DOI: 10.5061/dryad.sxksn02z8
title: Adaptive specialization and constraint in morphological defenses of planktonic larvae

description: 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 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. 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. Spine
 lengths showed positive allometric scaling with carapace length while
 spine and carapace lengths, but not pigmentation, had significant
 phylogenetic signals. The negative relationship we observed between
 pigmentation and spine length supports our defense specialization
 hypothesis. 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. 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. 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.
description: 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.
description: 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.