean cell sizes provide some morphological evidence substantiating formal species distinctions. In providing evidence that satisfies the biological, phylogenetic, ecological, and morphological species concepts, we classify and formally name Breviolum faviinorum n. sp., primarily associated with Caribbean corals belonging to the Caribbean subfamily Faviinae; B. meandrinium n. sp., associated with corals belonging to the family Meandrinidae; and B. dendrogyrum n. sp., a symbiont harbored exclusively by the threatened coral Dendrogyra cylindrus. These findings support the primary importance of niche diversification (i.e. host habitat) in the speciation of symbiotic dinoflagellates.

Reef-building corals in the genus Porites are one of the most important constituents of Indo-Pacific reefs. Many species within this genus tolerate abnormally warm water and exhibit high specificity for particular kinds of endosymbiotic dinoflagellates that cope with thermal stress better than those living in other corals. Still, during extreme ocean heating, some Porites exhibit differences in their stress tolerance. While corals have different physiological qualities, it remains unknown whether the stability and performance of these mutualisms is influenced by the physiology and genetic relatedness of their symbionts. We investigated two ubiquitous Pacific reef corals, Porites rus and Porites cylindrica, from warmer inshore and cooler offshore reef systems in Palau. While these corals harbored a similar kind of symbiont in the genus Cladocopium (within the ITS2 C15 subclade), rapidly evolving genetic markers revealed evolutionarily diverged lineages corresponding to each Porites species living in each reef habitat. Furthermore, these closely related Cladocopium lineages were differentiated by their densities in host tissues, cell volume, chlorophyll concentration, gross photosynthesis, and photoprotective pathways. When assessed using several physiological proxies, these previously undifferentiated symbionts contrasted in their tolerance to thermal stress. Symbionts within P. cylindrica were relatively unaffected by exposure to 32℃ for 14 days, whereas P. rus colonies lost substantial numbers of photochemically compromised symbionts.Heating reduced the ability of the offshore symbiont associated with P. rus to translocate carbon to the coral. By contrast, high temperatures enhanced symbiont carbon assimilation and delivery to the coral skeleton of inshore P. cylindrica. This study indicates that large physiological differences exist even among closely related symbionts, with significant implications for thermal susceptibility among reef-building Porites.