The Gutless Marine Tubificid Phallodrilus planus, a Flattened Oligochaete with Symbiotic Bacteria. Results from Morphological and Ecological Studies

The anatomy of Phallodrilus planus Erseus, 1979, a relatively large interstitial tubificid from shallow subtidal sands off Bermuda, is characterized by an unequal development of the muscular layer which results in a flattening of the body shape. Like its relative P. leukodermatus , it lacks completely the digestive tract and nephridia, but is regularly associated with a thick subcuticular layer of two different gram-negative bacteria which are involved in sulphide oxidation. This is shown by ultrastructural, histochemical and physiological data and affects the biological and ecological situation of these aberrant oligochaetes. The mutualistic nature of this bacteria/animal association is discussed.     

Social rank in winter flocks of Willow Tits Parus montanus

The social hierarchies in winter of ten flocks of Willow Tits Parus montanus were studied when the birds were foraging naturally and when visiting feeders. All the flocks consisted of one adult mated pair together with two juvenile males and two juvenile females (probably pairs). All flocks studied had a stable composition and the hierarchies remained constant throughout the study period. The hierarchies were linear and unilateral. The adults of each sex dominated the respective juveniles and within each age group the male dominated the female. The dominance relationships between the age and sex groups were not consistent. Although the males dominated all the females in six flocks, in one flock the adult female dominated both the juvenile males, but only one of them in three other flocks. The degree of aggression between flock-members was 0.8 encounters per hour, and males initiated 94% of all attacks. Body-weight explained 77% of the variation in dominance rank. It is suggested that the dominance rank of a male is also a function of his seniority, while the rank of a juvenile female is correlated with the rank of her mate.     

DIFFERENTIATION OF FORAGING NICHE AMONG TITS, PARUS SPP., IN NORWAY DURING WINTER

The winter foraging behaviour of Willow Tit Parus montanuss, Coal Tit P. ater and Crested Tit P. cristatus was studied in several spruce-dominated, coniferous forest areas in which either Willow Tit alone, Willow Tit and Coal Tit, or all three species together were present. In the areas where Crested Tits were absent, Willow Tits foraged significantly more often in the outermost parts of spruce branches and less frequently on the parts of branches closer to the trunk, than in the area in which Crested Tits were present. In the area in which all three species were present, the same change in foraging pattern of Willow Tits was found in mixed flocks in which Crested Tits were lacking. The foraging pattern of Coal Tits was unaffected by the presence of members of either or both the other two tit species. It is suggested that the expansion of the feeding niche of Willow Tit in the absence of Crested Tit is a result of ecological release, due to a reduction in the degree of interspecific competition.     

Morphological and Ecophysiological Adaptations of the Marine Oligochaete Tubificoides benedii to Sulfidic Sediments

SYNOPSIS. The marine oligochaete worm Tubificoides benedii inhabitscoastal tidal sediments in which sulfide can reach toxic concentrations.The role of external ironsulfide deposition in sulfide detoxificationis discussed together with a review of morphological and ecophysiologicaladaptations of T. benedii to sulfide. The body wall of T. benediiturns black in the presence of sulfide. Histochemical studiesand micro-X-rayanalyses provide evidence for the reaction ofiron in the mucus layer above the cuticle of the worm with environmentalsulfide to produce ironsulfide. The deposited ironsulfides areeither reoxidized or shed off through moulting, a process otherwiseunknown in oligochaetes. However, calculations on the diffusionrate of sulfide into T. benedii show that the deposition ofironsulfides do not play an important role in sulfide detoxification.The first and last few segments of T. benedii are not blackenedby sulfide and do not appear to precipitate sulfide. The diffusionrate of sulfide through these segments is so rapid that internalsulfide concentrations reach levels inhibitory to cytochromec oxidase, the key enzyme of aerobic respiration, within minutes.When internal sulfide concentrations increase to toxic levels,reliance on an anaerobic metabolism represents a successfulmechanism of sulfide tolerance in T. benedii. Metabolic adaptationsto hypoxia and sulfide include the maintenance of aerobic pathwaysdespite low oxygen or high sulfide concentrations and the abilityto gain energy through anaerobic pathways when oxygen and/orsulfide concentrations become limiting     

Spontaneous All-or-Nothing Action Potentials in the Ciliate Bursaridium difficile

The electrical membrane properties and the swimming behaviour of the freshwater ciliate Bursaridium difficile were studied by current clamp recordings and video analysis. The resting membrane potential was –45 ± 6 mV (mean ± SD, n = 80), and the input resistance and membrane capacitance were 109 ± 42 megaohms (MΩ) (n = 63) and 457 ± 150 picofarads (pF) (n = 42), respectively. Based on an estimated surface area of 6.8 × 10^-4 cm², the corresponding specific membrane resistance and capacitance are 7.4 × 10⁴Ω× cm² and 0.7 μF/cm². Bursaridium difficile generates spontaneous, all-or-nothing action potentials with a well-defined threshold in normal medium. The spontaneous firing frequency was 0.22 ± 0.06 Hz (n = 80). The maximum rate of rise of the action potentials was less than 1 V/s, and they displayed a prolonged plateau phase (0.5–1 s). The action potentials were abolished in nominal Ca²⁺-free solution and are thus Ca²⁺-spikes. The swimming pattern of Bursaridium in homogeneous surroundings is composed of forward swimming periods interrupted by regular, short periods of backward swimming followed by a change in the forward swimming direction. The turning frequency corresponded to the spontaneous firing frequency, and only forward swimming was observed in nominal Ca²⁺-free solution. The periods of backward swimming activity are thus linked to the spontaneous action potentials.     

Subordination in mixed-age bird flocks–a removal study

During the winters of 1979 to 1986, flocks (7–17 per season, 78 total) of Willow Tits Parus montanus (generally consisting of an adult pair and four juveniles) were studied in a subalpine mixed forest in Central Norway. The mean survival rate between December and early April for juveniles (0.32) was significantly lower than that found for adults (0.74). As it has previously been found that adult Willow Tits, being dominant, prevent the juveniles in a flock from using preferred foraging sites, a removal experiment was made to see if the survival of juveniles improved when living in flocks with no adults present. After removal of the adult pair from 13 flocks in early January, the juveniles from these flocks survived significantly less well, up to early April, than either the juveniles in 11 flocks in which the adults were present (controlled for flock size) or those in 14 flocks consisting of an adult pair and four juveniles. Despite a skewed access to the resources in favour of dominant adults, the cost of being a subordinate juvenile is probably outweighed by the improved predator evasion and improved food finding efficiency due to the greater experience of the adult pair possessing the territory.     

The frequency of multi‐queen colonies increases with altitude in a Nearctic ant

1. Most ants in boreal and alpine habitats are facultatively polygynous, i.e. their colonies may contain one or several queens. It was investigated how the proportion of polygynous colonies varies along an elevation gradient from 60 to 2700 m in the Nearctic ant Temnothorax rugatulus (Emery). 2. Across all populations, the proportion of polygynous colonies was positively correlated with altitude. The correlation was considerably stronger when only populations in the narrow area of the Chiricahua Mts, Arizona, were compared. 3. The dominance of polygynous colonies at high altitudes may be associated with selection against solitary colony founding by young queens. In areas with short summers and long winters, hibernation mortality of solitarily founding queens may select for alternative reproductive tactics, such as polygyny and colony founding by budding. 4. Colony founding tactics need to be taken into account to more fully understand altitudinal and latitudinal patterns of ant faunas.     

Sex-differences in nest defence in Fieldfares Turdus pilaris in relation to their size and physical condition

The nest defence of solitary-breeding Fieldfares Turdus pilaris against a human intruder, a corvid and a hawk was studied in a mountain birch forest in central Norway in 1990–2002. Females defended their nests against a human intruder more vigorously than did males before hatching, and vice versa after hatching. Although both sexes increased their nest defence, only males showed a significant increase and showed a greater defence than females at the chick stage. Females with 1-week-old nestlings had longer wings, were heavier and in a better physical condition than those that failed to get nestlings to that stage. Females, but not males, lost condition during nesting. Birds in better condition were more aggressive. The pattern of nest defence by males and females against the corvid was similar to that shown against human intruders, whereas males took greater risks than females towards the raptor. There was weak evidence that birds that were more successful showed greater levels of nest defence. The sex-role reversal in nest defence may be connected to differences in costs in relation to the renesting potential and to the physical condition of the sexes.