Effects of population density and female body mass on litter size in European roe deer at a continental scale

Laterality in roe deer embryos implantation

Female reproductive success is one of the most important life-history traits to be monitored when determining population dynamics in free-ranging ungulates. Several studies have described how phenotypic characteristics of the mother, climatic conditions, population status, and habitat can impact on potential reproductive output in wild ungulates. However, little is known regarding the internal, physiological factors, that may account for differences in implantation rates. The present study investigated the differences in implantation rates and site on the basis of site and number of ovulations through the examination of about 3000 intact uteri collected from pregnant roe deer does (Capreolus capreolus). Although ovulation occurs with the same frequency in the left and right ovary, we revealed a higher frequency of embryos implantation in the left uterine horn in odd litter size, demonstrating that embryos can migrate between the uterine horns. In our study, a greater proportion of reproductive wastage was associated to females with three and four corpora lutea and interestingly, in relation to the site of ovulation, the percentage of corpora lutea that did not correspond to a fetus was higher in the right ovary than in the left one (73.2% vs. 26.8%). Our research described for the first time the absence of laterality in ovulation and the presence of laterality in implantation in roe deer, thus laying the foundations for in-depth studies about the functionality of this uterine side and for comparisons with populations located in other geographical areas to understand whether it is a widespread phenomenon or a local adaptation.

Relative influence of inter- and intraspecific competition in an ungulate assemblage modified by introduced species

Interspecific competition from introduced and naturally colonizing species has potential to affect resident populations, but demographic consequences for vertebrates have rarely been tested. We tested hypotheses of interspecific and intraspecific competition for density, body mass, and fertility of adult female Roe Deer (Capreolus capreolus) across a heterogeneous forest landscape occupied by two introduced deer species: Mediterranean Fallow Deer (Dama dama); and subtropical Reeve's Muntjac (Muntiacus reevesi). Species-specific deer densities in buffers around culling locations of 492 adult female Roe Deer, sampled over seven years, were extracted from spatially explicit models calibrated through annual nocturnal distance sampling. Roe Deer fertility and body mass were related to species-specific deer densities and extent of arable lands using piecewise structural equation models. Reeve's Muntjac density was lower at higher Fallow Deer densities, suggesting interspecific avoidance via interference competition, but greater when buffers included more arable land. Roe Deer body mass was marginally greater when buffers included more arable land and was independent of deer densities. However, Roe Deer fertility was unrelated to female body mass, suggesting that fertility benefits exceeded an asymptotic threshold of body condition in this low-density population. However, Roe Deer fertility was slightly greater rather than reduced in areas with greater local Roe Deer density, suggesting negligible intraspecific competition. In contrast, Roe Deer was less fertile in areas with greater Reeve's Muntjac densities; thus, interspecific exceeded intraspecific competition in this assemblage. In contrast, we found no support for any effects of Fallow Deer density on Roe Deer density, body mass, or fertility. Complex networks of interspecific competition operating in this deer assemblage include: interspecific interference from Fallow Deer exceeded habitat effects for Reeve's Muntjac; and interspecific competition from introduced, smaller sedentary Reeve's Muntjac reduced fertility, unlike intraspecific, or potential competition with larger, more mobile, Fallow Deer for native Roe Deer. Mechanisms driving Roe Deer fertility may include interspecific behavioral interference or stress-resource depletion is considered less likely because Roe Deer fertility was independent of body mass. Findings emphasize the importance of ensuring appropriate management strategies for controlling invasive species.

Sequential analysis of δ15 N in guard hair suggests late gestation is the most critical period for muskox calf recruitment

RATIONALE

Analysis of stable isotopes in tissue and excreta may provide information about animal diets and their nutritional state. As body condition may have a major influence on reproduction, linking stable isotope values to animal demographic rates may help unravel the drivers behind animal population dynamics.

METHODS

We performed sequential analysis of δ¹⁵ N values in guard hair from 21 muskoxen (Ovibos moschatus) from Zackenberg in high arctic Greenland. We were able to reconstruct the dietary history for the population over a 5-year period with contrasting environmental conditions. We examined the linkage between guard hair δ¹⁵ N values in 12 three-month periods and muskox calf recruitment to detect critical periods for muskox reproduction. Finally, we conducted similar analyses of the correlation between environmental conditions (snow depth and air temperature) and calf recruitment.

RESULTS

δ¹⁵ N values exhibited a clear seasonal pattern with high levels in summer and low levels in winter. However, large inter-annual variation was found in winter values, suggesting varying levels of catabolism depending on snow conditions. In particular δ¹⁵ N values during January-March were linked to muskox recruitment rates, with higher values coinciding with lower calf recruitment. δ¹⁵ N values were a better predictor of muskox recruitment rates than environmental conditions.

CONCLUSIONS

Although environmental conditions may ultimately determine the dietary δ¹⁵ N signal in muskox guard hairs, muskox calf recruitment was more strongly correlated with δ¹⁵ N values than ambient snow and temperature. The period January-March, corresponding to late gestation, appears particularly critical for muskox reproduction.

Hematological and Serum Biochemical Values of Free-Ranging Roe Deer (Capreolus capreolus) in Poland

This study presents the hematological and serum biochemical values of physically captured roe deer (Capreolus capreolus). The study material was blood sampled from roe deer captured with the use of a specialist trap mesh and no anesthesia. Blood samples were collected from 122 roe deer from January to April in 2016, 2017, and 2018 in the Lublin region of Poland. The hematological and biochemical variables were determined with results showing statistically significant differences between the mean values of RBC, HCT, and HB according to sex. Reference intervals should be more specific to the broad physical versus chemical capture categories.

Population development and landscape preference of reintroduced wild ungulates: successful rewilding in Southern Italy

Background

In the past decades, the abandonment of traditional land use practices has determined landscape changes inducing reforestation dynamics. This phenomenon can be contrasted with rewilding practices, i.e., the reintroduction of animals that may promote the recovery of landscape diversity. In this study, we explore the dynamics of expansion of two reintroduced populations of wild ungulates, Italian roe deer (Capreolus capreolus italicus) and red deer (Cervus elaphus), assessing their contribution in the recovery of landscape diversity.

Methods

By using direct and indirect information on the two species, collected by nocturnal and diurnal surveys and camera trapping, we modelled a habitat suitability map, and estimated the density and distribution of the populations. We also performed a land use changes analysis, combining the presence of wild ungulates and livestock.

Results and Discussion

We demonstrated that deer dispersed gradually from their release location, increasing in population size, and this occurred in the entire study area. Moreover, we show that areas with lower grazing density are significantly affected by forest encroachment. A possible interpretation of this result could be that wild grazers (roe deer and red deer) prefer semi-open areas surrounded by the forest. This, in association with other factors, such as domestic grazing, could be one of the main responsible in maintaining landscape mosaic typical of the Apennine mountain, confirming the value of grazers as a landscape management tool. Moreover, we show the possibility to conserve through reintroduction the vulnerable C.c. italicus.

Dentition and body condition: tooth wear as a correlate of weight loss in roe deer

Background

In many mammalian species, once the permanent teeth have erupted, the only change to dentition is a gradual loss of tooth surface/height through wear. The crown of the teeth cannot be repaired once worn. When dental crown tissue has been depleted due to wear, the animal is expected to have a suboptimal body condition. We evaluated the role of tooth wear in causing a reduction of physical condition in adult roe deer females (Capreolus capreolus).

Results

The progressive wearing of the lower cheek teeth was assessed in a Northern Apennines (Italy) population with a new scoring scheme based on objectively described tooth characteristics (morphotypes) being either present or absent. Eviscerated body mass and mandible length, which is a good proxy for body size in roe deer, were related to the tooth wear score by the use of linear regressions. The sum of wear scores for molariform teeth correlated most strongly with body condition (i.e., eviscerated body mass/mandible length), showing the importance of the entire chewing surface for acquiring energy by food comminution, chewing, and digestion. In comparison with individuals of comparable size experiencing minor tooth wear, the body mass of those with the most advanced stage of tooth wear was decreased by 33.7%. This method was compared to the height and the hypsodonty index of the first molar, the most commonly used indices of tooth wear. The sum of molariform wear scoring scheme resulted in a more suitable index to describe the variation in body condition of roe deer.

Conclusions

Describing tooth wear patterns in hunted populations and monitoring at which tooth wear level (and therefore dental morphotype) an animal is no longer able to sustain its physical condition (i.e. when it begins to lose body mass) can be a useful tool for improving the management of the most widespread and abundant deer species in Europe. At the same time, such an approach can clarify the role of tooth wear as a proximate cause of senescence in ungulates.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12983-021-00433-w.

Early life investment in antlers and body growth reflects adult performance in roe deer population under supplementary feeding conditions

Recent research has challenged the idea that cervid antlers are such costly traits, supporting the assertion early-life antler investment is an honest signal of adult phenotypic quality. However, inferences were made based on antler measurements while growing (velvet) and thus, studies on fully-formed clean antlers are needed to avoid possible bias caused by the inter-individual variation in antler growth phenology. We studied a semi-captive population of European roe deer inhabiting a sub-Mediterranean area (Valsemana research station) and living under optimal conditions (ad libitum food supply and veterinary care). Based on repeated measurements taken from 146 individuals, we assessed whether allocation to secondary sexual traits during early life affected body mass or antler development during adulthood. Furthermore, we evaluated which body measurements better predicted future male quality. Additionally, using 488 individuals, we described age-class-specific variation in male body measurements and assessed the decline in antler size between adult and senescent stages (i.e. magnitude of senescence). Results agree with the assertion that there is no negative effect of a high investment in antler during early life on adult antler size or body mass, but we suggest the use of clean antlers as a more robust and reliable measure. The variables that better predicted body mass during adulthood were yearling body mass and body size at 6 months. Antler score between 10 and 18 months resulted in the best indicator of adult antler size. Finally, we support the idea that the magnitude of senescence in antler size is smaller in environments with higher resource availability during winter.

First Insights into the Population Genetic Structure and Heterozygosity-Fitness Relationship in Roe Deer Inhabiting the Area between the Alps and Dinaric Mountains

Simple Summary

We determined the genetic variability, population structure, and influence of genetic factors on two parameters of fitness (body mass and reproductive ability) in roe deer females in the contact zone between the Alps and the Dinaric Mountains by utilizing microsatellite variations in 214 individuals collected throughout Slovenia, Central Europe. Spatial differences in the genetic diversity of the species can be explained by population history, different approaches to population management and/or different connectivity among subpopulations. The population genetic structure confirms the high side fidelity of roe deer, but also shows the existence of admixtures of genes among different areas. We found evidence that genetic factors, including individual heterozygosity, influence body mass, confirming that heterozygosity positively affects fitness in wild populations. However, as the effect of genetic factors is usually masked or overruled by the influence of environmental factors, i.e., availability of resources, data on the joint influence of external and intrinsic factors on fitness and other life-history traits are needed to better predict the population dynamics of targeted species, which would enable sustainable, science-based population management.

Abstract

Across its pan-European distribution, the European roe deer (Capreolus capreolus) faces a wide diversity of environmental and climatic conditions; therefore, several factors, including intrinsic ones, shape life-history traits and cause significant variability in parameters of fitness. By utilizing microsatellite variations in 214 roe deer females collected throughout Slovenia, Central Europe, we determined the genetic variability and population structure of this species in the contact zone between the Alps and the Dinaric Mountains, i.e., over a wider area where data on the genetic outlook for this—the most common and widespread European wild ungulate—have been completely lacking so far. Throughout the country, we found moderate microsatellite diversity (Ho = 0.57–0.65) in relation to the observed heterozygosity reported for other roe deer populations in Europe. Spatial differences in genetic diversity of the species in Slovenia can be explained by population history linked to varying approaches to population management and/or different connectivity among subpopulations in topographically differentiated habitats. A country-wide pattern of genetic structure is clearly defined by separation of the populations into three groups present in the following regions: (i) Southern sub-Mediterranean and Karst regions, (ii) Central Slovenia, and (iii) the Sub-Pannonian Region in the north-east. This is also confirmed by evidencing a moderate isolation by distance, especially by separating southern samples (coastal Slovenia) from others. Levels of genetic differentiation vary among populations, which can be explained by the effect of natural geographical barriers or the presence of anthropogenic barriers such as urban areas and highways. In the subset of 172 yearling females, we analyzed the influence of genetic advantage (individual heterozygosity) and other genetic data (reflected in the structuring of the population) on body mass and reproductive ability. We found evidence that genetic factors influence the body mass of roe deer yearling females (explaining altogether 18.8% of body mass variance), and the level of individual heterozygosity alone also positively affected body mass, which is in accordance with the theory that heterozygosity is commonly positively correlated with fitness in wild populations. However, we did not uncover any effect of heterozygosity on two parameters of reproductive ability (fertility and potential reproductive outcome), indicating that several other factors, especially environmental ones, have a predominant effect on the parameters of fitness in roe deer.

Reproductive plasticity of female white-tailed deer at high density and under harsh climatic conditions

Life-history strategies of female ungulates usually depend on density-dependent and independent processes affecting body condition. Using a long-term data set on life-history traits of female white-tailed deer (2002-2014), we investigated the influence of population density and environmental factors on the reproductive effort of females. We also evaluated post-reproductive consequences on body condition using body mass, body fat, and body protein contents in the autumn following conception. We found that under high densities, females had a lower reproductive rate, which corresponds to a conservative reproduction strategy. However, females born at high density were more likely to reproduce and conceive larger litter size than females born at low density, a possible consequence of strong selective pressure in early life. Body condition was affected by reproduction; lactation had a large negative impact on body mass and body reserves, and conception, irrespectively of litter size, had a negative impact on body fat. Our long-term study demonstrates that plasticity in life-history strategies is a major determinant of reproductive potential for females living at high density and under harsh climates.

Modeling reproduction of whitetail deer and its applications

Many environmental factors, such as annual precipitation, temperature variations, and the embedded stochasticity of natural systems, affect resource availability from one region to the next, such that animal survival and reproduction rates differ by region. For species exhibiting phenotypic plasticity, embedding phenotypes in a model of population dynamics becomes important, as region-driven plastic responses play a significant role when estimating parameters values. In this paper, we discuss how to include observable characteristics and climate patterns in estimates of reproduction rates of whitetail deer (Odocoileus virginianus). Using many studies already available in the literature, we establish a strong correlation between reproduction rate and both body weight and USDA plant hardiness zone. We demonstrate the accuracy of the estimated whitetail deer fecundity rates for various geographical regions in North America and show that Bergmann's rule is necessary to maintain similar biological fitness between various spatial distributions of deer populations. We demonstrate that the standard deviation of the weight distribution has almost no effect on reproduction rate estimates for adult deer populations. However, statistical analysis reveals sensitivity of fawn reproduction rates to environmental stochasticity. We incorporate the reproduction function in a stage- and gender-based model and prove the existence of a stable solution. Finally, we demonstrate a possible application of the model using harvested deer weights, without collecting reproduction data directly.