Variation among females in egg lipid content and developmental success of echinoderms from McMurdo Sound, Antarctica

Increasing Temperature Results in Higher Allocation of Energy to Protein Synthesis in Sea Urchin Larvae (Lytechinus pictus)

AbstractIt is well established that metabolic processes change with temperature and size. Yet the underlying physiological mechanisms are less well understood regarding how such processes covary within a species and particularly so for developmental stages. Physiological analysis of larvae of the sea urchin Lytechinus pictus revealed that protein was the major biochemical substrate supporting metabolism. The complex dynamics of protein synthesis, turnover, and accretion changed during growth, showing a sevenfold decrease in the ratio of protein accretion to protein synthesis (protein depositional efficiency). To test hypotheses of physiological variation with rising temperature, larvae were reared over a temperature range experienced by this species in its ambient habitat. The thermal sensitivity of protein synthesis was greater than respiration (thermal sensitivity values of 3.7 and 2.4, respectively). Bioenergetic calculations revealed a disproportionate increase in energy allocation toward protein synthesis with rising temperature. These differential temperature sensitivities result in metabolic trade-offs of energy acquisition and expenditure, thereby altering physiological homeostasis. Such insights are of value for improving predictions about limits of biological resilience in a warming ocean.

Eggs as energy: revisiting the scaling of egg size and energetic content among echinoderms

Marine organisms exhibit substantial life-history diversity, of which egg size is one fundamental parameter. The size of an egg is generally assumed to reflect the amount of energy it contains and the amount of per-offspring maternal investment. Egg size and energy are thought to scale isometrically. We investigated this relationship by updating published datasets for echinoderms, increasing the number of species over those in previous studies by 62%. When we plotted egg energy versus egg size in the updated dataset we found that planktotrophs have a scaling factor significantly lower than 1, demonstrating an overall trend toward lower energy density in larger planktotrophic eggs. By looking within three genera, Echinometra, Strongylocentrotus, and Arbacia, we also found that the scaling exponent differed among taxa, and that in Echinometra, energy density was significantly lower in species with larger eggs. Theoretical models generally assume a strong tradeoff between egg size and fecundity that limits energetic investment and constrains life-history evolution. These data suggest that the evolution of egg size and egg energy content can be decoupled, possibly facilitating response to selective factors such as sperm limitation which could act on volume alone.

Possible effects of global environmental changes on Antarctic benthos: a synthesis across five major taxa

Because of the unique conditions that exist around the Antarctic continent, Southern Ocean (SO) ecosystems are very susceptible to the growing impact of global climate change and other anthropogenic influences. Consequently, there is an urgent need to understand how SO marine life will cope with expected future changes in the environment. Studies of Antarctic organisms have shown that individual species and higher taxa display different degrees of sensitivity to environmental shifts, making it difficult to predict overall community or ecosystem responses. This emphasizes the need for an improved understanding of the Antarctic benthic ecosystem response to global climate change using a multitaxon approach with consideration of different levels of biological organization. Here, we provide a synthesis of the ability of five important Antarctic benthic taxa (Foraminifera, Nematoda, Amphipoda, Isopoda, and Echinoidea) to cope with changes in the environment (temperature, pH, ice cover, ice scouring, food quantity, and quality) that are linked to climatic changes. Responses from individual to the taxon-specific community level to these drivers will vary with taxon but will include local species extinctions, invasions of warmer-water species, shifts in diversity, dominance, and trophic group composition, all with likely consequences for ecosystem functioning. Limitations in our current knowledge and understanding of climate change effects on the different levels are discussed.

Not my "type": larval dispersal dimorphisms and bet-hedging in opisthobranch life histories

When conditions fluctuate unpredictably, selection may favor bet-hedging strategies that vary offspring characteristics to avoid reproductive wipe-outs in bad seasons. For many marine gastropods, the dispersal potential of offspring reflects both maternal effects (egg size, egg mass properties) and larval traits (development rate, habitat choice). I present data for eight sea slugs in the genus Elysia (Opisthobranchia: Sacoglossa), highlighting potentially adaptive variation in traits like offspring size, timing of metamorphosis, hatching behavior, and settlement response. Elysia zuleicae produced both planktotrophic and lecithotrophic larvae, a true case of poecilogony. Both intracapsular and post-hatching metamorphosis occurred among clutches of "Boselia" marcusi, E. cornigera, and E. crispata, a dispersal dimorphism often misinterpreted as poecilogony. Egg masses of E. tuca hatched for up to 16 days but larvae settled only on the adult host alga Halimeda, whereas most larvae of E. papillosa spontaneously metamorphosed 5-7 days after hatching. Investment in extra-capsular yolk may allow mothers to increase larval size relative to egg size and vary offspring size within and among clutches. Flexible strategies of larval dispersal and offspring provisioning in Elysia spp. may represent adaptations to the patchy habitat of these specialized herbivores, highlighting the evolutionary importance of variation in a range of life-history traits.