A phylogenetic review of the genus Hexabathynella Schminke, 1972 (Crustacea, Malacostraca, Bathynellacea): with a description of four new species

The genus Hexabathynella (Crustacea, Malacostraca, Bathynellacea) is revised in the sense of the phylogenetic systematics and four new species are described from South Africa ( H. monoaethetasca sp. nov. and H. africana sp. nov. ) and America ( H. schrieveri sp. nov. and H. virginiae sp. nov. ). A comparative analysis of all observable outer structures distributed in 18 known and four new species resulted in a re-evaluation of 18 characters and character states. The phylogenetic analysis using the program PAUP yielded one most-parsimonious tree, which suggests the grouping of ( H. decora (( H. halophila  +  H. aotearoae ) + ( H. pauliani ( H. monoaethetasca  + H. africana )))) + ( H. knoepffleri ( H. nicoleiana ( H. hebrica , H. tenera , H. longiappendiculata , H. breviappendiculata , H. nestica ) +  H. virginiae (( H. minuta ( H. valdecasasi + H. otayana )) + ( H. hessleri + H. muliebris ))) +  H. paranaensis ( H. szidati + H. schrieveri )). The tree is 57 steps long and has a consistency index of 0.6140, a retention index of 0.7982 and a rescaled consistency index of 0.4901. The result does not agree with the previous analyses on the genus. In terms of sampling and coding, the characters used in the previous study are critically assessed.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 147 , 71–96.     

COMPARATIVE SPERMATOLOGY OF THREE SPECIES OF DONAX (BIVALVIA) FROM SOUTH AFRICA

The fine structure of the sperm and spermatogenesis in threespecies of Donax (D. madagascariensis, D. sordidus and D. serra)are described. Although the morphology of the sperm of all speciesis very similar, each has unique features. Donax madagascariensisand D. sordidus reportedly hybridize in regions of sympatryand their spermatozoa are morphologically closer to one anotherthan to D. serra. All sperm are of the primitive type with ahead(about 2 µmu; long), mid-piece of four mitochondria andtail. The head comprises a barrel-shaped nucleus which is cappedby a small, complex acrosome. The structure of the acrosomeis typical of heterodont bivalves. During spermatogenesis thepattern of nuclear chromatin condensation is granular. Glycogenfirst appears in the cytoplasm of spermatids, and in the maturesperm is sited in the mid-piece and base of the acrosome. (Received 15 May 1989; accepted 25 June 1989)     

Mycorrhiza modulates aboveground tri‐trophic interactions to the fitness benefit of its host plant

1. Arbuscular mycorrhiza (AM), the association of AM fungi and plant roots, may alter morphological and physiological attributes of aboveground plant parts and thereby influence plant‐associated organisms such as herbivores and their natural enemies, predators and parasitoids. 2. The interactions between AM and the players of aboveground tri‐trophic systems have mainly been considered in isolation from each other. The effects of AM on aboveground herbivore–carnivore population dynamics and the consequences to plant fitness are unknown. 3. We explored AM‐induced compensatory mechanisms for AM‐promoted proliferation of the herbivorous spider mite, Tetranychus urticae Koch, on whole bean plants, Phaseolus vulgaris L. Vegetative and reproductive plant growth, AM fungal colonisation levels, and mite densities were assessed on spider mite‐infested plants colonised or not by the AM fungus Glomus mosseae Nicol. & Gerd, and harbouring the natural enemy of the spider mites, the predatory mite Phytoseiulus persimilis Anthias‐Henriot or not. 4. AM symbiosis modulated the aboveground tri‐trophic system to the fitness benefit of the plant. AM‐increased plant productivity outweighed the fitness decrease due to AM‐promoted herbivory: at similar vegetative growth, mycorrhizal plants produced more seeds than non‐mycorrhizal plants. 5. AM‐increased spider mite population levels were compensated for by enhanced population growth of the predators and increased plant tolerance to herbivory. 6. AM‐enhanced predator performance looped back to the AM fungus and stabilised its root colonisation levels, providing the first experimental evidence of a mutually beneficial interaction between AM and an aboveground third trophic level natural enemy.     

Arbuscular mycorrhiza enhances preference of ovipositing predatory mites for direct prey‐related cues

Most terrestrial plants are associated with arbuscular mycorrhizal fungi but research on the effects of arbuscular mycorrhizal symbiosis on aboveground plant‐associated organisms is scarcely expanded to tri‐trophic systems. The arbuscular mycorrhizal fungus Glomus mosseae Nicol. & Gerd. enhances fitness of the two‐spotted spider mite Tetranychus urticae Koch and its natural enemy, the predatory mite Phytoseiulus persimilis Athias‐Henriot, via changes in host plant and prey quality, respectively. In the present study, it is hypothesized that gravid P. persimilis are able to recognize arbuscular mycorrhiza‐enhanced prey quality and behave accordingly. In two experiments, on leaf arenas and in cages, P. persimilis is given a choice between prey patches deriving from mycorrhizal and non‐mycorrhizal bean plants (Phaseolus vulgaris L.) as feeding and oviposition sites. The use of cages allows the manipulation of distinct patch components acting as possible cues to guide predator foraging and oviposition behaviours, such as eggs produced and traces (webbing and faeces) left by the spider mite females. Both experiments show that P. persimilis preferentially resides close to prey fed on mycorrhizal plants. The cage experiment reveals that P. persimilis uses direct prey‐related cues, mainly derived from eggs, to discern prey quality and preferentially oviposits close to prey from mycorrhizal plants. This is the first study to document that predators recognize arbuscular mycorrhiza‐induced changes in herbivorous prey quality via direct prey‐related cues.