Cruickshank, Robert Hamish; (1997) Evolution of uniparental genetic systems in dermanyssine mites (Acari: Mesostigmata). Doctoral thesis , UCL (University College London).

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Abstract

An exhaustive survey of uniparental genetic systems (those in which at least some individuals only transmit the genome of one parent to their offspring) within the Metazoa is presented including a new scheme for the classification of such systems (chapter 1). This is followed by a critical review of 13 different hypotheses proposed to account for the evolution of these systems (chapter 2). The hypothesis of Schrader and Hughes-Schrader, originally proposed in 1931 (Q. Rev. Biol. 6: 411-438), is then introduced. This states that arrhenotoky (in which males arise from unfertilised eggs whilst females arise from fertilised eggs) evolves via an intermediate pseudoarrhenotokous stage (in which although males are produced biparentally they eliminate the genome of paternal origin at some point prior to spermatogenesis) rather than directly from a zygogenetic ancestor. The remainder of this thesis is concerned with testing this hypothesis. Criticisms of the hypothesis of Schrader and Hughes-Schrader made by Hartl and Brown in 1970 (Theor. Popul. Biol. 1: 165-190) are re-examined in the light of more recent evidence and found to be invalid. Further evidence is cited from the recent literature in favour of the hypothesis of Schrader and Hughes-Schrader. A comprehensive review of the genetic systems of the Acari (mites and ticks) is used to ask whether our current state of knowledge in this field is sufficient to test the hypothesis of Schrader and Hughes-Schrader in this group. This reveals that the missing component required for such a test is a reliable hypothesis of phylogenetic relationships (chapter 3). A molecular phylogeny of the Dermanyssina (Acari: Mesostigmata) based on 755 base pairs of 28S ribosomal DNA is presented and this is shown to support the hypothesis of Schrader and Hughes-Schrader (chapters 4 and 5) A published morphological data set for the Dermanyssina is analysed and combined with the molecular data set in a variety of ways. An analysis of character conflict between the data sets is used to make an assessment of the suitability of the morphological characters for phylogenetic inference (chapter 6). Finally the hypothesis of Schrader and Hughes-Schrader is used to ask why is it always the males which are the haploid sex in haplodiploid species and ideas are presented for the future research (chapter 7).

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