Luca Canova

Sexual Dimorphism in Melanin Pigmentation, Feather Coloration and Its Heritability in the Barn Swallow (Hirundo rustica)

Melanin is the main pigment in animal coloration and considerable variation in the concentrations of the two melanin forms (pheo- and eumlanin) in pigmented tissues exists among populations and individuals. Melanin-based coloration is receiving increasing attention particularly in socio-sexual communication contexts because the melanocortin system has been hypothesized to provide a mechanistic basis for covariation between coloration and fitness traits. However, with few notable exceptions, little detailed information is available on inter-individual and inter-population variation in melanin pigmentation and on its environmental, genetic and ontogenetic components. Here, we investigate melanin-based coloration in an Italian population of a passerine bird, the barn swallow (Hirundo rustica rustica), its sex- and age-related variation, and heritability. The concentrations of eu- and pheomelanin in the throat (brown) and belly (white-to-brownish) feathers differed between sexes but not according to age. The relative concentration of either melanin (Pheo:Eu) differed between sexes in throat but not in belly feathers, and the concentrations in males compared to females were larger in belly than in throat feathers. There were weak correlations between the concentrations of melanins within as well as among plumage regions. Coloration of belly feathers was predicted by the concentration of both melanins whereas coloration of throat feathers was only predicted by pheomelanin in females. In addition, Pheo:Eu predicted coloration of throat feathers in females and that of belly feathers in males. Finally, we found high heritability of color of throat feathers. Melanization was found to differ from that recorded in Hirundo rustica rustica from Scotland or from H. r. erythrogaster from North America. Hence, present results show that pigmentation strategies vary in a complex manner according to sex and plumage region, and also among geographical populations, potentially reflecting adaptation to different natural and sexual selection regimes, and that some coloration components seem to be highly heritable.

Reproduction and population density affect humoral immunity in bank voles under field experimental conditions

Abstract Density dependence is a common feature in the dynamics of animal populations. Availability of food resources critical to immunity is likely to be one of the mechanisms mediating the effect of population density on individual fitness. The ability to mount an immune response to an antigen is also affected by levels of immunosuppressive hormones associated with reproduction or mediating the response to ecological and social stress. We assessed variation in condition and intensity of humoral immune response to a T-cell-dependent antigen in bank voles (Clethrionomys glareolus) by experimentally altering population density before immunisation. Consistent with our prediction, males had lower humoral immunocompetence in the breeding than in the non-breeding season. Contrary to our expectation, males did not show enhanced immunocompetence and females showed depressed humoral immune response under experimentally lowered population density. Variation of immune response in relation to population density depended on sex, with females but not males showing lower immune response under experimentally reduced density. We conclude that humoral immunity of bank voles was affected by reproduction and social environment rather than by population density.

Foraging, feeding and time‐activity niches of eight species of breeding seabirds in the coastal wetlands of the Adriatic Sea

Abstract We studied the three main components of trophic niches in the richest assemblages of breeding gulls and terns in Italy (8 species) that typify the communities of the large deltas of Mediterranean Europe. Each species feeds mainly on fish, except for the gull‐billed tern that feeds essentially on terrestrial vertebrates. Other prey contributed slightly to the energy balance, although small invertebrates prevailed numerically in the diets of the Mediterranean and black‐headed gulls. The seabirds cumulatively consumed a variety of fish, in frequencies that closely reflected the latters abundance. Selection of fish species by each seabird were strongly determined by the birds foraging habitat, and not by any preference for particular prey. The size of the prey was related to the size of the seabird. The diurnal rhythms of feeding activity were uniform, and the time component did not contribute to niche segregation. Dietary patterns suggest that within the overall space of their niches, the seabirds...

Viability Is Associated with Melanin-Based Coloration in the Barn Swallow (Hirundo rustica)

Pigmentation of body surface in animals can have multiple determinants and accomplish diverse functions. Eumelanin and pheomelanin are the main animal pigments, being responsible of yellow, brownish-red and black hues, and have partly common biosynthetic pathways. Many populations of vertebrates show individual variation in melanism, putatively with large heritable component. Genes responsible for eu- or pheomelanogenesis have pleiotropic but contrasting effects on life-history traits, explaining the patterns of covariation observed between melanization and physiology (e.g. immunity and stress response), sexual behavior and other characters in diverse taxa. Yet, very few studies in the wild have investigated if eu- and pheomelanization predict major fitness traits like viability or fecundity. In this correlative study, by contrasting adult barn swallows (Hirundo rustica) matched for age, sex, breeding site, and year and date of sampling, we show that males but not females that survived until the next year had paler, relatively more eu- than pheomelanic pigmentation of ventral body feathers. Better performance of individuals that allocate relatively more to eumelanogenesis was expected based on previous evidence on covariation between eumelanic pigmentation and specific traits related to immunity and susceptibility to stress. However, together with the evidence of no covariation between viability and melanization among females, this finding raises the question of the mechanisms that maintain variation in genes for melanogenesis. We discuss the possibility that eu- and pheomelanization are under contrasting viability and sexual selection, as suggested by larger breeding and sperm competition success of darker males from other barn swallow subspecies.

Feeding habits of Triturus vulgaris, T. cristatus and T. alpestris (Amphibia, Urodela) in the northern apennines (Italy)

Abstract Although the aquatic cycle of some newts spans the entire year with various life stages, newt diet had only been studied during single phases of the cycle. We analyzed the diet of the warty newt, alpine newt and smooth newt, living syntopically in the same pond, during all the life stages (larvae, juveniles, neotenics, adults) and throughout one entire annual cycle. Food samples were obtained by stomach‐flushing 876 newts. The newts were found to exploit a large variety of prey, mainly aquatic insects (imagoes and larvae), and other aquatic invertebrates, together with small numbers of terrestrial Arthropoda that had fallen into the pond. The dietary similarity among species and life stages was high. Although newts were able to exploit most of the range of available prey sizes, on average they selected prey size in relation to their own weight. The frequency of capture of some prey differed significantly between day and night. The six most frequent prey, equivalent to 83% of prey items, were capt...

Colony site selection by eight species of gulls and terns breeding in the ≪Valli di Comacchio≫ (Italy)

Abstract Former studies of nesting habitat selection by seabirds have been limited to single species, or two‐species assemblages, and have not assessed the influence of interspecific interactions. We studied the nest distribution of eight species of seabirds, breeding in mixed colonies, in order to investigate the influence of any specific preferences for foraging and nesting habitats, of habitat availability, and of social interactions. The distribution of the foraging zones did not influence colony location. The topography of the islets (mainly their size) influenced the distribution of the colonies in only two species (yellow‐legged gulls and little terns). Each species significantly preferred certain types of nesting habitats for its nest site, differing in cover and type of vegetation. Yellow‐legged gulls and Little terns acted as ≪monospecific colonialists≫, slender‐billed gulls and black‐headed gulls tend to be ≪plurispecific colonialists≫, and Mediterranean gulls, sandwich terns, gull‐billed terns...

Residence in water by the newts Triturus vulgaris, T cristatus and T. alpestris in a pond in northern Italy

The annual cycle of residence in water differed considerably among the three syntopic newts Triturus vulgaris, T cristatus and T. alpestris at a pond in northern Italy. T. vulgaris were resident in water for only short periods, which were used exclusively for reproduction. Adult T cristatus were present in the water for 3-4 months after reproduction, and regained weight during autumn. T. alpestris were present throughout the year; branchiate juveniles and neotenics were more abundant than adults.

Resource partitioning between the bank vole Clethrionomys glareolus and the wood mouse Apodemus sylvaticus in woodland habitats

Abstract Spatial and food resource use, and activity time were studied in syntopical populations of bank vole Clethrionomys glareolus and wood mouse Apodemus sylvaticus in woodland habitats. In every habitat, the two species selected different microhabitats; the abundance of thin vegetation and size and dispersion of overstorey trees were generally the variables that segregated the microhabitat, but no constant preferences were shown by the two species in every habitat. Time activity rhythms were significantly different, with the bank vole showing a multi‐phase diel activity, while the wood mouse was strictly nocturnal. However, the diets of the two species overlapped almost completely; the wood mouse showed a higher preference for a seed‐formed diet, while the bank vole showed both folivore and granivore feeding habits. The differences in microhabitat selection and activity time rhythms suggested a shifting in resource use due to competition between the two species; the absence of significant differences...

Influence of snow cover on prey selection by Long-eared Owls Asio otus

During winter the composition of the diet of the Long-eared Owls present at a roost varied in relation to the ground snow cover; birds and riparial rodents increased when ground cover was complete. A comparison between diet and prey availability (assessed by trapping) showed that small mammal species were mostly preyed upon in relation to their abundance; the scarce presence of Insectivores in the diet is apparently due to their reduced seasonal availability. Long-eared Owls behaved as adaptable predators; their dietary specialization in Northern Europe may be due to the great abundance of Microtinae at high latitude.

Immune and Stress Responses Covary with Melanin-Based Coloration in the Barn Swallow

Eumelanin and pheomelanin are the main endogenous pigments in animals and melanin-based coloration has multiple functions. Melanization is associated with major life-history traits, including immune and stress response, possibly because of pleiotropic effects of genes that control melanogenesis. The net effects on pheo- versus eumelanization and other life-history traits may depend on the antagonistic effects of the genes that trigger the biosynthesis of either melanin form. Covariation between melanin-based pigmentation and fitness traits enforced by pleiotropic genes has major evolutionary implications particularly for socio-sexual communication. However, evidence from non-model organisms in the wild is limited to very few species. Here, we tested the hypothesis that melanin-based coloration of barn swallow (Hirundo rustica) throat and belly feathers covaries with acquired immunity and activation of the hypothalamic–pituitary–adrenal (HPA) axis, as gauged by corticosterone plasma levels. Individuals of both sexes with darker brownish belly feathers had weaker humoral immune response, while darker males had higher circulating corticosterone levels only when parental workload was experimentally reduced. Because color of belly feathers depends on both eu- and pheomelanin, and its darkness decreases with an increase in the concentration of eu- relative to pheomelanin, these results are consistent with our expectation that relatively more eu- than pheomelanized individuals have better immune response and smaller activation of the HPA-axis. Covariation of immune and stress response arose for belly but not throat feather color, suggesting that any function of color as a signal of individual quality or of alternative life-history strategies depends on plumage region.