A multiplex set of microsatellite markers for the scarlet rosefinch (Carpodacus erythrinus)

Cardueline finches have become important models in studies of sexual selection and evolution of carotenoid‐based ornamentation. Here, we describe eight new polymorphic microsatellites isolated from the Scarlet rosefinch (Carpodacus erythrinus) and four from the House finch (Carpodacus mexicanus). Together with the cross‐species amplification of additional loci, originally published for two species of songbirds, we optimized a multiplex panel for C. erythrinus allowing genotyping of 22 polymorphic loci. Number of alleles and heterozygosity per locus in a sample of 34 individuals ranged from three to 38 and from 0.27 to 0.94, respectively.     

Influence of temporal fluctuations in seed abundance on the foraging behaviour of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

The simultaneous study of the temporal dynamics of foraging behaviour, diet and seed abundance is essential to assess the way in which resources affect the behaviour and ecology of harvester ants. Here, we evaluate how fluctuations in grass seed abundance during three consecutive growing seasons influenced the foraging behaviour and diet of the harvester ants Pogonomyrmex rastratus, P. mendozanus and P. inermis in the central Monte desert, Argentina. Seed abundance of the most consumed grasses varied greatly through ant activity season, and ants altered their foraging behaviour in response to those changes. Foragers spent more time travelling and searching for food, and their foraging trips took longer during the low seed availability season. Foraging distance was very similar among species and, contrary to our expectations, did not vary between seasons. Foraging success of P. rastratus and P. inermis increased during the high availability season. This matched the seasonal pattern of foraging activity, suggesting that colonies may detect seed abundance and regulate their foraging effort with the rate of forager success. Although grass seeds were the main item in the diet of the three species, P. mendozanus, and to a lesser extent P. rastratus, turned more generalist when grass seeds were scarce. In contrast, P. inermis showed a very narrow diet breadth, only harvesting grass seeds in both seasons. Our results indicate the relevance of seed availability on foraging behaviour of harvester ants, which should be taken into account when predicting and evaluating the effect of ants on seed resources as well as numerical responses of harvester ant populations to the temporal and spatial variations in grass seed abundance.     

Biometric sex discrimination is unreliable when sexual dimorphism varies within and between years: an example in Eurasian Oystercatchers Haematopus ostralegus

Molecular sexing of birds has been possible for over a decade, but for practical reasons many studies still use biometric data for sex discrimination. In some species, the sexes are easy to distinguish but sexual dimorphism is often more subtle, requiring the use of statistical analyses of biometric measurements to discriminate sexes. These models are usually parameterized and validated using data from a limited number of sites and years. However, the resulting discriminant functions are often applied to other populations and periods. A crucial, but usually untested, assumption is that sexual dimorphism does not vary in time and space. Here we illustrate the consequences of violation of this assumption in Eurasian Oystercatchers Haematopus ostralegus , a species for which most studies have relied on biometric sexing. Using biometric data from captures of known-sex birds, we show that sexual dimorphism varied substantially in time and even reversed in some months and years. Furthermore, some biometric traits used in sexing changed gradually over time, causing a reduction in sexual dimorphism. We show that the consequences of this variation on sex discrimination in Oystercatchers are subtle and easily overlooked, but can result in inaccurate and strongly male- or female-biased sex-ratio estimates. We recommend that biometric sexing should be avoided in Oystercatchers unless specific calibration for each month, year and area is carried out. This recommendation also applies to other species where biometric traits may depend on environmental conditions. We argue that this condition might apply to many bird species and therefore advise caution when interpreting results based on biometric sex discrimination.     

Behavioural flexibility does not prevent numerical declines of harvester ants under intense livestock grazing

1. Human‐induced rapid environmental change may decrease food resources and create unfavourable conditions for native species. Organisms showing a flexible foraging behaviour can exploit novel or alternative foods and are more likely to persist, whereas less flexible organisms might suffer starvation and numerical reductions. 2. This study assessed whether declines in the quality and availability of seeds prompted by grazing provoke behavioural and numerical responses in Pogonomyrmex mendozanus ants, and aimed to test whether behavioural flexibility buffers habitat degradation and prevents numerical declines. 3. Heavy grazing caused seed reductions, especially of the highly consumed and preferred grass seeds, and triggered two kinds of ant responses. Ants expanded their diet by incorporating a greater proportion of non‐seed items, and they reduced foraging activity. As a consequence, the rate of food intake per colony lessened, particularly that of carbohydrate‐rich seeds like grass seeds. Colony density under heavy grazing also fell. 4. Habitat degradation triggered a cascade of mechanisms that starts with a decrease in the seed resources and continues with changes in ant behaviour. However, behavioural responses were insufficient to prevent ant numerical declines. The results of this study suggest that the reduction in the colony density under habitat degradation was provoked by ant nutritional deficit and starvation, and predict a deterioration in body condition, colony performance and reproduction of ants, which deserve further assessment.     

MHC‐dependent survival in a wild population: evidence for hidden genetic benefits gained through extra‐pair fertilizations

Females should prefer to be fertilized by males that increase the genetic quality of their offspring. In vertebrates, genes of the major histocompatibility complex (MHC) play a key role in the acquired immune response and have been shown to affect mating preferences. They are therefore important candidates for the link between mate choice and indirect genetic benefits. Higher MHC diversity may be advantageous because this allows a wider range of pathogens to be detected and combated. Furthermore, individuals harbouring rare MHC alleles might better resist pathogen variants that have evolved to evade common MHC alleles. In the Seychelles warbler, females paired with low MHC‐diversity males elevate the MHC diversity of their offspring to levels comparable to the population mean by gaining extra‐pair fertilizations. Here, we investigate whether increased MHC diversity results in higher life expectancy and whether there are any additional benefits of extra‐pair fertilizations. Our 10‐year study found a positive association between MHC diversity and juvenile survival, but no additional survival advantage of extra‐pair fertilizations. In addition, offspring with a specific allele (Ase‐ua4) had a fivefold longer life expectancy than offspring without this allele. Consequently, the interacting effects of sexual selection and pathogen‐mediated viability selection appear to be important for maintaining MHC variation in the Seychelles warbler. Our study supports the prediction that MHC‐dependent extra‐pair fertilizations result in genetic benefits for offspring in natural populations. However, such genetic benefits might be hidden and not necessarily apparent in the widely used fitness comparison of extra‐ and within‐pair offspring.     

Relationship between histology,development and tumorigenesis of mammary gland in female rat

The mammary gland is a dynamic organ that undergoes structural and functional changes associated with growth, reproduction, and post-menopausal regression. The postnatal transformations of the epithelium and stromal cells of the mammary gland may contribute to its susceptibility to carcinogenesis. The increased cancer incidence in mammary glands of humans and similarly of rodents in association with their development is believed to be partly explained by proliferative activity together with lesser degree of differentiation, but it is not completely understood how the virgin gland retains its higher susceptibility to carcinogenesis. During its developmental cycle, the mammary gland displays many of the properties associated with breast cancer. An early first full-term pregnancy may have a protective effect. Rodent models are useful for investigating potential breast carcinogens. The purpose of this review is to help recognizing histological appearance of the epithelium and the stroma of the normal mammary gland in rats, and throughout its development in relation to tumorigenic potential.     

Influence of temporal fluctuations in seed abundance on the diet of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

Harvester ants usually go through temporal fluctuations in environmental seed abundance and composition which could influence their behaviour and ecology. The aim of this study was to evaluate how these fluctuations influence the diet of Pogonomyrmex rastratus, P. pronotalis and P. inermis (Hymenoptera, Formicidae) in the central Monte desert during three consecutive growing seasons. Although seeds were the main item in the diet, these ants turned more generalist when seed abundance of the most consumed species (grasses Aristida spp., Trichloris crinita, Pappophorum spp., Digitaria californica and Stipa ichu) was low. Accordingly, diversity of items in the diet decreased with seed abundance in a logarithmical fashion, showing higher foraging efficiency for seeds at higher seed abundance. Seed diversity, however, was not related to seed abundance as ants always included several species in their diet, with alternating prevalence. The proportion of the most consumed species increased logarithmically in the diet of P. rastratus and P. pronotalis along with their abundance in the environment probably as a consequence of diet switching (from forb and shrub seeds to grass seeds) and by an increase in foraging efficiency at higher seed densities. In contrast, foraging activity of P. inermis was very low at low seed abundance and its diet included only the five grasses. Among the most consumed species, proportion in the diet was not associated with relative abundance in the environment. Aristida spp., Pappophorum spp. and D. californica were overall highly selected. However, the flexibility in the diet of P. pronotalis and P. rastratus and the low foraging activity of P. inermis during periods of low resource abundance could attenuate potential top‐down effects in the central Monte desert. This study shows that bottom‐up effects are important in ant‐seed interactions and should be considered when predicting and evaluating ants' effects on seed resources.     

Extra‐pair fertilizations contribute to selection on secondary male ornamentation in a socially monogamous passerine

Despite considerable research effort, it remains unclear whether extra‐pair fertilizations (EPF) drive the evolution of male secondary ornamentation in socially monogamous systems. In this study, we test the hypothesis that EPF contribute to the evolution or maintenance of male feather ornamentation in a sexually dichromatic passerine, the Scarlet Rosefinch, Carpodacus erythrinus. We show that the colouration of ornamental breast feathers is a good predictor of basic sources of variation in male annual reproductive output in rosefinches and that the annual realized reproductive success of males is positively associated with measures of ornamental colouration only when gains and losses because of EPF are considered. The results indicate that EPF in rosefinches may rely on absolute (good genes) rather than self referential (genetic complementarity) criteria of mate choice. Our study corroborates the potentially important role of EPF in the evolution and/or maintenance of elaborate male ornaments in socially monogamous taxa.     

Few parasites,and no evidence for Wolbachia infections,in a freshwater ostracod inhabiting temporary ponds

Biological systems with asexual reproduction have often attracted research on parasites and host immune defence, because parasites are expected to be better able to exploit genetically less diverse populations. In addition, maternally inherited parasitic microorganisms such as Wolbachia can directly alter the reproductive systems of their hosts and induce parthenogenesis. In the freshwater ostracod Eucypris virens, both sexual and asexual reproduction is known, and we speculated that parasite pressures might help to explain their co‐existence. This species complex inhabits shallow, often eutrophic temporary water bodies, conditions that should provide ample opportunities for parasite infections. We surveyed natural populations of E. virens throughout its Europe‐wide range for natural parasites, and particularly tested for the presence of intracellular Wolbachia bacteria. Surprisingly, the results indicate that very few E. virens populations support parasite infections. We also found no evidence for the presence of Wolbachia in the populations screened. The results therefore show that parasitic infections do not play a role in the maintenance of sex in this system. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 207–216.