The eye and some effects of light on locomotor activity in Nephrops norvegicus

The compound eye of Nephrops norvegicus (L.) is of the superposition type, well-adapted to the low levels of light prevailing at the sea bed during the activity periods of the species. Only the proximal retinal shielding pigment responds to light, the distal retinal shielding pigment being in the dark-adapted position at all times. The response of the proximal pigment appears to vary seasonally. Field observations compared light intensity at the sea bed with the numbers of N. norvegicus caught by trawl at various times of day in the Irish Sea in summer and winter. Laboratory experiments were combined with these field data to indicate that light is an important modulator of locomotor activity in this species.     

Current versus future reproduction: an experimental test of parental investment decisions using nest desertion by mallards (<Emphasis Type="Italic">Anas platyrhynchos</Emphasis>)

Past investment in offspring may be important in determining a parent's ability to reproduce in the future and, hence, should affect the relative value of current offspring. However, there have been surprisingly few clear tests of whether animals actually adjust parental care in response to diminished opportunities for future reproduction. We modified the experimental protocol of Sargent and Gross [Behav Ecol Sociobiol (1985) 17:43–45] to examine offspring desertion by mallards ( Anas platyrhynchos), and decoupled the influence of past investment from expected current benefits by controlling for the effect of offspring age on clutch value. Using 9 years of nest mortality data, we accounted for the increasing prospects of egg survival with clutch age by calculating clutch sizes throughout incubation with equivalent expected benefits. Applying this approach, we experimentally reduced 203 clutches at two different incubation stages such that they had equivalent expected benefits but differed in the amount of past investment. Nest desertion rates did not differ between early- and late-incubated clutches that had equivalent expected benefits. Rather, the probability of desertion increased with the severity of the clutch reduction treatment. These results suggest that female mallards adjust parental care according to the expected benefits of current offspring, rather than to diminished prospects for future reproduction due to past investment. We further examined whether females assessed expected benefits on the basis of clutch size alone or clutch size adjusted for the age of the clutch. Using Akaike's Information Criterion, the most parsimonious model to explain the probability of deserting an experimentally reduced clutch included both the proportion of the clutch remaining and clutch age. Thus, female mallards appear to fine-tune their level of parental care not only according to the relative number of offspring in the clutch, but also to the increased prospects for offspring survival as they age.     

Intraspecific variation of photosynthesis,respiration and photoprotective carotenoids in<Emphasis Type="Italic"> Gracilaria birdiae</Emphasis> (Gracilariales: Rhodophyta)

In most rhodophytes, the quenchers zeaxanthin or lutein seem to be used for carotenoid photoprotection next to β-carotene. However, our study shows that the tropical intertidal alga Gracilaria birdiae possesses high concentrations of antheraxanthin, as well as lower concentrations of both zeaxanthin and violaxanthin. In higher plants and some algal groups, these three oxygenated carotenoids are known to protect photosystem II in a xanthophyll cycle. We were able to manipulate the carotenoid concentrations in G. birdiae by varying irradiance and temperature in laboratory experiments. Higher concentrations of violaxanthin were found in dark incubations and higher concentrations of zeaxanthin in light incubations, which is an indication that a xanthophyll cycle is active in G. birdiae. Our results also suggest a biosynthesis pathway from lycopene to β,β-carotene and β-cryptoxanthin in the light and synthesis of new lycopene in darkness. This would imply that the production of functional carotenoids is regulated by their need in photoprotection. Despite cultivation in the laboratory under the same conditions for at least 6 years, there were differences in photosynthetic properties and carotenoid dynamics between algae obtained from a population close to the Equator and another population close to the Tropic of Capricorn. These differences most probably have their origin in genetic differentiation mediated by ambient irradiance and temperature regimes. Four phycoerythrin-deficient mutant strains of G. birdiae were studied as well. Photosynthetic properties and carotenoid dynamics were basically the same in the mutants and the wild strains, but two green strains had remarkably low dark respiratory rates. This is an indication of low production of metabolites, which may be a competitive disadvantage.     

Twilight fighting in the evening brown butterfly,<Emphasis Type="Italic"> Melanitis leda</Emphasis> (L.) (Nymphalidae): age and residency effects

Butterflies are conspicuous among animals that fight for mating opportunities because it is not clear how contest costs could accrue. Nevertheless, the bulk of research in this group suggests that contests are settled on the basis of asymmetries in fighting ability (the superior competitor hypothesis). There is also a consistent effect on contest escalation due to apparent 'confusion' over residency, which could result from resident butterflies playing different tactics than non-residents, or from a causal link between residency and fighting ability. I addressed these hypotheses by studying contest behavior in the crepuscular species Melanitis leda (L.) (Nymphalidae) over a 5-month period in tropical Australia. Males competed via conspicuous two-stage maneuvers of a form unique among butterflies. Prior residents won 77% of all contests. Non-resident males arrived and perched in occupied sites until challenged by incumbent residents, and the aggressiveness of these interlopers increased as a function of the time before they were detected. Contest winners also tended to be younger than losers, and contest escalation was negatively related to both the age of the losing male and the magnitude of the between-combatant age asymmetry. These results are consistent with the superior competitor hypothesis based upon age as a determinant (or correlate) of fighting ability, but also suggest residency has a unique influence on contest behavior. Further research is clearly required to unravel the effects of age, residency and other potential biophysical determinants of fighting ability in this species.     

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.     

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