What limits predator detection in blue tits (<Emphasis Type="Italic">Parus caeruleus</Emphasis>): posture,task or orientation?

To detect threats and reduce predation risk prey animals need to be alert. Early predator detection and rapid anti-predatory action increase the likelihood of survival. We investigated how foraging affects predator detection and time to take-off in blue tits (Parus caeruleus) by subjecting them to a simulated raptor attack. To investigate the impact of body posture we compared birds feeding head-down with birds feeding head-up, but could not find any effect of posture on either time to detection or time to take-off. To investigate the impact of orientation we compared birds having their side towards the attacking predator with birds having their back towards it. Predator detection, but not time to take-off, was delayed when the back was oriented towards the predator. We also investigated the impact of foraging task by comparing birds that were either not foraging, foraging on chopped mealworms, or foraging on whole ones. Foraging on chopped mealworms did not delay detection compared to nonforaging showing that foraging does not always restrict vigilance. However, detection was delayed more than 150% when the birds were foraging on whole, live mealworms, which apparently demanded much attention and handling skill. Time to take-off was affected by foraging task in the same way as detection was. We show that when studying foraging and vigilance one must include the difficulty of the foraging task and prey orientation.Communicated by P.A. Bednekoff     

A field test of the intraspecific brood parasitism hypothesis in the golden egg bug (<Emphasis Type="Italic"> Phyllomorpha laciniata</Emphasis>)

In natural populations of golden egg bugs ( Phyllomorpha laciniata), females lay eggs on plants where they develop unattended, or on conspecifics, where they remain firmly glued until the nymphs hatch and start an independent life. Mortality rates among eggs laid on plants are higher than among eggs carried by adults. Because females cannot lay eggs on themselves, in order to improve offspring survival, they have to lay eggs on other individuals. Two hypotheses have been proposed to explain egg carrying: (1) the mating pair intraspecific brood parasitism hypothesis suggests that females dump eggs on copulating pairs, and (2) the paternal care hypothesis suggests that the system is driven mainly by males accepting eggs to improve the survival rates of their own offspring. Our data from the field show that 77% of the eggs are carried by males, because more males than females carry eggs, and because males carry a greater number of eggs. In addition, we show that mating males carry more recently laid eggs than single males. These results support the view that egg carrying is performed predominantly by males and that eggs are laid on males by their current mating partner, probably between repeated copulations. Males are likely to accept eggs, despite intermediate levels of paternity, because they cannot discriminate in favour of their own eggs, because rejected eggs will face 97% mortality rates on plants, and because they do not suffer mating costs when they carry eggs. However, females carry 23% of the eggs, but no differences in egg carrying have been found between mating and single females, suggesting that this is not the result of egg dumping while females are copulating. Egg carrying by females could reflect low levels of intraspecific parasitism, which is likely to reflect the low rate of successful attempts by egg-laying females who try to oviposit on other conspecifics rather indiscriminately, in an effort to improve the survival of their offspring.     

Acid dissolution methods for heavy metals determination in pine needles

Microwave digestion procedures using HNO₃, HNO₃+H₂O₂, HNO₃+HClO₄, HF mixtures and dry ashing with HF were investigated for heavy metals analysis by either inductively coupled plasma-optical emission spectroscopy (ICP-OES) or ICP-mass spectrometry (ICP-MS) in pine needles. The HF digestion procedures gave about 1.5 times higher values than a mixture of HNO₃+H₂O₂ alone. For Ti determination in needles, the HF procedure using dry ashing is thus recommended. The mean concentrations amounted to 900 mg/kg for Fe and 21.8 mg/kg for Ti in needles collected at an area polluted by a stainless steel works. Those concentrations were 10.6 and 4.3 times higher than in needles collected at an area nearby a pulp mill complex (84.5 mg/kg Fe and 5.0 mg/kg Ti).     

Call structure may affect male mating success in the quacking frog<Emphasis Type="Italic"> Crinia georgiana</Emphasis> (Anura: Myobatrachidae)

We investigated the relationship between mating success, male size and variation in the advertisement call in the frog Crinia georgiana under field conditions. Mating success in 91 males was determined by following 32 females as they moved through the chorus. Our analyses indicated that successful males had a higher number of pulses in the first note and/or called at a higher rate. However, we did not detect a significant relationship between mating success and dominant frequency, the property that varied most strongly with body size, suggesting that size is not an important influence on mate choice in this species. Even so, smaller males were more successful if they called at a higher rate whereas larger males were more successful if they had more pulses in their first note. Accordingly, males of different size may use different calling tactics to attract females. These results provide a framework for further experimental studies aimed at investigating the independent impacts of both inter- and intra-sexual selection on the advertisement call and body size of C. georgiana.     

Lipid deposition and sexual maturation in cohorts of<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> (Gunnerus) originating from Bergen (60°N) and Tromsø (69°N) reared in Tromsø, Norway

Two cohorts of Calanus finmarchicus (Gunnerus), with habitats in Bergen (60°N) and Tromsø (69°N), were reared from copepodite stage III (CIII) in mesocosms in Tromsø from April 24 1998 to June 30 1998. The aim was to study whether the two cohorts diverged phenotypically with respect to indication of physiological preparation for diapause as opposed to initiating another generation. At the end of the experiment the fractions of the cohorts that had reached sexual maturation, based on observed stage shifts to adults, was ~45% within the Bergen cohort and ~35% for the Tromsø cohort, within which males appeared before females. Examination of the mandibular gnathobase of copepodites at stage V (CV) revealed that <10% of the Bergen cohort, but >40% of the Tromsø cohort were ready for ecdysis, eventually to become adults in the same year. The physiological expression of the range in individual maturity within the cohorts was revealed in individual carbon and nitrogen content. Both cohorts incorporated the storage lipids wax esters (WE) and triacylglycerols (TAG) rapidly, primarily during CV (0.16–0.21 µg total neutral lipid ind ^-1 day ^-1), with no significant difference. Lipid storage was incorporated from CIII and the maximum was reached at the CV stage. Presumably due to excess food, high WE, TAG and free fatty acid levels were observed in both cohorts. A relative decrease in neutral lipids was observed later in females from both cohorts. We suggest that part of the Bergen population, but also a fraction of the Tromsø population, prepared for diapause in CV. A possible reason for the sexual maturation among the rest of the CV copepodites could be a shift in life "strategy" caused by an unusually high rise in temperature in the mesocosms during the last 10 days of the experiment.     

Chemosensory cues allow courting male garter snakes to assess body length and body condition of potential mates

When choosing between two potential mates, a male may benefit by picking a larger (longer and/or more heavy-bodied) female because she is likely to produce more or larger offspring. Males of many species use visual cues to evaluate the sizes of their mates, but in some situations (at night or in a crowded mating swarm), vision may be useless. Potentially, males may be able to use chemical cues that convey information about female body size. We manipulated cues available to free-ranging male garter snakes (Thamnophis sirtalis parietalis) in large courting aggregations near communal dens in Manitoba, Canada. Males not only directed disproportionate courtship to longer and heavier-bodied females, but also courted most vigorously in response to lipids extracted from the skins of such females. Our data show that with a flick of his tongue, a male garter snake can identify not only a female's body length, but also her body condition.     

Specificity of two temperate dinoflagellate–anthozoan associations from the north-western Pacific Ocean

Whilst many studies of symbiotic dinoflagellate diversity have focused on tropical reef environments, only a few have explored the degree and pattern of divergence of these endosymbionts at high latitudes. In this study, the genetic diversity and specificity of symbiotic dinoflagellates associated with two common anthozoan hosts in the north-western Pacific Ocean was studied in four different seasons during a period of 1 year. Partial nucleotide sequences of 28S and complete ITS1 ribosomal DNA regions were used to identify, genetically, the endosymbionts extracted from the scleractinian Alveopora japonica and the actinarian Heteractis sp. A. japonica harbours symbionts belonging to Symbiodinium of clade F, while Heteractis sp. associates with Symbiodinium of clade C. Moreover, no seasonal changes in the endosymbiont community were detected in these two associations during this study. This is the first evidence that these two temperate cnidarian–microalgae symbioses are stable. Furthermore, we tested the apparent specificity of the Heteractis sp.– Symbiodinium sp. clade C association, by performing alga-infection experiments with aposymbiotic hosts, and monitoring the uptake and persistence of homologous and heterologous symbionts. The findings confirm the association patterns detected in the field and show that Heteractis sp. only establishes a successful association with Symbiodinium cells of clade C, at least among the heterologous symbionts occurring in the study area. Our results are consistent with the idea that selective pressures in highly fluctuating temperate environments might have granted symbiosis-specificity an adaptive value.Communicated by T. Ikeda, Hakodate     

Ecology of a corallivorous gastropod,<Emphasis Type="Italic"> Coralliophila abbreviata</Emphasis>, on two scleractinian hosts. II. Feeding,respiration and growth

Coralliophila abbreviata is a corallivorous gastropod that has been observed to cause large feeding scars on reef-building corals on Floridian and Caribbean reefs. We detected differences in the population structure (length-frequency distribution and sex ratios) of C. abbreviata populations living on two coral host taxa, Acropora palmata and Montastraea spp., in the Florida Keys in a previous study. We hypothesize that diet (host) has a major influence on snail population structure and, thus, we characterize metabolism, feeding and growth for snails residing on these coral taxa. Here, we present results of a reciprocal transplant experiment demonstrating that the taxon of the host influences snail growth rates, as indicated by changes in shell and body tissue weight. Regardless of the host from which they were drawn, snails resident on A. palmata grew faster than those resident on Montastraea spp. Thus, diet influences snail population structure. However, the tissue of Montastraea spp. provides more N and C per area of tissue than that of A. palmata. Respiration rates and tissue composition of snails collected from the two host taxa did not differ. Therefore, snails feeding on Montastraea spp. should have to consume less tissue per day to satisfy their metabolic requirements compared to snails feeding on A. palmata. Feeding rates for snails on A. palmata were measured in the laboratory over 48 h (1–9 cm² coral tissue snail⁻¹ day⁻¹) and estimated from feeding scars observed in the field (weekly mean rate of 1.07 cm² coral tissue snail⁻¹ day⁻¹). The lack of definition of snail feeding scars on Montastraea spp. required the calculation of coral tissue consumption rates based on estimated minimum carbon requirements. Calculated feeding rates for C. abbreviata were 0.13–0.88 cm² coral tissue day⁻¹ snail⁻¹, when feeding on Montastraea spp., and 0.44–3.28 cm² coral tissue day⁻¹ snail⁻¹, when feeding on A. palmata. The calculated range for the latter is consistent with measured rates. Thus, C. abbreviata exhibits high variation in growth parameters in response to environmental variability and/or food source. At mean levels of snail density on reefs off Key Largo, Fla., 20% of A. palmata colonies lose between 1.32 and 9.84 cm² tissue day⁻¹, while 50% of Montastraea spp. colonies lose between 1.04 and 7.04 cm² tissue day⁻¹. Together with published coral tissue regeneration rates, these results suggest that if sustained, such rates of predation could have a serious effect on the viability of these coral populations on Florida's reefs.     

Reproductive conflict in animal societies: hierarchy length increases with colony size in queenless ponerine ants

Dominance interactions determine reproductive status in many animal societies, including many cooperatively breeding vertebrates and eusocial Hymenoptera without queen-worker dimorphism. Typically, the dominant individual monopolises reproduction, and subordinates behave like helpers. In Dinoponera queenless ants, workers are totipotent females and can potentially reproduce, yet only the top-ranking worker actually reproduces. Individual workers ranked immediately below the dominant breeder worker (gamergate) are hopeful reproductives. Whether or not a worker benefits from joining the hierarchy of high-ranking workers depends on the trade-off between the probability of becoming dominant and reproducing directly, and the colony-level cost of an additional lazy high ranker. Inclusive fitness models predict that the length of the dominance hierarchy depends on relatedness, colony size, and the linearity of the hierarchy. Here, we test the effect of colony size by comparing hierarchy length among three species that differ in colony size (Dinoponera australis: median=14 workers, quartiles=10 and 19 workers; D. gigantea: median=41, quartiles=33 and 74; D. quadriceps: median=78, quartiles=55 and 90). Although difficulties in defining where the hierarchy ends hamper comparisons, the results are in broad agreement with the predictions. Hierarchies are close to the predicted lengths and are longer in species with larger colonies (one, three and three workers in the three species in order from smallest to largest colony vs two, three and four predicted). These conclusions are further supported by determining Kokko and Lindström's λ index of skew, which is smaller (i.e. characteristic of a longer hierarchy) in species with larger colonies.     

Feeding preferences,seasonal gut repletion indices,and diel feeding patterns of the sea urchin<Emphasis Type="Italic"> Tripneustes gratilla</Emphasis> (Echinodermata: Echinoidea) on a coastal habitat off Toliara (Madagascar)

The feeding biology of the echinoid Tripneustes gratilla from a seagrass bed off Toliara, on the south-west coast of Madagascar, was investigated during the summer and winter seasons. Repletion indices of the gut of T. gratilla varied seasonally, in such a way that higher amounts of food occurred in the gut in winter than in other seasons. Conversely, a more detailed analysis of one summer and one winter sample of the gut tissue dry weights revealed higher weights in summer (February) than in winter (August). This was interpreted as a varying capability of nutrient storage and closely related to the feeding activity of the echinoid. This inverse relationship between feeding activity and nutrient storage was suggested to be dependent on gonadal growth. Indeed, higher food consumption was observed during the post-spawning period (August), that is, when most of the energy accumulated was used up for gonadal growth. Low feeding activity occurred when a sufficient amount of energy was accumulated in gut tissues (February), the time corresponding to the initiation of gonadal growth. Investigations on the feeding habits, using Ivlev's electivity index, revealed preferential feeding of T. gratilla on Syringodium isoetifolium, the dominant seagrass species found in the gut. This was partly related to the higher availability of that particular seagrass species in the field. However, its soft and terete leaf blade's morphology also makes it easier to manipulate and ingest. Studies on the feeding behaviour indicated the presence of a diel feeding cycle in T. gratilla individuals in both summer and winter seasons. Yet, its pattern varied between the two studied months (one summer and one winter) as the cycle was less contrasted during period of active feeding, i.e. in winter compared to summer. This study provides novel information on how intrinsic factors, such as physiological state, can govern the feeding activity of T. gratilla living in a seagrass habitat.