The buccal capsule of Aduncospiculum halicti (Nemata: Diplogasterina): an ultrastructural and molecular phylogenetic study

Abstract

The buccal capsule of Aduncospiculum halicti (Diplogasterina) is compared with that of Zeldia punctatu (Cephalobina) and Caenorhabditis elegans (Rhabditina). Characters are mapped on an independent DNA-based phylogenetic tree (inferred from RNA polymerase I1 and rDNA sequences) to test evolutionary hypotheses. Irrespective of dimorphism, the buccal capsule wall of A. halicti consists of an anterior to posterior series of six cuticular structures classically termed rhabdions. These are defined according to their internal differentiations, discontinuities in profiles, and underlying tissues. Homologies of rhabdions 1 and 2 in A. halicti are proposed on the basis of position and association with adjacent tissues, consistent with those of Cephalobina and Rhabditina. Rhabdion 3 is associated with radial epithelial cells as is the mesorhabdion in C. elegans; this contrasts with Z. punctata, where a rhabdion in a similar position is associated with radial muscle cells. Dorsal and subventral teeth in A. halicti comprise rhabdions 4 and 5; this may be homologous with a corresponding region in Z. punctuta but contrasts with C. elegans, where the corresponding region consists of a single metarhabdion. These characters, when mapped on the sequence-based tree, suggest that A. halicti and Diplogasterina share with C. elegans and other Rhabditina derived characters, including a mesorhabdion associated with epithelial cells, but retain some apparently primitive features shared with Cephalobina. RCsumC: La capsule buccale d'Aduncospiculum halicti (Diplogasterina) est comparke a celle de Zeldia punctata (Cephalobina) et a celle de Caenorhabditis elegans (Rhabditina). Les caractkres sont cartographiks sur un arbre phylogknktique bask sur I'ADN (d'aprks I'ARN polymkrase I1 et les skquences d'ADNr) en vue d'kprouver des hypothkses kvolutives. Sans tenir compte du dimorphisme, la paroi de la capsule buccale d'A. halicti est constituke d'une skrie de six structures cuticulaires appelkes rhabdions orientkes de l'avant a l'arrikre. Ces strutures se distinguent par des diffkrenciations internes, des profils discontinus et par les tissus qui leur sont sous-jacents. Des homologies des rhabdions 1 et 2 chez A. halicti sont proposees en fonction de leur position et de leur association aux tissus adjacents, caractkristiques semblables 2 celles qui prkvalent chez les Cephalobina et les Rhabditina. Le rhabdion 3 est associee a des cellules kpithkliales radiales, comme dans le mksorhabdion de C. elegans; chez Z. punctata, un rhabdion en position semblable est associk a des cellules musculaires radiales. Les dents dorsales et sub-ventrales d'A. halicti sont formkes des rhabdions 4 et 5; il s'agit peut-ttre la d'une configuration homologue d'une region correspondante chez Z. punctata, mais cette configuration diffkre de celle qui prkvaut chez C. elegans chez lequel la rkgion similaire comporte un seul mktarhabdion. Ces caractkres, lorsqu'intkgrks dans l'arbre phylogknktique bask sur I'ADN, semblent indiquer qu'A. halicti et les Diplogasterina on...

Ultrastructure of the post–corpus of Zeldia punctata (Cephalobina) for analysis of the evolutionary framework of nematodes related to Caenorhabditis elegans (Rhabditina)

“…In Teratocephalus, as in Z. punctata, these cells have six mononucleate muscle cells, suggesting that Z. punctata (Cephalobina) conserves the primitive condition and that the Rhabditina and Diplogastrina share the derived state indicative of a unique common ancestry; the distribution of this character is thus congruent with phylogenetic interpretations of 18S DNA and RNA polymerase II sequences. This also agrees with the buccal capsule character of a double set of radial epithelial cells revealed by TEM, which are unique to the Rhabditina and Diplogastrina (Baldwin et al 1997b).…”

“…This problem has been underscored since the application of TEM in rede¢ning previously misinterpreted characters of the buccal capsule (Baldwin & Eddleman 1995;De Ley et al 1995;Baldwin et al 1997b;Dolinski et al 1998). …”

An Evolutionary Framework for the Study of Developmental Evolution in a Set of Nematodes Related toCaenorhabditis elegans

“…More recently, hypotheses of homology and development of the buccal region have been tested (Baldwin et al, 1997;De Ley et al, 1995). These three relatively independent morphological systems provide interesting comparisons because some developmental patterns appear to be relatively congruent with extant taxonomy (e.g., male tails), others are not well known (e.g., vulval lineages) and still others (e.g., buccal region) may be highly homoplasious and difficult to interpret phylogenetically.…”

Simple methods for morphological observation of nematodes

“…For example, the stomata of some diplogastrid nematodes are asymmetric and anisotopic, and close examination is required to understand its structure correctly. Baldwin et al (1997) and Giblin-Davis et al (2006) employed transmission electron microscopy (TEM) to interpret the stomatal structure of Acrostichus halicti and Parasitodiplogaster larvigata. Light microscopy and a video-capture system were used to understand muscular movements and reconstruct complicated three-dimensional morphology of diplogastrids stoma (Fürst von Lieven and Sudhaus, 2000).…”