A permanent snow cover for several months is typical for large parts of Norway, Sweden and Finland. Snow layers thicker than about 20 cm insulate the soil surface and stabilize the ground temperature close to 0°C. Many ground-living invertebrates are active at this temperature in the subnivean air space. From this "base camp", some invertebrates migrate upwards to use the snow as a substrate. The intranivean fauna consists of springtails (Collembola) and mites (Acari) that are small enough to move within the narrow pores between snow crystals. The supranivean fauna consists of various invertebrates that are active on the snow surface. Some of them are Collembola that have migrated through the snow layers. However, most of them are larger insects and spiders which migrate between the subnivean and supranivean habitats following air channels which are naturally created along tree stems, bushes etc. penetrating the snow. Likewise, certain Chironomidae and Plecoptera, hatching from winter-open rivers and brooks, are active on the snow surface. The supranivean arthropod fauna has the following characteristics: 1. It is a weather dependent assemblage of species, coming and going with changes in air temperature, cloud cover, and wind. Below ca. -6°C animals are absent, but at temperatures around or above zero, many groups can be simultaneously active on snow. 2. The snow surface fauna shows phenological changes throughout the winter, as certain species and groups are mainly active during certain months. 3. Some invertebrates are highly specialized and take advantage of the snow surface as an arena in their life cycle. Examples are Hypogastrura socialis (Collembola), and the two wingless insects Chionea sp. (Diptera: Limoniidae) and Boreus sp. (Mecoptera). They use the smooth snow surface for efficient migration. Chionea sp. and Boreus sp. lay their eggs during the snow-covered period, while H. socialis migrates to create new colonies. The cold tolerant spider Bolephthyphantes index is unique in constructing webs in small depressions on the snow, to catch migrating Collembola. Various adaptations for using the snow as a substrate are discussed. Besides physiological and morphological adaptations, snow surface arthropods show special behavioural adaptations. Most conspicuous is the ability of several Collembola species to navigate during migration, using the position of the sun for orientation. Furthermore, in Collembola and Mecoptera, jumping as an original mechanism to escape predators has independently evolved into a migrating mechanism. An evolutionary potential exists for more invertebrate groups to take advantage of snow as a substrate in their life cycle. For instance, several more cold tolerant spiders might evolve the ability to catch migrating Collembola on snow.
The morphology of the male salivary glands of eighteen species of Panorpidae from China was studied using light microscopy. The results show that the male salivary glands differ markedly both at generic and specific levels. In Neopanorpa, the salivary glands consist of only two simple long secretory tubes extending to the fifth or sixth abdominal segment, whereas in Sinopanorpa, the salivary glands are composed of six extremely elongated secretory tubes. In Panorpa, the salivary glands are quite diverse, comprising two simple short secretory tubes only extending to the prothorax in the P. amurensis group (P. liui and P. jilinensis), six long tubes in the P. centralis group, eight to twelve in the P. diceras group and of a very variable number in the P. davidi group (especially in P. bifasciata and P. subambra). Morphology of the male salivary glands should be included in future studies on the systematics and phylogeny of the Panorpidae. and Na Ma, Shu-Yu Liu, Bao-Zhen Hua.
We examined effects of seasonality, larval food availability and larval rearing density on sperm length, sperm transfer rates and body size in the bivoltine scorpionfly Panorpa vulgaris. Males of the first annual generation were larger and had larger sperm. Comparing individuals of two summer generations showed that adult males resulting from group bred, ad libitum fed larvae were larger but had smaller sperm than males resulting from singly kept, food deprived larvae. Thus, sperm size is not a simple function of body size. Instead, we suggest that sperm size modification was caused by varying rearing densities. Group bred individuals produced smaller sperm but transferred at higher rate. This indicates a trade-off between sperm number and sperm size as predicted by evolutionary models of sperm production. Given the strong influence of larval history in our present work, we recommend that future studies investigating the consequences of varying sperm competition risk or intensity on male gametic strategies should also control for larval history in order to avoid distorting effects.