Giorgio Malacarne

Yolk testosterone levels and dietary carotenoids influence growth and immunity of grey partridge chicks

Early maternal effects in the form of substances accumulated in the egg, such as carotenoids and hormones, can be physiologically relevant for a good development of offspring. It has been found in different species that testosterone (T) can be beneficial to offspring by increasing growth rate, but detrimental by reducing immunocompetence and increasing oxidative stress. Carotenoids on the other hand are suggested to be beneficial because they can counteract the oxidative stress and the immune-depressive effect of T. In this study we analyzed the effect of prenatal T exposure in the grey partridge. We injected eggs with three doses of T (high, intermediate, and physiological). After hatching, chicks exposed to a prenatal high dose of T were fed with two diets (rich or poor) differing in beta-carotene content. We found a significant effect of T on both chick growth and cell-mediated immunity, with high T doses resulting in detrimental effects while low doses were beneficial. Detrimental effects of the high dose of T on immunity were mitigated by beta-carotene consumed in the diet. The differences between groups were observed in the early period of life (age 10 days for mass, and age 10 and 21 days for immunity), and disappeared in the following period, and up to 1 and 2 years later. Overall, our observations show that T in the egg is not detrimental but beneficial, and that negative effects are found only at supraphysiological concentrations. The negative effects of T on immunity could be balanced if chicks could consume a diet rich in beta-carotene.

Effects of β-carotene supplementation on chick growth, immune status and behaviour in the grey partridge, Perdix perdix

Carotenoids are important for various functions during chick development. Since these pigments cannot be synthesized, they can be considered limited resources that the mother optimally allocates between herself and her offspring (maternal effect). Some studies have examined the effects of carotenoids on growth and immune function but little is known about their role in behaviour. In this study of the grey partridge, we conducted two supplementation experiments: (1) laying females were fed with beta-carotene enriched or impoverished diets; (2) chicks were fed directly with beta-carotene enriched or impoverished diets. We then evaluated the effects of this carotenoid on chick growth, immunocompetence and anti-predator behaviour (reactions to a raptor model). In the first experiment, the beta-carotene enriched diet given to mothers did not cause any difference in chick physiology. In the second experiment, beta-carotene supplementation of chicks had a significant beneficial effect on their growth and immune response, although their behavioural reactions did not differ in relation to the diet. Therefore, beta-carotene supplementation had beneficial effects on growth and immunocompetence only when directly supplied to chicks. The beneficial effect reported in other species for begging or pecking behaviours was not confirmed for the anti-predator behaviour of grey partridge chicks.

Response of benthic invertebrate assemblages to varying drought conditions in the Po river (NW Italy)

In the rivers of northern Italy, the presence of water is typically continuous all year long, although in the last five decades there has been a conspicuous increase in drought periods, mainly caused by human impacts and climate change. The aim of this study was to assess the impact of the length of the drought periods on macroinvertebrate assemblages. We collected invertebrates in four reaches of the Po river, characterised by different periods of absence of surface water. We found significant differences among the stations in invertebrate abundance and taxa richness, with a decrease in the more drought‐affected stream reaches. Collector‐gatherers significantly increased as the drought period lengthened, while the opposite occurred for scrapers and shredders. The areas with a discontinuous presence of water were mainly colonised by small, fast‐growing, plurivoltine organisms. A main result of our study is that only a few taxa appear to be able to survive in reaches with intermittent flow, underlining the great ecological difference between perennial and naturally intermittent streams. Our results suggest that the recent increase of droughts will likely cause an impoverishment of benthic communities in prealpine rivers.

Delayed maturation in passerine birds: an examination of plumage effects and some indications of a related effect in song

In some passerine species, 1st-year males are clearly distinguishable from adults; they have a different, typically dull, plumage. At least 15 explanations of the delayed plumage maturation of 1st-year males have been proposed. In the present study, we investigate if there is a similar widespread phenomenon regarding song, i.e. if males of some species have a distinct song in their first breeding season (delayed song maturation). A comparative analysis of 137 West Palearctic passerines showed that detailed data on how the song changes with age in breeding males is available for only a few species. Moreover, it is difficult to assess whether the song features continue to change considerably year after year or if, as we suggest, the main difference is between 1st-year vs 2-years and older males. We found that species with a suggested delay in song maturation were mostly those with delayed plumage maturation; a preliminary comparison suggests that these species have greater longevity. We also discuss the evolutionary significance of delayed song and plumage maturation and we suggest some possible directions for future research on these phenomenona.

Variations of body mass and immune function in response to food unpredictability in magpies

The effects of food unpredictability on body mass regulation have been studied in a few species of birds. It has been shown that small passerines can counteract variability of food resources by actively regulating their body reserves through an increase of mass. However, it was recently found that, with unpredictable food availability, quails and hooded crows do not adopt an adaptive fattening strategy but lose mass. At present, little is known about the effects of food unpredictability on other body parameters, such as immune functions and blood variables. In this study, we analysed the responses to food abundance and unpredictability by performing two experiments of controlled food administration in the magpie, a passerine intermediate in size between small passerines and crows. Body mass, leukocyte abundance, haematocrit, spleen mass and immune reaction to phytohaemagglutinin (PHA) were assessed during a 15-d period. In the first experiment, the food release was predictable (same amount each day), but the quantity of food varied in four groups of birds. Low food levels induced a greater decrease in mass. In the second experiment, the same average quantity of food was supplied, but with predictable or unpredictable (random) schedules. As previously reported for crows and quails, magpies did not adaptively increase their mass in response to food unpredictability. Furthermore, there was a decrease of haematocrit and immune response to PHA. It appears that a body mass decrease in the magpie can be induced by a reduction of either food abundance or food predictability, and it is accompanied by a worsening of health state.

Is the song of black redstart males an honest signal of status

We analyzed song differences between adults and subadults of the Black Redstart (Phoeni-curus ochruros) breeding in the Western Alps and found differences both among individuals and between the two age categories. The song parameters utilized for differentiation of individuals were different from those used for adults and subadults. A playback experiment simulating territory intrusion revealed that adults reacted more quickly to the broadcast of an adult song, whereas the reverse was found for subadults. Females did not react to the playback. The results of this study do not support the hypothesis that subadult males mimic female or juvenile behavior (Female or Juvenile Mimicry Hypothesis) nor the Non-adaptive Hypothesis which predicts an equal response to adult and subadult intrusions. We suggest that subadult Black Redstarts honestly signal their status with both visual and acoustic cues. The Status Signaling and the Polyterritorial Deception Hypotheses both seem to explain the data collected for this species.

Bill colour and body condition in the Moorhen Gallinula chloropus

Capsule We found yellow to be an honest signal of health status.

Reproduction of the pallid swift (Apus pallidus) in relation to weather and aerial insect abundance

Abstract The reproductive activity of swifts is affected by seasonal fluc tuations of aerial insects which are largely unpredictable, depending day by day on climatic conditions. In this work we investigated whether the parental food provisioning is influenced by hourly fluc tuations of insect abundance or if adults maintain a constant feeding rate. We found during each day that the amount of food delivered to nestlings was not related to hourly insect availability. We also verified that daily insect abundance is related to daily minimum and maximum temperature (38% of variability explained) and is unrelated to rainfall. Finally we compared, during different reproductive seasons, the aerial insect abundance and the biomass (eggs and nestlings) produced by adult swifts. Insect abundance was constantly high from June to September and did not precisely match the main period of biomass production (first clutch), which reached a maximum in July.

Influence of mating preferences on yolk testosterone in the grey partridge

In precocial bird species, the eggs constitute most of the maternal investment because parents do not feed the young after they hatch. Maternal testosterone in egg yolk influences the embryo’s and chick’s development. Females deposit testosterone in the eggs as a response to the environment experienced during the laying period, including the quality of their mate. To assess the relevance of the female’ sm ate selection on egg characteristics in the grey partridge, Perdix perdix, we tested breeding females in a choice trial where they were allowed to choose between two males. After the choice trials, females were mated either with their preferred male (P group) or with the nonpreferred one (NP group). Although eggs laid by females of the two groups did not differ significantly in mass, females of the P group laid eggs with a higher yolk testosterone concentration than females of the NP group. This study agrees with previous work pointing out that partner attractiveness may play an important role in the transfer of maternally derived egg components. 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. Maternal effects imply that the environment and the phenotype of the mother affect the progeny’s phenotype (Mousseau & Fox 1998). In oviparous vertebrates, all the resources needed by the embryo to develop must be present in the egg laid by the female. After the eggs are laid, no further adjustments to their components

Feeding of Perla grandis nymphs (Plecoptera: Perlidae) in an Apennine first order stream (Rio Berga, NW Italy)

Abstract Feeding habits of Perla grandis (Rambur) nymphs have been investigated in the Rio Berga, an Apenninic stream of Northwestern Italy. In this study, we analysed gut contents of 50 nymphs of this species, with the aim to investigate feeding preferences. Nymphs were collected from a single riffle, of which benthic coenosis was also determined. We detected a change in the diet during ontogenesis, with small instars feeding mainly on detritus and large instars strictly carnivorous. We also detected the existence of an evident trophic selection: diet was almost entirely dominated by Chironomidae, independently from their availability on the substratum. This finding is discussed on the basis of ecological and ethological considerations.