Alejandro Damian-Serrano, Steven H.D. Haddock, Casey W. Dunn
Corresponding author: Alejandro Damian-Serrano, email: [email protected]
Predators have evolved dedicated body parts to capture and subdue prey. As different predators specialize on distinct prey taxa, their tools for prey capture diverge into a variety of adaptive forms. Studying the evolution of predation is facilitated by a predator clade with structures used exclusively for prey capture and with significant morphological variation. Siphonophores, a clade of colonial cnidarians, satisfy these criteria particularly well, capturing prey with their tentilla (tentacle side branches). Earlier work has shown that extant siphonophore diets correlate with the different morphologies and sizes of their tentilla and nematocysts. We hypothesize that evolutionary specialization on different prey types has driven the phenotypic evolution of these characters. To test this hypothesis, we: (1) measured multiple morphological traits from fixed siphonophore specimens using microscopy and high-speed video techniques, (2) built a phylogenetic tree of 45 species, and (3) analyzed the evolutionary associations between siphonophore nematocyst characters and prey type data from the literature. Our results show that siphonophore tentillum structure has strong evolutionary associations with prey type and size specialization, and suggest that shifts between prey-type specializations are linked to shifts in tentillum and nematocyst size and shape. In addition, we generated hypotheses about the diets of understudied siphonophore species based on these characters. Thus, the evolutionary history of tentilla shows that siphonophores are an example of ecological niche diversification via morphological innovation and evolution. This study contributes to understanding how morphological evolution has shaped present-day oceanic food webs.
#Keywords Siphonophores, tentilla, nematocysts, predation, specialization, character evolution
#Repository Index
##Supplementary Materials
-All the Appendices references in the manuscript text can be found in Supplementary_materials/Online_Appendices
-The R code, raw data, sequence alignments, microscopy metadata, and R packages used are in Supplementary_materials/Dryad and will be deposited in a Dryad repository upon submission to Systematic Biology.
-All the phylogenetic tree files are located in Supplementary_materials/TreeBase, and will be uploaded to treebase
##Tables and Figures
-All original figures in the manuscript can be found in Figures_final
-All original tables rendered in the manuscript and the Online Appendices can be found in Final_tables
##Preliminary Analyses
-Anterior versions and preliminary analyses can be found in the Scrap folder
-The working files used to generate the Online Appendices as PDFs can be found in Supplementary_mateirals/PagesNumbersAppendixFiles