Host movement dominates the predicted effects of climate change on parasite transmission between wild and domestic mountain ungulates

Climate change is shifting the transmission of parasites, which is determined by host density, ambient temperature and moisture. These shifts can lead to increased pressure from parasites, in wild and domestic animals, and can impact the effectiveness of parasite control strategies. Understanding the interactive effects of climate on host movement and parasite life histories will enable targeted parasite management, to ensure livestock productivity and avoid additional stress on wildlife populations. To assess complex outcomes under climate change, we applied a gastrointestinal nematode transmission model to a montane wildlife-livestock system, based on host movement and changes in abiotic factors due to elevation, comparing projected climate change scenarios with the historic climate. The wildlife host, Alpine ibex (Capra ibex ibex), undergoes seasonal elevational migration, and livestock are grazed during the summer for eight weeks. Total parasite infection pressure was more sensitive to host movement than to the direct effect of climatic conditions on parasite availability. Extended livestock grazing is predicted to increase parasite exposure for wildlife. These results demonstrate that movement of different host species should be considered when predicting the effects of climate change on parasite transmission, and can inform decisions to support wildlife and livestock health.

[Brucellosis in Alpine ibex: 10 years of research and expert assessments]

Brucellosis due to Brucella melitensis affects domestic and wild ruminants, as well as other mammals, including humans. Despite France being officially free of bovine brucellosis since 2005, two human cases of Brucella melitensis infection in the French Alps in 2012 led to the discovery of one infected cattle herd and of one infected population of wild Alpine ibex (Capra ibex). In this review, we present the results of 10 years of research on the epidemiology of brucellosis in this population of Alpine ibex. We also discuss the insights brought by research and expert assessments on the efficacy of disease management strategies used to mitigate brucellosis in the French Alps.

Targeted strategies for the management of wildlife diseases: the case of brucellosis in Alpine ibex

The management of infectious diseases in wildlife reservoirs is challenging and faces several limitations. However, detailed knowledge of host-pathogen systems often reveal heterogeneity among the hosts' contribution to transmission. Management strategies targeting specific classes of individuals and/or areas, having a particular role in transmission, could be more effective and more acceptable than population-wide interventions. In the wild population of Alpine ibex (Capra ibex-a protected species) of the Bargy massif (French Alps), females transmit brucellosis (Brucella melitensis) infection in ~90% of cases, and most transmissions occur in the central spatial units ("core area"). Therefore, we expanded an individual-based model, developed in a previous study, to test whether strategies targeting females or the core area, or both, would be more effective. We simulated the relative efficacy of realistic strategies for the studied population, combining test-and-remove (euthanasia of captured animals with seropositive test results) and partial culling of unmarked animals. Targeting females or the core area was more effective than untargeted management options, and strategies targeting both were even more effective. Interestingly, the number of ibex euthanized and culled in targeted strategies were lower than in untargeted ones, thus decreasing the conservation costs while increasing the sanitary benefits. Although there was no silver bullet for the management of brucellosis in the studied population, targeted strategies offered a wide range of promising refinements to classical sanitary measures. We therefore encourage to look for heterogeneity in other wildlife diseases and to evaluate potential strategies for improving management in terms of efficacy but also acceptability.

Variation in the ontogenetic allometry of horn length in bovids along a body mass continuum

Allometric relationships describe the proportional covariation between morphological, physiological, or life-history traits and the size of the organisms. Evolutionary allometries estimated among species are expected to result from species differences in ontogenetic allometry, but it remains uncertain whether ontogenetic allometric parameters and particularly the ontogenetic slope can evolve. In bovids, the nonlinear evolutionary allometry between horn length and body mass in males suggests systematic changes in ontogenetic allometry with increasing species body mass. To test this hypothesis, we estimated ontogenetic allometry between horn length and body mass in males and females of 19 bovid species ranging from ca. 5 to 700 kg. Ontogenetic allometry changed systematically with species body mass from steep ontogenetic allometries over a short period of horn growth in small species to shallow allometry with the growth period of horns matching the period of body mass increase in the largest species. Intermediate species displayed steep allometry over long period of horn growth. Females tended to display shallower ontogenetic allometry with longer horn growth compared to males, but these differences were weak and highly variable. These findings show that ontogenetic allometric slope evolved across species possibly as a response to size-related changes in the selection pressures acting on horn length and body mass.

High Shedding Potential and Significant Individual Heterogeneity in Naturally-Infected Alpine ibex (Capra ibex) With Brucella melitensis

Wildlife reservoirs of infectious diseases raise major management issues. In Europe, brucellosis has been eradicated in domestic ruminants from most countries and wild ruminants have not been considered important reservoirs so far. However, a high prevalence of Brucella melitensis infection has been recently identified in a French population of Alpine ibex (Capra ibex), after the emergence of brucellosis was confirmed in a dairy cattle farm and two human cases. This situation raised the need to identify the factors driving the persistence of Brucella infection at high prevalence levels in this ibex population. In the present paper, we studied the shedding pattern of B. melitensis in ibex from Bargy Massif, French Alps. Bacteriological examinations (1-15 tissues/samples per individual) were performed on 88 seropositive, supposedly infected and euthanized individuals. Among them, 51 (58%) showed at least one positive culture, including 45 ibex with at least one Brucella isolation from a urogenital sample or a lymph node in the pelvic area (active infection in organs in the pelvic area). Among these 45 ibex, 26 (30% of the total number of necropsied animals) showed at least one positive culture for a urogenital organ and were considered as being at risk of shedding the bacteria at the time of capture. We observed significant heterogeneity between sex-and-age classes: seropositive females were most at risk to excrete Brucella before the age of 5 years, possibly corresponding to abortion during the first pregnancy following infection such as reported in the domestic ruminants. The high shedding potential observed in young females may have contributed to the self-sustained maintenance of infection in this population, whereas males are supposed to play a role of transmission between spatial units through venereal transmission during mating. This heterogeneity in the shedding potential of seropositive individuals should be considered in the future to better evaluate management scenarios in this system as well as in others.

Sociospatial structure explains marked variation in brucellosis seroprevalence in an Alpine ibex population

In a context of (re)emerging infectious diseases with wildlife reservoirs, understanding how animal ecology shapes epidemiology is a key issue, particularly in wild ungulates that share pathogens with domestic herbivores and have similar food requirements. For the first time in Europe, brucellosis (Brucella melitensis), a virulent zoonosis, persisted in an Alpine ibex (Capra ibex) population and was transmitted to cattle and humans. To better understand disease dynamics, we investigated the relationships between the spatial ecology of ibex and the epidemiology of brucellosis. Combining home range overlap between 37 GPS-collared individuals and visual observations of 148 visually-marked individuals monitored during the 2013-2016 period, we showed that females were spatially segregated in at least 4 units all year round, whereas males were more prone to move between female units, in particular during the rutting period. In addition to ibex age, the spatial structure in females largely contributed to variation in seroprevalence in the whole population. These results suggest that non-sexual routes are the most likely pathways of intraspecific transmission, crucial information for management. Accounting for wildlife spatial ecology was hence decisive in improving our ability to better understand this health challenge involving a wildlife reservoir.

Evidence of reduced individual heterogeneity in adult survival of long-lived species

The canalization hypothesis postulates that the rate at which trait variation generates variation in the average individual fitness in a population determines how buffered traits are against environmental and genetic factors. The ranking of a species on the slow-fast continuum - the covariation among life-history traits describing species-specific life cycles along a gradient going from a long life, slow maturity, and low annual reproductive output, to a short life, fast maturity, and high annual reproductive output - strongly correlates with the relative fitness impact of a given amount of variation in adult survival. Under the canalization hypothesis, long-lived species are thus expected to display less individual heterogeneity in survival at the onset of adulthood, when reproductive values peak, than short-lived species. We tested this life-history prediction by analysing long-term time series of individual-based data in nine species of birds and mammals using capture-recapture models. We found that individual heterogeneity in survival was higher in species with short-generation time (< 3 years) than in species with long generation time (> 4 years). Our findings provide the first piece of empirical evidence for the canalization hypothesis at the individual level from the wild.

Onset of autumn shapes the timing of birth in Pyrenean chamois more than onset of spring

In seasonal environments, birth dates are a central component for a species' life history, with potential long-term fitness consequences. Yet our understanding of selective pressures of environmental changes on birth dates is limited in wild mammals due to the difficulty of data collection. In a context of rapid climate change, the question of a possible mismatch between plant phenology and birth phenology also remains unanswered for most species. We assessed whether and how the timing of birth in a mountain mammal (isard, also named Pyrenean chamois, Rupicapra pyrenaica pyrenaica) tracked changes in plant growing season, accounting for maternal traits, individual heterogeneity and population density. We not only focused on spring conditions but also assessed to what extent onset of autumn can be a driver of phenological biological events and compared the magnitude of the response to the magnitude of the environmental changes. We relied on a 22-year study based on intensively monitored marked individuals of known age. Births were highly synchronized (80% of kids born within 25 days) and highly repeatable (84%; between-female variation of 9.6 days, within-female variation of 4.2 days). Individual phenotypic plasticity allows females to respond rapidly to interannual changes in plant phenology but did not prevent the existence of a mismatch: a 10-day advance in the autumn or spring plant phenology led to 3.9 and 1.3 days advance in birth dates, respectively. Our findings suggest that plant phenology may act as a cue to induce important stages of the reproductive cycle (e.g. conception and gestation length), subsequently affecting parturition dates, and stressed the importance of focusing on long-term changes during spring for which females may show much lower adaptive potential than during autumn. These results also question the extent to which individual plasticity along with high heterogeneity among individuals will allow species to cope with demographic consequences of climate changes.

Age-specific survival and annual variation in survival of female chamois differ between populations

In many species, population dynamics are shaped by age-structured demographic parameters, such as survival, which can cause age-specific sensitivity to environmental conditions. Accordingly, we can expect populations with different age-specific survival to be differently affected by environmental variation. However, this hypothesis is rarely tested at the intra-specific level. Using capture-mark-recapture models, we quantified age-specific survival and the extent of annual variations in survival of females of alpine chamois in two sites. In one population, survival was very high (>0.94; Bauges, France) until the onset of senescence at approximately 7 years old, whereas the two other populations (Swiss National Park, SNP) had a later onset (12 years old) and a lower rate of senescence. Senescence patterns are therefore not fixed within species. Annual variation in survival was higher in the Bauges (SD = 0.26) compared to the SNP populations (SD = 0.20). Also, in each population, the age classes with the lowest survival also experienced the largest temporal variation, in accordance with inter-specific comparisons showing a greater impact of environmental variation on these age classes. The large difference between the populations in age-specific survival and variation suggests that environmental variation and climate change will affect these populations differently.

Sex- and age-specific survival of the highly dimorphic Alpine ibex: evidence for a conservative life-history tactic

1. Age-specific survival of 215 males and 117 females of the highly sexually dimorphic Alpine ibex Capra ibex (L.) was assessed from a 21-year capture-mark-recapture (CMR) programme (1983-2004). The study covered two contrasted periods of population performance (high performance from 1983 to 1997 vs. low performance from 1998 onwards). 2. Based on current life-history theories for sexually dimorphic species, we expected that survival should decrease with age in both sexes, female survival should be buffered against environmental variations, male survival should decrease during the low performance period, and adult survival should be lower in males than females during the low performance period. 3. Survival of both sexes was strongly affected by age, with the four age classes (yearling, prime-aged adults of 2-8 years of age, old adults of 8-13 years of age, and senescent adults from 13 years of age onwards) generally reported for large herbivores. 4. Survival of females at all ages, and of yearling and prime-aged males, was buffered against environmental variations and was the same during periods of high and low population performance. The survival of old males decreased in years of low population performance. 5. All marked yearlings (32 females, 56 males) survived to age 2. Survival of prime-aged females (0.996 +/- 0.011) was higher than for other large herbivores, but similarly to other large herbivore species, it declined slowly and regularly with increasing age afterwards. Male survival was 5-15% higher each year than that of males of other large herbivores. Males enjoyed very high survival when prime-aged (0.981 +/- 0.009) and as old adults (high-performance period: 0.965 +/- 0.028, low-performance period: 0.847 +/- 0.032). 6. The very high survival of males, coupled with their prolonged mass gain, suggests a highly conservative reproductive tactic. Male ibex differ from similar-sized herbivores by showing a nearly indeterminate growth in horn size and body mass. By surviving to an advanced age, males may enjoy high reproductive success because of their large size.

Temporal Variation in Fitness Components and Population Dynamics of Large Herbivores

▪ Abstract  In large-herbivore populations, environmental variation and density dependence co-occur and have similar effects on various fitness components. Our review aims to quantify the temporal variability of fitness components and examine how that variability affects changes in population growth rates. Regardless of the source of variation, adult female survival shows little year-to-year variation [coefficient of variation (CV <10%)], fecundity of prime-aged females and yearling survival rates show moderate year-to-year variation (CV <20%), and juvenile survival and fecundity of young females show strong variation (CV >30%). Old females show senescence in both survival and reproduction. These patterns of variation are independent of differences in body mass, taxonomic group, and ecological conditions. Differences in levels of maternal care may fine-tune the temporal variation of early survival. The immature stage, despite a low relative impact on population growth rate compared with the adult stage, may be the critical component of population dynamics of large herbivores. Observed differences in temporal variation may be more important than estimated relative sensitivity or elasticity in determining the relative demographic impact of various fitness components.

Vigilance behavior in lactating female Alpine ibex

We compared time budgets of lactating females with those of nonbreeding females, yearlings, and adult males in a French Alpine ibex (Capra ibex ibex) population. We tested whether lactating females spent as much time as other sex-age classes feeding, moving, resting, and being vigilant. Females with young at heel fed and moved as much as other sex and age classes, but rested less and were more vigilant. The decrease in time spent resting was possibly a way to minimize costs due to increased vigilance. The higher vigilance rate is considered to be an antipredation behavior exhibited by lactating females to protect their young.

Adult survival pattern of the sexually dimorphic Alpine ibex (Capra ibex ibex)

Using recent developments in capture – recapture modeling, we analyzed the adult survival pattern of an Alpine ibex (Capra ibex ibex) population recently established in the northern Alps of France. Survival rates varied little over time and did not differ between the sexes. The survival rate was 0.97 (SE = 0.011). Recapture probabilities were stable over time but differed according to sex: 0.71 (SE = 0.035) for males versus 0.88 (SE = 0.033) for females. The absence of a between-sex difference in survival was not expected for a highly sexually dimorphic species. Environmental conditions, such as a low population density and a low pressure of limiting factors on population dynamics, could explain this absence of a survival cost of sexual selection for males. The high and rather constant survival rate of ibex over time is consistent with the idea that, in large mammals, individuals should be selected for maximizing their own adult survivorship.