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.
Domestic cats are the most numerous predators in Poland. They are commonly kept at farms but hardly controlled, so penetrate freely wide range of habitats. The work aimed at determining the range of greatest impact of cats by identifying patterns of their activity and area searching, over daily, monthly and annual cycles. The density index, estimated from transect counts, performed along standard routes, proved to be dependent on temperature, precipitation and time of the day. In spring and summer, cats presented a two-peaked activity pattern, while in cold seasons it was more stable throughout the day. In warm months cats were registered at a further distance from the buildings than in colder ones. The animals were much less active when rain was falling. Cats’ responses on noticing an observer showed that the further they were from the edges of settlements the more timid and cautious they became. The results showed that the potential pressure that cats may exert on their prey is the biggest around dawn and dusk and in summer. During a daytime it is confined to the immediate vicinity of build-up areas.
The acanthocephalan parasite Pomphorhynchus laevis (Müller, 1776) uses freshwater amphipods as its intermediate host. In order to complete the life cycle, the infected amphipod must be consumed by a fish, where the acanthocephalan will mature and reproduce. Parasite transmission, and therefore fitness, could be enhanced if infected amphipods fail to detect or avoid predatory fish. We compared the activity levels of infected and non-infected amphipods, Echinogammarus stammeri (Karaman, 1931), in both the presence and absence of odours from its natural, definitive host, the fish Leuciscus cephalus (L.). Throughout the experiment, infected amphipods were more active than were non-infected individuals. The non-infected amphipods reduced their activity after the addition of fish odours, but the infected amphipods failed to show a significant decrease. The failure of infected amphipods to reduce activity levels in the presence of fish odour may reflect a parasite strategy to increase its chances of transmission by making its amphipod host more vulnerable to predation by fish.