Phylogeography of Acartia tonsa Dana, 1849 (Calanoida: Copepoda) and phylogenetic reconstruction of the genus Acartia Dana, 1846

Abstract

The calanoid copepod, Acartia tonsa Dana, 1849 is one of the most abundant and well-studied estuarian species with a worldwide distribution. In this research, we use the mitochondrial cytochrome oxidase subunit I gene to study the phylogeography of A. tonsa by analyzing sequences from specimens collected in the western Gulf of Mexico (GOM) along with all sequences from previous research. We reconstruct the phylogeny for the genus Acartia Dana, 1846 and highlight numerous potential misidentifications of Acartia species deposited in GenBank. The incorrect taxonomy assigned to some of these sequences results in apparently paraphyletic relationships. This study demonstrates that A. tonsa is a species complex with multiple, deeply diverging, lineages of varying geographic affinities. Multiple new lineages are found in the Texas GOM that is basal to northwestern Atlantic lineages with phylogenetic connectivity also observed between Brazil and the Texas GOM. Results show two major phylogeographic breaks in the North American continent, one at the border between the Gulf of Mexico and the Northwest Atlantic, and the other at about 35°N. One of the major clades in the A. tonsa species complex shows a clear pattern of divergence that follows the prevailing currents. Within this clade, older lineages are found in the western GOM while newer lineages are found in the eastern GOM and the southern coast of the northwest Atlantic, with the youngest lineages diversifying in the north. The results show that A. tonsa can be used as a model species for observing phylogeographical structuring of coastal plankton along the American continent.

Patterns of Cryptic Diversity and Phylogeography in Four Freshwater Copepod Crustaceans in European Lakes

“…With these rates, all the three pairs of cryptic species in our data would have diverged already in the Miocene, from 6 to 26 Ma (Table 7). While this appears unexpected in the context of European biogeography, in the context of copepod systematics these estimates are not exceptional: similar or even deeper cryptic lineages are frequently observed [20,21,26,44,45,[89][90][91]104,105]. Several studies on the phylogeography of freshwater copepods (including European populations) have pointed to the Early Miocene as a possible time of initial divergence [21,26,76].…”

“…It should be noted that copepod populations also overall show extreme mitochondrial DNA diversity [90]. Interestingly, this is not only for geographically isolated freshwater populations, but also for marine species, where populations from relatively close locations can demonstrate high variability [11,20,[44][45][46][47]50,[86][87][88][89][90][91][92]. These "intra-species" levels are extraordinary in comparison with vertebrate and invertebrate taxa, which commonly show <3% intraspecific and >2% interspecific variation [93][94][95].…”

“…No morphological differences were found in populations of N. hibernica (Kochanova, unpubl. ) The slow rate of morphological evolution relative to molecular evolution is emerging as a general pattern in copepods [41,91,[104][105][106], and indicates that modern morphological resemblance does not necessarily mirror cladogenetic events [11,77].…”

Toward a global reference database of COI barcodes for marine zooplankton

“…COI barcode reference sequences are available for many-if not most-of the more abundant and/or ecologically important species from coastal ocean areas, as well as surface layers (epipelagic zone) of the open ocean. Additional effort is needed for taxonomically challenging taxa, including species of the genus Acartia (Figueroa et al 2020) and family Paracalanidae (Cornils and Held 2014;Moon et al 2010), as well as representatives of bathy-and abyssopelagic taxa, which remain under-sampled. Rapid progress is being made with COI barcoding of copepods.…”

Feeding and reproduction including diapausing egg production as cold-water adaptations for overwintering of <i>Acartia steueri</i> (Copepoda, Calanoida) in Okkirai Bay, Sanriku, northern Japan

“…Among neritic Acartia copepods, A. tonsa also has a wide geographical distribution and different life history strategies including diapausing egg production pro-cesses, in each habitat (Caudill & Bucklin 2004, and citations therein). Molecular techniques revealed that A. tonsa has experienced geographical isolation resulting in the divergence of multiple, distinct cryptic lineages (Caudill & Bucklin 2004, Chen & Hare 2011, Costa et al 2014, Figueroa et al 2020). The results of these studies indicate the possible presence of cryptic species also in A. steueri, and molecular biological methods are considered to be extremely useful for elucidating the diversity of life histories in this copepod.…”