THE ORIGIN OF THE SPINNING APPARATUS IN SPIDERS

• 1 Previous attempts to explain the evolution of spider silk have relied heavily on conjecture. The formulation of testable historical hypotheses to replace such speculation is discussed.
• 2 The importance of phylogenetic reconstructions and other historical hypotheses for use in generating and testing hypotheses concerning the evolution of specific adaptations is examined. Recent ideas on arachnid phylogeny are reviewed and their relevance to the problem of silk evolution in spiders is explored.
• 3 Evidence from the analysis of three historical problems (origin of spinnerets, origin of silk glands, original selective pressure favouring evolution of silk) is reviewed from three different frames of reference (in-group analysis, out-group analysis, convergence analysis). Several lines of evidence are found which suggest that silk use originated in spiders due to selective pressures associated with reproduction (specifically, the transfer of sperm or the protection of eggs).
• 4 The prevalence of segmental appendages retained for use in manipulating genital products in both arachnids and non-arachnid arthropods and the probable placement of spinnerets near the genital opening in ancestral spiders suggest that spinnerets represent modified gonopods.
• 5 The most primitive types of silk glands are retained in virtually all spiders, in part, for use in the construction of sperm webs and egg sacs. Similar silk glands are found near the genital opening in many male spiders and used in building a portion of the sperm web.
• 6 The silk of adult arthropods other than spiders is used largely in manipulating or protecting sex cells. If there are multiple functions, use in reproduction is typically one of them. Thus, there is evidence for strong selective pressure favouring the evolution of silk for use in reproduction.
• 7 Two hypotheses are proposed which are consistent with the conclusion that silk in spiders evolved for reproductive needs (the spermatophore-sperm web and egg sac hypotheses). Testable predictions of each hypothesis are proposed.

     

Decomposition Analysis of Competitive Symmetry and Size Structure Dynamics

An analysis is introduced, based on the decomposition of relativegrowth rates, to examine the mode of competition (i.e. whethercompetition is symmetric or asymmetric), the size-dependenceof growth, and their interdependence. In particular, the basisfor two commonly held views is examined: (1) that the type ofresource limitation determines the mode of competition, and(2) that asymmetric competition always leads to size-divergencebetween unequal competitors. It is shown that in field-grownmillet plants, competition for light was symmetric at low densityand asymmetric at high density. However, size variation at lowdensity decreased during growth, because small plants had greaterrelative growth rates than larger plants. Size variation stayedconstant at high density, since plants of all sizes had equalaverage relative growth rates. Based on these results and ageneral discussion, it is proposed that the type of resourcelimitation does not determine the mode of competition. Competitionfor light can be symmetric, and foraging for heterogeneouslydistributed soil resources can produce asymmetric competitionbelow-ground. Furthermore, the mode of competition alone doesnot determine size structure dynamics. Size-dependence of resourceconversion efficiency and allocation can modify the effectsof resource uptake on growth. Pennisetum americanum‘Custer ’; mode of competition; size structure dynamics; plant growth analysis     

Improved Coated Vesicle Isolation Allows Better Characterization of Clathrin Polypeptides

Postmicrosomal pellets from plant sources are grossly contaminatedwith nbosomes. Previous purifications of clathrin coated vesicles(CCV) from such subcellular fractions have therefore often involvedan RNase treatment. Performed at 30°C, this step inherentlycarries with it the dangers of proteolysis. We document herea method for CCV isolation which avoids this. Through the inclusionof suitable antiproteases in the homogenizing and subsequentisolation media, we have also been able to improve the qualityof CCV recovered from plant tissues. As a result we have tentativelybeen able to identify clathrin light chains from zucchini hypocotyland pea cotyledon CCV. Similar to light chains from bovine brainthese polypeptides are heat stable, can be solubilized fromneutralized TCA precipitates, bind calcium and clathrin heavychains. However, in contrast to brain CCV the two light chainsof plant CCV are some 10 kDa heavier. Key words: Antiproteases, Ca²⁺-binding, clathrin coated vesicles, clathrin heavy chains, clathrin light chain(s), heat stability, pea cotyledons, RNase, zucchini hypocotyls     

Nuisance growth of Juncus bulbosus: the roles of genetics and environmental drivers tested in a large‐scale survey

1. Invasive species can transform aquatic ecosystems, and the nuisance growth of the freshwater macrophyte Juncus bulbosus has become a problem in many lakes and rivers in northern Europe. It affects biodiversity strongly and conflicts with human uses, not least compromising the generation of hydroelectricity. The causes of the proliferation of these massive stands of J. bulbosus are not finally resolved, however. 2. In this study, a wide range of catchment, lake and sediment parameters (n = 34) were assessed for 139 lakes in Southern Norway, with the aim of explaining the presence or absence of J. bulbosus and to assess potential drivers behind its prolific growth. 3. Juncus bulbosus was more often present in lakes with lower pH and phosphate concentrations, and a higher element ratio of dissolved inorganic nitrogen (DIN) to total phosphorus (DIN : TotP). 4. Despite the many parameters measured across substantial environmental gradients, none explained nuisance growth. Genetic screening (amplified fragment length polymorphism fingerprinting) of plants from a subset of lakes and additional river sites also showed no genetic differences between the various growth forms. A macrophyte trophic index, however, suggested that the most problematic growth occurred in the most oligotrophic lakes. 5. The lack of consistent patterns may reflect either factors not assessed in our survey, or that the current extension of stands represents a gradual cumulative response over time, not characterised effectively in our snapshot survey. Nevertheless, we can now exclude some putative causes of nuisance growth, including in particular genetics and N‐deposition.     

Muscular anatomy of a whipspider, Phrynus longipes (Pocock) (Arachnida: Amblypygi), and its evolutionary significance

Skeletal muscles in the whipspider Phrynus longipes are surveyed and compared with those of other chelicerates to clarify the evolutionary morphology and phylogenetic relationships of the arachnids. Representatives of 115 muscle groups are described and illustrated, and their possible functions are proposed. Principal results of this analysis include new functional models for the operation of the pharyngeal and sternocoxal mechanisms in Amblypygi and a greatly expanded list of apparently unique synapomorphies supporting the monophyly of Pedipalpi (= Amblypygi, Schizomida, Thelyphonida).     

HEDONIC SPREADABILITY OPTIMA OF SELECTED EDIBLE FATS

A panel of untrained judges was asked to assess spreadability of selected solid edible fat samples (butter, margarine, low fat products) of different temperature with regard to hedonic preferences. Instrumental measurements were performed by cone penetration with constant load. The statistical analysis of the ranked sensory data showed significant spreadability optima in the apparent yield value range of approximately 30–60 kPa. Differences between the selected fats were not observed.     

Distribution and genetic divergence of two parapatric sibling ant species in Central Europe

The two sibling ant species Temnothorax nylanderi and Temnothorax crassispinus are widely distributed throughout deciduous forests in Europe. Their resemblance in morphology and similar ecological requirements suggest that they evolved from the same ancestral species in different glacial refugia and re-immigrated into Central Europe after the last ice age. Here, we show that the two species are parapatrically distributed in south-eastern Germany and hybridize along a narrow contact zone close to the continental divide. Phylogeographical data based on the mitochondrial genes cytochrome oxidase subunit I and cytochrome b suggest that the dominant haplotypes for T. nylanderi and T. crassispinus might have diverged already 1.5–2 Mya. Intraspecific variability is extremely low in both species, which might be explained by severe bottlenecks during rapid postglacial expansion into Central Europe.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 223–234.     

Winter tourism increases stress hormone levels in the Capercaillie Tetrao urogallus

Montane and alpine habitats in Europe remained relatively undisturbed until the beginning of the last century. Today, outdoor recreation activities are a major economic factor in alpine regions. Many tourism areas coincide with winter habitats of shy and endangered species. The Western Capercaillie Tetrao urogallus has suffered from rapid population declines during recent decades over much of its range. In central Europe, many Capercaillie are exposed to intensive human recreation activities in their habitats, which may contribute to this decline. However, little is known about their susceptibility to human recreation activities. This study assessed whether human recreation in winter evokes physiological stress responses in several populations of Capercaillie. During two winters, we sampled 1130 Capercaillie droppings in Germany and Switzerland of populations at various distances from winter recreation activities and measured concentrations of faecal corticosterone metabolites. Capercaillie in relatively dense and homogeneous mountain forests dominated by Norway Spruce Picea abies showed markedly increased stress hormone levels closer to locations with winter recreation activity. However, this physiological response to human recreation was not detectable in forests dominated by various pine species and a heterogeneous structure. Capercaillie may be particularly sensitive to recreation because any factor affecting their fine‐tuned physiological and behavioural adaptations to survive under harsh winter conditions may lead to harmful fitness costs.     

The influence of leaf litter on zooplankton in floodplain wetlands: changes resulting from river regulation

1. The loss of input of leaf litter through clearing of riparian vegetation may result in significant changes to aquatic ecosystems. River red gums (Eucalyptus camaldulensis) surrounding floodplain wetlands in the Murray–Darling Basin, Australia, contribute large quantities of leaf litter, but the quality of this resource may change depending on the timing of inundation. 2. We used experimental mesocosms to test the hypotheses that zooplankton would have a greater abundance with an input of leaf litter and that fewer zooplankton would emerge from egg banks in cleared than forested wetlands. The experiment was carried out in summer/autumn and in spring to test a third hypothesis that zooplankton would respond to changes in the timing of wetland inundation as a result of river regulation. 3. In summer/autumn, leaf litter reduced zooplankton abundance by 89% at the beginning of the experiment through its influence on water quality. Only a few taxa (Polyarthra spp., Colurella spp. and the cladoceran Family Moinidae) responded positively to leaf litter when water quality improved later in the experiment, indicating a switch in the role of leaf litter from a non‐trophic to a trophic pathway. 4. In spring, microcrustaceans emerged in smaller numbers from sediment sourced from cleared compared to forested wetlands, reflecting different communities in these two wetland types and/or disturbances to the sediment that interfere with emergence. 5. Although leaf litter appears not to be an important resource for zooplankton in floodplain wetlands, riparian clearing may have lasting effects on future emerging zooplankton communities. Additionally, river regulation may have considerable impacts on the influence of leaf litter on zooplankton, which has implications for the management of floodplain river systems.