Parborlasia corrugatus

Parborlasia corrugatus (McIntosh, 1876)

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Overview

Comprehensive Description

Parborlasia corrugatus is a conspicuous heteronemertean marine worm that occurs across the South American, sub-Antarctic, and Antarctic regions at depths ranging from the intertidal to 3950 meters. It is a large worm, reaching a length of up to 2 meters, with a wet mass exceeding 140 grams. It can be quite abundant, with reported densities ranging from 0.3 to 26.2 individuals/square meter, and is an important scavenger in antarctic benthic systems. (Heine et al. 1991; Thornhill et al. 2008 and references therein).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Description

Lookalikes

Thornhill et al. (2008) reported the detection (based on DNA analysis) of two potential cryptic species that were previously considered to be P. corrugatus: one putative species in Antarctica and the sub-Antarctic islands and a second putative species in southern South America. Additionally, South American P. corrugatus were further partitioned into two haplotype networks, one along the western region of the Argentinean continental shelf and a second along Burdwood Bank. Unfortunately, these Parborlasia populations were difficult to differentiate morphologically, a problem common to many nemertean taxa. The presence of potentially cryptic species raises taxonomic issues concerning which lineage should retain the original name. In the case of P. corrugatus, the type specimen originated from the Kerguelen Archipelago in the sub-Antarctic (McIntosh 1876, cited in Thornhill et al. 2008), which is outside of the area sampled by Thornhill et al. Thus, further sampling will be necessary before this issue can be resolved. (Thornhill et al. 2008)

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Ecology

Reproduction

Parborlasia corrugatus is dioecious (i.e., it has separate sexes). It is a broadcast spawner (releasing gametes--eggs and sperm--into the water), presumably reproducing throughout the year. (Thornhill et al. 2008 and references therein)

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Associations

Parborlasia corrugatus is reported to have a diverse diet including detritus, diatoms, sponges, anemones, polychaetes, gastropods, amphipods, isopods, and/or vertebrate carrion (Thornhill et al. 2008 and references therein). Like many nemerteans, P. corrugatus appears to be chemically defended and distasteful to other organisms. There are no reports of predation upon these worms. Their toxic and feeding-deterrent characteristics are probably the result of the epithelial production of copious acidic mucus (pH = 3.5), although other toxic or noxious metabolites may be present. Although P. corrugatus are rich in nutrients and energy and might be expected to be high-quality prey, potential predators may in fact avoid ingestion of this species. (Heine et al. 1991)

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Evolution and Systematics

Systematics and Taxonomy

To assess patterns of diversity, Mahon et al. (2010) examined a fragment of the mitochondrial 16S rRNA gene from larval and adult nemerteans (n = 192) from 53 sites along the western Antarctic Peninsula. They identified 20 distinct lineages having an uncorrected genetic distance (p) greater than 5% to the nearest sister taxon or group, 19 of which have not been genetically characterized in previous studies. Additionally, the putatively dominant adult species in the region, Parborlasia corrugatus, was found to comprise only 4.3% of larvae sampled (n = 3 out of 69 samples from 12 locations). Of 47 nemertean species recorded from Antarctic waters, 20 are heteronemerteans and therefore could have a pelagic pilidium larval phase. These results suggest that Antarctic biodiversity is underestimated, and that unknown species of nemerteans await description from Southern Ocean waters. (Mahon et al. 2010)

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Phylogeography

The Antarctic Polar Front (APF) is an area hypothesized to form an open-ocean dispersal barrier characterized by marked temperature change (3 to 4 °C), deep water, and the intense Antarctic Circumpolar current. The APF formed following the break up of the South American and Antarctic continents that led to the creation of a seaway, the Drake Passage, and the establishment of the Antarctic Circumpolar Current. Biologically, the hypothetical result of this separation was the isolation of Antarctic fauna for between 20 million and 41 million years. In their phylogeographic investigation of Parborlasia corrugatus,  Thornhill et al. (2008) found that patterns of mitochondrial gene diversity indicate that there is a single, broadly distributed population of Parborlasia corrugatus found around large areas of Antarctica and the sub-Antarctic islands. However, they found no evidence of genetic connectivity (and therefore recent gene flow) between this population and individuals sampled in southern South America. Thus, the APF represents a significant barrier to open-ocean dispersal over evolutionary time, although dispersal events have occurred since the establishment of the APF more than than 20 million years ago. (Thornhill et al. 2008)

An allozyme survey, using starch-gel electrophoresis, was carried out by Rogers et al. (1998) on eight populations of Parborlasia corrugatus collected from locations around the South Orkney Islands, Antarctica. The observed levels of genetic differentiation between populations of P. corrugatus and the significant heterozygote deficiencies were unexpectedly high, given that this species has been reported to have a long-lived planktotrophic larva, facilitating genetic mixing over long distances. Rogers et al. hypothesised that recruitment of P. corrugatus in the South Orkney Islands originates from genetically distinct populations located in the Weddell Sea and to the west of the Antarctic Peninsula. Shifts in the relative position of the Weddell Sea Front, Weddell-Scotia Confluence, and Scotia Front relative to the South Orkney Islands could provide a mechanism for variation in the origin of recruits over time. (Rogers et al. 1998)

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

References

Heine, J. N., McClintock J. B., Slattery M., & Weston J. (1991).  ENERGETIC COMPOSITION, BIOMASS, AND CHEMICAL DEFENSE IN THE COMMON ANTARCTIC NEMERTEAN PARBORLASIA-CORRUGATUS MCINTOSH. Journal of Experimental Marine Biology and Ecology. 153, 15-25.
Mahon, A. R., Thornhill D. J., Norenburg J. L., & Halanych K. M. (2010).  DNA uncovers Antarctic nemertean biodiversity and exposes a decades-old cold case of asymmetric inventory. Polar Biology. 33, 193-202.
Rogers, A. D., Clarke A., & Peck L. S. (1998).  Population genetics of the Antarctic heteronemertean Parbolasia corrugatus from the South Orkney Islands . Marine Biology. 131, 1-13.
Thornhill, D. J., Mahon A. R., Norenburg J. L., & Halanych K. M. (2008).  Open-ocean barriers to dispersal: a test case with the Antarctic Polar Front and the ribbon worm Parborlasia corrugatus (Nemertea: Lineidae). Molecular Ecology. 17, 5104-5117.