Phylomorphometrics reveal ecomorphological convergence in pea crab carapace shapes (Brachyura, Pinnotheridae)

Abstract

Most pea crab species (Crustacea: Decapoda: Brachyura: Pinnotheridae) are characterized by their symbiotic lifestyle, often thought to be obligate parasites or commensals (Baeza, 2015). The degree of host dependency is, however, still unclear for most species. The species within the subfamily Pinnotherinae are known to be endo-or ectosymbiotic inhabitants of bivalves, polyplacophorans, gastropods, holothurians, echinoids, brachiopods, and ascidians (de Gier & Becker, 2020). Although some species have a broad host spectrum spanning across various phyla, most species of Pinnotherinae are considered to be specialists. This means that these species are only inhabiting specific genera or orders within a host phylum. Several species of the two smaller subfamilies (Pinnixinae and Pinnixulalinae) are also found in bivalve, or in/on holothurian hosts in their adult stages, but most are considered to be free-living or tube/ burrow-dwelling, sharing this habitat with a worm, ghost shrimp, or mud lobster as a host (inquilism; see Palacios Theil et al., 2016;

Ecomorphological convergence in the walking leg dactyli of two clades of ascidian‐ and mollusc‐associated shrimps (Decapoda: Caridea: Palaemonidae)

“…In this way, scale was set to ‘uniform’ and centroid size was not taken into account. Species were coloured in the morphospaces based on their host association (similar to de Gier, 2023). Morphospaces with all species annotated in the plot can be found in the supplementary datafile (Figures S2 and S3; numbers in Table S1).…”

“…Phylomorphospaces were built in R using the packages phytools, geiger and ape (see above). The similarity‐based measures C 1 to C 4 with corresponding P‐values and 1000 replicates (de Gier, 2023; Stayton, 2015) were calculated using the R package convevol v. 1.3 (Stayton, 2018). The convergence measures and their calculations are described by Stayton (2015).…”

“…Two phylogenetically informed ANOVAs (phylogenetic generalized least squares; PGLS) were performed in a similar way as the one described by de Gier (2023). This was done to investigate the impact of host choice on the shape variation in the 2D data of the two studied clades, while controlling for independence of the residuals from the phylogeny (Adams & Collyer, 2018; Mundry, 2014).…”

“…Dactylus shape data were acquired from taxonomic literature. No notable intraspecific variation in the third pereiopod dactylus shape has been recorded for the included species, so one specimen for each species was used (as in de Gier, 2023). For the newly acquired SEM images, collection material was used that was obtained during historical and recent expeditions and has been deposited in the decapod collection of Naturalis Biodiversity Center (previously Rijksmuseum van Natuurlijke Historie; RMNH.CRUS.D).…”

“…A Procrustes (M)ANOVA with a residual randomization permutation procedure (1000 permutations, RRPP) (Collyer & Adams, 2021) was performed to detect significant effects of the host associations on the placement of the species in the morphospaces, and a pairwise test was performed to find significant differences in the mean shape data in relation to host specificity. Distance between the mean shapes ( d ), upper confidence level (UCL (95%)) and p ‐values associated with the mean shape distances (Pr > d ) are given (de Gier, 2023).…”