The complete mitochondrial sequence of the"living fossil" Tricholepidion gertschi: structure, phylogenetic implications, and the description of a novel A/T asymmetrical bias

Nardi, F. ; Frati, F. ; Carapelli, A. ; Dallai, R. ; Boore, J.

Lawrence Berkeley National Laboratory

关键词: Amber;    59;    Insects;    Genes;    Affinity;   

DOI  :  10.2172/960401
RP-ID  :  LBNL-50963
RP-ID  :  DE-AC02-05CH11231
RP-ID  :  960401

美国|英语

来源: UNT Digital Library

【 摘 要 】

Traditionally, the 'Apterygota' has been thought to consist of five orders of wingless hexapods (Protura, Collembola, Diplura, Microcoryphia and Zygentoma) believed to be collectively basal to insects (i.e., the Pterygota). However, some studies have questioned this affinity with insects (Dallai, Abele, Spears, Nardi). Further, within these groups are hotly debated issues, including the monophyly of Entognata (Koch, 1997; Kukalova Peck, 1987), the monophyly of Diplura (Bilinski, 1993; Stys and Bilinski, 1990), the affinity between Collembola and Protura (Dallai, 1994; Kristensen, 1981) and the position of Lepidotrichidae (below). In fact, these relationships constitute one of the most debated issues in hexapod phylogeny. The family Lepidotrichidae was first described by (Silvestri, 1912) (1912: 'Lepidothricinae') from a Baltic Amber fossil (Lepidothrix pilifera Menge). The only living representative of this family is Tricholepidion gertschi Wygodzinski. Since this species was first described (Wygodzinsky, 1961) its phylogenetic position has been difficult to establish, due to an 'array of unique characters' that are difficult to interpret in a phylogenetic framework. Tricholepidion (and therefore the whole family Lepidotrichidae) has been considered either as belonging to the order Zygentoma (Kristensen, 1997; Wygodzinsky, 1961), or basal to the rest of the Zygentoma plus the Pterygota (Beutel, 2001; Bitsch and Bitsch, 2000; Staniczek, 2000), although the significance of some of the morphological characters on which these analyses are based have been questioned (Dallai et al., 2001; Kristensen, 1997). If the latter hypothesis proved to be true, the family Lepidotrichidae, would better deserve the ordinal rank. Since studies based on morphological characters have failed to give a satisfactory answer, a broad scale molecular study is under way ((Nardi et al., 2001), Frati et al, submitted, il Gomphiocephalus) in order to use mitochondrial genome sequences to study the evolution and differentiation of the most basal hexapod groups, including Tricholepidion. Mitochondrial genomics, that is analysis of various features of the mitochondrial genome such as gene order and the analysis of the concatenated sequence of its genes, has proved to be a very powerful tool for the study of ancient phylogenetic relationships (Boore, 2000; Boore and Brown, 1995; Boore and Brown, 1998; Garcia-Machado et al., 1999; Hwang et al., 2001; Nardi et al., 2001), and its application seems to be appropriate for the problem under study ((Nardi et al., 2001), this study). In addition, complete mitochondrial sequences, with the advent of automatic sequencing tools, are accumulating rapidly, but there is a strong bias towards the better known or economically important groups, while only two sequences have been produced for the more basal, and evolutionarily more intriguing, hexapod orders. The complete sequence of the mitochondrial genome of Tricholepidion gertschi is the second among apterygotans, following the collembolan T.bielanensis (Nardi et al., 2001).