Fluctuating asymmetry and genetic variability in the roe deer (Capreolus capreolus): a test of the developmental stability hypothesis in mammals using neutral molecular markers

Skull asymmetry in various sheep breeds: Directional asymmetry and fluctuating asymmetry

Sheep (Ovis aries) play an important role in the economy of Turkey and the Balkan Peninsula due to their use in farming. As a domesticated species, sheep's morphometric and morphological diversity is likely determined by selective breeding practices rather than geographic distribution. This study aimed to analyse four different sheep breed skulls and reveal skull asymmetry using geometric morphometric methods. For this purpose, 2D images of 52 sheep skulls from different breeds were analysed from the dorsal view of the skull, using 28 landmarks. In the comparison of sheep skulls from the dorsal view, the first principal components for directional asymmetry (DA) and fluctuating asymmetry (FA) were 32.98% and 39.62% of the total variation, respectively. Sharri and Ivesi (Awassi) sheep breeds had the broadest distribution of skull shapes among the breeds, while Lara e Polisit was the most conservative breed. DA was used as a measure of biomechanical constraints, and FA was used as an indicator of environmental stress. Consistent with DA, both differences in centroid size and shape between breeds were statistically significant. No differences between males and females related to asymmetry were revealed. Ivesi sheep revealed the highest fluctuating asymmetry. Geometric morphometric methods proved to be a useful tool for distinguishing differences in the shape of the skull of different sheep breeds and also can be useful for taxonomic purposes.

The Reliability of Fluctuating Asymmetry in Population Estimation: The Case of Feedlot Red Deer

Three FA indices showed correlations with age and magnitude of traits, but not in general. Significant correlations between magnitude of traits and their FA were more pronounced in AFA (12 traits) than in RFA (10 traits) in all age classes except yearlings. For the tray tine form (curvature), FA significantly correlated with its magnitude in young, middle-aged and ripe stags, which indicates that the trait is a reliable indicator of asymmetry. Significant differences in AFA among age classes were found in four traits (weight of dry antlers, volume of antlers, distal circumference of beams and total length of crown tines). By RFA, a significant difference among age classes was only found for the distal circumference of beams. Thus, AFA is a more vulnerable condition index. Contrary to other research findings, developmental instability was more pronounced in older age classes. In yearlings, no significant FA dependence on the trait of antler size was detected, but in certain traits, an asymmetry detected at an early age remains visible later as well, although in stags grown under relatively optimal (especially trophic) environment conditions, developmental instability was present anyway. This proposes two hypotheses for further research: Competition may be manifested even under controlled conditions, which might jeopardize the developmental stability of certain individuals, or some traits will show developmental instability regardless of relatively good environmental conditions.

Does stress mess with rodents' heads? Influence of habitat amount and genetic factors in mandible fluctuating asymmetry in South American water rats (Nectomys squamipes, Sigmodontinae) from Brazilian Atlantic rainforest remnants

Loss of developmental stability can lead to deviations from bilateral symmetry (i.e. Fluctuating Asymmetry - FA), and is thought to be caused by environmental and genetic factors associated with habitat loss and stress. Therefore, levels of FA might be a valuable tool to monitor wild populations if FA serves as an indicator of exposure to stress due to impacts of habitat loss and fragmentation. In studies examining FA and habitat fragmentation, FA levels are often explained by loss of genetic variation, though few studies have addressed FA's use as indicator of environmental impact. Here, we investigated whether habitat loss, genetic variation, and/or inbreeding affect the developmental instability in Brazilian Atlantic forest populations of a Neotropical water rat (Nectomys squamipes). We sampled individuals from eight sites within Atlantic forest remnants with different amounts of available forest habitat and assessed FA levels with geometric morphometric techniques using adult mandibles. We used observed heterozygosity (Ho) and inbreeding coefficient (Fis), from seven microsatellite markers, as a proxy of genetic variation at individual and population levels. Populations were not significantly different for shape or size FA levels. Furthermore, interindividual variation in both shape and size FA levels and interpopulational differences in size FA levels were best explained by chance. However, habitat amount was negatively associated with both interpopulational variance and average shape FA levels. This association was stronger in populations living in areas with <28% of forest cover, which presented higher variance and higher average FA, suggesting that Nectomys squamipes might have a tolerance threshold to small availability of habitat. Our work is one of the first to use FA to address environmental stress caused by habitat loss in small mammal populations from a Neotropical biome. We suggest that shape FA might serve as a conservation tool to monitor human impact on natural animal populations.

Developmental instability and phenotypic evolution in a small and isolated bear population

We explored fluctuating asymmetry (FA) and morphological integration (MI) in the skull of the small, highly inbred and divergent Apennine bear (Ursus arctos marsicanus), to explore its uniqueness and investigate any potential effects of inbreeding depression. We used 3D geometric morphometrics contrasting Apennine bears with other two large outbred bear populations from Scandinavia and Kamchatka as controls. Shape divergence and variability were explored by a principal component analysis on aligned coordinates of 39 landmarks. Procrustes ANOVA, morphological disparity and the global integration index were used to explore FA, shape variance and MI. By remarking Apennine bears as a highly divergent phenotype, we recorded the highest FA and deviation from self-similarity compared with the other two control populations. We conclude that Apennine bears are likely facing developmental instability as a consequence of inbreeding depression, whereas the divergent trait covariance pattern may represent a potential source of evolutionary novelties. We discuss the implications for the conservation and management of this imperiled taxon.

Long-term stress level in a small mammal species undergoing range expansion

Rapid climate change is currently altering species distribution ranges. Evaluating the long-term stress level in wild species undergoing range expansion may help better understanding how species cope with the changing environment. Here, we focused on the white-footed mouse (Peromyscus leucopus), a widespread small mammal species in North-America whose distribution range is rapidly shifting northward. We evaluated long-term stress level in several populations of P. leucopus in Quebec (Canada), from the northern edge of the species distribution to more core populations in Southern Quebec. We first tested the hypothesis that populations at the range margin are under higher stress than more established populations in the southern region of our study area. We then compared four measures of long-term stress level to evaluate the congruence between these commonly used methods. We did not detect any significant geographical trend in stress level across our study populations of P. leucopus. Most notably, we found no clear congruence between the four measures of stress level we used, and conclude that these four commonly used methods are not equivalent, thereby not comparable across studies.

Study of non-metric characters of the skull to determine the epigenetic variability in populations of the European wildcat (Felis silvestris silvestris) and domestic cats (Felis catus)

We studied the variability of non-metric cranial traits, mainly foramina, of European wildcats (Felis silvestris silvestris) and domestic cats (Felis catus) from Germany based on 28 non-metric traits in 211 skulls. The domestic cats were grouped together as a statistical population. The wildcats were divided into two populations: Harz and Hesse, which were further subdivided, based on traffic infrastructure, natural landscape, and in the Harz, on time period. Epigenetic variability, epigenetic distance and the fluctuating asymmetry were calculated to assess genetic variability, possible depressions and population stability. The epigenetic variability Iev of the wildcat groups ranged from 0.27 (Hesse II) to 0.40 (Harz I). The difference in Iev between all specimens from Harz and Hesse respectively was less (Iev = 0.37 Harz and 0.31 Hesse). Compared to other studies these values are not assumed to indicate genetic depression. The epigenetic distance between the wildcat samples is 0.0774 overall, and in each case higher between sub-groups of the Harz and Hesse than between groups within these regions, respectively. The significant epigenetic distance between Harz and Hesse might indicate—at least past formerly—restricted connectivity between these regions. The fluctuating asymmetry for wildcats in total is 11.74% and in the sub-groups it ranges from 8.47 to 16.14%. These values are below 20% are at the lower range known from populations of other mammal species. The use of fluctuating asymmetry had also been discussed critically in its usefulness to assess viability of populations.

Genetic structure of phenotypic robustness in the collaborative cross mouse diallel panel

Developmental stability and canalization describe the ability of developmental systems to minimize phenotypic variation in the face of stochastic micro-environmental effects, genetic variation and environmental influences. Canalization is the ability to minimize the effects of genetic or environmental effects, whereas developmental stability is the ability to minimize the effects of micro-environmental effects within individuals. Despite much attention, the mechanisms that underlie these two components of phenotypic robustness remain unknown. We investigated the genetic structure of phenotypic robustness in the collaborative cross (CC) mouse reference population. We analysed the magnitude of fluctuating asymmetry (FA) and among-individual variation of cranial shape in reciprocal crosses among the eight parental strains, using geometric morphometrics and a diallel analysis based on a Bayesian approach. Significant differences among genotypes were found for both measures, although they were poorly correlated at the level of individuals. An overall positive effect of inbreeding was found for both components of variation. The strain CAST/EiJ exerted a positive additive effect on FA and, to a lesser extent, among-individual variance. Sex- and other strain-specific effects were not significant. Neither FA nor among-individual variation was associated with phenotypic extremeness. Our results support the existence of genetic variation for both developmental stability and canalization. This finding is important because robustness is a key feature of developmental systems. Our finding that robustness is not related to phenotypic extremeness is consistent with theoretical work that suggests that its relationship to stabilizing selection is not straightforward.

Testing the relationship between human occupancy in the landscape and tadpole developmental stress

Amphibian population declines are widespread; the main causal factors are human related and include habitat fragmentation due to agriculture, mining, fires, and urban development. Brazil is the richest country in species of amphibians, and the Brazilian regions with the greatest amphibian diversity are experiencing relatively high rates of habitat destruction, but there are presently relatively few reports of amphibian declines. It is thus important to develop research methods that will detect deterioration in population health before severe declines occur. We tested the use of measurements of fluctuating asymmetry (FA) taken on amphibian larvae to detect anthropogenic stress. We hypothesized that greater human occupancy in the landscape might result in more stressful conditions for amphibians. We conducted this study at the Espinhaço mountain range in southeastern Brazil, using as a model an endemic species (Bokermannohyla saxicola, Hylidae). We chose two tadpole denticle rows and eye-nostril distance as traits for FA measurement. We measured percent cover of human-altered habitats in the landscape around tadpole sampling points and measured FA levels in sampled tadpoles. We found FA levels to differ among localities but found no relationship between human modification of the landscape and tadpole FA levels. Levels of FA in the traits we examined may not be strongly affected by environmental conditions, or may be affected by local variables that were not captured by our landscape-scale measures. Alternatively, populations may be genetically differentiated, affecting how FA levels respond to stress and obscuring the effects of anthropogenic disturbance.

Developmental stability covaries with genome-wide and single-locus heterozygosity in house sparrows

Fluctuating asymmetry (FA), a measure of developmental instability, has been hypothesized to increase with genetic stress. Despite numerous studies providing empirical evidence for associations between FA and genome-wide properties such as multi-locus heterozygosity, support for single-locus effects remains scant. Here we test if, and to what extent, FA co-varies with single- and multilocus markers of genetic diversity in house sparrow (Passer domesticus) populations along an urban gradient. In line with theoretical expectations, FA was inversely correlated with genetic diversity estimated at genome level. However, this relationship was largely driven by variation at a single key locus. Contrary to our expectations, relationships between FA and genetic diversity were not stronger in individuals from urban populations that experience higher nutritional stress. We conclude that loss of genetic diversity adversely affects developmental stability in P. domesticus, and more generally, that the molecular basis of developmental stability may involve complex interactions between local and genome-wide effects. Further study on the relative effects of single-locus and genome-wide effects on the developmental stability of populations with different genetic properties is therefore needed.

Turtle carapace anomalies: the roles of genetic diversity and environment

BACKGROUND

Phenotypic anomalies are common in wild populations and multiple genetic, biotic and abiotic factors might contribute to their formation. Turtles are excellent models for the study of developmental instability because anomalies are easily detected in the form of malformations, additions, or reductions in the number of scutes or scales.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we integrated field observations, manipulative experiments, and climatic and genetic approaches to investigate the origin of carapace scute anomalies across Iberian populations of the European pond turtle, Emys orbicularis. The proportion of anomalous individuals varied from 3% to 69% in local populations, with increasing frequency of anomalies in northern regions. We found no significant effect of climatic and soil moisture, or climatic temperature on the occurrence of anomalies. However, lower genetic diversity and inbreeding were good predictors of the prevalence of scute anomalies among populations. Both decreasing genetic diversity and increasing proportion of anomalous individuals in northern parts of the Iberian distribution may be linked to recolonization events from the Southern Pleistocene refugium.

CONCLUSIONS/SIGNIFICANCE

Overall, our results suggest that developmental instability in turtle carapace formation might be caused, at least in part, by genetic factors, although the influence of environmental factors affecting the developmental stability of turtle carapace cannot be ruled out. Further studies of the effects of environmental factors, pollutants and heritability of anomalies would be useful to better understand the complex origin of anomalies in natural populations.

Evolutionary history shapes the association between developmental instability and population-level genetic variation in three-spined sticklebacks

Developmental instability (DI) is the sensitivity of a developing trait to random noise and can be measured by degrees of directionally random asymmetry [fluctuating asymmetry (FA)]. FA has been shown to increase with loss of genetic variation and inbreeding as measures of genetic stress, but associations vary among studies. Directional selection and evolutionary change of traits have been hypothesized to increase the average levels of FA of these traits and to increase the association strength between FA and population-level genetic variation. We test these two hypotheses in three-spined stickleback (Gasterosteus aculeatus L.) populations that recently colonized the freshwater habitat. Some traits, like lateral bone plates, length of the pelvic spine, frontal gill rakers and eye size, evolved in response to selection regimes during colonization. Other traits, like distal gill rakers and number of pelvic fin rays, did not show such phenotypic shifts. Contrary to a priori predictions, average FA did not systematically increase in traits that were under presumed directional selection, and the increases observed in a few traits were likely to be attributable to other factors. However, traits under directional selection did show a weak but significantly stronger negative association between FA and selectively neutral genetic variation at the population level compared with the traits that did not show an evolutionary change during colonization. These results support our second prediction, providing evidence that selection history can shape associations between DI and population-level genetic variation at neutral markers, which potentially reflect genetic stress. We argue that this might explain at least some of the observed heterogeneities in the patterns of asymmetry.

Mandible asymmetry and genetic diversity in island populations of the common shrew, Sorex araneus

Mandibles from 13 island and six mainland populations of common shrews from the west coast of Scotland were subjected to geometric morphometric analysis in order to investigate the relationship between genetic diversity and fluctuating asymmetry. Although population mean shape fluctuating asymmetry (FA) and size FA were significantly inversely correlated with population genetic diversity this result was substantially due to one island. Sanda, the smallest island with by far the lowest genetic diversity, also had the highest FA. When Sanda was removed from the analysis, the relationship was not significant. There was no relationship between genetic diversity and FA at the individual level, whether measured as mean locus heterozygosity or d(2). In general, if genetic variation affects FA at all, the effect is weak and may only be of biological interest in very small populations.