SEXUAL DIMORPHISM IN THE DEVELOPMENT OF SCENT STRUCTURES FOR THE OBLIGATE MONOGAMOUS EURASIAN BEAVER (CASTOR FIBER)

Genetic structure of Eurasian beaver in Romania: insights after two decades from the reintroduction

Once exploited for fur, meat, and extracting the yellowish exudate called castoreum, the Eurasian beaver disappeared from Romania during the eighteenth century. After, the reintroductions carried out two decades ago are currently thriving in the Danube River basin. Using nine nSSR markers, we analysed samples from 98 individuals, and we found no genetic substructure, suggesting high dispersal and gene flow capabilities. The stepwise mutation model (SMM) indicated the existence of a recent genetic bottleneck, though the Eurasian beaver retains high levels of genetic diversity and population growth facilitated variation in nSSR loci. A fine-scale spatial correlation in females was detected, contrasting with males’ dispersal on longer distances. While the movement and establishment of individuals’ new territories were made under natural predation pressure, the mix following natural expansion improved the fitness and could contribute to a higher genetic diversity than the source population. With any reintroduction, a focus on capturing individuals from various geographic origins, as well as securing many and suitable founding individuals (adults, subadults, and juveniles) with mixed origins, could secure the post-genetic bottleneck recovery and higher genetic diversity. Beyond this conservation success, future management strategies should consider building a National Action Plan (NAP) for the species, including a permanent genetic monitoring programme for Eurasian beaver.

Socio-ecological features other than sex affect habitat selection in the socially obligate monogamous Eurasian beaver

Habitat selection is a context-dependent mechanism, in which both the internal state as well as external factors affect the behavior and decisions of an individual. This is well known for polygamous mammals, which are typically sexually dimorphic, and often express great variability in behavior and habitat selection between individuals as well between the sexes. Among monogamous mammals, however, variability in habitat selection should be explained by group characteristics and the presence of offspring rather than by sex. We evaluated this hypothesis in a socially monogamous rodent, the Eurasian beaver (Castor fiber), in a saturated Norwegian population. For the first time in this species we applied GPS tracking devices (N = 22 adult beavers, in 15 territories, 2009–2013), and used resource selection functions (i) to document population-wide habitat selection and the importance of ‘territory’ therein, and (ii) to evaluate which socio-ecological factors explained potential individual differences in habitat selection. We found that variation in habitat selection was stronger between territories than between years or individuals nested by territory. We identified that family size and the presence of kits, but not sex, explained individual variation in habitat selection. Adults with kits and/or larger families tended to exhibit low risk-taking behavior (avoiding human-related variables such as roads, buildings, and agricultural land), and stayed close to their main lodge (parental care). Our results show that habitat selection is a context-dependent mechanism even in a species which expresses very little behavioral and morphological dimorphism.

Sexual dimorphism and condition dependence in the anal pad of the small Indian mongoose (Herpestes auropunctatus)

Secondary sexual traits tend to be sexually dimorphic, and theory predicts that such traits should also be condition-dependent in a sex-specific manner. We investigate these phenomena in a field study of the small Indian mongoose (Herpestes auropunctatus (Hodgson, 1836); formerly Herpestes javanicus (É. Geoffroy Saint-Hillaire, 1818)), in the first attempt at understanding secondary sexual traits and sexual selection in this species. Small Indian mongooses are solitary and nonterritorial, and they likely depend on chemical (scent) rather than visual or acoustic signals for communication. Additionally, they possess a fleshy projection around their anus, the anal pad, thought to aid in scent-marking. Our results revealed strong male-biased sexual dimorphism in mass, skull and body lengths, canine diameters, and anal pad area. After controlling for the influence of body length, males were 31% heavier and possessed anal pads that were 68% larger than females’. Additionally, anal pad size was positively related to body size in males but not in females and was condition-dependent in males but not in females. Taken together, our findings provide indirect evidence that the anal pad might have evolved, at least in part, via sexual selection.

Sexual Dimorphism in Territorial Scent Marking by Adult Eurasian Beavers (Castor fiber)

Mammalian scent marking is often associated with territorial defense. However, males and females may demonstrate different activity patterns and play different roles. Female mammals nurture the young during lactation, while males purportedly perform other tasks more frequently, such as territorial maintenance and defense. This paper investigates the contribution made by mated pairs of adult males and females to territorial scent-marking in the obligate monogamous Eurasian beavers (Castor fiber). We hypothesized that both sexes should show territorial behavior, and predicted that they deposit a higher proportion of scent marks at borders. We also hypothesized that a sexual dimorphism exists due to reproductive constraints on the females, and predicted that males should invest significantly more in scent-marking behavior than females during summer. We obtained behavioral data by radio tracking six mated pairs of Eurasian beavers during spring and summer 2000-2001 on two rivers in southeastern Norway. Our results showed that both males and females clustered their scent marks near territorial borders, but males deposited a larger number of scent marks than females and spent more time at borders. Males were also found to have a higher scent marking rate and scent marks per night than females during summer, but not during spring. Overall, scent marks per night were higher in males than females. We conclude that both males and females Eurasian beavers carry out territorial behavior by scent marking, but males carry a larger part of the territorial defense during summer when females lactate. Our results are discussed in the light of the codefense hypothesis.

Resident beavers (Castor canadensis) do not discriminate between castoreum scent marks from simulated adult and subadult male intruders

Subadult intruding beavers (Castor spp.) could be expected to pose a higher threat than adults to territory holders because, unlike adults who usually own a territory, subadults need to acquire a territory and a mate to reproduce successfully. We tested the responses of territorial beavers ( Castor canadensis Kuhl, 1820) to simulated intrusions by adult and subadult males. Territorial intrusion was simulated through scent playback experiments that exposed residents to castoreum from adult and subadult strangers simultaneously. We obtained responses from 13 resident beavers. Neither sniffing response nor physical or total responses differed between castoreum from adults and subadults. This was true for both sexes combined and separate. There was also no significant correlation between the mass of the scent donor and the response intensity. We found no evidence that territorial beavers responded differentially to castoreum scent marks from intruders of different ages. Either beavers consider all strange intruders as posing a high threat and hence do not treat them differentially or castoreum does not contain sufficient information to allow beavers to discriminate between age classes. We suggest that rather than directly assessing intruders by means of intrinsic information contained in the scent mark, beavers assess their competitors through scent matching.