Extra-pair paternity and antiparasitic defence

Background:Extra-pair paternity(EPP)in birds provides benefits in terms of more offspring,and characteristics for maintenance of this behaviour have been the subject of investigation.Microorganisms are known to be transmitted during mating,especially when mating with multiple partners,and factors reducing this cost of multiple mating are expected.Further,plumage brightness and colour intensity have been shown to be important traits to benefits from multiple mating as predicted by sexual selection.The aim of this study was to investigate the relationship between the rate of extra-pair paternity and the relative size of the uropygial gland at the interspecific level,as the uropygial gland is an exocrine gland hypothesized to produce antiparasitic substances and further identified to affect plumage brightness.Because of the expected benefits of large uropygial gland in scenarios of sexual selection,we predicted a positive correlation with EPP.Methods:We collected information from the literature of uropygial gland size and frequency of extra-pair paternity of 60 avian species of different families and explored the predicted positive correlation between them.We did so with means of comparative analyses that considered phylogenetic relationship as random factor and included body mass as covariate.We used Markov chain Monte Carlo generalized linear mixed models that were weighted by number of nests used to estimate extra-pair paternity.Results:We detected a positive relationship between level of extra-pair paternity and uropygial gland size at an interspecific level.This finding is consistent with the prediction.Conclusions:We discuss the importance of this result in scenarios of sexual selection and argue that the detected relationship may have arisen by utilizing antiparasitic secretions through secondary sexual characters indicating parasite resistance.

Context-dependent insect predation pressure on an avian ectoparasite

Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host–parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.

Functional groups of Sahelian trees in a semiarid agroforestry system of Senegal

Aims Addressing plant responses to water stress is critical to understand the structure of plant communities in water-limited environments and to forecast their resilience to future changes in climate.In a semiarid agroforestry system in the Sahelian savannah of Leona(Senegal),we selected nine common tree species and explored their stress-resistance mechanisms.These species represent a variety of life forms and are of high regional socio-economic importance.We hypothesized that different species would show different suites of traits to cope with water stress and expected to identify functional groups differing in strategies to withstand water shortage.Methods Along a dry and a wet season,we monitored four traits reflecting above-and below-ground strategies of resource acquisition such as predawn leaf water potential(ψpd),specific leaf area(SLA),leaf thickness and leaf area index(LAI).We also measured two mor-phological traits:trunk diameter and tree height.LAI andψpd were measured six times during the dry and rainy seasons,and the other traits were measured once.Important Findings We identified two functional classes subdivided into two func-tional groups of each class.The first class included deciduous and semi-deciduous species that generally had large SLA,low leaf thickness and small-to-intermediate inter-seasonal varia-tions inψpd.The second class included evergreen species of two functional groups that differ in SLA,leaf thickness and the mag-nitude of inter-seasonal variations ofψpd throughout the year.The four functional groups identified in this study represent plant strategies differing in their response to changing environmental conditions.