Nematology, 2012, Vol. 14(2), 151-158 Tokens of love: possible diagnostic value of mating plugs and refractive secretory uterine structures in Trichodorus (Diphtherophorina: Trichodoridae) Wilfrida DECRAEMER 1,2,* 1 Royal Belgian Institute of Natural Sciences, Department of Invertebrates, Vautierstraat 29, B-1000 Brussels, Belgium 2 Ghent University, Department of Biology, Ledeganckstraat 35, B-9000 Ghent, Belgium Received: 11 May 2011; revised: 26 May 2011 Accepted for publication: 26 May 2011; available online: 20 July 2011 Summary – Within the Trichodoridae, mating plugs have only been recorded from Trichodorus species. They can be observed as a clear plug within the vagina/vulva but may also be present in the uteri. These secretory structures are diverse in size, varying between 4 and 27 μm in length, and in shape from simple unipartite tubular structures to bipartite with a central indentation or with a tail-like end. All mating plugs possess a central canal that can vary in diameter. Within Trichodorus, the shape and structure of the mating plugs can provide additional diagnostic information at species level. Keywords – copulatory plug, morphology, taxonomy. Mating plugs or copulatory plugs have been described from a wide range of animal phyla, vertebrates (e.g., rep- tiles, rodents, birds, primates) as well as invertebrates (e.g., insects, arachnids, nematodes). Mating plugs are mostly mucoid, gelatinous substances secreted by male secretory cells associated with the reproductive system as in, for example, the male somatic gonad in Caenorhab- ditis elegans (Palopoli et al., 2008) or by female perivul- var glands as in the free-living marine nematode Calomi- crolaimus compridus (Gourbault & Vincx, 1988). These secretory plugs are placed by the male over the vulva as in Scutellonema cavenessi (Demeure et al., 1980) or into the female vulva/vagina as in Trichodorus minzi De Waele & Cohn, 1992, thereby obstructing or preventing females from mating with subsequent males and so for- ming a possible option to reduce male competition. Re- cently, Timmermeyer et al. (2010) observed that for C. re- manei, plugging did not influence female attractiveness or reduce mating rates but increased female fitness. The authors presumed that a mating plug may present an as yet unknown nutritional benefit for the female or a posi- tive physiological effect. Jensen (1982) described the re- productive behaviour of Chromadorita tenuis (Schneider, 1906) in which females possess four spermathecae and mate only once during their life. Superfluous sperm that * E-mail: Wilfrida.decraemer@naturalsciences.be cannot be stored is rejected through the vulva. No block- ing vulva plug has been observed but sometimes sperm cells in the form of a mucous mass over the vulva could be present. Fürst von Lieven et al. (2005) showed that in a Myolaimus species with males lacking spicules, mating is basically a matter of male gonoduct secretions. The au- thors unravelled a complex system of at least six different secretions of the male gonoduct. The vas deferens sub- stances used for attachment of the male to the female and inflation of the vulval sac was considered most likely to be homogeneous with the glue-forming mating plugs. Within the Trichodoridae, vaginal secretory plugs have only been recorded from Trichodorus species. The illus- tration of the vulva region of a female of Trichodorus proximus Allen, 1957 (now T. obtusus Cobb, 1913 see Decraemer, 1995) showing a small thickening at the dis- tal vagina in the original drawing might represent the first illustration of a copulatory plug. Other illustrations of ap- parent copulatory plugs are found for T. aquitanensis Bau- jard, 1980 (Fig. 1G in Baujard, 1980), and T. primitivus (de Man, 1880) and T. variopapillatus Hooper, 1972 (re- spectively, Pl IV 3 and Pl. IV 16, 18 and 21 in Decraemer, 1980). Geraert et al. (1980) described refractive structures resembling copulatory plugs along the length of the uteri of several specimens of T. variopapillatus and considered © Koninklijke Brill NV, Leiden, 2012 DOI:10.1163/138855411X581703 Also available online - www.brill.nl/nemy 151