Evolutionary implications of analyses of complete mitochondrial genomes across order Zoantharia (Cnidaria: Hexacorallia)

Abstract

Cnidarians are early‐diverging metazoans, but evolutionary aspects of some taxa are still poorly understood, as in the order Zoantharia (Anthozoa: Hexacorallia). Zoantharians have been divided into two suborders based on the arrangement of the fifth septae as complete (Macrocnemina) or incomplete (Brachycnemina). Previous molecular phylogenetic analyses have indicated the need for re‐evaluation as Macrocnemina has been found to be paraphyletic. Despite many phylogenetic studies, the recovery of complete mitochondrial genomes (mt‐genomes) for systematic and evolutionary studies of zoantharians has been limited. The present study represents the first to sequence the complete mt‐genomes of members of eight of nine zoantharian families. Although all examined mt‐genomes had the same gene order arrangement, there were variations among mt‐genomes' sizes, nucleotide substitution rates, and introns. Only two species did not have the cox1 intron, which harbors a gene coding a homing endonuclease of the LAGLIDADG type. Our mitogenomic analyses also showed relatively high nucleotide diversity in mt‐DNA regions other than the standard regions traditionally considered for DNA barcoding of this group. Phylogenetic analyses using 13 mt‐genome protein‐coding genes recovered a fully resolved tree with clear separation between macrocnemic representatives. Ancestral state reconstruction analyses revealed three main transitions in arrangement of the marginal musculature through the evolutionary history of the order. An “early” transition from reticulate mesogleal to a cteniform endodermal arrangement was followed by transitions that occurred in the common ancestor of the Brachycnemina and family Hydrozoanthidae. Our results indicate the need for clarification of higher‐level phylogeny and taxonomy of Zoantharia.

Extreme mito-nuclear discordance within Anthozoa, with notes on unique properties of their mitochondrial genomes

“…Corallimorpharia [64], Actiniaria [65], and Zoantharia [62]. This endonuclease appears to be more common in some orders (Zoantharia, Corallimorpharia) than others (Scleractinia).…”

“…Utilizing a total of 202 complete or near-complete mitochondrial (mt) genomes, we were able to examine mito-nuclear discordance within the Anthozoa and explore the unique mt genome properties of all orders belonging to this sub-phylum of Cnidaria. In addition to the mt genomes newly assembled here, most of the previously published mt genomes [16, 38, 62] that we included in our analyses had been assembled from the raw sequence data from Quattrini et al [27, 42]. This large dataset of mt genomes further demonstrates the utility of off-target reads generated from target-capture data for the assembly of mt genomes and adds to the growing knowledge of mt genome evolution within the sub-phylum Anthozoa.…”

Evidence of genetic isolation between two Mediterranean morphotypes of Parazoanthus axinellae

“…A multidisciplinary approach should include (1) reproductive biology of both morphotypes in sympatry, (2) field experiments to evaluate substrate specificity 26 , (3) studies of chemodiversity 49 , (4) naturalistic studies 16 and (5) more variable molecular markers (e.g. RAD sequencing 50 ; Terzin et al unpublished) and/or sequencing of the complete mitochondrial genome 51 .…”

Phylogenetics and Mitogenome Organisation in Black Corals (Anthozoa: Hexacorallia: Antipatharia): An Order-Wide Survey Inferred From Complete Mitochondrial Genomes

“…Gene order and content are highly conserved across the antipatharian order, consistent with previous findings (Brugler and France, 2007;Kayal et al, 2013) with the absence of the COX1 intron as the main notable variation. Internal gene rearrangements have been reported within all hexacoral orders (Emblem et al, 2011;Lin et al, 2014;Foox et al, 2015), but it appears that antipatharians are an exception, along with zoantharians (Poliseno et al, 2020). The stable structural arrangement in these two orders may be linked to the slow rate of nucleotide substitution in anthozoans (Hellberg, 2006) .…”