On-line version ISSN 0034-7744
Rev. biol. trop vol.59 n.4 San José Dec. 2011
The Bobbit worm dilemma: a case for DNA
(Reply to Salazar-Vallejo et al. 2011. Giant Eunicid Polychaetes (Annelida) in shallow tropical and temperate seas. Rev. Biol. Trop. 59-4: 1463-1474)
Department of Marine Biology, Texas A&M University at Galveston, P.O. Box 1675, Galveston, TX 77553; firstname.lastname@example.org
Whoever came up with the name "Bobbit worm"? It must be a fairly recent idea, given that the "regretful incident" in the Bobbit family only happened in 1993. Unfortunately, it is not clear who coined the name or when it was first used. The name does not do the worms justice and is misleading. For example, one of the explanations for the name that comes up when googling "Bobbit worm" is that the female bites off the male's penis after copulation (seriously? Since when do they have penises?!). Neither are there any reports of eunicids attacking body parts of unsuspecting humans in their vicinity. The jaws resemble scissors, which is another possible explanation for the name, although actually, the "Bobbit incident" was committed with a carving knife.
Not only is the name misleading with regard to the nature of the worms, it also leads to taxonomic confusion. Some sources specifically apply it to what they believe is Eunice aphroditois, others use it for any large eunicid. Given that not even eunicid taxonomists agree on the identity of E. aphroditois (well, taxonomists rarely agree with each other, but that's a different story), it is not too surprising that untrained aquarists or recreational divers lump all the species together under one easily memorable common name.
Does size matter? Salazar-Vallejo et al. cite reports of eunicid worms of over 3 m length. The Australian museum even holds a specimen that reportedly was nearly 6 m long when collected (Fauchald 1992 and pers. comm.). (As a side note: six meters is long, but it's still far from the longest worm ever reported. That honor falls to the nemertean Lineus longissimus which can grow to 30 m in length and probably at least twice as long when fully stretched out [McIntosh 1873-1874]). The main problem with using size in taxonomic studies is that even big worms start out as tiny worms and probably take many years to reach their full length and segment number. In most cases we do not know which characters are size-dependent. In traditional, type-based taxonomy, this can pose serious problems.
Salazar-Vallejo et al. conducted a lot of detective work to reconstruct the taxonomic history of Eunice aphroditois and other large Eunice species and make a convincing case for splitting E. aphroditois into several species reflecting different morphologies. Their main conclusion is that more type material, including neotypes and topotypes, needs to be examined to tease apart species and delineate their differences and intraspecific variation.
While I believe that the suggested work is crucial for resolving this and similar taxonomic dilemmas, I would also argue that molecular data should be added to this equation. The decreasing costs for DNA sequencing allow more and more researchers access to the technology or opportunities for collaboration. Molecular data may not be necessary for each and every species description, but for complicated taxonomic problems, such as that of the large eunicids, DNA would add an independent, objective line of evidence.
An impediment for molecular work on annelids is that museum and ecological collections are usually formalin fixed. Formalin is still the best solution for preserving annelid morphology, but it crosslinks with DNA and proteins, making the extraction of quality DNA difficult if not impossible. Protocols for DNA extraction from formalinized tissue or for enzymatically repairing DNA do exist (Schander & Kenneth 2003, Skage & Schander 2007), but they are cumbersome and not reliably successful. New specimens would have to be collected from the type locations and tissue samples preserved in an appropriate manner while ensuring that voucher specimens are available for morphological studies. In many cases, especially for large worms, a small piece of tissue, such as a parapodium, can be preserved for molecular work, whereas the remainder of the specimen is fixed in formalin. That way, the same specimen can be studied morphologically and genetically.
In conclusion, Salazar Vallejo et al.'s approach of examining color images of "Bobbit worms" from around the world highlights some of the taxonomic problems encountered in this group. I fully support the call for examining more topotypes and neotypes of the species in question, but strongly suggest incorporation of molecular data as well. Genetics will never replace morphology in taxonomic studies, but will add a new dimension and perhaps clarity in delineating species. Rather than using one or the other data source, I believe that "Bobbit worms" are a good case in point for a combination of morphological and molecular data to provide a more complete picture of the evolutionary history of these terrifying and ugly creatures.
Christiansen, P. 2008. Terrifying and ugly sea creatures. Gareth Stevens, New York, USA. [ Links ]
Galtier, N., B. Nabholz, S. Glémin & G.D.D. Hurst. 2009. Mitochondrial DNA as a marker of molecular diversity: a reappraisal. Mol. Ecol. 18: 4541-4550. [ Links ]
Nygren, A., E. Norlinder, M. Panova & F. Pleijel. 2011. Colour polymorphism in the polychaete Harmothoe imbricata (Linnaeus, 1767). Mar. Biol. Res. 7: 54-62. [ Links ]
Schander, C. & H.M. Kenneth. 2003. DNA, PCR and formalinized animal tissue - a short review and protocols. Organisms Diversity & Evolution 3: 195-205. [ Links ]
Schulze, A. 2006. Phylogeny and genetic diversity of palolo worms (Palola, Eunicidae, Polychaeta) from the tropical North Pacific and the Caribbean. Biol. Bull. 210: 25-37. [ Links ]
Skage, M. & C. Schander. 2007. DNA from formalin-fixed tissue: extraction or repair? That is the question. Mar. Biol. Res. 3: 289-295. [ Links ]
Zanol, J., K.M. Halanych, T.H. Struck & K. Fauchald. 2010. Phylogeny of the bristle worm family Eunicidae (Eunicida, Annelida) and the phylogenetic utility of noncongruent 16S, COI and 18S in combined analyses. Mol. Phyl. Evol. 55: 660-676. [ Links ]
Received 04-I-2011. Corrected 20-IV-2011. Accepted 31-V-2011.