Social partner discrimination based on sounds and scents in Asian small-clawed otters (Aonyx cinereus).

Ability to discriminate familiar conspecifics is an essential competence in any group-living species, ensuring socio-spatial cohesion, but in many animals, such as mustelids, the relative importance of the different communicative modalities for discrimination is poorly understood. In otters, there is evidence of intra-specific variation in physical appearance and in feces chemical profile, but the potential for acoustic identity coding as well as for identity decoding in visual, acoustic and olfactive domains remains unexplored. We investigated the acoustic structure of contact calls in five captive groups of small-clawed otters and found that it is possible to reliably assign one particular call to a given adult male caller. Females discriminated between familiar and unfamiliar adult males based on their sound (playback) and smell (feces) but not based on their picture, suggesting abilities to memorize and use acoustic and olfactive signatures in their daily social life.

Have sex or not? Lessons from bacteria.

Sex is one of the greatest puzzles in evolutionary biology. A true meiotic process occurs only in eukaryotes, while in bacteria, gene transcription is fragmentary, so asexual reproduction in this case really means clonal reproduction. Sex could stem from a signal that leads to increased reproductive output of all interacting individuals and could be understood as a secondary consequence of primitive metabolic reactions. Meiotic sex evolved in proto-eukaryotes to solve a problem that bacteria did not have, namely a large amount of DNA material, occurring in an archaic step of proto-cell formation and genetic exchanges. Rather than providing selective advantages through reproduction, sex could be thought of as a series of separate events which combines step-by-step some very weak benefits of recombination, meiosis, gametogenesis and syngamy.

Can low densities of carnivores result in genetic depletion? An investigation within French polecat populations.

Carnivores as top predators are commonly found in relatively low densities even in optimal habitats. Despite a lack of empirical studies, it could be suspected that long-term low density could result in genetic depletion. The genetic structure of European polecat Mustela putorius natural populations was investigated by allozyme electrophoresis in five distinct areas. Density estimates significantly differed among sites from 0.17 to 0.83 individuals/km2 with an average of 0.56 individuals per km2, resulting in a scattered distribution. Genetic structure varied among distinct populations both in number of polymorphic loci and heterozygosity. Polecats from Brittany revealed a very low observed heterozygosity (H(O) = 0.028) whereas mean heterozygosity reached H(O) = 0.072 in Brière. That the lowest heterozygosity levels and highest inbreeding coefficient F(IS) were significantly associated with the lowest densities suggests that low densities may affect populations of carnivores. Both the loss of polymorphic loci and the reduction in heterozygosity rates suggest a density-dependent effect and population density can be arguably regarded as a factor affecting genetic diversity in top carnivores.

European mink-polecat hybridization events: hazards from natural process?

Determining the significance of hybridization events raises essential issues both in conservation and in evolutionary biology. Here, we report a genetic investigation of sympatric polecat and endangered European mink populations. Although the two species were morphologically very similar, the European mink and the polecat were easily discriminated from allozymes and microsatellites and showed a high level of private alleles (effective number of alleles: mink=1.45 and polecat=3.09). Nevertheless, the allozymic polymorphism remained lower in the European mink (4 loci, 10.5%) than in polecat (9 loci, 23.7%). Similarly, from microsatellite data, the polymorphism only reached 36% at 0.99 in the European mink; whereas in the polecat, the polymorphism reached 82% at 0.99. Natural hybridization events between two native species were detected. Because of the low fertility of hybrids, interbreeding could be regarded as producing "hybrid sink" that leads to a progressive assimilation of mink by polecat. Nonetheless, pure mink populations inhabited streams in western France, and hybridization events were only detected in areas where mink were rare and now presumed disappeared. Rather than revealing the poor efficiency of the specific recognition system, our results suggest that hybridization is associated with the scarcity of mating partners.

Mating system and genetic variance in a polygynous mustelid, the European polecat.

The population genetic implications of mating system were investigated in European polecat Mustela putorius populations from western France, combining radiotracking survey and allozyme variation analysis. Mating period occurred from February to June and polecats showed a strategy of successive polygyny, a male consorting with 1.44 females during a brief period (2.9 days). Relatedness was largely sex biased, females (21%) being almost twice more related than males (13%) suggesting a natal philopatry. Nonetheless, breeding dispersal pattern appeared relatively complex. Males were the sex dispersing but the main strategy for male polecats consisted of short-term mating excursions in adjacent females ranges whereas long-distance dispersal only constituted an alternative breeding strategy. Despite their allozymic polymorphism level reaching 24% at p<0.05 for 38 scored loci, populations showed a high heterozygote deficiency as revealed by the F(IS) index averaging F(IS) = 0.383. Thus the mating system of such solitary mustelids may be poorly efficient to prevent inbreeding within populations.

Decline in endangered species as an indication of anthropic pressures: the case of European mink Mustela lutreola Western population.

Populations of threatened species, especially predators at the top of the food chain, may be affected by anthropic pressures. The endangered western population of European mink Mustela lutreola has shown a large decline over 50% of its natural range. M. lutreola disappeared from northwestern France between 1984 and 1997, and the decline was associated with an increase in mustelid trapping, changes in watercourse quality, and habitat modifications due to agricultural practices. The pattern of decline showed a fragmentation restricting the minks into very small areas. Trapping was the first known cause of mortality. Although feral American mink Mustela vison may compete with autochthonous carnivores, M. lutreola had disappeared from streams before the introduction of the American species, suggesting that competitive interactions were not responsible. Furthermore, American mink has never been found or has remained rare in 62.4% of the area from which M. lutreola has disappeared. During the past 25 years, permanent grassland surfaces were reduced by 40%, whereas fodder culture increased by 470%, causing considerable habitat changes. Furthermore, 55.7% of water courses were classified as being of bad quality or polluted. Therefore, our data suggests that a conjunction of intensive trapping, alterations in water quality and habitat modification was critical for the European mink's decline. Although there are difficulties in ascribing specific cause to distribution changes in a top predator, this decline can be regarded as an indication for anthropic pressures on natural habitats.

Variations in call and morphology in male water frogs: taxonomic and evolutionary implications.

In Anurans, the specific mate recognition system (SMRS), which contributes to prezygotic isolation, is mainly based on morphological and call features. This is why such criteria are used by zoologists for taxonomic identification. In hybridogenetic water frogs (Rana ridibunda, R. lessonae, R. perezi, R. kl. grafi and R. kl. esculenta), hybridization opens up the question of the efficiency of these criteria for taxon identification and of the specific recognition system in this context. Variation in both morphological and call features revealed both significant mean differences among taxa but also large overlapping among individuals belonging to different taxa. Thus, using call or morphometrical features in order to identify water frogs may be hazardous. Moreover, species differ poorly in their specific mate recognition system, facilitating hybridization events, and therefore suggesting that postzygotic mechanisms may be prevalent over prezygotic mechanisms.

Time budget as related to feeding tactics of European polecat Mustela putorius.

The time budget of five male and four female European polecats was studied in western France through radiotracking surveys. Their activity level averaged 7 h and 31 min without any significant differences between males and females. However two phases, foraging and travelling, were not similarly distributed in both sexes. Despite a strong sexual dimorphism, females spent more time foraging than males. Travelling, i.e. time devoted to linear movements was more important in males than females. Variations in activity phase duration were correlated with the proportions of food categories, suggesting that the dispersion of available resources directly influenced polecat activity. The exploitation of prey showing an aggregative distribution such as anurans led to a decrease in general activity whereas the consumption of rodents, which were more regularly distributed, was correlated to the foraging activity. Mating and breeding also affected the activity duration. Thus it seems that the time budget of polecats resulted from a compromise between social organization and trophic constraints.

Genetic heterozygosity in polecat Mustela putorius populations from western France.

Allozymic variations were investigated in 49 European polecats Mustela putorius from Western France by starch gel electrophoresis. Out of 31 surveyed loci, eight (25.8%) were shown polymorphic and observed heterozygosity averaged 0.057. Deviations from Hardy-Weinberg equilibrium and heterozygote deficiency suggest that populations were not in panmixia. Heterozygotes for two loci or more totalled 42.9% of individuals. Thus, although carnivores were previously considered as less variable, polecat populations from Western France showed a high genetic variability.