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

Abstract

Organisms have limited resources available to invest in reproduction, causing a trade‐off between the number and size of offspring. One consequence of this trade‐off is the evolution of disparate egg sizes and, by extension, developmental modes. In particular, echinoid echinoderms (sea urchins and sand dollars) have been widely used to experimentally manipulate how changes in egg size affect development. Here, we test the generality of the echinoid results by (a) using laser ablations of blastomeres to experimentally reduce embryo energy in the asteroid echinoderms (sea stars), Pisaster ochraceus and Asterias forbesi and (b) comparing naturally produced, variably sized eggs (1.7‐fold volume difference between large and small eggs) in A. forbesi . In P. ochraceus and A. forbesi , there were no significant differences between juveniles from both experimentally reduced embryos and naturally produced eggs of variable size. However, in both embryo reduction and egg size variation experiments, simultaneous reductions in larval food had a significant and large effect on larval and juvenile development. These results indicate that (a) food levels are more important than embryo energy or egg size in determining larval and juvenile quality in sea stars and (b) the relative importance of embryo energy or egg size to fundamental life history parameters (time to and size at metamorphosis) does not appear to be consistent within echinoderms.

Cannibalism of newly metamorphosed juvenile sea stars

“…Or is this an example of animals that are desperate to feed following an energetically expensive metamorphic transition that has burned up their energetic reserves? The former is supported by the observation that A. forbesi juveniles can survive for months without feeding or growing (Mead 1900, Trackenberg et al 2020, and the latter is supported by field observations of cannibalism in "young" sea stars when "pressed by hunger" (Mead 1899). Observations of cannibalism in juvenile sea stars have been noted in efforts to aquaculture tropical seastars (Luidia clathrata; Brocco-French and Allen, unpublished observations), invasive sea stars (Asterias amurensis; M. Byrne, personal communication) and sunflower stars (Pycnopodia helianthoides; J. Hodin, personal communication) from the northern Pacific.…”

“…Experiments were conducted at William & Mary (W&M) in Williamsburg, Virginia, USA, and at the Bowdoin College Schiller Coastal Studies Center (SCSC) on Orrs Island, Maine, USA between 2015 and 2016. Adult A. forbesi were collected in Rockland, Maine, USA, spawned through injection of 100 µmol/L 1-methyladenine, and the resulting larvae were reared to metamorphosis as in Trackenberg et al (2020). To determine the relationship between juvenile cannibalism and juvenile density, juveniles were randomly placed into beakers with filtered sea water (FSW) at densities of 1, 2, 10, and 20 juveniles/beaker and counted every day for 2 weeks.…”

Carryover effects in a sea star: juvenile resource availability does not compensate for a poor larval environment

“…When the first larvae developed brachiolar arms and the beginnings of a juvenile rudiment, beakers were no longer cleaned to allow biofilm growth (Cameron and Hinegardner 1974) and a blue mussel shell (Mytilus edulis) was placed in each beaker to encourage larval settlement (Trackenberg et al 2020). Shells and beakers were checked for settlement once per day and age at settlement was recorded.…”

Mapping the correlations and gaps in studies of complex life histories

“…While life‐history stages can be quite different from each other in terms of morphology, trophic mode and even habitat, phenotypic and genetic correlations between life‐history stages are ecologically and evolutionarily important. For example, larval size and size at metamorphosis are positively correlated in frogs (Relyea, 2001), marine invertebrates (Trackenberg et al, 2020), and insects (Tammaru, 1998; Tammaru et al, 2004). If traits are correlated across stages, an early‐life experience may determine performance later in the life history (i.e., “carry‐over” or “latent’ effects Pechenik, 2006) for example, juvenile body size and/or growth can be affected by temperature (moths, Galarza et al, 2019; sticklebacks, Kim et al, 2018), food availability (mussels, Phillips, 2002; frogs, Warne & Crespi, 2015), and season length (frogs, Prokic et al, 2021; frogs, Szekely et al, 2020; damselflies, Tuzun & Stoks, 2018;) of the larval stage.…”

“…While life-history stages can be quite different from each other in terms of morphology, trophic mode and even habitat, phenotypic and genetic correlations between life-history stages are ecologically and evolutionarily important. For example, larval size and size at metamorphosis are positively correlated in frogs (Relyea, 2001), marine invertebrates (Trackenberg et al, 2020), and insects…”