Effects of embryo energy, egg size, and larval food supply on the development of asteroid echinoderms

Antarctic cushion star Odontaster validus larval performance is negatively impacted by long-term parental acclimation to elevated temperature

Cross-generational responses, when the parents' environment influences offspring performance, may contribute to species resilience to climate change in rapidly warming regions such as coastal Antarctica. Adult Antarctic sea stars Odontaster validus were conditioned in the laboratory to two temperature treatments (ambient, 0 °C and warming, +3 °C) for two years, and their gametes were used to generate larval offspring. The response of their larvae to five temperatures (0 °C, 1 °C, 2 °C, 3 °C, and 4 °C) was examined over 145 days. Adults conditioned to 3 °C produced significantly smaller eggs compared with those from 0 °C conditioned adults. After fertilisation, larval size, development, and survival were comparable in offspring from 0 °C and 3 °C conditioned parents. After 34 days of development, while survival was greater in offspring from 3 °C adults, offspring size was reduced during the transition from the gastrula to the bipinnaria larva. After ~50 days, survival in larvae from 3 °C conditioned adults decreased, and larval development was arrested at the bipinnaria stage (the exception being for larva reared at 4 °C which reached the early-brachiolaria). By the end of the experiment (145 days), offspring of the 0 °C conditioned adults had greater survival (17.6-34.3 %) and growth (final size = 697 to 773 μm) and had reached the early-brachiolaria larval stage, compared to those from the 3 °C conditioned adults (survival 7.0-19.3 %; growth final size = 380 to 624 μm) with early-brachiolaria larval stages mostly absent. Long-term acclimation of adults in elevated temperatures projected for the end of the century did not result in positive carryover outcomes for offspring, and did not lead to offspring being better suited to elevated temperatures. While O. validus adults may survive exposure to projected warming and produce viable gametes, their larval offspring may have lower developmental success. The downstream effects of poor recruitment of a key species such as O. validus would have important outcomes for coastal Antarctic ecosystems.

Scope for Developmental Plasticity of Feeding Larvae of a Holothuroid, Contrasted with Other Echinoderm Larvae

AbstractFeeding larvae of echinoderms appear to differ in scope for adaptive developmental plasticity in response to food. Extension of the ciliary band on narrow arms supported by skeletal rods, as in echinoid and ophiuroid larvae, may enable a greater increase in maximum clearance rate per cell added, conferring greater advantages from developing longer ciliary bands when food is scarce. Formation of the juvenile mouth and water vascular system at a new site, as in echinoid and asteroid larvae, permits extensive growth of the juvenile rudiment during larval feeding, with advantages from earlier or more growth of the rudiment when food is abundant. In contrast, plasticity in storage of nutrients is unrelated to the form of the ciliary band or the site of formation of the juvenile's mouth. Feeding larvae (auriculariae) of holothuroids lack arms supported by skeletal rods and formation of the mouth at a new site but as a unique feature store nutrients in hyaline spheres. In this study, more food for auriculariae of Apostichopus californicus resulted in juveniles (pentactulae) with longer and wider bodies and larger hyaline spheres, but effects of food supply on the size of most body parts of auriculariae were small. Auriculariae with more food developed relatively larger stomachs and larger posterior hyaline spheres, indications of greater nutrient storage. Auriculariae with less food developed relatively wider mouths and differed in some exterior dimensions, which might enhance the capture of food. Plasticity is limited in rudiment development and perhaps in structures for feeding, but plasticity in nutrient storage can provide advantageous compromises between duration of growth as a feeding larva and the condition of juveniles formed at metamorphosis.