Is it time to 'wave' goodbye to 'nictating' nematodes?

Nematology , 2010, Vol. 12(2), 309-310 Short communication Is it time to ‘wave’ goodbye to ‘nictating’ nematodes? Laura M. K RUI TB OS and Michael J. W ILSON ∗ In a recent issue of Nematology , we published a paper on nematode behaviour and, in particular, the ability of some nematodes to raise their bodies above the substrate (Kruitbos et al. , 2009). This behaviour is called either ‘body waving’ or more frequently ‘nictation’ or alternatively ‘nictitation’ and was originally described in the 1920s (Augustine, 1922; Payne, 1923). It has been reported in many nematodes, including the free-living Caenorhabditis elegans (Kiontke & Sudhaus, 2006), the entomopathogenic nematodes Steinernema carpocapsae and S. scapterisci (Campbell & Gaugler, 1993) and parasites of humans including Necator americanus and Ancylostoma duodenale (Hass et al. , 2005). In Kruitbos et al. (2009) we chose to use the term ‘body waving’ rather than ‘nictation’ and here we argue that in the context of this behaviour the word ‘nictation’ should be discarded as it is nonsensical. In the Oxford English Dictionary the verb to nictate is defined as “to wink” or “to blink” and it is derived from the Latin nictat- , the past participle stem of nictare , “wink”. Biologists may also know this term from the nictating or nictitating membrane, the transparent or translucent third eyelid present in some animals, including various reptiles, birds and sharks. In this instance, the Latin derivation makes perfect sense, but how does it relate to nematodes standing on their tails? We believe the discrepancy comes from this behaviour being described in an important and frequently cited paper written in German (Volk, 1950). Volk (1950) studied nematodes associated with earthworms and beetles. He observed that one species, Rhabditis stammeri , was able to raise its body off the substrate which it then waved, and he concluded that this behaviour aided attachment to beetles for phoretic transport. Volk (1950) described the behaviour as “winken” – the German for ‘to wave’. To our knowledge, the earliest use of nictitating to de- scribe this behaviour is by Hesling (1966) who studied swarming behaviour of the two mycophagous nematodes Ditylenchus myceliophagus and Aphelenchoides compos- Institute of Biological and Environmental Sciences, University of Aberdeen, UK, AB24 3UU ∗ Corresponding author, e-mail: [email protected] Received: 27 April 2009; revised: 10 August 2009 Accepted for publication: 11 August 2009 ticola. Neither of these nematodes body waved, but Hes- ling used the term “nictitating” (Hesling, too, used in- verted commas) in relation to previous work by Staniland (1957). Staniland (1957) did indeed describe body waving in Rhabditis sp. but used neither the words nictating nor nictitating in his manuscript. We can only assume that, prior to Hesling (1966), somebody believed that this behaviour should have a lati- nate name and during translation ‘winken’ and ‘winking’ were confused and now nematodes ‘nictate’. Another possible explanation for this use of ‘nictate’ is that in certain Latin dictionaries nicto , although literally meaning “moving the eyelids up and down”, can, in a figurative sense, also mean “to exert oneself, to strive”. It could be argued that a nematode standing up could be described as ‘striving’. However, biological nomenclature should be derived from the literal meaning of words, but even if figurative derivations were acceptable, nictate may still be inappropriate. The figurative use is attributed to the Roman poet and philosopher Lucretius in his work, De Rerum Natura , a poem in six books. However, W.E. Leonard, one editor of Lucretius, emends nictari (to wink) to nixari (to struggle). Thus, if the nematodes are indeed ‘struggling’ we should call the behaviour ‘nixation’. In all earlier papers and some more recent ones (Hass et al. , 2005), nictation referred to nematodes merely raising their bodies from the substrate. However, Campbell and Gaugler (1993) redefined the term “nictation” for when more than 95% of the nematode’s body was raised, and used the term “body waving” for when 30-95% was raised. We did not make this distinction in our work, as we doubt there is any difference in the ecological function between the two behaviours, and also feel that such cat- egorisation would inevitably be subjective. This behav- iour is typically observed from above using a microscope. When nematodes raise their bodies, they are vertically ori- entated, making it impractical to use eyepiece graticules to measure the extent of body raising. Furthermore, on © Koninklijke Brill NV, Leiden, 2010 DOI:10.1163/138855409X12506855979794 Also available online - www.brill.nl/nemy 309