Geographic phenetic variation of two eastern-Mediterranean non-commensal mouse species, Mus macedonicus and M. cypriacus (Rodentia: Muridae) based on traditional and geometric approaches to morphometrics

The genetic diversity of the genus Mus (Linnaeus, 1758) in the eastern part of the North Caucasus

Background

There are two species of Mus in the Caucasus: M. musculus and M. macedonicus. M. musculus is widespread in the Caucasus, where the species is found everywhere from the Black to the Caspian Sea. M. macedonicus is ubiquitous Transcaucasia. The most north-astern border of its distribution in the Caucasus, according to the literature, is located in the Derbent region, near the border between Dagestan and Azerbaijan.

Results

Cytochrome b mt-DNA of genus Mus research in this study in the Eastern Caucasus. About 70% of M. musculus haplotypes from the lowlands of Dagestan were recorded for the first time. One of these haplotypes accounts for approximately 25% of the total species diversity of haplotypes. M. macedonicus was found in only one locality, the Sarykum barchans, where this species prevails in number and accounts for 70% of the total number mice of the genus Mus. The species is characterized by low values of genetic diversity and nucleotide variability, which may indicate that the population originated from a small number of founders and may explain its relative isolation from the main range. The dating of the appearance of the ancestors of M. musculus in the east of the Russian Caucasus corresponds to 99-66 thousand years ago (at a mutation rate of 3-10% per million years).

Conclusion

The results obtained suggest that the history of the appearance of M. musculus in the Eastern Caucasus is more ancient and is not associated with human agricultural activities.

We believe that possibly the ancestral range of M. musculus covered the eastern and western coasts of the Caspian Sea in the territory of southern Dagestan, Azerbaijan, and Iran. In this paper M. macedonicus, a Balkan-Asia Minor species, was registered for the first time in the North Caucasus. This species was registered in the center of Dagestan, where it inhabits sympatrically (on the territory) and syntopically (on the same biotope) with M. musculus. The low values of genetic diversity of M. macedonicus in the North Caucasus suggest that the population originated from a small group of founders.

Morphological evidence for early dog domestication in the European Pleistocene: New evidence from a randomization approach to group differences

The antiquity of the wolf/dog domestication has been recently pushed back in time from the Late Upper Paleolithic (~14,000 years ago) to the Early Upper Paleolithic (EUP; ~36,000 years ago). Some authors questioned this early dog domestication claiming that the putative (EUP) Paleolithic dogs fall within the morphological range of recent wolves. In this study, we reanalyzed a data set of large canid skulls using unbalanced- and balanced-randomized discriminant analyses to assess whether the putative Paleolithic dogs are morphologically unique or whether they represent a subsample of the wolf morpho-population. We evaluated morphological differences between 96 specimens of the 4 a priori reference groups (8 putative Paleolithic dogs, 41 recent northern dogs, 7 Pleistocene wolves, and 40 recent northern wolves) using discriminant analysis based on 5 ln-transformed raw and allometrically size-adjusted cranial measurements. Putative Paleolithic dogs are classified with high accuracies (87.5 and 100.0%, cross-validated) and randomization experiment suggests that these classification rates cannot be exclusively explained by the small and uneven sample sizes of reference groups. It indicates that putative Upper Paleolithic dogs may represent a discrete canid group with morphological signs of domestication (a relatively shorter skull and wider palate and braincase) that distinguish them from sympatric Pleistocene wolves. The present results add evidence to the view that these specimens could represent incipient Paleolithic dogs that were involved in daily activities of European Upper Paleolithic forager groups.

Genetics of murine craniofacial morphology: diallel analysis of the eight founders of the Collaborative Cross

Using eight inbred founder strains of the mouse Collaborative Cross (CC) project and their reciprocal F1 hybrids, we quantified variation in craniofacial morphology across mouse strains, explored genetic contributions to craniofacial variation that distinguish the founder strains, and tested whether specific or summary measures of craniofacial shape display stronger additive genetic contributions. This study thus provides critical information about phenotypic diversity among CC founder strains and about the genetic contributions to this phenotypic diversity, which is relevant to understanding the basis of variation in standard laboratory strains and natural populations. Craniofacial shape was quantified as a series of size-adjusted linear dimensions (RDs) and by principal components (PC) analysis of morphological landmarks captured from computed tomography images from 62 of the 64 reciprocal crosses of the CC founder strains. We first identified aspects of skull morphology that vary between these phenotypically 'normal' founder strains and that are defining characteristics of these strains. We estimated the contributions of additive and various non-additive genetic factors to phenotypic variation using diallel analyses of a subset of these strongly differing RDs and the first eight PCs of skull shape variation. We find little difference in the genetic contributions to RD measures and PC scores, suggesting fundamental similarities in the magnitude of genetic contributions to both specific and summary measures of craniofacial phenotypes. Our results indicate that there are stronger additive genetic effects associated with defining phenotypic characteristics of specific founder strains, suggesting these distinguishing measures are good candidates for use in genotype-phenotype association studies of CC mice. Our results add significantly to understanding of genotype-phenotype associations in the skull, which serve as a foundation for modeling the origins of medically and evolutionarily relevant variation.

A Skull Might Lie: Modeling Ancestral Ranges and Diet from Genes and Shape of Tree Squirrels

Tropical forests of Central and South America represent hotspots of biological diversity. Tree squirrels of the tribe Sciurini are an excellent model system for the study of tropical biodiversity as these squirrels disperse exceptional distances, and after colonizing the tropics of the Central and South America, they have diversified rapidly. Here, we compare signals from DNA sequences with morphological signals using pictures of skulls and computational simulations. Phylogenetic analyses reveal step-wise geographic divergence across the Northern Hemisphere. In Central and South America, tree squirrels form two separate clades, which split from a common ancestor. Simulations of ancestral distributions show western Amazonia as the epicenter of speciation in South America. This finding suggests that wet tropical forests on the foothills of Andes possibly served as refugia of squirrel diversification during Pleistocene climatic oscillations. Comparison of phylogeny and morphology reveals one major discrepancy: Microsciurus species are a single clade morphologically but are polyphyletic genetically. Modeling of morphology-diet relationships shows that the only group of species with a direct link between skull shape and diet are the bark-gleaning insectivorous species of Microsciurus. This finding suggests that the current designation of Microsciurus as a genus is based on convergent ecologically driven changes in morphology.

The morphology of the mouse masticatory musculature

The mouse has been the dominant model organism in studies on the development, genetics and evolution of the mammalian skull and associated soft-tissue for decades. There is the potential to take advantage of this well studied model and the range of mutant, knockin and knockout organisms with diverse craniofacial phenotypes to investigate the functional significance of variation and the role of mechanical forces on the development of the integrated craniofacial skeleton and musculature by using computational mechanical modelling methods (e.g. finite element and multibody dynamic modelling). Currently, there are no detailed published data of the mouse masticatory musculature available. Here, using a combination of micro-dissection and non-invasive segmentation of iodine-enhanced micro-computed tomography, we document the anatomy, architecture and proportions of the mouse masticatory muscles. We report on the superficial masseter (muscle, tendon and pars reflecta), deep masseter, zygomaticomandibularis (anterior, posterior, infraorbital and tendinous parts), temporalis (lateral and medial parts), external and internal pterygoid muscles. Additionally, we report a lateral expansion of the attachment of the temporalis onto the zygomatic arch, which may play a role in stabilising this bone during downwards loading. The data presented in this paper now provide a detailed reference for phenotypic comparison in mouse models and allow the mouse to be used as a model organism in biomechanical and functional modelling and simulation studies of the craniofacial skeleton and particularly the masticatory system.