Abstract
Abstract Morphological defences of plankton can include armour, 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 intraspecific 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 defences against the dual threats of UVR and predation or specialized defences 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 defence from predation (long spines) or UVR (dark pigments), at the expense of the other trait. We examined (a) the relationship between spine lengths and pigmentation, (b) the scaling of spine lengths with body size, and (c) 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 defence 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 behaviours resulting in related species facing similar predation threats. Our results improve understanding of the evolution of the larval morphology of crabs, morphological defences in the plankton and evolutionary responses of morphology to multiple spatially segregated selective forces. A free Plain Language Summary can be found within the Supporting Information of this article.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.