Phylogenomic and morphological relationships among the botryllid ascidians (Subphylum Tunicata, Class Ascidiacea, Family Styelidae)

Abstract

Ascidians (Phylum Chordata, Class Ascidiacea) are a large group of invertebrates which occupy a central role in the ecology of marine benthic communities. Many ascidian species have become successfully introduced around the world via anthropogenic vectors. The botryllid ascidians (Order Stolidobranchia, Family Styelidae) are a group of 53 colonial species, several of which are widespread throughout temperate or tropical and subtropical waters. However, the systematics and biology of this group of ascidians is not well-understood. To provide a systematic framework for this group, we have constructed a well-resolved phylogenomic tree using 200 novel loci and 55 specimens. A Principal Components Analysis of all species described in the literature using 31 taxonomic characteristics revealed that some species occupy a unique morphological space and can be easily identified using characteristics of adult colonies. For other species, additional information such as larval or life history characteristics may be required for taxonomic discrimination. Molecular barcodes are critical for guiding the delineation of morphologically similar species in this group.

First Record of Colonial Ascidian, Botrylloides diegensis Ritter and Forsyth, 1917 (Ascidiacea, Stolidobranchia, Styelidae), in South Korea

“…In this study, we selected the mitochondrial cytochrome c oxidase subunit 1 (COI) for the detection of one-and two-toned color B. diegensis in South Korea. The COI was identified as the marker of choice for species discrimination [28] and has been effectively used for detecting NIS [8,29] and botryllids [27,30]. As a result, we recognized the presence of B. diegensis in South Korea based on DNA barcoding analysis.…”

“…Several widely distributed botryllids, including B. diegensis, have been misidentified, and the correct identification of these species is critical for understanding their biology and spread, as well as for detecting the spread of additional species [27]. Preliminary molecular analyses revealed that these one-toned color colonies included specimens attributable to B. diegensis.…”

“…Only two Botrylloides, B. magnicoecum and B. violaceus, have been reported by Rho [19,[33][34][35][36][37][38][39][40]. However, in 2021, Nydam et al [27] first reported B. diegensis in Japan and these specimens were collected in 2005-2009 in three localities of Japan. Thus, we supposed that B. diegensis was introduced to the Northwest Pacific region before 2006.…”

The Onset of Whole-Body Regeneration in Botryllus schlosseri: Morphological and Molecular Characterization

“…i.e., many species regenerate the whole body via asexual budding or upon extensive injury, others have more restrained regenerative potential (Alié et al, 2020;Nydam et al, 2021). Tunicates of the group of Botryllinae and in particular Botryllus schlosseri have been used for several decades as experimental laboratory models (Manni et al, 2019).…”

Whole body regeneration and developmental competition in two botryllid ascidians

“…If WBR is truly absent in B. schlosseri , as our study suggests, and in S. brakenhielmi (which is simply a speculation), that reduces the taxonomic breadth of WBR. The remaining species documented to have vascular budding, with currently well-resolved phylogenetic positions, all fall within a single clade, notably to the exclusion of B. schlosseri [ 45 , 46 ]. Thus, if the third hypothesis is correct, vascular budding and WBR evolved once within one clade of the Botryllinae and appear to be predominantly linked to coping with environmental adversity—either for survival after major injury or as a mechanism to allow for colony dormancy and future recovery.…”