Brood sex ratio and male UV ornamentation in blue tits (<Emphasis Type="Italic">Cyanistes caeruleus</Emphasis>): correlational evidence and an experimental test

Sex-allocation theory predicts that females paired to attractive males should bias the brood sex ratio towards male offspring, as these would inherit the attractiveness of their father. We studied sex allocation based on male ornamentation in blue tits. Brood sex ratios varied with male UV coloration in an age-dependent manner. For juvenile males, the proportion of sons increased with increasing UV ornamentation, which is in agreement with previous findings from a Swedish population. However, the relationship between UV ornamentation and brood sex ratio was reversed for adult males, with females paired to less UV-ornamented adult males producing more sons. This pattern fits with the observation that, in our population, less UV-ornamented adult males sire the majority of extra-pair young. To test the causality of the association between brood sex ratio and male coloration, we experimentally manipulated crown colour largely within the natural range. We created two groups of males: one with higher and one with lower UV reflectance, UV(+) and UV(−), respectively. Contrary to our expectations, there was no significant treatment effect. However, in UV(−), but not UV(+) males, the proportion of sons was negatively correlated with male coloration before manipulation. This suggests that the UV(−) treatment caused males that were more UV ornamented to decline more in attractiveness, as shown in a similar experiment in Sweden. However, given that correlational patterns differ between these populations, similarities in experimental results should not be taken as evidence for consistent patterns of adaptive sex allocation in this species.     

Herbicide exposure affects the chemical recognition of a non native predator in common toad tadpoles (<Emphasis Type="Italic">Bufo bufo</Emphasis>)

Summary. In amphibians and fishes, evidence is increasing that chemical cues from injured conspecifics can play a role in the chemical labelling and learned recognition of unfamiliar predators. In this laboratory study, we tested the prediction that prior chemical exposure to a non-native predator feeding on conspecific tadpoles will subsequently allow tadpoles of the common toad (Bufo bufo) to recognize the chemical cues specifically released by this starved predator. Furthermore, we investigated the vulnerability of this chemically-mediated process to herbicide contamination. With these aims in view, groups of tadpoles were kept either unexposed or exposed for ten days to chemical cues from Turkish crayfish (Astacus leptodactylus) previously fed on tadpoles, both in uncontaminated water and in the presence of four sublethal concentrations of amitrole (0.01, 0.1, 1 and 10 mg.l⁻¹). We then assessed the effects of the six conditioning treatments on general activity and behavioural response to chemical cues from starved crayfish. Larval treatments did not affect the general activity of the tadpoles. By contrast, the treatments had significant effects on the behavioural response to the test solution prepared form starved crayfish. The only tadpoles to show an antipredator behavioural response to the chemical stimulation from starved crayfish belonged to the groups derived from chemical exposure to tadpole-fed crayfish in uncontaminated water and in contaminated water with the lowest concentration of amitrole (0.01 mg.l⁻¹). Conversely, this chemical stimulation produced no behavioural change in the control group or in the groups derived from exposure to tadpole-fed crayfish in contaminated water containing 0.1, 1 and 10 mg.l⁻¹ of amitrole. This study demonstrates that chemical cues released during the predator’s feeding activity can subsequently be used by common toad tadpoles in the recognition of an unfamiliar predator. In addition, our results show that the presence of sublethal amitrole concentrations can impair this recognition process. Such a pesticide effect might be especially detrimental for amphibian populations threatened by invasive predators.     

Possible causes and consequences of philopatry and breeding dispersal in red-backed shrikes <Emphasis Type="BoldItalic">Lanius collurio</Emphasis>

Studies of animal breeding dispersal have often focused on possible causes, whereas its adaptive significance has received less attention. Using an information-theoretic approach, we assessed predictions of four hypotheses relating to causes and consequences of breeding dispersal in a migratory passerine, the red-backed shrike Lanius collurio. As predicted by the reproductive performance hypothesis, probability of breeding dispersal in females (though not in males) decreased with increasing annual average number of fledglings produced in the past year, but there was no association with conspecific reproductive performance in either sex. The site choice hypothesis, stating that individuals disperse to improve breeding site quality, received support in males only, as dispersal probability was positively associated to a measure indicating low territory quality. The social constraints hypothesis, referring to dispersal in relation to intraspecific interactions, received little support in either sex. The predation risk hypothesis was hardly supported either. Consequences of dispersal were marginal in both sexes because neither fledgling production in females, nor territory quality in males improved after dispersal. In addition, males settled on territories closer to the forest edge than those occupied predispersal, which is opposite to the prediction of the predation risk hypothesis. We conclude that own reproductive success was the major factor determining dispersal behavior in females, whereas territory quality and possibly predation risk were most important in males. Overall, breeding dispersal appeared not to be adaptive in this dense population inhabiting an optimal habitat.     

Chemical mimicry in an incipient leaf-cutting ant social parasite

Some social parasites of insect societies are known to use brute force when usurping a host colony, but most use more subtle forms of chemical cheating either by expressing as few recognition cues as possible to avoid being recognized or by producing similar recognition cues to the host to achieve positive discrimination. The former “chemical insignificance” strategy represents a more general adaptive syndrome than the latter “chemical mimicry” strategy and is expected to be characteristic of early evolutionary stages of social parasitism. We tested this hypothesis by experimentally analyzing the efficiency by which Acromyrmex echinatior leaf-cutting ants recognize intruding workers of the incipient social parasite Acromyrmex insinuator. The results were consistent with the parasite being “chemically insignificant” and not with the “chemical mimicry” hypothesis. Gas chromatography–mass spectrometry analysis of cuticular hydrocarbon profiles showed that social parasite workers produce significantly fewer hydrocarbons overall and that their typical profiles have very low amounts of hydrocarbons in the “normal” C29–C35 range but large quantities of unusually heavy C43–C45 hydrocarbons. This suggests that the C29–C35 hydrocarbons are instrumental in normal host nestmate recognition and that the C43–C45 compounds, all of which are dienes and thus more fluid than the corresponding saturated compounds, may reinforce “chemical insignificance” by blurring any remaining variation in recognition cues.     

Factors affecting simultaneous nitrification and denitrification in an SBBR treating domestic wastewater

An aerobic sequencing batch biofilm reactor (SBBR) packed with Bauer rings was used to treat real domestic wastewater for simultaneous nitrification and denitrification. The SBBR is advantageous for creating an anoxic condition, and the biofilm can absorb and store carbon for good nitrification and denitrification. An average concentration of oxygen ranging from 0.8 to 4.0 mg/L was proved very efficient for nitrification and denitrification. Volumetric loads of TN dropped dramatically and effluent TN concentration increased quickly when the concentration of average dissolved oxygen was more than 4.0 mg/L. The efficiency of simultaneous nitrification and denitrification (SND) increased with increasing thickness of the biofilm. The influent concentration hardly affected the TN removal efficiency, but the effluent TN increased with increasing influent concentration. It is suggested that a subsequence for denitrification be added or influent amount be decreased to meet effluent quality requirements. At optimum operating parameters, the TN removal efficiency of 74%–82% could be achieved.     

Fitness costs of an immune response in the house martin (<Emphasis Type="Italic">Delichon urbica</Emphasis>)

Immune responses constitute a major way for hosts to defend themselves against parasites. Because hosts do not habitually produce strong responses all the time, immune responses might be costly to produce or maintain. We tested experimentally if the production of a response to a challenge with a novel antigen resulted in a cost in terms of fitness using the highly colonial house martin Delichon urbica as a model system. We injected adult breeding birds during laying of the first clutch with either Newcastle disease virus (NDV) or a control injection, and the clutch was subsequently removed to induce relaying. NDV stimulates the non-specific immune system, causing production of antibodies during a period of more than 2 weeks. Accordingly, we found an increase in leukocyte counts in experimental birds compared to controls. Experimental treatment reduced the frequency of re-laying, caused a delay in timing of relaying and a reduction in brood size. Quality of nestlings in terms of body size, body mass and T-cell-mediated immune response did not differ significantly between treatments. Overall, seasonal reproductive success differed significantly between treatments, showing that the production of an immune response by adult birds is costly in terms of future fecundity.     

A nonparametric procedure for analyzing repeated measures of spatially correlated data

Many agricultural, biological, and environmental studies involve detecting temporal changes of a response variable, based on data observed at sampling sites in a spatial region and repeatedly over several time points. That is, data are repeated measures over time and are potentially correlated across space. The traditional repeated-measures analysis allows for time dependence but assumes that the observations at different sampling sites are mutually independent, which may not be suitable for field data that are correlated across space. In this paper, a nonparametric large-sample inference procedure is developed to assess the time effects while accounting for the spatial dependence using a block bootstrap. For illustration, the methodology is applied to describe the population changes of root-lesion nematodes over time in a production field in Wisconsin.