Egg quality, larval growth and phenotypic plasticity in a forcipulate seastar

Abstract

The present study provides the first clear evidence of larval developmental plasticity in forcipulate seastars and a relationship between egg size and developmental plasticity. Adult Pisaster ochraceus were collected from Point Caution (a wave-protected site) and Mar Vista (a wave-exposed site) on the San Juan Islands. Seastars from the wave-exposed site were larger and had larger pyloric caeca while those from the wave-protected site were smaller with smaller pyloric caeca. Bigger females produced smaller eggs with a low biochemical content/egg and smaller females produced bigger eggs with a high biochemical content/egg. Egg quality and larval food had a significant effect on larval growth, development and survival. Bipinnariae from large eggs were initially bigger with faster developmental rates than those from small eggs. When starved, the numbers of bipinnariae surviving later on in development were higher for those from large eggs than for those from small eggs. When fed, the numbers of larvae surviving was higher for those from small eggs. This suggests that for this species large and small eggs might have equivalent fitness depending on the environmental conditions in which the offspring develop. All bipinnariae responded to food scarcity by changing their form, with those from smaller eggs responding to food scarcity later than those from larger eggs. Starved early bipinnaria stages were longer and wider and fed bipinnariae were narrower and shorter. Wider bipinnariae with larger mouths and stomachs were able to progress to more advanced stages while those with smaller internal structures could not. Thus for this species the mere increase in bipinnaria length and width might be insufficient to ensure continued larval development under food-limiting conditions; changes in internal morphology such as increase in the size of the digestive tract might be necessary.