Determinants of local spider (Araneidae and Thomisidae) species richness on a regional scale: climate and altitude vs. habitat structure

Abstract.  1. The habitat heterogeneity hypothesis states that the more complex the habitat, the higher the species richness. The present study analyzes the effect of local factors on regional spider ( Araneidae and Thomisidae ) richness. The main objective is to disentangle the relative importance of habitat structure and other environmental variables.
2. Fifteen territorial units of 1 km² were sampled to obtain reliable and comparable inventories of the two spider families. Richness values were modelled using general regression models and a set of climate, topographic and vegetation structure variables. Pure and joint effects were computed via variation partitioning.
3. The results highlight the great importance of vegetation complexity, especially of grass and sub-shrub cover, in determining spider species richness.
4. The maximum temperature is the only climate variable significantly related to species richness, although its effect is combined with that of spatial and vegetation structure variables.
5. These results support the habitat heterogeneity hypothesis, and highlight the importance of taking vegetation complexity into account when managing habitats and where spider conservation is desired.     

Anatomy of Seedling Roots of Tropical Maize (Zea mays L.) Cultivars at Low Water Supply

Establishment of maize seedlings can be difficult at low soilmoisture content. Anatomy of root metaxylem vessels may influencethe capacity for water transport and respective genotypic differencesmight be useful for selection purposes. To test this, six tropicalmaize (Zea mays L.) cultivars were grown in large PVC tubescontaining a sandy substrate at 5% (M5) and 10% (M10) moisturecontents for 2 weeks. The percentage changes in root diametersdue to M5 was similar for most cultivars but differed for mainroot types. Root diameters were not consistently related tometaxylem structure, but in a few cases, thin roots had smallerdiameter metaxylem vessels. The M5 treatment reduced the numberof late metaxylem vessels of primary roots by about 0 to 20%,while effects on nodal roots were slight. Generally, the ratioof cross-sectional areas between late and early metaxylem vesselsincreased from primary to seminal and nodal roots. Within thecultivar Tuxpefio this ratio was much reduced by M5. A few cultivarsmaintained the combined cross-sectional areas of metaxylem vesselsat M5 in some main root types, but only one cultivar could achievethis for the total of cross-sectional areas of metaxylem vessels,calculated over all root axes, by increasing the number of seminaland nodal roots. These anatomical traits seemed to be mostlyconstitutive with limited response to an actual environment,but they could be decisive for the suitability of a cultivarto an environment with frequent water shortages during seedlingestablishment. Key words: Metaxylem vessels, water stress, tropical maize     

Combining traditional morphometrics and molecular markers in cryptic taxa: towards an updated integrative taxonomic treatment for Veronica subgenus Pentasepalae (Plantaginaceae sensu APG II) in the western Mediterranean

The aim of this study was to quantify the phenotypic differences amongst the taxa included in Veronica subgenus Pentasepalae, represented in the western Mediterranean area. In combination with previously obtained data on genotypic differences, this enabled the recognition of eight taxonomic units. The delimitation of the boundaries among species and subspecies was mainly based on molecular data, whereas the best characters to discriminate taxa were selected after an accurate study of herbarium material and living populations. Such a selection was also supported by a detailed morphometric study of 30 quantitative leaf traits in 88 populations. Several morphological characters, including the length of the trichomes, length of the petiole and leaf division, were found to be robust, and could be useful in the identification of the taxa involved. As a conclusion, a key to the taxa is proposed, as well as a complete nomenclatural treatment for the group, which includes the typification of several names. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 68–87.     

The first humans travelling on ice: an energy‐saving strategy?

Economy of locomotion is a constant challenge for animals, particularly when related to migrations and travelling. The present study focuses on human locomotion and particularly on the development of ice skating. The aim of our research was to understand whether an environmental feature such as a strong presence of lakes (frozen in winter) could force humans to develop ice skates in order to limit the energy cost of travelling. We hypothesized that the energy-saving principle was a determinant factor in the development of human locomotion on ice. Five healthy adult participants took part in the experiments, during which we recorded the speed (1.2 ± 0.3 m s⁻¹) and metabolic energy cost (4.6 ± 0.9 J kg⁻¹ m⁻¹) associated with travelling on bone skates. Simulations were also performed to demonstrate whether the benefit given by the use of skates was different in the areas where ice skating appears to have evolved originally. The gain reachable by using bone skates could lead to an extremely high energy saving (equal to 10% of the energy needed to survive during the cold season) and differs significantly between the regions considered in the present study. An analysis of the geometrical shape of lakes associated with fractal analysis of their distribution suggests that, in order to better adapt to the severe conditions imposed by the long lasting winters, Finnish populations could benefit more than others from developing this ingenious locomotion tool. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 1–7.     

Effect of host instar on host discrimination of heterospecific‐parasitised hosts by sympatric parasitoids

1. Interspecific competition among hymenopteran parasitoids may shape their behavioural strategies for host resource exploitation. In order to reduce or prevent competition, many parasitoid species have evolved the ability to discriminate between unparasitised hosts and hosts parasitised by another parasitoid species (i.e. heterospecific host discrimination). However, discriminatory ability might be affected by host instar. 2. This study reports the first results on whether host instar can influence the use of heterospecific‐parasitised hosts by sympatric parasitoids of the genus Aphytis (Hymenoptera: Aphelinidae). 3. Aphytis melinus and Aphytis chrysomphali discriminated between unparasitised and heterospecific‐parasitised hosts when they found a third‐instar host (high quality), with a tendency to multi‐parasitise. However, this discrimination was not observed in the second instar (lower size). 4. The behavioural strategies adopted towards multi‐parasitise third‐instar hosts varied between both species. Aphytis chrysomphali reduced its clutch size in heterospecific‐parasitised hosts, whereas A. melinus tended to probe them for longer than healthy hosts. 5. Overall, our results highlight the importance of host instar in the study of intrinsic competition between parasitoids.     

ACROSOME DIFFERENTIATION IN THE SPERMATOGENESIS OF CIONA INTESTINALIS*

The process of acrosome formation in the course of spermatogenesis of Ciona intestinalis has been investigated. At the flute-beak-shaped tip of the head of the mature spermatozoon a small acrosomal vesicle(s) is described. The vesicles migrate to a region where the outer and inner nuclear membranes fuse thus giving rise to a “dense plate”. At the same time the chromatin begins to organize into longitudinally oriented strands which become attached to the inner side of the dense plate. The possible relationships between the dense plate, the formation of the acrosome and the orientation of the chromatin is discussed.     

The ultrastructure of the protonephridial system of Götte's larva of Stylochus mediterraneus (Polycladida, Platyhelminthes)

The protonephridial system of Götte's larva of Stylochus mediterraneus was studied by electron microscopy. There is one protonephridium on each side of the body, formed by one terminal and one canal cell. The terminal filtration apparatus is formed by a single cell (the terminal cell) with several globular processes, the largest of which includes the nucleus. Fingers of cytoplasm (leptotriches) from each process penetrate the lumen surrounding the bundle of cilia and fingers from adjacent processes interdigitate to form a pattern of convoluted slits which constitute the weir. The single canal cell is inserted internally to the terminal cell at the top of the weir and encloses the lumen without a junction. Septate junctions are present between the terminal and canal cells. The lumen of the canal cell is smooth-walled for most of its length and cilia arise and terminate at all levels of the terminal and canal cells. Posterior to the larval mouth opening, the canal cell crosses the epithelium and the lumen ramifies to form the excretory opening. The terminal apparatus closely resembles that found in the freshwater planarian Bdellocephala brunnea .