Year

2006

Degree Name

PhD

Department

School of Biological Sciences - Faculty of Science

Abstract

This thesis studies the phylogenetic relationships in the Hymenoptera as well as the mitochondrial (mt) genomics of the group with a comparative approach. My principal purposes were to (1) reconstruct the phylogenetic relationshisps among the Apocrita, and (2) characterize the mt genome of the Hymenoptera and its utility as a phylogenetic marker both within the Apocrita and within the Holometabola. In order to achieve these aims: (1) 550 bp of the 18S gene were sequenced in 87 apocritan taxa and analyzed using a Bayesian phylogenetic approach, including the sequences of two mitochondrial genes (cox1, 16S) and another nuclear gene (28S) from Dowton and Austin (2001). Although the phylogeny of the Apocrita was not totally resolved, I was able to support some groups. In particular, the monophyly of the Proctotrupomorpha, and within this group the Chalcidoidea as sister taxon to the Diapriidae + Monomachidae + Maamingidae clade were consistenly recovered and supported by high posterior probabilities. (2) Most of the mt genome of the sawfly Perga condei was sequenced. 12 protein coding genes, 16 trn genes, and the small and large rRNA genes, for a total of 13,416 bp. This mt genome has a conserved gene order, with the exception that tnaLCUN was not found in the position considered ancestral to insects and crustaceans (Boore et al. 1998, Flook et al. 1995). Apart from this rearrangement, the organization of the genes in Perga condei matches perfectly with distant species such as Drosophila melanogaster (Lewis et al. 1994) or Triatoma dimidiata (Dotson and Beard 2001). The base composition, the amino acid composition, and the codon usage of the mt genome of P. condei were reported. Similar to other insect mt genomes, this genome is A+T rich, and there is a correlation between the base composition and amino acid occurrence, with A+T rich codons predominating. (3) Two other mt genomes of the Hymenoptera were also sequenced. The mt genome of Vanhornia eucnemidarum and of Primeuchroeus sp., both from the suborder Apocrita. Within the Apocrita, high rates of molecular evolution, compositional bias and gene rearrangements had been reported (Dowton and Austin 1997, Dowton et al. 2003). The mt genomes of Vanhornia and Primeuchroeus are further evidence of an increased rate of gene rearrangement within the Apocrita. In particular, there is a total of six trn genes rearranged in Vanhornia eucnemidarum. Additionally, several non-coding regions were found in the mt genome of Vanhornia eucnemidarum. One of these non-coding regions is around 600 bp long and has a high AT content, but does not seem to correspond to the typical A+T rich region present in other insect mt genomes. There are at least nine trn genes rearranged in the mt genome of Primeuchroeus sp. Further, the large and small rRNA genes are inverted. In both species, rearrangements of trn genes are the most common. The gene rearrangements found in the mt genomes of the hymenopteran taxa sequenced were characterized; however no synapomorphies were detected. Since the rate of gene rearrangement appears to be increased in this group of insects, only with increased taxon sampling will phylogeneticaly informative rearrangements be found. (4) Finally, the mt genome sequences previously described were tested as phylogenetic markers to reconstruct relationships both within the Holometabola and within the Hymenoptera. Results indicated that phylogenetic analyses using mt genomes were susceptible to outgroup and ingroup selection as well as analytical model. Analyses excluding 3rd codon positions were found to be the best model to analyze this type of data, but an increased taxonomic sampling within the Apocrita as well as within the outgroups is required to recover appropriate phylogenetic relationships.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.