Ceratophysella sigillata (Collembola, Hypogastruridae) has a life cycle which may extend for >2 years in a temperate climate. It exists in two main morphs, a winter-active morph and a summer-dormant morph in central European forests. The winter-active morph often occurs in large aggregations, wandering on leaf litter and snow surfaces and climbing on tree trunks. The summer-dormant morph is found in the upper soil layers of the forest floor. The cryobiology of the two morphs, sampled from a population near Bern in Switzerland, was examined using Differential Scanning Calorimetry to elucidate the roles of body water and the cold tolerance of individual springtails. Mean (SD) live weights were 62 ± 16 and 17 ± 6 µg for winter and summer individuals, respectively. Winter-active springtails, which were two feeding instars older than summer-dormant individuals, were significantly heavier (by up to 4 times), but contained less water (48% of fresh weight [or 0.9 g g-1 dry weight]) compared with summer-dormant animals (70% of fresh weight [or 2.5 g g-1 dry weight]). Summer-dormant animals had a slightly greater supercooling capacity (mean (SD) -16 ± 6°C) compared with winter-active individuals (-12 ± 3°C), and they also contained significantly larger amounts of both total body water and osmotically inactive (unfrozen) water. In the summer morph, the unfrozen fraction was 26%, compared to 11% in the winter morph. The ratio of osmotically inactive to osmotically active (freezable) water was 1 : 1.7 (summer) and 1 : 3.3 (winter); thus unfrozen water constituted 59% of the total body water during summer compared with only 30% in winter. Small, but significant, levels of thermal hysteresis were detected in the winter-active morph (0.15°C) and in summer-dormant forms (0.05°C), which would not confer protection from freezing. However, the presence of antifreeze proteins may prevent ice crystal growth when feeding on algae with associated ice crystals during winter. It is hypothesised that in summer animals a small decrease in freezable water results in a large increase in haemolymph osmolality, thereby reducing the vapour pressure gradient between the springtail and the surrounding air. A similar decrease in freezable water in winter animals will not have such a large effect. The transfer of free water into the osmotically inactive state is a possible mechanism for increasing drought survival in the summer-dormant morph. The ecophysiological differences between the summer and winter forms of C. sigillata are discussed in relation to its population ecology and survival.
Materials of Hypogastruridae, Odontellidae, Neanuridae, Onychiuridae and Isotomidae from East Africa were studied. Several new species are described: Acherontiella kowalskiorum sp. n., Furculanurida grandcolasorum sp. n., Stachorutes dallaii sp, n., and Paleonura cassagnaui sp, n. Friesea vrorovi Tshelnokov, 1977 and Tullbergia kilimanjarica (Delamare Deboutteville, 1953) are redescribed. Stachorutes arlei (Thibaud & Massoud, 1980) is a new combination. Identification keys for Friesea Dalla Torre, 1895 with 2 + 2 eyes and Stachorutes Dallai, 1973 are given.
Ceratophysella sigillata uses protrusible vesicles on its antennae and posterior end as sticky landing devices to avoid tumbling upon landing. This technique facilitates its orientated movement during winter migration. It allows the animal to use directional jumps without rebounding even when climbing tree trunks. The antennal vesicles are present only in the surface active morphs of C. sigillata, and only these individuals jump readily. The vesicles are everted only when the animal has time to prepare the jump. In an escape leap, they are not protruded and therefore the animal tumbles upon landing.
Two new species belonging to the genus Willemia are described: W. bedosae sp. n. and W. christianseni sp. n. Redescriptions of Willemia dubia Christiansen & Bellinger, 1980 and W. similis Mills, 1934 are provided. Willemia vashtia Wray, 1950 is a new synonym of W. similis. These four species and four other of the genus constitute the Willemia anophthalma-group. This group is characterized by one feature not shared by the other species of the genus: the presence of setae a l on abdominal sternum IV. A comparative table and an identification key are given for these eight species, as well as some remarks on their habitats.