The evolution of meiosis and sexual reproduction

It has been argued that because intermediate states would not be advantageous, it is impossible for natural selection to account for the evolution of meiosis and sexual reproduction. The argument is invalid because a reasonable hypothesis is presented. The hypothesis is developed from a consideration of unicellular eukaryotes and prokaryotes and is that the ancestral eukaryote had a form of parasexual cycle with 'somatic' or 'mitotic' recombination. Later mitosis, then meiosis evolved. In multicellular organisms genetic recombination then usually became restricted to meiosis. Several predictions are made that could be tested in the near future. A conclusion is that we have been misled by treating meiosis and genetic recombination as more or less synonomous. The question of the ultimate origin of recombination is more obscure but it is pointed out that recombination could give the most immediate advantage early in the origin of life, particularly with a hypercycle model. It could result in the combination of advantageous quasi-species (short nucleotidc sequences) into one genome, and it could eliminate ineffective combinations. There are discussions of the scientific role of hypotheses for the origin of complex biological features and on the biological success of cooperative units of DNA.     

Uncovering diversity of Australian Eucalyptus‐constrained felt scales (Hemiptera: Coccoidea: Eriococcidae)

Several felt scale (Eriococcidae) lineages show deep, phylogenetically constrained, host use. The most diverse of these host‐constrained lineages is Australian, associated with plants in the family Myrtaceae, and the most diverse sublineage within this group is associated with Eucalyptus. Here we use Bayesian analysis of morphological data to estimate relationships among the eucalypt‐feeding species of this group. We identify an unusual species for which we erect the monotypic genus Heathcotia Hardy & Beardsley gen.n. , with type species Heathcotia crypta Hardy & Beardsley sp.n. , and recover a clade comprised of six new species closely related to Lachnodius hirtus Maskell. We erect the genus Lobimargo Hardy & Gullan gen.n. for the latter clade, designate Lobimargo sagittisetus Hardy & Beardsley sp.n. as its type species, transfer Lachnodius hirtus to the genus as Lobimargo hirtus (Maskell) comb.n. and describe the five other new species: Lobimargo brookesae Hardy & Beardsley sp.n., Lobimargo donaldsoni Hardy & Gullan sp.n. , Lobimargo latrobeus Hardy & Beardsley sp.n. , Lobimargo rhipidotrichus Hardy & Gullan sp.n. and Lobimargo williamsi Hardy & Gullan sp.n. A lectotype is designated for L. hirtus. The adult female of each species, the first‐instar nymph of L. sagittisetus, the second‐instar female of L. hirtus and the adult male of L. williamsi are described and illustrated. A key is provided to the adult females of all eriococcid genera found on eucalypts and of all Lobimargo species. Adult females of Lobimargo have been found on stems, sometimes causing shallow pits, and on foliage or under bark, but may move to the latter habitat for oviposition.     

Early Responses of Excised Stem Segments to Auxins

The elongation rate of lupin hypocotyl and pea stem segmentswas measured every minute after the addition of various auxinsand auxin precursors. After a latent period the growth-rateincreased to a peak, fell to a minimum, and with most compoundsincreased to a second maximum. Compounds used include indol-3yl-aceticacid (IAA), indol-3yl-acetamide, naphth-2yl-oxyacetic acid,naphth- lyl-acetamide, and indol-3yl butyric acid. The extensibilityof the cell walls of the lupin segments was measured with anInstron Universal Testing Instrument at intervals after theaddition of IAA and it was shown that the lag period beforethe extensibility increased was longer than that for the growth-rate. Kinetic studies were made of the effect of Actinomycin D onIAA-induced growth. RNA synthesis during the first 20 and 40min after IAA addition was also examined in segments exposedto labelled RNA precursors during these times. The results supportthe conclusion that RNA synthesis is not necessary for the initialaction of auxin on elongation.     

A numeric, geographic and structural analysis of the Hakea falcata group (Proteaceae)

Specimens placed earlier under Hakea falcata are shown to comprise four species: H. falcata, H. ulicina, H. erecta and H. cygna. Failure by previous authors to cite types, or the correct type, led to the placement of subsequently collected H. falcata specimens (sensu R. Br.) under H. ambigua in Australian herbaria. The relationships of the five taxa are explored phenetically using metric multidimensional scaling and cluster analysis. Flowers provide the best diagnostic characters for separating H. falcata and H. ambigua , while fruits and seeds are better for H. erecta and H. cygna. All species are endemic to SW Australia, except H. ulcina , which is endemic to SE Australia. Two subspecies of H. cygna are recognized, based on populations with disparate leaf morphology. Each taxon has a distinctive leaf anatomy with all but H. falcata highly sclerophyllous.