Mitochondrial diversity inGonionemus(Trachylina:Hydrozoa) and its implications for understanding the origins of clinging jellyfish in the Northwest Atlantic Ocean

Abstract

Determining whether a population is introduced or native to a region can be challenging due to inadequate taxonomy, the presence of cryptic lineages, and poor historical documentation. For taxa with resting stages that bloom episodically, determining origin can be especially challenging as an environmentally-triggered abrupt appearance of the taxa may be confused with an anthropogenic introduction. Here, we assess diversity in mitochondrial cytochrome oxidase I sequences obtained from multiple Atlantic and Pacific locations, and discuss the implications of our findings for understanding the origin of clinging jellyfish Gonionemus in the Northwest Atlantic. Clinging jellyfish are known for clinging to seagrasses and seaweeds, and have complex life cycles that include resting stages. They are especially notorious as some, although not all, populations are associated with severe sting reactions. The worldwide distribution of Gonionemus has been aptly called a “zoogeographic puzzle” and our results refine rather than resolve the puzzle. We find a relatively deep divergence that may indicate cryptic speciation between Gonionemus from the Northeast Pacific and Northwest Pacific/Northwest Atlantic. Within the Northwest Pacific/Northwest Atlantic clade, we find haplotypes unique to each region. We also find one haplotype that is shared between highly toxic Vladivostok-area populations and some Northwest Atlantic populations. Our results are consistent with multiple scenarios that involve both native and anthropogenic processes. We evaluate each scenario and discuss critical directions for future research, including improving the resolution of population genetic structure, identifying possible lineage admixture, and better characterizing and quantifying the toxicity phenotype.

Peer Review #2 of "The highly toxic and cryptogenic clinging jellyfish Gonionemus sp. (Hydrozoa, Limnomedusae) on the Swedish west coast (v0.1)"

“…Based on consistent morphological characters, some authors either maintained the murbachii name (Rottini, 1979) or considered the two forms to be subspecies (Naumov, 1960). Govindarajan et al (2017) found that differences in mitochondrial COI sequences were also consistent with the vertensmurbachii forms; but noted that these differences do not correspond to the Atlantic -Pacific division suggested by Naumov (1960). Owing to their episodic nature and the lack of continuity in observations of late 19th and early 20th century G. murbachii and contemporary populations in the G. murbachii type locality, Govindarajan et al (2017) conservatively referred to the more toxic, putative murbachii lineage as Gonionemus sp.…”

“…1) using a DNeasy Blood & Tissue Kit (Qiagen, USA) according to the manufacturer's protocol. A 135~650 base pair portion of the mitochondrial COI gene was amplified and sequenced using primers from Folmer et al (1994) using the approach described in Govindarajan et al (2017). PCR conditions were 3 minutes at 95°C; 35 cycles of 95°C 30s; 48°C 30s, 72°C 1 min; and 5 minutes at 72°C.…”

“…Sequence chromatograms were evaluated and assembled using Geneious version 9.0.5 (https://www.geneious.com/). Assembled sequences were aligned with sequences representing the 7 haplotypes in Govindarajan et al (2017; Table 1). Representatives of additional haplotypes from Gonionemus sp.…”

“…Representatives of additional haplotypes from Gonionemus sp. sequences that were deposited on GenBank after Govindarajan et al (2017) were identified in a preliminary alignment and were then added to the alignment dataset with the Swedish sequences. Alignments were conducted using ClustalW (Larkin et al, 2007) in the Geneious platform with default parameters.…”

Distribution of the highly toxic clinging jellyfish Gonionemus sp. around the island of Martha’s Vineyard, Massachusetts, USA

“…has a complex life cycle that includes an adult medusa stage, a planula larval stage, and a benthic polyp stage, that allows for numerous dispersal mechanisms (Perkins 1903, Joseph 1925, Mikulich 1970, Kakinuma 1971. The adult medusae can reach up to 3 cm in diameter (Govindarajan et al 2017) and have adhesive structures located towards the distal ends of their tentacles which they use to cling to eelgrass (Kramp 1961;Bakker 1980). Fertile adults release gametes which fertilize and form planula larvae, which settle and develop into polyps.…”