Biodiversity and species–environment relationships of the demersal fish assemblage at the Great Meteor Seamount (subtropical NE Atlantic), sampled by different trawls

Quantitative data collected with different bottom trawls at the Great Meteor Seamount (subtropical NE Atlantic, 30°N; 28.5°W) in 1967, 1970 and 1998 are compared. Bootstrap estimates of total catch per unit effort increased from 6.96 and 10.8 ind. m^-1 h^-1 in 1967 and 1970, respectively, to 583.98 ind. m^-1 h^-1 in 1998. Gear effects and an effect of gear over time accounted for 47.1% and 20% of species variability. Further significant factors were time of day and habitat, while season was not significant. A total of 43 species was collected. Including supplementary species information, a grand total of 46 species was found associated with the Great Meteor Seamount. Diversity was higher in 1967 and 1970 (Shannon's diversity: H'=2.5 and 1.6) than in 1998 (H'=0.9). Species-environment relationships are discussed in terms of a sound-scattering layer-interception hypothesis, i.e. utilisation of prey from a diurnally moving sound-scattering layer for the bentho-pelagic community. This is probably augmented by concentration effects in a circular current around the seamount (Taylor-column). Long-term changes are discussed with respect to a decrease in biodiversity due to considerable increases in Macroramphosus scolopax and Capros aper. In 1998, the increase of abundance of Trachurus picturatus and the respective decreases for genuine benthic species were likely to have been caused by a change of gear.     

Female bank voles (Clethrionomys glareolus) prefer dominant males; but what if there is no choice?

Both intra-sexual competition between males and female mate choice have been found to affect mating behaviour in rodents. We studied female choice in the bank vole (Clethrionomys glareolus) under circumstances where male-male competition was excluded and the female could interact and mate freely with the males. Mating behaviour was observed in two situations: (1) the female encountered two males with a clear dominance relationship; and (2) the two males were equal in their social status. In all tests where a female in postpartum oestrus had a choice between males of different social rank she mated with the dominant one. When choosing between an even pair of males there was no difference in the frequency of lordotic responses, mounts or intromissions the female exhibited with either male before mating with one of them. The mean ejaculation latency was significantly longer in the tests with an even pair of males than in the tests where male hierarchy was clear. These results show that bank vole females are able to discriminate males according to their social status and strongly prefer dominant males as mating partners. However, when the females were presented with two equal males, they seemed to be unable to make a choice. The ability to choose the mating partner when the males are clearly different may be an important direct benefit for the female in terms of time saved during mating and thus decreased risk of predation and infanticide. Received: 16 March 1995/Accepted after revision: 11 February 1996     

Blue eggs do not reduce nest predation in the song thrush,Turdus philomelos

Summary Many passerine birds with open cup-shaped nests lay blue or blue-green eggs. In thrushes, blue eggs may be cryptic and provide camouflage by imitating spots of light on green leaves. Alternatively, egg coloration may be selectively neutral because nest predators detect nests and not eggs, or it may be maladaptive because organisms are not always well adapted to their present environment. I evaluated these hypotheses by studying predation on artificial song thrush (Turdus philomelos) nests with quail eggs, painted either white, blue, or spotted (cryptic to a human eye). Corvids were the major nest predators. For concealed as well as exposed nests, I found no differences in the predation rates of nests with white, blue, or spotted eggs. Predators apparently detected the nests, and not the eggs, first. In a second experiment, I placed egg groups without nests in trees to study the effect of color per se. The predation rate of the spotted egg groups was significantly lower than that of the white and blue egg groups, for concealed as well as exposed egg groups. These results suggest that blue eggs in the song thrush are not cryptic but may be selectively neutral or even maladaptive with regard to nest predation.     

Feeding of Clausocalanids (Calanoida,Copepoda) on naturally occurring particles in the northern Gulf of Aqaba (Red Sea)

A total of 12 feeding experiments were conducted in the northern Gulf of Aqaba during spring (March/April) and autumn (September/October) 2002 at the Marine Science Station (MSS) in Aqaba. Females of three species of clausocalanids were selected: Clausocalanus farrani, C. furcatus and Ctenocalanus vanus. Natural occurring particle (NOP) larger than 5 μm were investigated as food source. The ambient chlorophyll a concentration at sampling depth (∼70 m) ranged between 0.15 and 1.00 μg chl a l⁻¹ and NOP concentrations ranged between 1.78 and 14.0 × 10³ cells l⁻¹ during the sampling periods. The division of particles into five size classes (5–10, 10–20, 20–50, 50–100 and >100 μm) revealed that most of the particles were found in the size classes below 50 μm (81–98%), while most of the natural occurring carbon (NOC) was concentrated in the size classes larger than 20 μm (70–95%). Ingestion rates were food density dependent rather than size dependent ranging between 0.02 and 1.65 × 10³ NOP ind⁻¹ day⁻¹ and 0.01 and 0.41 μg NOC ind⁻¹ day⁻¹, respectively, equivalent to a body carbon (BC) uptake between 0.4 and 51.8% BC day⁻¹. The share of the size classes to the total ingestion resembled in most cases the size class composition of the natural particle community.     

Inorganic skeleton of the demosponge Halichondria panicea. Seasonality in spicule production in the Baltic Sea

Seasonality in spicule production of the demosponge Halichondria panicea (Pallas, 1766) was studied in the Western Baltic from July 1992 to July 1993. Spicule production increased in parallel with increasing temperatures in spring, being most pronounced during summer after release of larvae. Large proportions of up to 30% immature spicules occurred in the population during skeleton production peaks, and this resulted in reduction of mean spicule dimensions by ≃20%. Effects on spicule width were more obvious than on spicule length. In winter, when wave forces were largest, higher percentages of mineral skeleton were observed: 50% of dry weight compared to 40% in summer. Enhanced spicule densities in the tissues were not attained by marked spicule production but through a reduction in organic content by shrinking. In spring, growth of body tissue was faster than the build-up of skeleton, so that the relative amount of the latter was reduced. The indirect, growth-related developments of the skeleton were inversely proportional to temperature and directly to salinity, silicate concentrations and wave energy. Spicule size and the number of immature spicules were correlated with temperature and only slightly with salinity. No correlation with oxygen concentration or pH could be detected. Received: 3 April 1997 / Accepted: 8 August 1997     

Temporal increase in nest defence intensity of the willow tit (Parus montanus): parental investment or methodological artifact?

Summary Nest defence responses of experimentally naive and revisited willow tits (Parus montanus) towards a predator model were studied near Oulu, northern Finland, in 1988–1989. Intensity was measured with three variables in 228 trials at 90 nests. Two hypotheses explaining the temporal changes in the nest defence behavior were examined. In naive birds the nest defence intensity was positively correlated with the brood age, supporting the parental investment hypothesis. The number of previous trials did not cause additional variation in nest defence behavior in comparison between naive and revisited birds. Similarly, experiences in a previous breeding attempt did not affect the nest defence behavior during the course of the subsequent brood. Thus, the temporal increase in multiply visited nests was not due to the birds becoming familiar with the nest threat, i.e., no support was found for the so-called positive reinforcement hypothesis. We think that methodological problems in avian nest defence studies can hide the adaptive significance of the behavior, not explain it. Offprint requests to: S. Rytkönen     

Cell-cell recognition system in gorgonians: description of the basic mechanism

A comparative investigation of the chemical composition of Thalassiosira antarctica var. antarctica vegetative and resting stages revealed C:N and C:chl a ratios to be lower in vegetative cells. These trends primarily reflect vegetative levels of C/cell below, and N/cell and chl a/cell levels above those of spores. There was a change in chemical composition with the initial formation of resting spores, and spores continued to modify their composition while maintained in a cyclic light/dark regime for about one and one half weeks. Most notable was a net increase in carbon and chlorophyll a per cell. Spores then subjected to darkness for over one week appeared to retain most of the carbon and chlorophyll a previously synthesized. These findings support the idea that resting spores enhance the survival capabilities of a species under adverse conditions.     

The kin recognition system of carpenter ants (Camponotus spp.)

Summary Hamilton's (1964) hypothesis linking haplodiploidy and eusociality in the Hymenoptera could be reconciled with the occurrence of polygyny and multiple insemination if workers are able to distinguish full (3/4 related) sisters from other familiar matri- and patrilines within the colony, and direct altruistic behavior toward them preferentially. We examined this possibility in small genetically mixed nests of the carpenter ant Camponotus floridanus, formed by the transfer of worker pupae from two unrelated source colonies. In 120 h of observation on 12 queenright and 12 queenless nests, more than 15,000 behavioral interactions were recorded. Workers antennated familiar nonkin significantly more frequently than familiar sisters. However, they failed to discriminate consistently between kin and non-kin in food exchanges and grooming. Aggressive behavior was occasionally observed in some queenless nests, but almost never in the presence of a queen. When aggression did occur, it was directed significantly more often toward non-kin. Though related adult workers did not cooperate preferentially, the biases in antennation and aggression do indicate an ability to discriminate familiar kin from familiar nonkin, which may be employed in other contexts such as the rearing of reproductive brood.     

The costs of secondary sexual characters in the lekking great snipe (Gallinago media)

Summary Recent studies of the lekking great snipe (Gallinago media) have shown that male mating success increases with display rate and the amount of white on the tail. An obvious question then arises: what is setting the limits to male display rate and to the evolution of even whiter tails? In this study the costs of these two traits are considered. In the case of the white on the tail, almost no predation was observed during the display period. However, predation on the winter grounds and/or during migration cannot be ruled out. Males differed in the amount of white on the tail between years. It is suggested that increasing the amount of white is costly, though the reason for this is still unknown. In the case of display rate, it is shown that predation cannot be a considerable cost, again because of the near absence of predation on the leks. Instead, it is shown that male displays are energetically costly. The daily energy expenditure of displaying males was estimated to be on average 4 times the basal metabolic rate, which is close to the supposed maximum sustainable work load for birds. Furthermore, males lost on average 1.8 g per h (1.7% of the body mass) which is about 7.2 g (6.8%) during a night of display activity. Males do gain some weight during the day when no displays are performed but loose on average 9 g during an 11-day period in the early part of the breeding season. These results indicate that high energetic demands set the limits to male display performance and that males do not have to trade off the benefit of attracting females by their displays against a cost of attracting predators. Offprint requests to: J. Höglund     

Effect on fishes of two toxic polypeptides isolated from Anemonia sulcata

The effects of two toxic polypeptides isolated from Anemonia sulcata Pennant (Anthozoa) were tested on Gadus morhua, Pleuronectes platess and Platichthys flesus. In tramuscular injections caused paralysis and death, with symptoms similar to those of death caused by lack of oxygen. In cod, the LD₅₀ dose of Toxin II was 50 times higher chan that of Toxin I (Toxin I=6.9 mg/kg, Toxin II=0.14 mg/kg). Flatfish were less sensitive. The LD₅₀ of Toxin II was 0.37 mg/kg for Platichthys flesus and 0.38 mg/kg for Pleuronectes platessa. Both toxins are less lethal to fishes than to crustaceans.