Coming out of your shell or crawling back in: multiple interphylum host switching events within a clade of bivalve- and ascidian-associated shrimps (Caridea: Palaemonidae)

Abstract

Marine symbiotic Palaemonidae, comprising over 600 species, live in association with marine invertebrates of different phyla, like Cnidaria, Echinodermata, Mollusca, Porifera, and Tunicata. A phylogenetic study is performed on a clade of bivalve- and ascidian-associated endosymbiotic shrimp species (Caridea: Palaemonidae), using morphological and molecular data. A Total Evidence approach is used in order to include all currently known ingroup species in an evolutionary framework. Ancestral state reconstruction analyses are performed to identify host-switching events and ancestral ranges. The clade, including Ascidonia, Conchodytes, Dactylonia, Odontonia, and Pontonia, and various smaller genera, is recovered as monophyletic, with an ascidian-associated ancestral host state. At least six interphylum host switches are tentatively identified, with members of Odontonia and Notopontonia switching back to an ascidian host affiliation after the ancestral host switch of the clade including Conchodytes, Odontonia and related genera, from an ascidian- to a bivalve host. The clade including Ascidonia and Pontonia was recovered to have an ancestor with an East Pacific/Atlantic distribution. The other studied genera remained in the original ancestral Indo-West Pacific range. We hypothesize that similar internal environments of shrimp hosts from different phyla will function as hot spots for interphylum host switching in various lineages of symbionts.

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

“…Host-switching events seem to have occurred a few times in ectosymbiotic clades within the Palaemonidae, mainly between echinoderm and cnidarian hosts (Horká et al, 2016). In endosymbiotic lineages, like Clades 5 and 6 of Horká et al (2016; see below), these events are hypothesized to have happened much more frequent (de Gier et al, 2022). The endosymbiotic mollusc-and ascidian-associated palaemonid species are generally grouped in two clades (Figure 1; de Gier et al, 2022;de Gier & Fransen, 2023), from hereon called the 'Conchodytes clade' and the 'Anchistus clade'.…”

“…In endosymbiotic lineages, like Clades 5 and 6 of Horká et al (2016; see below), these events are hypothesized to have happened much more frequent (de Gier et al, 2022). The endosymbiotic mollusc-and ascidian-associated palaemonid species are generally grouped in two clades (Figure 1; de Gier et al, 2022;de Gier & Fransen, 2023), from hereon called the 'Conchodytes clade' and the 'Anchistus clade'. The first clade includes the larger genera Ascidonia Fransen, 2002, Conchodytes Peters, 1852, Dactylonia Fransen, 2002, Odontonia Fransen, 2002and Pontonia Latreille, 1829, in addition to some minor, often monotypic genera (de Gier et al, 2022).…”

“…In a more recent study by Chow et al (2021), the 'Conchodytes clade' makes up part of a large clade including even some free-living deep-sea species (Clade IIIC), while the 'Anchistus clade' can be found in a different branch together with most of the outgroups in this study (Clade IIIH). The endosymbiotic lifestyle of these clades seems to be mirrored by their morphological variation: lots of species exhibit morphological adaptations that seem to be linked to an endosymbiotic lifestyle (Bruce, 1990)-after Bruce (1990); (i) Anchistus miersi (De Man, 1888)-after de Gier and Fransen (2023); (j) Neoanchistus cardiodytes Bruce, 1975-after Bruce (1975; (k) Polkamenes nobilii (Holthuis, 1952)-after de Gier and Fransen (2023); (l) Ensiger custoides (Bruce, 1977)-after de Gier and Fransen (2023); (m) Dasella ansoni Bruce, 1983-after Bruce (1983. Shrimp dimensions not to scale.…”

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

“…In addition, symbiotic members of the families Portunidae (e.g., the cnidarian-and echinoderm-associated members of Lissocarcinus White, 1849 andCaphyra Guérin, 1832) and Varunidae (the burrowdwelling Sestrostoma Davie & Ng, 2007) have also evolved adapted walking-leg dactyli, carapace shapes, and cryptic camouflage (Davie & Ng, 2007;Evans, 2018). Two clades of endosymbiotic shrimp (Caridea: Palaemonidae), which share a similar lifestyle with ascidian-and bivalve-associated pea crabs, evolved similar morphological features, mainly in the round, swollen shape of their abdomen and smooth carapace (de Gier et al, 2022;Fransen, 1994).…”

Further evidence of the symbiotic acorn barnacle, Chelonibia testudinaria (Linnaeus, 1758) (Balanomorpha, Chelonibiidae) on sheepshead, Archosargus probatocephalus (Walbaum, 1792) (Perciformes, Sparidae), and in total 5 families and 2 orders of fishes (formerly superclass Pisces, now gigaclass Actinopterygii)

“…SAB attachment to fishes would not seem to be much of a host switch. Symbionts switch to new hosts with similar structures (De Gier et al, 2022). Some of the known hosts of SAB have structures similar to fishes.…”