Biomedical subjects

Raphaël Arlettaz

Publications and source records attributed to Raphaël Arlettaz.

4 recordsLinked to original sources

PubMed2007

Echolocation and passive listening by foraging mouse-eared bats Myotis myotis and M. blythii.

The two sibling mouse-eared bats, Myotis myotis and M. blythii, cope with similar orientation tasks, but separate their trophic niche by hunting in species-specific foraging microhabitats. Previous work has shown that both species rely largely on passive listening to detect and glean prey from substrates, and studies on other bat species have suggested that echolocation is ;switched off' during passive listening. We tested the hypothesis that mouse-eared bats continuously emit echolocation calls while approaching prey. Echolocation may be needed for orientation while simultaneously listening for prey. Because these sibling species forage in different microhabitats and eat different prey, we also compared their echolocation behaviour and related it to their ecology. Both species used echolocation throughout prey approach, corroborating a functional role for echolocation during gleaning. Captive bats of both species emitted similar orientation calls, and pulse rate increased during prey approach. Between the search to approach phases, call amplitude showed a sudden, dramatic drop and bats adopted ;whispering echolocation' by emitting weak calls. Whispering echolocation may reduce the risks of masking prey-generated sounds during passive listening, the mouse-eared bats' main detection tactic; it may also avoid alerting ultrasound-sensitive prey. In several cases M. myotis emitted a loud buzz made of 2-18 components when landing. We hypothesise that the buzz, absent in M. blythii at least when gleaning from the same substrate, is used to assess the distance from ground and refine the landing manoeuvre. Our findings have implications for niche separation between sibling species of echolocating bats, support a role for echolocation during passive listening and suggest a functional role for buzzes in landing control.

Animals↗

PubMed2005

A noninvasive technique to evaluate human-generated stress in the black grouse.

The continuous development of tourism and related leisure activities is exerting an increasingly intense pressure on wildlife. In this study, a novel noninvasive method for measuring stress in the black grouse, an endangered, emblematic species of European ecosystems that is currently declining in several parts of its European range, is tested and physiologically validated. A radiometabolism study and an ACTH challenge test were performed on four captive black grouse (two of each sex) in order to get basic information about the metabolism and excretion of corticosterone and to find an appropriate enzyme-immunoassay (EIA) to measure its metabolites in the feces. Peak radioactivity in the droppings was detected within 1 to 2 hours. Injected (3)H-corticosterone was excreted as polar metabolites and by itself was almost absent. A cortisone-EIA was chosen from among seven tested EIAs for different groups of glucocorticoid metabolites, because it cross-reacted with some of the formed metabolites and best reflected the increase of excreted corticosterone metabolites, after the ACTH challenge test. Concentrations of the metabolites from fecal samples collected from snow burrows of free-ranging black grouse were within the same range as in captive birds. The noninvasive method described may be appropriate for evaluating the stress faced by free-living black grouse populations in the wild, particularly in mountain ecosystems where human disturbance, especially by winter sports, is of increasing conservation concern.

Adrenocorticotropic Hormone↗

PubMed2004

Causal mechanisms underlying host specificity in bat ectoparasites.

In parasites, host specificity may result either from restricted dispersal capacity or from fixed coevolutionary host-parasite adaptations. Knowledge of those proximal mechanisms leading to particular host specificity is fundamental to understand host-parasite interactions and potential coevolution of parasites and hosts. The relative importance of these two mechanisms was quantified through infection and cross-infection experiments using mites and bats as a model. Monospecific pools of parasitic mites (Spinturnix myoti and S. andegavinus) were subjected either to individual bats belonging to their traditional, native bat host species, or to another substitute host species within the same bat genus (Myotis). The two parasite species reacted differently to these treatments. S. myoti exhibited a clear preference for, and had a higher fitness on, its native host, Myotis myotis. In contrast, S. andegavinus showed no host choice, although its fitness was higher on its native host M. daubentoni. The causal mechanisms mediating host specificity can apparently differ within closely related host-parasite systems.

Animals↗

PubMed2003

Modeling habitat suitability for complex species distributions by environmental-distance geometric mean.

This paper presents a new habitat suitability modeling method whose main properties are as follows: (1) It is based on the density of observation points in the environmental space, which enables it to fit complex distributions (e.g. nongaussian, bimodal, asymmetrical, etc.). (2) This density is modeled by computing the geometric mean to all observation points, which we show to be a good trade-off between goodness of fit and prediction power. (3) It does not need any absence information, which is generally difficult to collect and of dubious reliability. (4) The environmental space is represented either by an expert-selection of standardized variables or the axes of a factor analysis [in this paper we used the Ecological Niche Factor Analysis (ENFA)]. We first explain the details of the geometric mean algorithm and then we apply it to the bearded vulture (Gypaetus barbatus) habitat in the Swiss Alps. The results are compared to those obtained by the "median algorithm" and tested by jack-knife cross-validation. We also discuss other related algorithms (BIOCLIM, HABITAT, and DOMAIN). All these analyses were implemented into and performed with the ecology-oriented GIS software BIOMAPPER 2.0.The results show the geometric mean to perform better than the median algorithm, as it produces a tighter fit to the bimodal distribution of the bearded vulture in the environmental space. However, the "median algorithm" being quicker, it could be preferred when modeling more usual distribution.

Algorithms↗