Certainty of paternity covaries with paternal care in birds

Summary Male investment in parental care has been hypothesized to be affected or not to be affected by their certainty of paternity, depending on the particular assumptions of theoretical models. We used data on paternal care and extra-pair paternity from 52 bird species to determine whether male parental care was related to certainity of paternity. Paternal care was measured as the relative male contribution to nest building, courtship feeding, incubation, and feeding of nestlings, respectively. Males of avian taxa did not provide less parental care during nest building, courtship feeding and incubation if the frequency of extra-pair paternity was high. However, male participation in feeding of offspring was significantly negatively related to the frequency of extra-pair paternity. This was also the case when the effects of potentially confounding variables such as developmental mode of offspring (which may result in males being freed from parental duties), extent of polygyny (which may result in less paternal care), and the frequency of multiple clutches during one breeding season (which may increase the probability of finding fertile females during the nestling period) were controlled statistically. These results suggest that the extent of paternal care has been affected by certainty of paternity, and that sex roles during the energetically most expensive parts of reproduction have been shaped by sperm competition.     

Adaptations of meadow pipits to parasitism by the common cuckoo

Summary The meadow pipit Anthus pratensis is one of the most frequent hosts in Europe parasitized by the common cuckoo Cuculus canorus. The cuckoo normally removes one or more of the host eggs and replaces them with one of its own. The aim of the present study, which was conducted in an upland area of Central Norway, was to test the following question: assuming the cuckoo has laid a mimetic egg (which is slightly larger than and slightly different in color from that of a meadow pipit egg), under what circumstances are the parent meadow pipits able to detect such parasitism? The reaction of the meadow pipits to artificial parasitism was tested. Plastic model cuckoo eggs were used that bore a striking resemblance to real cuckoo eggs found in other meadow pipit nests in the same area. In addition, in some experiments a stuffed cuckoo dummy was used. The meadow pipits tolerated the experimental procedures and remained in their nests when given an artificial cuckoo egg, with or without removal of one of the host's eggs. However, when a host egg was removed and replaced with an artificial cuckoo egg, and at the same time a stuffed cuckoo dummy was presente, 50% of the birds deserted their nests. The difference between this result and the results of the other experiments was statistically significant. When only the stuffed cuckoo was presented, without any egg manipulations, the meadow pipits reacted in the same way as in the egg experiments. We conclude that the meadow pipit is capable of detecting whether or not its nest has been parasitized, provided it has observed the cuckoo near the nest site. Furthermore, because of the results of our experiments, we reject the hypothesis that the cuckoo has evolved egg removal behavior in order to prevent the host from assessing an increase in egg numbers.     

A hydromechanical principle for particle retention in Mytilus edulis and other ciliary suspension feeders

It is generally thought that the laterofrontal cirri of the bivalve gill act as filters that retain suspended particles in the through current and transfer the particles onto the frontal surface of the gill filaments. In Mytilus edulis calculations indicated that if water passed between the branching cilia of the cirri that are assumed to constitute the filter the pressure drop needed would amount to about 10 times the actual pressure drop across the whole gill. Thus, instead of acting as filters the laterofrontal cirri seem to move water. Presumably, the cirri together with the frontal cilia produce the water currents along the frontal surface of the gill filaments. Particle retention in the bivalve gill implies the transfer of suspended particles from the current of water about to enter an interfilamentar space into a neighbouring frontal surface current. The complex three-dimensional pattern of flow that arises where the 2 systems of current meet is characterized by steep velocity gradients. Particles that enter such steep, steady velocity gradients become exposed to transverse forces that cause the particles to migrate perpendicularly to the direction of flow. Whether particles enter the surface current, i.e. are retained, or they stay within the through current andescape, depends primarily upon particle size, and upon the steepness and height of the gradients within the boundary zone between the surface current and through current. Further studies are needed to evaluate the capacities and relative importance of this hydromechanical particle-trapping mechanism in suspension feeding bivalves. It is suggested that in downstream particle-retaining systems, e.g. on the tentacles of polychaetes and entoprocts, velocity gradients between through currents and surface currents also act as the particle-collecting mechanism.     

Male sperm whale (Physeter macrocephalus) acoustics in a high-latitude habitat: implications for echolocation and communication

Sperm whales (Physeter macrocephalus) are deep-diving predators foraging in meso- and bathypelagic ecosystems off the continental shelves. To investigate the ecophysiological and communicative function of various click types from male sperm whales in a high-latitude habitat, we deployed a large-aperture array of calibrated hydrophones off northern Norway (N69, E15). Data show that sperm whales in this habitat produce three click types: usual clicks, creak clicks and, occasionally, slow clicks. Usual clicks and creak clicks exhibit short duration, profound directionality and a frequency content suited for echolocation on meso- and bathypelagic fish and squids. The acoustic properties and low repetition rate of usual clicks are suited for long-range echolocation, whereas creak clicks have properties equivalent to signals in buzzes, the terminating pulse trains known from echolocating bats during prey capture. From these source parameters and the high acoustic activity during foraging dives, it is concluded that echolocation is an important sensory cue in prey location. Sound pressure levels of creak clicks and usual clicks measured off the acoustic axis suggest that sperm whales may be subjected to eavesdropping by conspecifics, thereby conveying information about food aggregations at estimated ranges of 6 km for creak clicks and 16 km for usual clicks. Slow clicks exhibit low directionality, low-frequency emphasis and a reduced repetition rate, suggesting that this click type is more suited for communication than for echolocation. Slow clicks can be detected by submerged conspecifics at ranges up to 60 km. Thus, sperm whales producing slow clicks may represent an odontocete species that utilizes long-range sound communication.     

Gill pump characteristics of the soft clamMya arenaria

Pumping rates in the soft clamMya arenaria, collected in June 1987 in the Great Belt, Denmark, were determined as rates at which clams cleared suspensions of algae,Dunaliella marina. The frictional resistance of the siphons to water flow was estimated by studying the effect of excision of the siphons at the base on the rate of water pumping. The frictional resistance was also calculated from the Poiseuille equation. Excision of the siphons had no measurable effect on the pumping rate, and calculations indicated pressure losses ranging between 0.3 to 1.2 mm H₂O. This is consistent with the conception that the capacity of filter feeding bivalves to process large amounts of water depends upon a low resistance to water flow in the siphons.     

Fluid mechanics of the mussel gill: The lateral cilia

Quantitative data on the water currents produced by the ciliary tracts of the gill filaments are needed to understand the fluid mechanics of suspension feeding in bivalves, as well as in other ciliary suspension feeders. This paper investigates the water currents produced by the bands of lateral cilia, as studied on isolated gill filaments, gill fragments, and intact gills of the mussel Mytilus edulis L with severed adductor muscles. The metachronally beating cilia produce oscillatory currents near the oscillating enveloping surface of the ciliary bands and rectilinear currents, the interfilamentary through-currents, farther from the surface. It is suggested that the oscillatory currents play an important role in the fluid mechanical capture of suspended particles. In the intact gill the interfilamentary currents pass the bands of lateral cilia at velocities that are two or more times higher than those generated by the bands of isolated filaments. The mussel gill is compared with an optimized peristaltic pump.     

Factors influencing length of maternal care in brown bears (<Emphasis Type="Italic">Ursus arctos</Emphasis>) and its effect on offspring

Length of maternal care, i.e. the interval between successfully raised litters, is the most important factor explaining the variation in reproductive rate among brown-bear (Ursus arctos) populations. In this paper, we examine the variation in length of maternal care in radio-marked brown bears and its effect on their offspring in northern Sweden. Young stayed with their mothers for 1.4–1.5 or 2.4–2.5 (in one case 3.5) years and were weaned with body masses varying from 17 to 69 kg. The probability of yearling litters staying with their mother for a 2nd year increased with decreasing yearling body mass, and was higher for litters with two offspring than for litters with one or three to four offspring. Staying with their mothers for a 2nd year had a positive effect on mass gain in yearlings and this effect was more pronounced in litters with two than three to four offspring. Body mass of 2-year-olds was not related to age of weaning, suggesting that keeping offspring for an additional year mainly compensated for low yearling body mass. If large offspring body mass positively affects later offspring survival and reproduction, mothers may be able to optimize the length of maternal care according to the litter size and the size of their yearlings.Communicated by F. Trillmich     

Influence of body size on the uptake,depuration, and bioaccumulation of polychlorinated biphenyl congeners by Baltic Sea blue mussels,Mytilus edulis

The present study was designed to examine the influence of body size on the bioaccumulation of polychlorinated biphenyl (PCB) congeners by Baltic Sea blue mussels, Mytilus edulis L. This was done, firstly, by establishing the relationship (as a power function: PCB tissue conc = a tissue dry wt^b) between tissue concentration and body weight for seven PCB congeners (International Union of Pure and Applied Chemistry No. 52, 101, 105, 118, 138, 153, and 180) in field sampled mussels; and, secondly, by assessing the influence of body weight on the uptake clearance coefficients, the depuration rate coefficients and the calculated bioaccumulation factors (BAFs) of three ¹⁴C-labelled PCB congeners (IUPAC No. 31, 49, 153) in mechanistic kinetic experiments. Both the background tissue concentrations of PCB 138, PCB 153 and PCB 180 and the predicted BAF values in the kinetic experiments correlated negatively with body weight (b=-0.17 and-0.31, respectively). Of the two kinetic rate coefficients examined, only the uptake clearance rate showed weight dependency (b=-0.32, i.e. negative correlation with body weight), whereas depuration rates were unaffectd by body weight. Uptake clearance rates and BAFs adjusted for body weight increased with the octanol/water partition coefficient (K_ow) of the congener, whereas depuration rates dectreased with K_ow. These observations suggest that size-dependent bioaccumulation of hydrophobic organic contaminants (HOCs) in suspension-feeding bivalves is driven by size-related differences in uptake rate, although several other mechanisms may also affect bioaccumulation in natural mussel beds (e.g. sizerelated differences in lipid content, production, and contaminant exposure). From an ecotoxicological perspective size-dependent bioaccumulation implies not only that variability due to body size differences has to be dealt with in experimental designs, but also that several ecological factors such as size-specific predation and shifts in population structure may affect HOC cycling by dense populations of bivalve suspensionfeeders.     

Preferential allocation of food by magpies Pica pica to great spotted cuckoo Clamator glandarius chicks

Adult magpies Pica pica provide parasitic great spotted cuckoo Clamator glandarius nestlings with a diet very similar to that fed to their own chicks. In both naturally and experimentally parasitized nests, great spotted cuckoo chicks were fed at a higher rate than magpie chicks in the same nest. This preferential allocation of food by magpie parents to great spotted cuckoo chicks is consistent with the supernormal stimulus hypothesis, because this result implies that cuckoo chicks provide stronger stimuli for parental care than host chicks. Great spotted cuckoo chicks receive most of the food brought to the nest by the foster parents, because they exploit a series of stimuli which jointly (or sometimes individually) operate as a supernormal stimulus. This hypothesis predicts that if any stimulus is masked, the efficiency of the cuckoo in eliciting parental care will decrease. Here, we analyze experimentally the effects of two of these stimuli, preferential feeding of large nestlings and of nestlings with conspicuous palatal papillae. Firstly, when we experimentally introduced one medium-sized (7–9 days) cuckoo chick into an unparasitized magpie nest where the largest magpie chick was 12–15 days old, the cuckoo did not receive significantly more food than the average or the largest magpie chick. Secondly, when unparasitized nests were experimentally parasitized with a cuckoo chick that had its gape painted to mimic that of magpie chicks, the parasitic cuckoo received less food than the average magpie chick.