Phylosymbiosis and metabolomics resolve phenotypically plastic and cryptic sponge species in the genus Agelas across the Caribbean basin.

Fundamental to holobiont biology is recognising how variation in microbial composition and function relates to host phenotypic variation. Sponges often exhibit considerable phenotypic plasticity and also harbour dense microbial communities that function to protect and nourish hosts. One of the most prominent sponge genera on Caribbean coral reefs is Agelas. Using a comprehensive set of morphological (growth form, spicule), chemical and molecular data on 13 recognised species of Agelas in the Caribbean basin, we were able to define only five species (=clades) and found that many morphospecies designations were incongruent with phylogenomic and population genetic analyses. Microbial communities were also strongly differentiated between phylogenetic species, showing little evidence of cryptic divergence and relatively low correlation with morphospecies assignment. Metagenomic analyses also showed strong correspondence to phylogenetic species, and to a lesser extent, geographical and morphological characters. Surprisingly, the variation in secondary metabolites produced by sponge holobionts was explained by geography and morphospecies assignment, in addition to phylogenetic species, and covaried significantly with a subset of microbial symbionts. Spicule characteristics were highly plastic, under greater impact from geographical location than phylogeny. Our results suggest that while phenotypic plasticity is rampant in Agelas, morphological differences within phylogenetic species affect functionally important ecological traits, including the composition of the symbiotic microbial communities and metabolomic profiles.

Exposure to ultraviolet radiation (290-400 nm) causes oxidative stress, DNA damage, and expression of p53/p73 in laboratory experiments on embryos of the spotted salamander, Ambystoma maculatum.

Developing embryos of the spotted salamander, Ambystoma maculatum, exposed to ultraviolet radiation (UVR; 290-400 nm) in the laboratory show a significant sensitivity to UVB (290-320 nm) radiation. Embryos in laboratory experiments exhibited significant DNA damage during exposures to UVR despite a significant increase in the production of the protective pigment melanin in response to UVR exposure. DNA damage occurs as a result of both the direct effects of exposure to UVR, and the indirect effects are mediated by the production of reduced oxygen intermediates. The production of reactive oxygen species initiates the expression of p53/p73 that leads to either DNA repair or apoptosis. When similar experiments are conducted on salamander embryos exposed to solar UVR in vernal pools, the embryos show significantly less sensitivity and higher survivorship. The differences between laboratory and field experiments are a result of the attenuation of UVR caused by the accumulation of dissolved organic carbon within the pools of these wooded areas. These findings suggest that northeastern populations of spotted salamanders are sensitive to UVR but are not significantly affected by present-day irradiances of UVR in the field. These results do suggest that continued decreases in stratospheric ozone over temperate latitudes have the potential to affect spotted salamanders in their natural habitats.

Expression of homologues for p53 and p73 in the softshell clam (Mya arenaria), a naturally-occurring model for human cancer.

Homologues for human p53 (Hsp53) and p73 (Hsp73) genes were cloned and expression patterns for their corresponding proteins analysed in tissues from normal and leukemic softshell clams (Mya arenaria). These are the first structural and functional data for p53 and p73 cDNAs and gene products in a naturally occurring, non-mammalian disease model. Core sequence of the predicted clam p53 (Map53) and p73 (Map73) proteins is virtually identical and includes the following highly conserved regions: the transcriptional activation domain (TAD), MDM2 binding site, ATM phosphorylation site, proline rich domain, DNA binding domains (DBDs) II-V, nuclear import and export signals and the tetramerization domain. The core sequence is a structural mosaic of the corresponding human proteins, with the TAD and DBDs resembling Hsp53 and Hsp73, respectively. This suggests that Map53 and Map73 proteins may function similarly to human proteins. Clam proteins have either a short (Map53) or long (Map73) C-terminal extension. These features suggest that Map53 and Map73 may be alternate splice variants of a p63/p73-like ancestral gene. Map73 is significantly upregulated in hemocytes and adductor muscle from leukemic clams. In leukemic hemocytes, both proteins are absent from the nucleus and sequestered in the cytoplasm. This observation suggests that a non-mutational p53/p73-dependent mechanism may be involved in the clam disease. Further studies of these gene products in clams may reveal p53/p73-related molecular mechanisms that are held in common with Burkitt's lymphoma or other human cancers.

Oxidative stress, DNA damage and p53 expression in the larvae of atlantic cod (Gadus morhua) exposed to ultraviolet (290-400 nm) radiation.

Decreases in stratospheric ozone levels from anthropogenic inputs of chlorinated fluorocarbons have resulted in an increased amount of harmful ultraviolet-B (UVB, 290-320 nm) radiation reaching the sea surface in temperate latitudes (30-50 degrees N). In the Gulf of Maine, present-day irradiances of ultraviolet-A (UVA, 320-400 nm) radiation can penetrate to depths of 23 m and UVB radiation can penetrate to depths of 7-12 m, where the rapidly developing embryos and larvae of the Atlantic cod (Gadus morhua) are known to occur. Laboratory exposures of embryos and larvae of Atlantic cod to ultraviolet radiation (UVR) equivalent to a depth of approximately 10 m in the Gulf of Maine resulted in significant mortality of developing embryos and a decrease in standard length at hatching for yolk-sac larvae. Larvae at the end of the experimental period also had lower concentrations of UVR-absorbing compounds and exhibited significantly greater damage to their DNA, measured as cyclobutane pyrimidine dimer formation, after exposure to UVB radiation. Larvae exposed to UVB radiation also exhibited significantly higher activities and protein concentrations of the antioxidant enzyme superoxide dismutase and significantly higher concentrations of the transcriptional activator p53. p53 is expressed in response to DNA damage and can result in cellular growth arrest in the G1- to S-phase of the cell cycle or to programmed cell death (apoptosis). Cellular death caused by apoptosis is the most likely cause of mortality in embryos and larvae in these laboratory experiments, while the smaller size at hatching in those larvae that survived is caused by permanent cellular growth arrest in response to DNA damage. In addition, the sub-lethal energetic costs of repairing DNA damage or responding to oxidative stress may also contribute to poor individual performance in surviving larvae that could also lead to increases in mortality. The irradiances of UVB radiation that elicit these responses in cod larvae can occur in many temperate latitudes, where these ecologically and commercially important fish are known to spawn, and may contribute to the high mortality of cod embryos and larvae in their natural environment.

Effects of Flow and Seston Availability on Scope for Growth of Benthic Suspension-Feeding Invertebrates from the Gulf of Maine.

Metridium senile, the frilled sea anemone, and Modiolus modiolus, the northern horse mussel, are important members of benthic suspension-feeding assemblages at several rocky hard-bottom subtidal (30-35 m) sites in the Gulf of Maine. Measurements of food availability, rates of food capture, absorption efficiencies, and standard metabolic costs show that inshore populations of Metridium senile have a significantly lower scope for growth than offshore populations, despite higher mean concentrations of particulate organic matter inshore. Similar measurements and calculations for Modiolus modiolus reveal the opposite pattern. These differences persisted at both of these sites during two summers, 1989 and 1990, when differences in mean temperature were not physiologically significant. Thus temperature is precluded as the primary effect on metabolism and growth. We suggest that these physiological differences reflect a response to flow regime and food availability that appears to be manifested differently for Metridium senile and for Modiolus modiolus, a passive and an active suspension feeder, respectively. Results from a reciprocal transplant experiment, to measure growth rates, carried out over a one-year period support the calculated scope for growth during the season when maximum growth rates would be expected. The flux of seston appears to be an important factor affecting the organismal performance of the passive suspension feeder (M. senile), whereas the concentration of seston is more important for the active suspension feeder (M. modiolus).

Biological weighting function for the inhibition of phytoplankton photosynthesis by ultraviolet radiation.

Severe reduction of stratospheric ozone over Antarctica has focused increasing concern on the biological effects of ultraviolet-B (UVB) radiation (280 to 320 nanometers). Measurements of photosynthesis from an experimental system, in which phytoplankton are exposed to a broad range of irradiance treatments, are fit to an analytical model to provide the spectral biological weighting function that can be used to predict the short-term effects of ozone depletion on aquatic photosynthesis. Results show that UVA (320 to 400 nanometers) significantly inhibits the photosynthesis of a marine diatom and a dinoflagellate, and that the effects of UVB are even more severe. Application of the model suggests that the Antarctic ozone hole might reduce near-surface photosynthesis by 12 to 15 percent, but less so at depth. The experimental system makes possible routine estimation of spectral weightings for natural phytoplankton.

Photoadaptation and Protection against Active Forms of Oxygen in the Symbiotic Procaryote Prochloron sp. and Its Ascidian Host.

Superoxide dismutase, ascorbate peroxidase, and catalase activities were studied in the symbiotic photosynthetic procaryote Prochloron sp. and its ascidian host Lissoclinum patella. The protein-specific activities of these antioxidant enzymes in the Prochloron sp. and L. patella collected at different depths from the Great Barrier Reef, Australia, were directly proportional to irradiance, whereas the pigment concentrations in the Prochloron sp. were inversely proportional to irradiance. The presence of a cyanide-sensitive superoxide dismutase, presumably a Cu-Zn metalloprotein, in the Prochloron sp. extends the possible phylogenetic distribution of this protein. The concentration of UV-absorbing mycosporine-like amino acids is inversely proportional to irradiance in both the host and symbiont, suggesting that these compounds may not provide sufficient protection against UV radiation in high-irradiance environments. The significant differences in the specific activities of these antioxidant enzymes, cellular photosynthetic pigment concentrations, and UV-absorbing compounds from high- and low-irradiance habitats constitute an adaptive response to different photic environments. These photoadaptive responses are essential to prevent inhibition of photosynthesis by high fluxes of visible and UV radiation.

Photobiology of natural populations of zooxanthellae from the sea anemone Aiptasia pallida: assessment of the host's role in protection against ultraviolet radiation.

Natural populations of the sea anemone Aiptasia pallida containing endosymbiotic dinoflagellates were acclimated to different irradiance regimes, with and without ultraviolet radiation (UV). They showed a compensatory response in the amount of chlorophyll and the activities of enzymes responsible for detoxifying active species of oxygen that are produced by the interaction between visible or ultraviolet radiation and photosynthetically produced oxygen. Protection from active species of oxygen is essential to prevent the photooxidation of chlorophyll and the concomitant loss of productivity. Bulk analyses of chlorophyll showed differences between the populations exposed to varying irradiance regimes, but revealed no significant independent effect of UV. However, analysis by flow cytometry of the individual cells from treated populations did detect statistically significant differences in cell size and the amount of chlorophyll fluorescence per cell, which could be attributed to treatment with ultraviolet radiation. With flow cytometry we are able to detect the population variability that is undetectable by bulk measurements which is important in assessing the effects of environmental parameters in both symbiotic and free-living microalgae. Research using simultaneous measurements by flow cytometry could add considerable insight into the population dynamics of both zooxanthellae and host cells.