Regional population structure of a widely introduced estuarine invertebrate: Nematostella vectensis Stephenson in New England

Nematostella vectensis is an infaunal anemone occurring in salt marshes, lagoons and other estuarine habitats in North America and the United Kingdom. Although it is considered rare and receives protection in England, it is widely distributed and abundant in the United States, particularly along the Atlantic coast. Recent studies suggest that both anthropogenic dispersal and reproductive plasticity may significantly influence the genetic structure of N. vectensis populations. Amplified fragment length polymorphism (AFLP) fingerprinting of individuals from nine populations in the northeastern United States indicates that stable populations are maintained by both asexual and sexual reproduction; in some cases asexually reproducing lineages exist within sexually reproducing populations. F statistics reveal extraordinarily high degrees of genetic differentiation between populations, even those separated by very short distances (less than 100 m). Genetic distances show little to no correlation with geographical distances, consistent with a role for sporadic, geographically discontinuous dispersal coupled with limited gene flow. No single genotype was found at more than one site, despite apparent homogeneity of habitat. In contrast with reported genotypic distributions for Nematostella in the United Kingdom, where a single clonal genotype dominates at multiple sites through southern England, our data thus fail to support the hypothesis of a general-purpose genotype in the northeastern United States. However, they are consistent with important roles for reproductive plasticity, sporadic introductions and complex local population dynamics in determining the global and regional distribution of this species.     

Qualitative shift to indirect development in the parasitic sea anemone Edwardsiella lineata

Direct development lies at 1 end of a continuum that encompassesvarious degrees of indirect development. Indirect developmentexists where a larval stage is interposed between the embryoand the adult and undergoes metamorphosis, though the ecologicaland morphological distinctiveness of the larval stage relativeto the adult stage can vary tremendously. There are numerousempirical examples where direct development has evolved fromindirect development, but little empirical evidence describinga recent transition from direct to indirect development. Here,we suggest 4 criteria for defining indirect, and therefore metamorphic,life histories. We then apply these criteria to address theplanula–polyp transition in cnidarians, focusing on 2species in the anthozoan family Edwardsiidae. The lined seaanemone, Edwardsiella lineata, has made a qualitative shifttowards indirect development that coincides with, and was potentiallyfacilitated by, the evolution of endoparasitism. We compareE. lineata's development with that of a closely related seaanemone, Nematostella vectensis, where the nonfeeding planulagradually develops the morphology of the adult polyp. In E.lineata, a novel parasitic life history stage is interposedbetween the planula and the polyp. We discuss how the evolutionof endoparasitism could facilitate the evolution metamorphiclife histories.     

Testing aluminum addition as a tool for lake restoration in shallow,eutrophic Lake Sønderby,Denmark

Hydrobiologia - Internal phosphorus (P) loading in shallow lakes may delay recovery from previous high external loading for decades. In Lake Sønderby (8 ha, mean depth 2.8 m), Fyn...     

The contribution of the facultative feeding period to echinoid larval development and size at metamorphosis: a comparative approach

Planktotrophic invertebrate larvae have two dissociable stages during development, a facultative feeding period, whose length is determined by the amount of maternal provisioning in the egg, and an obligate feeding period, whose length is determined by the quantity of exogenous energy needed to reach metamorphic competence. Here we set out to experimentally test the impact of feeding during the facultative feeding period at two food concentrations (limiting and nonlimiting) on larval development time and juvenile quality. We used two closely related subtropical sand dollar species that differ in the quantity of maternal investment for these comparisons: Leodia sexiesperforata (large egg, long facultative feeding period) and Mellita tenuis (small egg, short facultative feeding period). We found that feeding during the facultative period accelerates development to metamorphosis only in M. tenuis and only at the high food ration. Feeding during the facultative feeding period had no effect on development time for M. tenuis at a food limiting concentration and for L. sexiesperforata at either food concentration. Furthermore, we found feeding during the facultative period to significantly increase quantity of carbohydrates and lipids at metamorphosis only for M. tenuis in nonlimiting food concentration. Thus, our data reveal a two-fold benefit of the facultative feeding period for a poorly provisioned species under high food conditions but little effect on a well-provisioned species. We discuss our results in reference to McEdward's [McEdward, L.R., 1997. Reproductive strategies of marine benthic invertebrates revisited: facultative feeding by planktotrophic larvae. Am. Nat. 150, 48-72] facultative feeding model.     

Influence of pH and redox on mobilization of inositol hexakisphosphate from oligotrophic lake sediment

It has been suggested that inositol hexakisphosphate (IP₆) contributes to the release of phosphorus (P) from lake sediments, but a mechanistic understanding remains elusive. We investigated the potential mobilization and mineralization of myo- and scyllo-IP₆ from the sediment of an oligotrophic Danish lake known to contain high concentrations of inositol phosphates. Solution ³¹P NMR spectroscopy was used to determine changes in myo- and scyllo-IP₆ in laboratory microcosms incubated under either oxic or anoxic conditions. In addition, we incubated sediment slurries adjusted to pH between 4.9 and 6.6, with and without addition of myo-IP₆, and induced redox changes by adding starch and sulfate. We observed no significant changes in myo- or scyllo-IP₆ after 1 year of incubation under anaerobic conditions. A sequential extraction procedure revealed that one half of the added myo-IP₆ was recovered in the humic acid fraction (acid-insoluble organic matter) and the other half in the fulvic acid fraction (acid-soluble organic matter). Reduction in redox potential by starch addition did not mobilize myo-IP₆, but myo-IP₆ bound to humic acids was released to the pore water when the pH was increased to ≥?5.8. This pH-induced mobilization of IP₆ occurred in parallel with increases in dissolved iron and organic matter, suggesting the release of IP₆ bound to humic acids through metal bridges. We conclude that myo-IP₆ mobilization from this oligotrophic lake sediment is driven by changes in pH rather than by changes in the redox potential.     

Psychosocial Mechanisms Linking the Social Environment to Mental Health in African Americans

Resource-poor social environments predict poor health, but the mechanisms and processes linking the social environment to psychological health and well-being remain unclear. This study explored psychosocial mediators of the association between the social environment and mental health in African American adults. African American men and women (n = 1467) completed questionnaires on the social environment, psychosocial factors (stress, depressive symptoms, and racial discrimination), and mental health. Multiple-mediator models were used to assess direct and indirect effects of the social environment on mental health. Low social status in the community (p < .001) and U.S. (p < .001) and low social support (p < .001) were associated with poor mental health. Psychosocial factors significantly jointly mediated the relationship between the social environment and mental health in multiple-mediator models. Low social status and social support were associated with greater perceived stress, depressive symptoms, and perceived racial discrimination, which were associated with poor mental health. Results suggest the relationship between the social environment and mental health is mediated by psychosocial factors and revealed potential mechanisms through which social status and social support influence the mental health of African American men and women. Findings from this study provide insight into the differential effects of stress, depression and discrimination on mental health. Ecological approaches that aim to improve the social environment and psychosocial mediators may enhance health-related quality of life and reduce health disparities in African Americans.     

Establishing a model organism: a report from the first annual Nematostella meeting

The sea anemone Nematostella vectensis has developed into a model organism for studying genome evolution and animal development.