1. 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).
2. 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.
3. 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.
4. We examined 1) the relationship between spine lengths and pigmentation, 2) the scaling of spine lengths with body size, and 3) phylogenetic constraint in spine lengths, pigmentation, and body size, among and within 21 species of laboratory-hatched and 23 species of field-collected crab larvae from Panama and California.
5. We found a negative relationship between spine length and pigmentation among species from laboratory and field. Within species, we found a marginally significant negative relationship among field-collected larvae.
6. Spine lengths showed positive allometric scaling with carapace length while spine and carapace lengths, but not pigmentation, had significant phylogenetic signals.
7. The negative relationship we observed between pigmentation and spine length supports our defense specialization hypothesis.
8. Positive allometric scaling of spine lengths means larger larvae are better defended from predators, which may indicate that larvae face greater predation risk as they grow larger.
9. Phylogenetic constraint may have arisen because related species encounter similar predation threats. Conversely, phylogenetic constraint in the evolution of spine lengths may induce convergent behaviors resulting in related species facing similar predation threats.
10. Our results improve understanding of the evolution of the larval morphology of crabs, morphological defenses in the plankton, and evolutionary responses of morphology to multiple spatially-segregated selective forces.

See Bashevkin SM, JH Christy, SG Morgan. 2019. Adaptive specialization and constraint in morphological defenses of planktonic larvae. Functional Ecology.

Phylogenetic methods are available in supplemental material S1.

Data collected from lab hatched larvae: "Publication lab data.csv"

Data collected from field collected larvae: "Publication field data.csv"

Phylogenetic tree: "infile.nex.con.tre"

Metadata on the morphology data: "Publication metadata.xlsx"

R scripts used for analysis: "Pigments spines R scripts.R"

Data have quality inspected and cleaned to remove cases with unusuable missing values so only cases used in the analyses for this manuscript are included.