Die Ektoplasmahülle von Heterostegina depressa (Foraminifera:Nummulitidae)

The structure of the rigid ectoplasm sheath was studied in living individuals of the large foraminifer Heterostegina depressa d'Orbigny 1826 (Nummulitidae). H. depressa is able to form pseudopods, which emerge from the marginal cord within a few minutes. Normally, however, the living test is entirely covered by a rigid hyalin elastic sheath, which is fixed to the substrate by terminally branched processes. In older individuals, the sheath is often incomplete and restricted to the marginal cord only. Probably, the sheath is secreted by the ectoplasm which fills the canal system of the chamber walls and the marginal cord, or it consists of transformed ectoplasm; we call it “Ektoplasmahülle”, and the processes radiating to all sides, “Ruhepseudopodien”. H. depressa is able to move while inside the elastic sheath by means of pseudopods which penetrate the sheath and attach themselves to the substrate out-side. In the same manner, H. depressa leaves a complete sheath by disrupting it through the tractive powers of the pseudopods. The procedure of breaking the sheath is described. Locomotion when leaving the sheath is performed in a zigzag manner (alternating action of several pseudopods). The sheath counteracts transportation by water movement and protects chamber formation (which takes place inside the sheath). Due to its symbiotic unicellular algae, H. depressa does not need to collect food particles; hence locomotion seems unneccssary. The formation of a rigid ectoplasm sheath may be connected with H. depressa's sessile mode of life.     

Benthic Foraminifera: morphology and growth in clone cultures of Heterostegina depressa

A three months old clone of 76 asexually produced F₂ Heterostegina depressa D'Obbigny, 1826 (Foraminifera) was subdivided into two groups which were cultivated for 5 months, one at 300 lux, the other at 600 lux. Nourishment was provided by symbiotic photosynthesizing algae. The 300-lux group added 1 whorl, the 600-lux group added 1/2 a whorl during the experiment, suggesting that the first group was nearer the optimum for growth than the second. Growth rates reacted but slowly to changes in environmental conditions. Also, specimens within the same culture dish showed great differences in response. In the 600-lux group, many specimens ceased to grow entirely, while others continued. Cessation of growth tends to produce a rounded test shape, by filling-in of the apertural angle, while rapid growth tends to be correlated with flaring tests (i.e., tests with an open spiral). In addition, there is a trend toward increased flaring during normal ontogenetic development. Shell damage is greater in rapidly growing individuals; walls are apparently thicker in slowly growing and in resting individuals. Ecological interpretation of morphological characteristics is hampered by: (1) a lag effect between growth response and environmental change; (2) slowing or termination of growth under stressful conditions with corresponding minor changes in morphology; (3) great variation in response between sibling individuals within the same culture dish; (4) aging effects.     

Queen fertility, egg marking and colony size in the ant Camponotus floridanus

In ant societies, workers do not usually reproduce but gain indirect fitness benefits from raising related offspring produced by the queen. One of the preconditions of this worker self-restraint is sufficient fertility of the queen. The queen is, therefore, expected to signal her fertility. In Camponotus floridanus, workers can recognize the presence of a highly fertile queen via her eggs, which are marked with the queen's specific hydrocarbon profile. If information on fertility is encoded in the hydrocarbon profile of eggs, we expect workers to be able to differentiate between eggs from highly and weakly fertile queens. We found that workers discriminate between these eggs solely on the basis of their hydrocarbon profiles which differ both qualitatively and quantitatively. This pattern is further supported by the similarity of the egg profiles of workers and weakly fertile queens and the similar treatment of both kinds of eggs. Profiles of queen eggs correspond to the cuticular hydrocarbon profiles of the respective queens. Changes in the cuticular profiles are associated with the size of the colony the queen originates from and her current egg-laying rate. However, partial correlation analysis indicates that only colony size predicts the cuticular profile. Colony size is a buffered indicator of queen fertility as it is a consequence of queen productivity within a certain period of time, whereas daily egg-laying rate varies due to cyclical oviposition. We conclude that surface hydrocarbons of eggs and the cuticular profiles of queens both signal queen fertility, suggesting a major role of fertility signals in the regulation of reproduction in social insects.