A Very Rare Malformation Affecting the Female Genital System of one Labronema Specimen (Dorylaimida, Dorylaimidae)

Several kinds of abnormalities or malformations affecting the female genital system of Dorylaimid nematodes have been repeatedly reported in longidorid forms, more occasionally in free-living taxa. These anomalies include total or partial duplication of the system, a didelphic-opisthodelphic condition, total or partial reduction of one genital branch, and the existence of two (or even three) vulvae (see Table 1 for a compendium of previous records). Radivojević (2005) described and discussed with some detail the nature of these anomalies.

One female of the genus Labronema Thorne, 1939, recently collected in the course of a nematological survey, shows one of the rarest abnormalities so far observed, as the individual lacks both vulva and vagina. The specimen was collected in a grassy and stony soil at 1,800 m.a.s.l. on the mountain of La Pandera, Province of Jaén, Spain. The individual represents a population belonging to a non-described species of the genus Labronema, which will be characterized and described in a separate contribution.

Leaving aside the absence of vulva and vagina, the general morphology (Fig. 1) and morphometry (Table 2) of this female are totally comparable to those observed in other females of the same population. In particular, the length of neither its genital branches (anterior 324 µm or 18% of body length, posterior 362 µm or 20% of body length) nor ovaries (anterior 107, posterior 87 µm) differ from those of normal females (207–368 µm or 13–20% of body length, 43–180 µm, respectively). Nonetheless, some differences are observed in the morphology of genital tract. On one hand, the posterior oviduct appears visibly inflated at its distal part and significantly longer (187 µm) than that observed in normal females (72–147 µm), probably due to fixation process, as the anterior one is comparable to that of normal females (140 and 43–180 µm, respectively). On the other hand, the uteri are apparently simple and tube-like (Fig. 1B,C) (vs complex, tripartite in normal females; Fig. 1F), and sperm cells, always abundant in normal females as the population is bisexual with both females and males nearly equally present, are not found within the genital tracts of the abnormal female. A somewhat similar anomaly was reported by Radivojević (2005) in Xiphinema dentatum, in this case also with a significant reduction of both uteri.

Figure 1

Light micrographs of Labronema sp. A–E and G–I, abnormal female; F, normal female. A: anterior region in median lateral view; B: posterior genital branch (arrow pointing at the supposed position of vulva); C, E: genital system (arrow pointing at the supposed position of vulva); F: posterior genital branch; G: lip region in lateral surface view; H: entire body; I: caudal region (arrow pointing at anus). (Scale bars: A, G, I = 10 µm; B, D = 50 µm; C, E, F = 100 µm).

Vulvaless or Vul mutants, which lack not only a vulva but also a vagina, have been generated in experimental studies with Caenorhabditis elegans (Horvitz and Sulston, 1980; Ferguson and Horvitz, 1985; Greenwald, 1997; Sternberg, 2005), Pristionchus pacificus (Eizinger and Sommer, 1997) and Oscheius tipulae (Dichtel-Danjoy and Félix, 2004), an indication that the developmental anomaly noted herein might have a genetic basis. Additionally, environmental conditions might drive the development of vulval anomalies, as demonstrated by Braendle and Félix (2008), in both wild-type and mutant animals of Caenorhabditis spp. As mentioned above, the abnormal female herein reported was collected at a moderately high elevation (1,800 m), and might be, for instance, exposed to an extremely stressful environment during its development.