Predators Induce Phenotypic Plasticity in Echinoderms across Life History Stages.

Area of Science:

• Marine Biology
• Developmental Biology
• Ecology

Background:

• Marine invertebrates with biphasic life cycles transition from benthic adults to planktonic larvae and back to benthic juveniles.
• Metamorphosis exposes newly settled juveniles to novel predators, often resulting in high mortality.
• Phenotypic plasticity allows juvenile invertebrates to develop defenses in response to predator cues, but timing can be critical.

Purpose of the Study:

• To investigate if planktonic echinoderm larvae alter their juvenile phenotypes in response to waterborne predator cues before settlement.
• To test the hypothesis that larvae can anticipate post-metamorphic predation risk and adjust defenses accordingly.

Main Methods:

• Larvae of green urchins (Strongylocentrotus droebachiensis) and Pacific sand dollars (Dendraster excentricus) were exposed to predator cues (crabs) during development and settlement.
• Control groups were maintained without predator cues.
• Juvenile morphology (spine length, number, disk area) and settlement timing were compared between exposed and control groups.

Main Results:

• Green urchin larvae exposed to predator cues settled with significantly more juvenile spines.
• Sand dollar larvae exposed to benthic predator cues settled earlier, with larger disk area, fewer, and shorter spines.
• Sand dollar larvae exposed to planktonic predator cues exhibited even more pronounced changes, settling sooner and larger with reduced spines.

Conclusions:

• Echinoderm larvae demonstrate phenotypic plasticity, altering juvenile morphology in response to predator cues detected in the water column.
• The specific defensive responses vary between species (urchins vs. sand dollars).
• Larvae may prioritize responses to planktonic threats over benthic ones, suggesting complex adaptive strategies during the vulnerable settlement phase.