Adaptive specialization and constraint in morphological defenses of planktonic larvae

Morphological defenses of plankton can include armor, spines, and coloration. Spines defend from gape-limited fish predators while pigmentation increases visibility to fishes but defends from ultraviolet radiation (UVR).
Planktonic crab larvae (zoeae) exhibit inter- and intra-specific variability in the lengths of defensive spines, extent of pigmentation, and body size. The determinants of this variability and the relationships among these traits are largely unknown.
Larvae may employ generalized defenses against the dual threats of UVR and predation or specialized defenses against their primary threat, with an unknown role of allometric or phylogenetic constraints. Generalization would result in longer spines compensating for the increased predation risk imposed by darker pigments, while specialization would lead to more investment in either defense from predation (long spines) or UVR (dark pigments), at the expense of the other trait.
We examined 1) the relationship between s...