Morphometric models for estimating bite force in Mus and Rattus: mandible shape and size perform better than lever-arm ratios.

Morphological traits are frequently used as proxies for functional outputs such as bite force performance. This allows researchers to infer and interpret the impacts of functional variation, notably in adaptive terms. Despite their mechanical bases, the predictive power of these proxies for performance is not always tested. In particular, their accuracy at the intraspecific level is rarely assessed, and they have sometimes been shown to be unreliable. Here, we compared the performance of several morphological proxies in estimating in vivo bite force, across five species of murine rodents, at the interspecific and intraspecific levels. Proxies used included the size and shape of the mandible, as well as individual and combined muscular mechanical advantage (temporalis, superficial masseter and deep masseter). Maximum voluntary bite force was measured in all individuals included. To test the accuracy of predictions allowed by the proxies, we combined linear regressions with a leave-one-out approach, estimating an individual's bite force based on the rest of the dataset. The correlations between estimated values and the in vivo measurements were tested. At the interspecific and intraspecific levels, size and shape were better estimators than mechanical advantage. Mechanical advantage showed some predictive power at the interspecific level, but generally not within species, except for the deep masseter in Rattus In a few species, size and shape did not allow us to predict bite force. Extrapolations of performance based on mechanical advantage should therefore be used with care, and are mostly unjustified within species. In the latter case, size and shape are preferable.

Changing landscapes of Southeast Asia and rodent-borne diseases: decreased diversity but increased transmission risks.

The reduction in biodiversity from land use change due to urbanization and agricultural intensification appears to be linked to major epidemiological changes in many human diseases. Increasing disease risks and the emergence of novel pathogens result from increased contact among wildlife, domesticated animals, and humans. We investigated the relationship between human alteration of the environment and the occurrence of generalist and synanthropic rodent species in relation to the diversity and prevalence of rodent-borne pathogens in Southeast Asia, a hotspot of threatened and endangered species, and a foci of emerging infectious diseases. We used data from an extensive pathogen survey of rodents from seven sites in mainland Southeast Asia in conjunction with past and present land cover analyses. At low spatial resolutions, we found that rodent-borne pathogen richness is negatively associated with increasing urbanization, characterized by increased habitat fragmentation, agriculture cover and deforestation. However, at a finer spatial resolution, we found that some major pathogens are favored by environmental characteristics associated with human alteration including irrigation, habitat fragmentation, and increased agricultural land cover. In addition, synanthropic rodents, many of which are important pathogen reservoirs, were associated with fragmented and human-dominated landscapes, which may ultimately enhance the opportunities for zoonotic transmission and human infection by some pathogens.

Sex reversal induces size and performance differences among females of the African pygmy mouse, Mus minutoides.

Differences in biological performance, at both intra- and inter-specific levels, have often been linked to morphology but seldom to behavioural or genotypic effects. We tested performance at the intraspecific level by measuring bite force in the African pygmy mouse, Mus minutoides. This species displays an unusual sex determination system, with sex-reversed, X*Y females carrying a feminizing X* chromosome. X*Y females cannot be differentiated from XX females based on external or gonadal morphology; however, they are known to be more aggressive. We found that bite force was higher in X*Y females than in other females and males. We then performed geometric morphometric analyses on their skulls and mandibles and found that the higher performance of X*Y females was mainly explained by a greater overall skull size. The effects of the X* chromosome thus go beyond feminization, and extend to whole-organism performance and morphology. Our results also suggest limited effects of behaviour on bite force.

Ecological and evolutionary influences on body size and shape in the Galápagos marine iguana (Amblyrhynchus cristatus).

Oceanic islands are often inhabited by endemic species that have undergone substantial morphological evolutionary change due to processes of multiple colonizations from various source populations, dispersal, and local adaptation. Galápagos marine iguanas are an example of an island endemic exhibiting high morphological diversity, including substantial body size variation among populations and sexes, but the causes and magnitude of this variation are not well understood. We obtained morphological measurements from marine iguanas throughout their distribution range. These data were combined with genetic and local environmental data from each population to investigate the effects of evolutionary history and environmental conditions on body size and shape variation and sexual dimorphism. Our results indicate that body size and shape are highly variable among populations. Sea surface temperature and island perimeter, but not evolutionary history as depicted by phylogeographic patterns in this species, explain variation in body size among populations. Conversely, evolutionary history, but not environmental parameters or island size, was found to influence variation in body shape among populations. Finally, in all populations except one, we found strong sexual dimorphism in body size and shape in which males are larger, with higher heads than females, while females have longer heads than males. Differences among populations suggest that plasticity and/or genetic adaptation may shape body size and shape variation in marine iguanas. This study will help target future investigations to address the contribution of plasticity versus genetic adaptation on size and shape variation in marine iguanas.

Habitat fragmentation alters the properties of a host-parasite network: rodents and their helminths in South-East Asia.

1. While the effects of deforestation and habitat fragmentation on parasite prevalence or richness are well investigated, host-parasite networks are still understudied despite their importance in understanding the mechanisms of these major disturbances. Because fragmentation may negatively impact species occupancy, abundance and co-occurrence, we predict a link between spatiotemporal changes in habitat and the architecture of host-parasite networks. 2. For this, we used an extensive data set on 16 rodent species and 29 helminth species from seven localities of South-East Asia. We analysed the effects of rapid deforestation on connectance and modularity of helminth-parasite networks. We estimated both the degree of fragmentation and the rate of deforestation through the development of land uses and their changes through the last 20 to 30 years in order to take into account the dynamics of habitat fragmentation in our statistical analyses. 3. We found that rapid fragmentation does not affect helminth species richness per se but impacts host-parasite interactions as the rodent-helminth network becomes less connected and more modular. 4. Our results suggest that parasite sharing among host species may become more difficult to maintain with the increase of habitat disturbance.

Non-random occurrence of Robertsonian translocations in the house mouse (Mus musculus domesticus): is it related to quantitative variation in the minor satellite?

The house mouse, Mus musculus domesticus, shows extraordinary chromosomal diversity driven by fixation of Robertsonian (Rb) translocations. The high frequency of this rearrangement, which involves the centromeric regions, has been ascribed to the architecture of the satellite sequence (high quantity and homogeneity). This promotes centromere-related translocations through unequal recombination and gene conversion. A characteristic feature of Rb variation in this subspecies is the non-random contribution of different chromosomes to the translocation frequency, which, in turn, depends on the chromosome size. Here, the association between satellite quantity and Rb frequency was tested by PRINS of the minor satellite which is the sequence involved in the translocation breakpoints. Five chromosomes with different translocation frequencies were selected and analyzed among wild house mice from 8 European localities. Using a relative quantitative measurement per chromosome, the analysis detected a large variability in signal size most of which was observed between individuals and/or localities. The chromosomes differed significantly in the quantity of the minor satellite, but these differences were not correlated with their translocation frequency. However, the data uncovered a marginally significant correlation between the quantity of the minor satellite and chromosome size. The implications of these results on the evolution of the chromosomal architecture in the house mouse are discussed.

Emotional experiences and psychological well-being in 51 countries during the COVID-19 pandemic.

The COVID-19 pandemic presents challenges to psychological well-being, but how can we predict when people suffer or cope during sustained stress? Here, we test the prediction that specific types of momentary emotional experiences are differently linked to psychological well-being during the pandemic. Study 1 used survey data collected from 24,221 participants in 51 countries during the COVID-19 outbreak. We show that, across countries, well-being is linked to individuals' recent emotional experiences, including calm, hope, anxiety, loneliness, and sadness. Consistent results are found in two age, sex, and ethnicity-representative samples in the United Kingdom (n = 971) and the United States (n = 961) with preregistered analyses (Study 2). A prospective 30-day daily diary study conducted in the United Kingdom (n = 110) confirms the key role of these five emotions and demonstrates that emotional experiences precede changes in well-being (Study 3). Our findings highlight differential relationships between specific types of momentary emotional experiences and well-being and point to the cultivation of calm and hope as candidate routes for well-being interventions during periods of sustained stress. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Cytonuclear discordance among Southeast Asian black rats (Rattus rattus complex).

Black rats are major invasive vertebrate pests with severe ecological, economic and health impacts. Remarkably, their evolutionary history has received little attention, and there is no firm agreement on how many species should be recognized within the black rat complex. This species complex is native to India and Southeast Asia. According to current taxonomic classification, there are three taxa living in sympatry in several parts of Thailand, Cambodia and Lao People's Democratic Republic, where this study was conducted: two accepted species (Rattus tanezumi, Rattus sakeratensis) and an additional mitochondrial lineage of unclear taxonomic status referred to here as 'Rattus R3'. We used extensive sampling, morphological data and diverse genetic markers differing in rates of evolution and parental inheritance (two mitochondrial DNA genes, one nuclear gene and eight microsatellite loci) to assess the reproductive isolation of these three taxa. Two close Asian relatives, Rattus argentiventer and Rattus exulans, were also included in the genetic analyses. Genetic analyses revealed discordance between the mitochondrial and nuclear data. Mitochondrial phylogeny studies identified three reciprocally monophyletic clades in the black rat complex. However, studies of the phylogeny of the nuclear exon interphotoreceptor retinoid-binding protein gene and clustering and assignation analyses with eight microsatellites failed to separate R. tanezumi and R3. Morphometric analyses were consistent with nuclear data. The incongruence between mitochondrial and nuclear (and morphological) data rendered R. tanezumi/R3 paraphyletic for mitochondrial lineages with respect to R. sakeratensis. Various evolutionary processes, such as shared ancestral polymorphism and incomplete lineage sorting or hybridization with massive mitochondrial introgression between species, may account for this unusual genetic pattern in mammals.

A unifying model for the analysis of phenotypic, genetic, and geographic data.

Recognition of evolutionary units (species, populations) requires integrating several kinds of data, such as genetic or phenotypic markers or spatial information in order to get a comprehensive view concerning the differentiation of the units. We propose a statistical model with a double original advantage: (i) it incorporates information about the spatial distribution of the samples, with the aim to increase inference power and to relate more explicitly observed patterns to geography and (ii) it allows one to analyze genetic and phenotypic data within a unified model and inference framework, thus opening the way to robust comparisons between markers and possibly combined analyses. We show from simulated data as well as real data that our method estimates parameters accurately and is an improvement over alternative approaches in many situations. The power of this method is exemplified using an intricate case of inter- and intraspecies differentiation based on an original data set of georeferenced genetic and morphometric markers obtained on Myodes voles from Sweden. A computer program is made available as an extension of the R package Geneland.

First discovery of parasite eggs in a vertebrate coprolite of the Late Triassic in Thailand.

A paleoparasitological investigation of a vertebrate coprolite from the Huai Hin Lat Formation (Upper Triassic) was carried out. Five morphotypes of potential parasite eggs or sporocysts were identified in the coprolite by microscopic analysis using thin section technique. The rounded or oval shape and thick shell of one of the five morphotypes suggests that it belongs to nematode of the order Ascaridida. Systematic assignment of other morphotypes cannot be done in detail but suggests that the host was parasitized by different species of parasites. This is the first record of parasites in terrestrial vertebrate hosts from the Late Triassic in Asia and it provides new information on parasite-host interactions during the Mesozoic era.

Melanistic coloration does not influence thermoregulation in the crepuscular gecko Eublepharis macularius.

Body coloration in ectotherms serves multiple biological functions, including avoiding predators, communicating with conspecific individuals, and involvement in thermoregulation. As ectotherms rely on environmental sources of heat to regulate their internal body temperature, stable melanistic body coloration or color change can be used to increase or decrease heat absorption and heat exchange with the environment. While melanistic coloration for thermoregulation functions to increase solar radiation absorption and consequently heating in many diurnal ectotherms, research on crepuscular and nocturnal ectotherms is lacking. Since crepuscular and nocturnal ectotherms generally absorb heat from the substrate, in these organisms melanistic coloration may have other primary functions beside thermoregulation. As such, in this work we hypothesized that the proportion of dorsal melanistic body coloration would not influence heating and cooling rates in the crepuscular gecko, Eublepharis macularius, and that changes in environmental temperature would not trigger color changes in this species. Temperature measurements of the geckos and of the environment were taken using infrared thermography and temperature loggers. Color data were obtained using objective photography and a newly developed custom software package. We found that body temperature reflected substrate temperatures, and that the proportion of melanistic coloration has no influence on heating or cooling rates or on color changes. These findings support that melanistic coloration in E. macularius may not be used for thermoregulation and strengthen the hypothesis that in animals active in low light conditions, melanistic coloration may be used instead for camouflage or other functions.

Dating cryptodiran nodes: origin and diversification of the turtle superfamily Testudinoidea.

The superfamily Testudinoidea is the most diverse and widely distributed clade of extant turtles. Surprisingly, despite an extensive fossil record, and increasing amount of molecular data available, the temporal origin of this group is still largely unknown. To address this issue, we used a comprehensive molecular dataset to perform phylogenetic and molecular dating analyses, as well as seven fossil constraints to calibrate the ages of the nodes in the phylogeny. The molecular dataset includes the complete mitochondrial genomes of 37 turtle species, including newly sequenced mitochondrial genomes of Phrynops hilarii, Emys orbicularis, Rhinoclemmys punctularia, and Chelonoidis nigra, and four nuclear markers. Our results revealed that the earliest divergences within crown testudinoids occurred around 95.0 Mya, in the early Late Cretaceous, earlier than previously reported, raising new questions about the historical biogeography of this group.

Flexible conservatism in the skull modularity of convergently evolved myrmecophagous placental mammals.

BACKGROUND: The skull of placental mammals constitutes one of the best studied systems for phenotypic modularity. Several studies have found strong evidence for the conserved presence of two- and six-module architectures, while the strength of trait correlations (integration) has been associated with major developmental processes such as somatic growth, muscle-bone interactions, and tooth eruption. Among placentals, ant- and termite-eating (myrmecophagy) represents an exemplar case of dietary convergence, accompanied by the selection of several cranial morphofunctional traits such as rostrum elongation, tooth loss, and mastication loss. Despite such drastic functional modifications, the covariance patterns of the skull of convergently evolved myrmecophagous placentals are yet to be studied in order to assess the potential consequences of this dietary shift on cranial modularity. RESULTS: Here, we performed a landmark-based morphometric analysis of cranial covariance patterns in 13 species of myrmecophagous placentals. Our analyses reveal that most myrmecophagous species present skulls divided into six to seven modules (depending on the confirmatory method used), with architectures similar to those of non-myrmecophagous placentals (therian six modules). Within-module integration is also similar to what was previously described for other placentals, suggesting that most covariance-generating processes are conserved across the clade. Nevertheless, we show that extreme rostrum elongation and tooth loss in myrmecophagid anteaters have resulted in a shift in intermodule correlations in the proximal region of the rostrum. Namely, the naso-frontal and maxillo-palatine regions are strongly correlated with the oro-nasal module, suggesting an integrated rostrum conserved from pre-natal developmental processes. In contrast, the similarly toothless pangolins show a weaker correlation between the anterior rostral modules, resembling the pattern of toothed placentals. CONCLUSIONS: These results reveal that despite some integration shifts related to extreme functional and morphological features of myrmecophagous skulls, cranial modular architectures have conserved the typical mammalian scheme.

Incorporating parasite systematics in comparative analyses of variation in spleen mass and testes sizes of rodents.

Parasite diversity is hypothesized to act on host life-history traits through investment in immunity. In order to incorporate the diversity of the parasite community that an individual host or a host species may face, two indices can be used: Taxonomic Species Richness and Taxonomic Entropy, where the taxonomic information is incorporated with the taxonomic weight. We tested whether these indices correlate with several morphological traits potentially implicated in immune defence and in reproduction, using data on gastrointestinal helminths and their rodent hosts sampled in Southeast Asia. We found no relationship between parasite diversity indices and either spleen mass or testes size at the intraspecific level, i.e. at the level of individuals. At the interspecific level, we found no relationship between the parasite diversity indices and testes size. However, we found that female spleen mass is significantly influenced by the specific species richness of parasites, whereas male spleen mass is influenced by individual mean parasite diversity indices. We concluded that female spleen mass may have evolved in response to gastrointestinal helminth pressure acting at species levels, while in males, the individual spleen mass could be constrained by other factors, such as the blood storage function of the spleen.

The phylogenetic relationships of geoemydid turtles from the Eocene Messel Pit Quarry: a first assessment using methods for continuous and discrete characters.

The geoemydid turtles of the Eocoene Messel Pit Quarry of Hesse, Germany, are part of a rich Western European fossil record of testudinoids. Originally referred to as "Ocadia" kehreri and "Ocadia" messeliana, their systematic relationships remain unclear. A previous study proposed that a majority of the Western European geoemydids, including the Messel geoemydids, are closely related to the Recent European representatives of the clade Mauremys. Another study hypothesised that the Western European geoemydid fauna is more phylogenetically diverse, and that the Messel geoemydids are closely related to the East Asian turtles Orlitia and Malayemys. Here we present the first quantitative analyses to date that investigate this question. We use continuous characters in the form of ratios to estimate the placement of the Messel geoemydids in a reference tree that was estimated from molecular data. We explore the placement error obtained from that data with maximum likelihood and Bayesian methods, as well as linear parsimony in combination with discrete characters. We find good overall performance with Bayesian and parsimony analyses. Parsimony performs even better when we also incorporated discrete characters. Yet, we cannot pin down the position of the Messel geoemydids with high confidence. Depending on how intraspecific variation of the ratio characters is treated, parsimony favours a placement of the Messel fossils sister to Orlitia borneensis or sister to Geoemyda spengleri, with weak bootstrap support. The latter placement is suspect because G. spengleri is a phylogenetically problematic species with molecular and morphological data. There is even less support for placements within the Mauremys clade.

Agro-Environmental Determinants of Leptospirosis: A Retrospective Spatiotemporal Analysis (2004-2014) in Mahasarakham Province (Thailand).

Leptospirosis has been recognized as a major public health concern in Thailand following dramatic outbreaks. We analyzed human leptospirosis incidence between 2004 and 2014 in Mahasarakham province, Northeastern Thailand, in order to identify the agronomical and environmental factors likely to explain incidence at the level of 133 sub-districts and 1982 villages of the province. We performed general additive modeling (GAM) in order to take the spatial-temporal epidemiological dynamics into account. The results of GAM analyses showed that the average slope, population size, pig density, cow density and flood cover were significantly associated with leptospirosis occurrence in a district. Our results stress the importance of livestock favoring leptospirosis transmission to humans and suggest that prevention and control of leptospirosis need strong intersectoral collaboration between the public health, the livestock department and local communities. More specifically, such collaboration should integrate leptospirosis surveillance in both public and animal health for a better control of diseases in livestock while promoting public health prevention as encouraged by the One Health approach.

Height and body mass influence on human body outlines: a quantitative approach using an elliptic Fourier analysis.

Many studies use representations of human body outlines to study how individual characteristics, such as height and body mass, affect perception of body shape. These typically involve reality-based stimuli (e.g., pictures) or manipulated stimuli (e.g., drawings). These two classes of stimuli have important drawbacks that limit result interpretations. Realistic stimuli vary in terms of traits that are correlated, which makes it impossible to assess the effect of a single trait independently. In addition, manipulated stimuli usually do not represent realistic morphologies. We describe and examine a method based on elliptic Fourier descriptors to automatically predict and represent body outlines for a given set of predicted variables (e.g., sex, height, and body mass). We first estimate whether these predictive variables are significantly related to human outlines. We find that height and body mass significantly influence body shape. Unlike height, the effect of body mass on shape differs between sexes. Then, we show that we can easily build a regression model that creates hypothetical outlines for an arbitrary set of covariates. These statistically computed outlines are quite realistic and may be used as stimuli in future studies.

Optimizing digitalization effort in morphometrics.

Quantifying phenotypes is a common practice for addressing questions regarding morphological variation. The time dedicated to data acquisition can vary greatly depending on methods and on the required quantity of information. Optimizing digitization effort can be done either by pooling datasets among users, by automatizing data collection, or by reducing the number of measurements. Pooling datasets among users is not without risk since potential errors arising from multiple operators in data acquisition prevent combining morphometric datasets. We present an analytical workflow to estimate within and among operator biases and to assess whether morphometric datasets can be pooled. We show that pooling and sharing data requires careful examination of the errors occurring during data acquisition, that the choice of morphometric approach influences amount of error, and that in some cases pooling data should be avoided. The demonstration is based on a worked example (Sus scrofa teeth) using a combinations of 18 morphometric approaches and datasets for which we identified and quantified several potential sources of errors in the workflow. We show that it is possible to estimate the analytical power of a study using a small subset of data to select the best morphometric protocol and to optimize the number of variables necessary for analysis. In particular, we focus on semi-landmarks, which often produce an inflation of variables in contrast to the number of available observations use in statistical testing. We show how the workflow can be used for optimizing digitization efforts and provide recommendations for best practices in error management.

Multiple loci linked to inversions are associated with eye size variation in species of the Drosophila virilis phylad.

The size and shape of organs is tightly controlled to achieve optimal function. Natural morphological variations often represent functional adaptations to an ever-changing environment. For instance, variation in head morphology is pervasive in insects and the underlying molecular basis is starting to be revealed in the Drosophila genus for species of the melanogaster group. However, it remains unclear whether similar diversifications are governed by similar or different molecular mechanisms over longer timescales. To address this issue, we used species of the virilis phylad because they have been diverging from D. melanogaster for at least 40 million years. Our comprehensive morphological survey revealed remarkable differences in eye size and head shape among these species with D. novamexicana having the smallest eyes and southern D. americana populations having the largest eyes. We show that the genetic architecture underlying eye size variation is complex with multiple associated genetic variants located on most chromosomes. Our genome wide association study (GWAS) strongly suggests that some of the putative causative variants are associated with the presence of inversions. Indeed, northern populations of D. americana share derived inversions with D. novamexicana and they show smaller eyes compared to southern ones. Intriguingly, we observed a significant enrichment of genes involved in eye development on the 4th chromosome after intersecting chromosomal regions associated with phenotypic differences with those showing high differentiation among D. americana populations. We propose that variants associated with chromosomal inversions contribute to both intra- and interspecific variation in eye size among species of the virilis phylad.