Cranial variation was studied across the geographical range of the Meriones meridianus species complex using 665 specimens from 112 localities. Morphometric results were compared with previously published data on genetic variation. Unsupervised model‐based clustering analysis implemented in Mclust software was employed to identify the number and content of morphological clusters. Three clearly defined morphological groups corresponding to mtDNA clades were found. The results of the morphometric analysis are consistent with the hypothesis that these 3 groups should be treated as distinct species; specifically, M. psammophilus Milne‐Edwards, 1871, M. penicilliger Heptner, 1933 and M. meridianus Pallas, 1773. M. psammophilus inhabits the Mongolian–Chinese part of the superspecies range, except for the Mongolian Dzungaria region, which is inhabited by M. meridianus. The range of the latter species extends westwards to north‐west Kazakhstan and Kalmykia. M. penicilliger inhabits the southern part of the superspecies range from Tian Shan to Turkmenistan. M. dahli is craniometrically similar to M. meridianus; hence, its species status remains questionable.
The dormice (Gliridae) represent a relatively small family of rodents, but exhibit considerable 21 variation in their cranial anatomy. The skull morphology of almost all genera of dormice was 22 described from osteological specimens by Wahlert et al. (1993). However, the rare desert 23 dormouse, Selevinia betpakdalaensis, was only assessed using previous descriptions and 24 photographic images, resulting in difficulties with assigning all cranial features within this 25 particular genus. In this study, the crania and mandibles of two adult individuals of this genus 26 were scanned using micro-computed tomography and virtually reconstructed. From these 27 reconstructions, we describe in detail the highly unusual cranial and mandibular morphology 28 of the desert dormouse and determine the states of the cranial and mandibular characters 29 described by Wahlert et al. (1993). These morphological characters were used to compare this 30 species with previously described dormouse genera, showing a clear resemblance between 31 Selevinia and the small mouse-tailed dormouse genus Myomimus. Derived morphological 32 features unique to Selevinia indicate clear adaptations to a desert-like environment, as well as 33 hinting towards an insectivorous diet and burrowing lifestyle.34 35 Selevin (Bashanov and Belosludov, 1941). Initially placed in Muridae based on its dental 39 formula, further analyses led to the first description of this species published in English 40 (Bashanov and Belosludov, 1941), in which it was placed in a new monospecific family, 41 Seleviniidae. These authors mentioned the close resemblance of the skull morphology of this 42 species with that of members of Gliridae (Myoxidae), but highlighted the atypical dental 43 structures within this species in comparison to dormice. Ognev (1947) identified the animal as 44 a highly derived dormouse and emphasised the resemblance of this species to Myomimus. He 45 therefore created the subfamily Seleviniinae within the family Gliridae. More recent analyses of the enamel structure in this animal and other dormice also incorporated Selevinia within 47 Gliridae, and no longer acknowledged Seleviniidae as a sister group of Gliridae (von Koenigswald, 1992). Storch (1994) assigned Myomimus and Chaetocauda to Seleviniinae 49 alongside Selevinia, regarding it as the most primitive of all extant dormice subfamilies. In 50 contrast, Yachontov and Potapova (1991) considered Selevinia to be more closely related to 51 Muscardinus and Glis, belonging to the subfamily Glirinae. Later, Potapova reasserted the close 52 relationship between Myomimus and Selevinia based on middle ear morphology (Potapova, 53 2001). Wahlert et al. (1993) placed Selevinia and Myomimus in the tribe Seleviniini, which, 54 joined with the tribe Leithiini, formed the subfamily Leithiinae. Due to the scarcity of accessible 55 specimens, Selevinia was not included in the phylogenetic analyses of the Gliridae based on 56 molecular data by Montgelard et al. (2003) or Nunome et al. (2007). The exact placement of ...
Phenotypic integration and modularity influence morphological disparity and evolvability. However, studies addressing how morphological integration and modularity change for long periods of genetic isolation are scarce. Here, we investigate patterns of phenotypic integration and modularity in the skull of phenotypically and genetically distinct populations of the Artic fox ( Vulpes lagopus ) from the Commander Islands of the Aleutian belt (i.e. Bering and Mednyi) that were isolated ca 10 000 years by ice-free waters of the Bering sea. We use three-dimensional geometric morphometrics to quantify the strength of modularity and integration from inter-individual variation (static) and from fluctuating asymmetry (random developmental variation) in both island populations compared to the mainland population (i.e. Chukotka) and we investigated how changes in morphological integration and modularity affect disparity and the directionality of trait divergence. Our results indicate a decrease in morphological integration concomitant to an increase in disparity at a developmental level, from mainland to the smallest and farthest population of Mednyi. However, phenotypic integration is higher in both island populations accompanied by a reduction in disparity compared to the population of mainland at a static level. This higher integration may have favoured morphological adaptive changes towards specific feeding behaviours related to the extreme environmental settings of islands. Our study demonstrates how shifts in phenotypic integration and modularity can facilitate phenotypic evolvability at the intraspecific level that may lead to lineage divergence at macroevolutioanry scales.
Populations of Arctic fox (Vulpes lagopus) in the Commander Islands, in the Russian Bering Sea, have been isolated since the Pleistocene and differ substantially in their cranial features from their mainland counterpart. Small rodents, the main prey of mainland Arctic foxes, are not found in the Commander Islands, where the main food source for Arctic foxes are large sea birds and marine mammals. Here we assessed whether differences in foraging strategy, particularly the size of available prey, could explain the observed differences in cranial features between mainland and island Arctic foxes. Because a large gape is necessary when foraging on large prey, we compared gape angles between islands and mainland in a sample of dry crania. We found an enlarged gape angle in both island populations. We also compared the rostrum to cranium length ratio and found it to be similar for the mainland and Bering Island Arctic foxes; however, a rostrum contraction was found in the Mednyi Island Arctic foxes. We show that cranial differences between mainland and Commander Islands fox populations could be explained by their different foraging ecology. Furthermore, the relative rostrum contraction in the Mednyi Island foxes provides further evidence for cranial resistance to deformation during biting. These results show the importance that distinct foraging strategies can have in Arctic fox divergent evolution, and, consequently, on future conservation plans for the two Commander Islands subspecies.
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