Bryozoans as substratum of fossil fistulose Foraminifera (Fam. Polymorphinidae)

In the Upper Cretaceous-Lower Tertiary sections exposed in the Curfs quarries at Berg (munic. Berg en Terblijt - also known as Geulhem, southern Netherlands) and some other localities, numerous foraminifers of the family Polymorphinidae with complete fistulose apertures have been found. These apertures, which are equipped with circular openings and auxiliary apertural chambers, branching and numerous narrow projecting tubes or stolons, have been widely reported, but their role has been the subject of controversy. The Dutch material shows the foraminifers attached with the apertural tubes to fragments of bryozoan colonies or molluscan shells, suggesting that the tubes could perhaps act as holdfast organs. Most specimens were found in calcarenites of the nearshore facies. The foraminifers cannot be treated as symbiotic organisms nor parasites but as epifauna in search of protection from mechanical destruction by waves and current action. The present case may be best explained as an adaptation of sessile foraminifers with fragile hyaline tests to live in highly disadvantageous, high-energy conditions.     

Ultrastructural Study on the Development of Babesia equi (Coccidia: Piroplasmia) in the Salivary Glands of its Vector Ticks1

The formation of Babesia equi sporozoites in the salivary glands of three tick species (Hyalomma anatolicum anatolicum, H. a. excavatum, Rhipicephalus turanicus) was studied by electron microscopy. The development was identical in all three vectors. On the 8th day post repletionem kinetes of B. equi had invaded alveoli of the nymphal salivary glands and were transformed to sporonts bounded by a single membrane. The sporonts were polymorphous bodies each with a highly lobed nucleus and numerous mitochondria. These stages persisted during ecdysis of the tick nymph to the adult stage. After attachment of these newly molted adults to a new host the formation of sporozoites was completed within five days. The sporonts occupied most of the infected alveolus and were extensively divided into cytoplasmic portions of various size. On the 4th day after attachment of the tick, sporozoite-anlagen, into each of which a nucleus and a mitochondrion were incorporated, appeared at the periphery of the sporonts. An apical complex with a polar ring, rhoptries, and micronemes was formed at the tip of each protruding anlage. Finally thousands of pyriform sporozoites (3.0 × 1.2 μm) filled the hypertrophied alveolus. This development is similar to sporogony in the genus Theileria.     

Using functional groups to investigate community response to environmental changes: two grassland case studies

Functional groups (FG) are an useful generalization to investigate environmental change effects on biotic communities. Assigning species to FGs is a contextual task and carries an arbitrary element, regardless of whether the grouping is obtained a priori or by sophisticated numerical methods. Using two grassland community case studies, we show that even simple FG allocation based on growth form, architecture and longevity (plants and mosses), or foraging characteristics (above-ground invertebrates) can be useful to increase our understanding of community processes. For example, the sensitivity of organisms to climate change increases with trophic rank and is higher in disturbed than in undisturbed communities. Complexity of interaction webs (in terms of web connectance), however, is larger in undisturbed than in disturbed communities. A significant and important relationship is likely to exist between anthropogenic disturbances, community complexity and the ecosystem effects of climate change. Trophic interactions may be disrupted much easier by climate changes in disturbed than in undisturbed communities where complexity may be buffering these effects.     

Habitat partitioning of native and exotic Daphnia in gradients of temperature and food: mesocosm experiments

1. Invasion of tropical zooplankton into temperate lakes provides an interesting opportunity to explore habitat segregation in a thermal gradient. 2. We explored differing vertical positioning of native and exotic Daphnia (Daphnia mendotae and Daphnia lumholtzi) in a large indoor mesocosm system (Plön plankton towers) during 2 month‐long experiments. The two towers were manipulated to provide gradients of both temperature (15–29 °C) and algal food (0.05–0.58 mg C L^?1) and a day–night cycle. 3. Both juvenile and adult D. lumholtzi showed a ‘typical’ vertical migration pattern, with higher densities in the epilimnion at night than during the day. They avoided the food‐poor middle layer. In contrast, D. mendotae adults showed little tendency to migrate into the epilimnion at night, remaining in the cooler hypolimnion while juveniles migrated. The vertical distribution of D. mendotae appeared unaffected by the presence of D. lumholtzi. 4. The strong migration behaviour of D. lumholtzi in the absence of fish cues suggests that this behaviour may be a constitutive trait. Habitat partitioning of the two species is probably the result of different thermal tolerances, with D. mendotae constrained to remaining in deeper water by high temperatures in the epilimnion and the tropical D. lumholtzi able to use the warm epilimnion at night.     

Functional symmetries in the schmelzmuster and morphology of rootless rodent molars

Morphology and schmelzmuster of rootless cheek teeth of 25 extant rodent genera were studied in relation to jaw movement. A differentiation between leading and trailing edges is observed regularly in enamel thickness and schmelzmuster. Similarities between antagonists are interpreted as 'functional symmetries'. Differences in the enamel thickness, the schmelzmuster and orientation of cutting edges are controlled by functional and phylogenetic constraints. The heterogenous sample allows discrimination between these two constraints. The most obvious functional constraint leads to the almost regular occurrence of radial enamel on the push sides of cutting edges. The degree of functional symmetry seems to be determined by phylogenetic limitations.     

Estimating the size at maturity in field populations of Daphnia (Cladocera)

• 1 Two methods for estimating the average body size at the onset of reproduction were applied to populations of Daphnia hyalina. The first, ‘average maturation size’, assesses maturity by the relative length of abdominal processes of Daphnia; the second, ‘size at first reproduction’ (SFR), calculates the size class in which 50% of the maximum proportion of egg-bearing females is reached.
• 2 The influence of environmental factors on the expression of the difference in length between the first and the second abdominal process was tested in the laboratory. Neither temperature nor chemical cues from predators affected the difference in length, but the processes were indistinguishable at very low food concentrations.
• 3 During one season, D. hyalina exhibited pronounced changes in fecundity, proportion of egg-bearing adults and SFR. The pattern obtained by the two methods was similar in many cases, although maturation size estimated by the first method was slightly smaller than SFR obtained by the second method. Neither method gave reliable results during times of starvation (clear-water phase).