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In theory, the loss of sexual reproduction is expected to result in the accumulation of deleterious mutations. In aphids, two main types of life cycle, cyclic and obligate parthenogenesis, represent respectively “sexual” and “asexual” reproductive modes. We used the complete pea aphid genome and previously published expressed sequence tags (ESTs) from two other aphid species. In addition, we obtained 100,000 new ESTs from five more species. The final set comprised four sexual and four asexual aphid species and served to test the influence of the reproductive mode on the evolutionary rates of genes. We reconstructed coding sequences from ESTs and annotated these genes, discovering a novel peptide gene family that appears to be among the most highly expressed transcripts from several aphid species. From 203 genes found to be 1:1 orthologs among the eight species considered, we established a species tree that partly conflicted with taxonomy (for Myzus ascalonicus). We then used this topology to evaluate the dynamics of evolutionary rates and mutation accumulation in the four sexual and four asexual taxa. No significant increase of the nonsynonymous to synonymous ratio or of nonsynonymous mutation numbers was found in any of the four branches for asexual taxa. We however found a significant increase of the synonymous rate in the branch leading to the asexual species Rhopalosiphum maidis, which could be due to a change in the mutation rate or to an increased number of generations implied by its change of life cycle. [ABSTRACT FROM AUTHOR]

To study gene repertoires and their evolution within aphids, we compared the complete genome sequence of Acyrthosiphon pisum (reference gene set) and expressed sequence tag (EST) data from three other species: Myzus persicae, Aphis gossypii and Toxoptera citricida. We assembled ESTs, predicted coding sequences, and identified potential pairs of orthologues (reciprocical best hits) with A. pisum. Pairwise comparisons show that a fraction of the genes evolve fast (high ratio of non-synonymous to synonymous rates), including many genes shared by aphids but with no hit in Uniprot. A detailed phylogenetic study for four fast-evolving genes ( C002, JHAMT, Apo and GH) shows that rate accelerations are often associated with duplication events. We also compare compositional patterns between the two tribes of aphids, Aphidini and Macrosiphini. [ABSTRACT FROM AUTHOR]

The damaging effect of aphids to crops is largely determined by the spectacular rate of increase of populational expansion due to their parthenogenetic generations. Despite this, the molecular processes triggering the transition between the parthenogenetic and sexual phases between their annual life cycle have received little attention. Here, we describe a collection of genes from the cereal aphid Rhopalosiphum padi expressed during the switch from parthenogenetic to sexual reproduction. After cDNA cloning and sequencing, 726 expressed sequence tags (EST) were annotated. The R. padi EST collection contained a substantial number (139) of bacterial endosymbiont sequences. The majority of R. padi cDNAs encoded either unknown proteins (56%) or housekeeping polypeptides (38%). The large proportion of sequences without similarities in the databases is related to both their small size and their high GC content, corresponding probably to the presence of 5′-unstranslated regions. Fifteen genes involved in developmental and differentiation events were identified by similarity to known genes. Some of these may be useful candidates for markers of the early steps of sexual differentiation. [Copyright &y& Elsevier]