Moose body mass variation revisited: disentangling effects of environmental conditions and genetics

Estimating body mass of wild pigs (Sus scrofa) using body morphometrics

Wild pigs (Sus scrofa) are invading many areas globally and impacting biodiversity and economies in their non-native range. Thus, wild pigs are often targeted for eradication efforts. Age- and sex-specific body measurements are important for informing these eradication efforts because they reflect body condition, resource availability, and fecundity, which are common indicators of population trajectory. However, body mass is often difficult to collect, especially on large individuals that require specialized equipment or multiple people to weigh. Measurements that can be rapidly taken by a single land or wildlife manager on any size wild pig without aid from specialized equipment would be beneficial if they accurately infer wild pig body mass. Our goals were to assess whether morphometric measurements could accurately predict wild pig body mass, and to provide tools to directly input these measures and estimate wild pig body mass. Using linear models, we quantified the relationship between body mass and morphometric measurements (i.e., body length, chest girth, ear length, eye to snout length, hindfoot length, shoulder length, and tail length) from a subset (n = 102) of wild pigs culled at the Mississippi Alluvial Valley, Mississippi, USA. We evaluated separate models for each individual morphometric measurement. We then used the model coefficients to develop equations to predict wild pig body mass. We validated these equations predicting body mass of 1592 individuals collected across eight areas in Australia, Guam, and the USA for cross-validation. Each developed equation remained accurate when cross-validated across regions. Body length, chest girth, and shoulder length were the morphometrics that best predicted wild pig body mass. Our analyses indicated it is possible to use the presented equations to infer wild pig body mass from simple metrics.

Within-individual leaf allometry and the evolution of leaf morphology: A multilevel analysis of leaf allometry in temperate Viburnum (Adoxaceae) species

A critical issue in evolutionary biology is understanding the relationship between macroevolutionary patterns of diversity and the origin of variation at the organismal level. Among-individual allometry, the relationship between the size and shape of a structure among organisms at a fixed developmental stage, is often similar to evolutionary allometry, the relationship between the size and shape of a structure among populations or species, and the genetic and developmental process that underlie allometric relationships at both levels are thought to influence evolutionary diversification. Metameric organisms present an additional level of allometry: the relationship between the size and shape of structures within individuals. We propose that within-individual allometry is also related to evolutionary diversification among metameric organisms. We explore this idea in temperate deciduous Viburnum (Adoxaceae) species that bear two types of leaves, that is, preformed and neoformed leaves, with contrasting patterns of development. Examination of within-individual, among-individual, among-population, and among-species allometry of leaf shape in both leaf types showed that the slopes of all allometric relationships were significantly different from isometry, and their sign was consistent across allometric hierarchies. Although the allometric slope of preformed leaves was constant across allometry levels, the allometric slope of neoformed leaves became increasingly steeper. We suggest that allometric variation underlying evolutionary diversification in metameric organisms may manifest among individuals and also among their repeated structures. Moreover, structures with contrasting patterns of development within metameric organisms can experience different degrees of developmental constraint, and this can in turn affect morphological diversification.

Habitat and climate shape growth patterns in a mountain ungulate

Uptake and use of energy are of key importance for animals living in temperate environments that undergo strong seasonal changes in forage quality and quantity. In ungulates, energy intake strongly affects body mass gain, an important component of individual fitness. Energy allocation among life-history traits can be affected by internal and external factors. Here, we investigate large-scale variation in body growth patterns of Alpine chamois Rupicapra rupicapra rupicapra, in relation to sex, age, temperature, and habitat variations across 31 (sub)populations in the Central European Alps. Taking advantage of an exceptionally large dataset (n = 178,175) of chamois hunted over 27 consecutive years between 1993 and 2019 in mountain ranges with different proportions of forest cover, we found that (i) patterns of body mass growth differ between mountain ranges, with lower body mass but faster mass growth with increasing proportion of forest cover and that (ii) the effect of spring and summer temperatures on changes in body growth patterns are larger in mountain ranges with lower forest cover compared to mountain ranges with higher forest cover. Our results show that patterns of body mass growth within a species are more plastic than expected and depend on environmental and climatic conditions. The recent decline in body mass observed in Alpine chamois populations may have greater impacts on populations living above the treeline than in forests, which may buffer against the effects of increasing temperatures on life-history traits.

When does weather synchronize life-history traits? Spatiotemporal patterns in juvenile body mass of two ungulates

Theory predicts that animal populations will be synchronized over large distances by weather and climatic conditions with high spatial synchrony. However, local variation in population responses to weather, and low synchrony in key weather variables or in other ecological processes may reduce the population synchrony. We investigated to what extent temperature and precipitation during different periods of the year synchronized juvenile body mass of moose and reindeer in Norway. We expected high synchronizing effect of weather variables with a high and consistent explanatory power on body mass dynamics across populations, and a weaker synchronizing effect of weather variables whose effect on body mass varied among populations. Juvenile body mass in both species was related to temperature and precipitation during several periods of the year. Temperature had the strongest explanatory power in both species, with a similar effect across all populations. There was higher spatial synchrony in temperature compared to precipitation, and accordingly temperature had the strongest synchronizing effect on juvenile body mass. Moreover, periods with strong explanatory power had stronger synchronizing effect on juvenile body mass in both species. However, weather variables with large variation in the effects on body mass among populations had weak synchronizing effect. The results confirm that weather has a large impact on the spatial structure of population properties but also that spatial heterogeneity, for instance, in environmental change or population density may affect how and to what extent populations are synchronized.

Phylogeography of moose in western North America

Subspecies designations within temperate species’ ranges often reflect populations that were isolated by past continental glaciation, and glacial vicariance is believed to be a primary mechanism behind the diversification of several subspecies of North American cervids. We used genetics and the fossil record to study the phylogeography of three moose subspecies (Alces alces andersoni, A. a. gigas, and A. a. shirasi) in western North America. We sequenced the complete mitochondrial genome (16,341 base pairs; n = 60 moose) and genotyped 13 nuclear microsatellites (n = 253) to evaluate genetic variation among moose samples. We also reviewed the fossil record for detections of all North American cervids to comparatively assess the evidence for the existence of a southern refugial population of moose corresponding to A. a. shirasi during the last glacial maximum of the Pleistocene. Analysis of mtDNA molecular variance did not support distinct clades of moose corresponding to currently recognized subspecies, and mitogenomic haplotype phylogenies did not consistently distinguish individuals according to subspecies groupings. Analysis of population structure using microsatellite loci showed support for two to five clusters of moose, including the consistent distinction of a southern group of moose within the range of A. a. shirasi. We hypothesize that these microsatellite results reflect recent, not deep, divergence and may be confounded by a significant effect of geographic distance on gene flow across the region. Review of the fossil record showed no evidence of moose south of the Wisconsin ice age glaciers ≥ 15,000 years ago. We encourage the integration of our results with complementary analyses of phenotype data, such as morphometrics, originally used to delineate moose subspecies, for further evaluation of subspecies designations for North American moose.

Moose selecting for specific nutritional composition of birch places limits on food acceptability

Despite decades of intense research, it remains largely unsolved which nutritional factors underpin food selection by large herbivores in the wild. We measured nutritional composition of birch foliage (Betula pubescens) available to, and used by, moose (Alces alces) in natural settings in two neighboring regions with contrasting animal body mass. This readily available food source is a staple food item in the diet of moose in the high‐fitness region, but apparently underutilized by moose in the low‐fitness region. Available birch foliage in the two regions had similar concentrations of macronutrients (crude protein [CP], fiber fractions, and water‐soluble carbohydrates [WSC]), although a notably lower variation of WSC in the low‐fitness region. For minerals, there were several area differences: available birch foliage in the low‐fitness region had less Mg (depending on year) and P, but more Ca, Zn, Cu, and Mn. It also had higher concentrations of some plant secondary metabolites: chlorogenic acids, quercetins, and especially MeOH‐soluble condensed tannins. Despite the area differences in available foliage, we found the same nutritional composition of birch foliage used in the two regions. Compared to available birch foliage, moose consistently used birch foliage with more CP, more structural fiber (mainly hemicellulose), less WSC, higher concentrations of several minerals (Ca, Zn, K, Mn, Cu), and lower concentrations of some secondary metabolites (most importantly, MeOH‐soluble condensed tannins). Our study conceptually supports the nutrient‐balancing hypothesis for a large herbivore: within a given temporal frame, moose select for plant material that matches a specific nutritional composition. As our data illustrate, different moose populations may select for the same composition even when the nutritional composition available in a given food source varies between their living areas. Such fastidiousness limits the proportion of available food that is acceptable to the animal and has bearings on our understanding and application of the concept of carrying capacity.

Reproduction in moose at their southern range limit

Reproduction is a critical fitness component in large herbivores. Biogeographic models predict that populations occurring at the edges of the range may have compromised reproductive rates because of inferior habitat at range peripheries. When reproductive rates are chronically low, ungulate populations may lack the resiliency to rebound quickly after periods of environmental stress, and this effect may be greatest for heat-sensitive organisms at their southern range limit. To assess the demographic vulnerability of moose (Alces alces), we studied relationships between reproductive rates, maternal age, and rump fat in the southernmost naturally occurring moose population in North America. For prime-aged moose in our study, pregnancy rates were high (92%), but moose aged < 3 or > 9 years had low pregnancy rates (32% and 38%, respectively). The relationship between rump fat and pregnancy was nonlinear such that a threshold of at least 2mm of rump fat yielded a high probability of being pregnant midwinter. In contrast, among pregnant moose, the probability of both producing a calf and recruiting it until spring increased linearly with rump fat. We also conducted a meta-analysis of pregnancy and twinning rates for adult (≥ 2 years) moose across a latitudinal gradient to compare reproductive rates from our study to other populations in North America. Moose living at southern latitudes tended to have lower reproductive rates than those living in the core of moose range, implying that southern moose populations may be demographically more vulnerable than northern moose populations.