Albrecht I. Schulte-Hostedde

RESTITUTION OF MASS–SIZE RESIDUALS: VALIDATING BODY CONDITION INDICES

Body condition can have important fitness consequences, but measuring body condition of live animals from wild populations has been the subject of much recent debate. Using the residuals from a regression of body mass on a linear measure of body size is one of the most common methods of measuring condition and has been used in many vertebrate taxa. Recently, the use of this method has been criticized because assumptions are likely violated. We tested several assumptions regarding the use of this method with body composition and morphometric data from five species of small mammals and with statistical simulations. We tested the assumptions that the relationship between body mass and body size is linear, and that the proportion of mass associated with energy reserves is independent of body size. In addition, we tested whether the residuals from reduced major axis (RMA) regression or major axis (MA) regression performed better than the residuals from ordinary least squares (OLS) regression as indices of body condition. We found no evidence of nonlinear relationships between body mass and body size. Relative energy reserves (fat and lean dry mass) were generally independent or weakly dependent on body size. Residuals from MA and RMA regression consistently explained less variation in body composition than OLS regression. Using statistical simulations, we compared the effects of violations of the assumption that true condition and residual indices are independent of body size on the OLS, MA, and RMA procedures and found that OLS performed better than the RMA and MA procedures. Despite recent criticisms of residuals from mass-size OLS regressions, these indices of body condition appear to satisfy critical assumptions. Although some caution is warranted when using residuals, especially when both inter- individual variation in body size and measurement error are high, we found no reason to reject OLS residuals as legitimate indices of body condition.

Hybridization between escaped domestic and wild American mink (Neovison vison)

The release of domesticated organisms into natural populations may adversely affect these populations through predation, resource competition, and the introduction of disease. Additionally, the potential for hybridization between wild and domestic conspecifics is of great concern because it can alter the evolutionary integrity of the affected populations. Wild American mink (Neovison vison) populations may be threatened not only by competition for resources with domestic mink originating from farms, but by breeding with such escapees. Using 10 microsatellite loci, we genotyped mink from Ontario, Canada, sampled from two farms, two putatively mixed populations in regions surrounding the mink farms, and two wild populations with no recent history of mink farming. Using individual‐based Bayesian population assignment, we identified four population clusters, including one wild, and three domestic populations. The latter were not clustered by farm but rather by distinct line‐bred colour phases. Population clustering also identified domestic and hybrid mink in the free‐ranging populations. Nearly two‐thirds of the mink sampled in the two putatively mixed populations (78% and 43%) were either farm escapees or descendants of escapees. Principal components analysis of allele frequencies supported our Bayesian assignment results. The power of our assignment test was assessed using simulated hybrid genotypes which suggested that our overall correct classification rate was 96.2%. The overwhelming presence of domestic animals and their hybridization with mink in natural populations is of great concern for the future sustainability of wild mink populations.

Species identification of North American guinea worms (Nematoda: Dracunculus) with DNA barcoding.

Dracunculus insignis is a nematode parasite that infects the subcutaneous tissues of mammals such as raccoon (Procyon lotor), mink (Neovison vison) and fisher (Martes pennanti). D. lutrae, a morphologically similar species, has only been recovered from the otter (Lontra canadensis). Species identification of these two North American guinea worms has only been achieved by morphology of males and host identity. As a result, where only female specimens are present, accurate identifications are not possible. To date, specimens recovered from otter have been assumed to be D. lutrae, while those from all other hosts are assumed to be D. insignis. This study uses DNA barcoding to differentiate between these two North American dracunculoids. Our results show that D. insignis is a ‘true’ generalist, showing little sequence divergence regardless of host association, although our studies did validate its occurrence in a new host — the otter. Interestingly, specimens of the host specialist, D. lutrae, showed some sequence divergence, although it was low. The finding of D. insignis in otter substantiates the need to supplement morphology‐based methods in providing species identifications for certain dracunculoids.

Baculum variation and allometry in the muskrat (Ondatra zibethicus): a case for sexual selection

Sexual selection is a powerful force that influences the evolution of a variety of traits associated with female mate choice and male–male competition. Although other factors have been implicated, sexual selection may be particularly important in the evolution of the genitalia. Traits under sexual selection typically have high phenotypic variance and positive allometry relative to non-sexual traits. Here, we test the hypothesis that the baculum (os penis) of the muskrat (Ondatra zibethicus) is under sexual selection by examining phenotypic variance and allometry relative to non-sexual traits. Muskrats were sampled from Ontario, Canada, and a variety of traits measured. Measurements included baculum length and width, and three non-sexual traits (skull length, skull width, hind foot length). We used coefficient of variation (CV) and allometric slopes calculated using reduced major axis regression to test our hypotheses. Baculum traits had significantly higher CV’s relative to non-sexual traits. Baculum traits also showed positive allometry, whereas all non-sexual traits had negative allometric relationships. In addition, baculum width had higher CV’s and steeper allometric slopes than baculum length, indicating that, in muskrat, baculum width may be more influenced by sexual selection than baculum length. Positive allometry of the baculum is consistent with other examples of mammalian genitalia, but contrasts with negative allometry found in many insects. Other examples of positive allometry and high phenotypic variance of the baculum have suggested that females may use the baculum as an indicator of male quality. “Good genes” indicator traits may be particularly important in species that mate in an environmental context that prohibits female assessment of male quality. Muskrats mate aquatically, and thus females may be unable to properly assess males prior to copulation.

Mink Farms Predict Aleutian Disease Exposure in Wild American Mink

Background Infectious diseases can often be of conservation importance for wildlife. Spillover, when infectious disease is transmitted from a reservoir population to sympatric wildlife, is a particular threat. American mink (Neovison vison) populations across Canada appear to be declining, but factors thus far explored have not fully explained this population trend. Recent research has shown, however, that domestic mink are escaping from mink farms and hybridizing with wild mink. Domestic mink may also be spreading Aleutian disease (AD), a highly pathogenic parvovirus prevalent in mink farms, to wild mink populations. AD could reduce fitness in wild mink by reducing both the productivity of adult females and survivorship of juveniles and adults. Methods To assess the seroprevalence and geographic distribution of AD infection in free-ranging mink in relation to the presence of mink farms, we conducted both a large-scale serological survey, across the province of Ontario, and a smaller-scale survey, at the interface between a mink farm and wild mink. Conclusions/Significance Antibodies to AD were detected in 29% of mink (60 of 208 mink sampled); however, seroprevalence was significantly higher in areas closer to mink farms than in areas farther from farms, at both large and small spatial scales. Our results indicate that mink farms act as sources of AD transmission to the wild. As such, it is likely that wild mink across North America may be experiencing increased exposure to AD, via disease transmission from mink farms, which may be affecting wild mink demographics across their range. In light of declining mink populations, high AD seroprevalence within some mink farms, and the large number of mink farms situated across North America, improved biosecurity measures on farms are warranted to prevent continued disease transmission at the interface between mink farms and wild mink populations.

Behavioural correlates of parasitism and reproductive success in male eastern chipmunks, Tamias striatus

An individual’s fitness is estimated by its lifetime reproductive success. In the polygynandrous sciurid mating system, male reproductive success is determined by an individual’s success in locating and defending receptive females. Personality traits are differences in behavioural reactions that are heritable, consistent across contexts and over time, and may have important fitness consequences. Little research has been conducted on the effect of personality on success in the competition for mates. We examined the relationship between behavioural traits, parasite load and male reproductive success (the number of offspring sired in one year) in the eastern chipmunk. We expected that behavioural traits would affect male reproductive success either directly, through their effect on success in locating and/or defending females, or indirectly, through their effect on parasite load. We measured trappability, activity level/exploratory behaviour, struggle rate and ecto- and endoparasite load. Eighty-two chipmunks (29 adult males, 24 adult females, 29 juveniles) were genotyped to determine paternity. Assuming that trappability is an indicator of boldness, we found that bolder males had more offspring when controlling for endoparasite load. Moreover, bolder males had a higher endoparasite load, caused either by depleted energy reserves or the immunosuppressive effects of testosterone. We conclude that boldness affects reproductive success both directly and indirectly (via parasite load) in male chipmunks; however, there appears to be a trade-off between the positive direct effect and the negative indirect effect on reproductive success.

Route Choice by Deer Mice (Peromyscus maniculatus): Reducing the Risk of Auditory Detection by Predators

Abstract The influence of predation risk on microhabitat selection in male adult deer mice (Peromyscus maniculatus) was examined using an enclosure experiment. The relative amount of time spent by the deer mice on coniferous leaf litter, hardwood leaf litter and logs was measured. Mice preferred dry coniferous litter over dry hardwood litter, but had no preference when both litter types were wet. Deer mice traveled more along logs placed on hardwood litter than on coniferous litter. Nocturnal mammalian and avian predators of deer mice often use sound to locate their prey, and mice rustling in hardwood leaf litter should be more easily detected. Therefore, deer mice restrict their movements to routes that reduce the risk of auditory detection by predators.

Stress and the microbiome: linking glucocorticoids to bacterial community dynamics in wild red squirrels

Bacterial diversity within animals is emerging as an essential component of health, but it is unknown how stress may influence the microbiome. We quantify a proximate link between the oral microbiome and hypothalamic–pituitary–adrenal (HPA) axis activity using faecal glucocorticoid metabolites (FGM) in wild red squirrels (Tamiasciurus hudsonicus). Not only was bacterial diversity lower at higher levels of FGM, but also between capture periods a change in bacterial relative abundance was related to an increase in FGM. These linkages between the HPA axis and microbiome communities represent a powerful capacity for stress to have multi-dimensional effects on health.

Validation and use of hair cortisol as a measure of chronic stress in eastern chipmunks (Tamias striatus)

Cortisol is a hormone released when animals experience stress. We validated the measurement of cortisol from hair for use in wildlife using wild chipmunks, and tested the use of hair cortisol by measuring cortisol from chipmunks captured in natural and logged sites.

Molecular epidemiology of Aleutian disease virus in free-ranging domestic, hybrid, and wild mink

Aleutian mink disease (AMD) is a prominent infectious disease in mink farms. The AMD virus (AMDV) has been well characterized in Europe where American mink (Neovison vison) are an introduced species; however, in North America, where American mink are native and the disease is thought to have originated, the virus’ molecular epidemiology is unknown. As such, we characterized viral isolates from Ontario free‐ranging mink of domestic, hybrid, and wild origin at two proteins: NS1, a nonstructural protein, and VP2, a capsid protein. AMDV DNA was detected in 25% of free‐ranging mink (45 of 183), indicating prevalent active infection. Median‐joining networks showed that Ontario AMDV isolates formed two subgroups in the NS1 region and three in the VP2 region, which were somewhat separate from, but closely related to, AMDVs circulating in domestic mink worldwide. Molecular analyses showed evidence of AMDV crossing from domestic to wild mink. Our results suggest that AMDV isolate grouping is linked to both wild endogenous reservoirs and the long‐term global trade in domestic mink, and that AMD spills back and forth between domestic and wild mink. As such, biosecurity on mink farms is warranted to prevent transmission of the disease between mink farms and the wild.