How do changes in parental investment influence development in echinoid echinoderms?

Abstract

Understanding the relationship between egg size, development time, and juvenile size is critical to explaining patterns of life-history evolution in marine invertebrates. Currently there is conflicting information about the effects of changes in egg size on the life histories of echinoid echinoderms. We sought to resolve this conflict by manipulating egg size and food level during the development of two planktotrophic echinoid echinoderms: the green sea urchin, Strongylocentrotus droebachiensis and the sand dollar, Echinarachnius parma. Based on comparative datasets, we predicted that decreasing food availability and egg size would increase development time and reduce juvenile size. To test our prediction, blastomere separations were performed in both species at the two-cell stage to reduce egg volume by 50%, producing whole- and half-size larvae that were reared to metamorphosis under high or low food levels. Upon settlement, age at metamorphosis, juvenile size, spine number, and spine length were measured. As predicted, reducing egg size and food availability significantly increased age at metamorphosis and reduced juvenile quality. Along with previous egg size manipulations in other echinoids, this study suggests that the relationship between egg size, development time, and juvenile size is strongly dependent upon the initial size of the egg.

Long-term and trans-life-cycle effects of exposure to ocean acidification in the green sea urchin Strongylocentrotus droebachiensis

“…Egg size is a classic proxy for egg quality. For example, smaller eggs can have reduced lipid content with negative consequences for larval fitness by increasing age at metamorphosis and reducing juvenile quality (Alcorn and Allen 2009;Bertram et al 2009). However, in our study, egg size appeared to be a poor predictor of the further negative impacts observed on settlement success (no effect of adult acclimation and larval culture pCO 2 was observed on egg diameter).…”

Effects of variation in egg energy and exogenous food on larval development in congeneric sea urchins

“…In most echinoderms, because of their regulative development, half-, quarter-, and even double-sized eggs can develop normally (McEdward 1996). While these tests seem ideal in some respects, results are not always consistent: larvae from larger eggs develop more rapidly than their half-sized siblings in many studies (Sinervo & McEdward 1988, Levitan 2000, Alcorn & Allen 2009, Allen 2012 but not all (Hart 1995, Emlet & HoeghGuldberg 1997, Allen et al 2006, and larvae from half-sized eggs resulted in smaller juveniles in some species (Hart 1995, Allen et al 2006, Alcorn & Allen 2009, Allen 2012 but not others (Sinervo & McEdward 1988, Allen 2012. Differences among blastomere separation studies may be due in part to the characteristic egg size of a particular species.…”

“…Alcorn & Allen (2009) and Allen (2012) tested for interactions between food level and egg size on size and age at metamorphosis using blastomere separations in 5 species of echinoids, with variable results: 2 species showed significant interactions for both size and age at metamorphosis (Strongylocentrotus droebachiensis and Echinarachnius parma), 1 showed significant interactions for size but not age (Arbacia punctulata), 1 showed significant interactions for age with no data for size (S. purpuratus), and for 1 species, Dendraster excentricus, egg size and food ration did not significantly interact for age or size at metamorphosis. One likely explanation for these differences is that interactions could be masked by species-specific differences in the maternal, genetic, and epigenetic background of regulation of larval development, making it difficult to compare across distantly related taxa if egg energy does not evolve in isolation from other life-history traits.…”

“…In general, planktotrophic echinoids with larger eggs reach metamorphosis more quickly than species with smaller eggs (Emlet 1995), though there is no clear relationship between egg size and size at metamorphosis (such effects may be masked by other factors both phylogenetic and experimental; Emlet et al 1987, Herrera et al 1996. Intraspecific comparisons of whole-and half-sized larvae (the latter produced via blastomere separations) also generally find that larvae from larger eggs reach metamorphosis sooner (Sinervo & McEdward 1988, Levitan 2000, Alcorn & Allen 2009, Allen 2012; but see Hart 1995, Emlet & Hoegh-Guldberg 1997, Allen et al 2006 for exceptions). Larvae of most planktotrophic echinoids also grow more rapidly and/or to larger sizes when food is abundant (Hart 1995, Miller & Emlet 1999, Allen et al 2006.…”

“…Larvae of most planktotrophic echinoids also grow more rapidly and/or to larger sizes when food is abundant (Hart 1995, Miller & Emlet 1999, Allen et al 2006. However, while the effects of egg energy and exogenous food have been separately described, much less is known about how the two interact (Alcorn & Allen 2009, Allen 2012. Thus, interspecific comparisons among closely related taxa can also shed light on whether there are interactive effects between egg energy and exogenous food availability that support the idea that large, energy-rich eggs act to reduce a larva's reliance on exogenous food resources.…”