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In molars without permanent eruption, wear deeply modifies the geometry of the crown. To test for a signature of diet on wear dynamics, the molar geometry was compared between commensal house mice, relying on an omnivorous-granivorous diet, and Sub-Antarctic relatives, characterized by a switch towards a more 'predatory' behaviour. Laboratory-bred offspring of commensal mice served as a reference by providing mice of known age. Molar geometry was quantified using dense 3D semi-landmark based descriptors of the whole molar row and the upper molar only. Laboratory offspring displayed a decreased rate of wear compared to their commensal relatives, due to reduced mastication in mice fed ad libitum. Sub-Antarctic mice displayed a similarly decreased rate of molar wear, in agreement with an optimization towards incisor biting to seize prey. Laboratory offspring and Sub-Antarctic mice were further characterized by straight molar rows, whereas in commensal mice, the erupting third molar deviated away from the longitudinal alignment with the other molars, due to masticatory loadings. Quantifying changes in molar geometry could thus contribute to trace subtle diet variations, and provide a direct insight into the constraints during mastication, shedding light on the functional role of adaptive changes in molar geometry. [ABSTRACT FROM AUTHOR]

Phenotypic variation is the raw material of evolution. Standing variation can facilitate response to selection along "lines of least evolutionary resistance", but selection itself might alter the structure of the variance. Shape was quantified using 2D geometric morphometrics in Palmatolepis conodonts through the Late Devonian period. Patterns of variance were characterized along the record by the variance‐covariance matrix (P‐matrix) and its first axis (Pmax). The Late Frasnian was marked by environmental oscillations culminating with the Frasnian/Famennian mass extinction. A shape response was associated with these fluctuations, together with a deflection of the Pmax and the P‐matrix. Thereafter, along the Famennian, Palmatolepis mean shape shifted from broad elements with a large platform to slender elements devoid of platform. This shift in shape was associated with a reorientation of Pmax and the P‐matrix, due to profound changes in the functioning of the elements selecting for new types of variants. Both cases provide empirical evidences that moving adaptive optimum can reorient phenotypic variation, boosting response to environmental changes. On such time scales, the question seems thus not to be whether the P‐matrix is stable, but how it is varying in response to changes in selection regimes and shifts in adaptive optimum. [ABSTRACT FROM AUTHOR]

Spiny mice of the Acomys cahirinus group display a complex geographical structure in the Eastern Mediterranean area, as shown by previous genetic and chromosomal studies. To better elucidate the evolutionary relationships between insular populations from Crete and Cyprus and continental populations from North Africa and Cilicia in Turkey, genetic and morphometric variations were investigated, based on mitochondrial D-loop sequences, and the size and shape of the first upper molar. The Cypriot and the Cilician populations show idiosyncratic divergence in molar size and shape, while Cretan populations present a geographical structure with at least three differentiated subpopulations, as shown by congruent distributions of haplogroups, Robertsonian fusions and morphometric variation. A complex history of multiple introductions is probably responsible for this structure, and insular isolation coupled with habitat shift should have further promoted a pronounced and rapid morphological evolution in molar size and shape on Crete and Cyprus. [ABSTRACT FROM AUTHOR]

While domestication has been well studied, with the recent recognition of the so-called 'domestication syndrome', the opposite process, feralization, has received far less attention. The commensal Western European house mouse (Mus musculus domesticus) lives in close contact with humans, and as such it lies between wild and domesticated animals. However, it also occurs in non-anthropogenic environments, forming feral populations, and hence provides the opportunity to document how feralization may impact morphology. In this study, three 'feral' populations from Orkney, the Kerguelen Archipelago and southern France were compared to Western European commensal populations. The shape and biomechanical properties of the jaw were analysed to assess the impacts of 'feralization' on an organ that is under major environmental pressures through its feeding function. Mandible shape varied mostly with climate and phylogeny, and feral populations differed only slightly from their geographically close relatives. In contrast, feral mice shared a biomechanical signature corresponding to a decrease in the superficial masseter/molar mechanical advantage, suggesting poorer molar biting performance. This is interpreted as a parallel response to a relaxation of environmental pressure, possibly due to a diet shift in feral habitats. [ABSTRACT FROM AUTHOR]

Abstract: Convergent evolution in similar environments constitutes strong evidence of adaptive evolution. Transported with people around the world, house mice colonized even remote areas, such as Sub‐Antarctic islands. There, they returned to a feral way of life, shifting towards a diet enriched in terrestrial macroinvertebrates. Here, we test the hypothesis that this triggered convergent evolution of the mandible, a morphological character involved in food consumption. Mandible shape from four Sub‐Antarctic islands was compared to phylogeny, tracing the history of colonization, and climatic conditions. Mandible shape was primarily influenced by phylogenetic history, thus discarding the hypothesis of convergent evolution. The biomechanical properties of the jaw were then investigated. Incisor in‐lever and temporalis out‐lever suggested an increase in the velocity of incisor biting, in agreement with observations on various carnivorous and insectivorous rodents. The mechanical advantage related to incisor biting also revealed an increased functional performance in Sub‐Antarctic populations, and appears to be an adaptation to catch prey more efficiently. The amount of change involved was larger than expected for a plastic response, suggesting microevolutionary processes were evolved. This study thus denotes some degree of adaptive convergent evolution related to changes in habitat‐related changes in dietary items in Sub‐Antarctic mice, but only regarding simple, functionally relevant aspects of mandible morphology. [ABSTRACT FROM AUTHOR]

Sustainable coexistence of similar, related species is generally expected to be achieved through character displacement, resulting in niche partitioning. The species Apodemus sylvaticus and Apodemus flavicollis are very similar both morphologically and ecologically, and have a large geographical overlap. Whether functional or biomechanical differences between these two species contribute to their coexistence remains unknown. A biomechanical model was created based on muscle data derived from dissections to estimate the maximum bite force. In addition, the dental microwear was analysed to test for evidence of a divergence in diet. Finally, geometric morphometric approaches were used to compare mandibular shapes. The results indicate that A. flavicollis, the slightly larger species, is optimized for biting at a larger gape angle. Apodemus sylvaticus appears to be slightly more specialized for grinding and biting at a narrower gape angle. However, the majority of shape variation in the mandible across both species follows the same pattern. No significant differences in microwear were observed between species, and thus, they appear to consume similar food types. These results suggest that character divergence resulting in niche partitioning has not occurred, possibly due to low resource competition. Alternatively, resource partitioning may occur through behavioural differences or differences in activity patterns. [ABSTRACT FROM AUTHOR]

Invasions and anthropogenic disturbances challenge species with rapid environmental changes. Understanding how organisms respond to these changes is of major concern for the future of biodiversity. The house mouse on a Sub- Antarctic island ( Guillou Island, Kerguelen Archipelago) had to face such challenges twice: first when invading the island two centuries ago; and nowadays when coping with an in-depth remodeling of its habitat due to a cohort of anthropogenic changes. Morphometric and biomechanical results show that the initial invasion triggered the evolution of a jaw shape adapted to the local food resources. Contemporary changes are also associated to changes in jaw morphology, but are not directly functionally relevant. Here, a complex response integrating feeding behaviour, investment in feeding structure, and degree of mineralization, may provide the mice with a better tool to benefit of wider resources utilization and/or better cope with intra-specific competition in a changing habitat. These Sub- Antarctic mice exemplify that success of invasive species rely on the capacity of facing rapidly varying environments through integrated, multi-faceted responses involving behaviour to morphology through life-history traits. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 513-526. [ABSTRACT FROM AUTHOR]

Island evolution may be expected to involve fast initial morphological divergence followed by stasis. We tested this model using the dental phenotype of modern and ancient common voles ( Microtus arvalis), introduced onto the Orkney archipelago (Scotland) from continental Europe some 5000 years ago. First, we investigated phenotypic divergence of Orkney and continental European populations and assessed climatic influences. Second, phenotypic differentiation among Orkney populations was tested against geography, time, and neutral genetic patterns. Finally, we examined evolutionary change along a time series for the Orkney Mainland. Molar gigantism and anterior-lobe hypertrophy evolved rapidly in Orkney voles following introduction, without any transitional forms detected. Founder events and adaptation appear to explain this initial rapid evolution. Idiosyncrasy in dental features among different island populations of Orkney voles is also likely the result of local founder events following Neolithic translocation around the archipelago. However, against our initial expectations, a second marked phenotypic shift occurred between the 4th and 12th centuries AD, associated with increased pastoral farming and introduction of competitors (mice and rats) and terrestrial predators (foxes and cats). These results indicate that human agency can generate a more complex pattern of morphological evolution than might be expected in island rodents. [ABSTRACT FROM AUTHOR]

North Africa is an intricate biogeographical region at the crossroads of immigration waves from tropical Africa and Asia. Species confined between various barriers ( Atlas Mountains, arid environments such as the Sahara in the south, water masses such as the Mediterranean Sea in the north, and the Atlantic Ocean in the west) were generally forced to adapt locally to environmental changes instead of tracking their habitat by shifting their distribution area. The present study aims at providing first insight into the evolution of the genus Mus, and more specifically of the western Mediterranean species Mus spretus in this area. The study relies on the abundant Late Pleistocene and Middle Holocene fossil assemblage from the El Harhoura 2 cave ( Rabat- Témara, Morocco). This exceptional record was studied using geometric morphometrics applied to first upper and lower molars, constituting the most informative and best preserved fossil remains for such small rodents. Two main issues were addressed. (1) Geometric morphometrics was used to clarify taxonomic status and phylogenetic relationships among fossil and modern species in this area. Morphometric analysis revealed good discrimination of most modern and fossil species but failed to document intermediate forms tracing anagenetic evolution. Not mutually exclusive, the occurrence of complex processes of morphological evolution in this genus such as parallel evolution and the action of stabilizing selection may make it difficult to translate patterns of morphological evolution into phylogenetic conclusions. (2) The record was shown to document a sequence of intraspecific evolution of M. spretus. The morphology of the molars through the fossil record of El Harhoura 2 was surprisingly stable despite extensive modern variation. The limited temporal variation largely failed to correlate to palaeoenvironmental proxies. The mouse fossil record at El Harhoura 2 thus presents an intriguing case of morphological stasis despite extensive environmental changes. This long-term stability may have been recently perturbed by anthropogenic factors including landscape changes and introduction of various competitors and predators, leading to a size reduction. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 599-621. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Past climatic fluctuations influenced forest habitats and impacted heavily the distribution of forest species, such as the edible dormouse, by changing the distribution and composition of forests themselves. Such effects may be valid for ongoing climate change as well. To improve our understanding of the edible dormouse's history and how it responded to changes in its environment, we investigated its variation across the understudied zone of Northern Turkey using two complementary markers of differentiation: the mitochondrial cytochrome b gene for genetics, and size and shape of the first upper molar for phenotypic differences. Genetic and morphometric results were strongly discrepant. Genetic analyses evidenced an amazing homogeneity throughout the Eurasian range of the edible dormouse, whereas morphometrics pointed to a complex, step-wise differentiation along the Black Sea coast, the main signal being an opposition between Easternmost and Westernmost Turkish dormice. The genetic homogeneity suggests that this phenotypic differentiation is not the inheritance of glacial refuges, but the consequence of a more recent post-glacial isolation. The transition between the European and Asian groups is located eastwards from the Marmara straits, undermining its claimed role as an efficient barrier but stressing the importance of climatic and vegetational factors. A secondary differentiation between populations from the Central Black Sea coast and Easternmost regions was evidenced, attributed to a complex interplay of climatic, topographic, anthropogenic, and ecological factors. Turkey, at the crossroad of European and Asian species, heavily impacted by the current global change including climatic and anthropogenic factors, appears of importance for understanding the historical dynamics of differentiation and exchanges between populations that shaped the current distribution of Eurasian species and their future survival. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••-••. [ABSTRACT FROM AUTHOR]

An ecomorphological approach of mandible shape through Fourier analyses combined with a paleodietary analysis of dental microwear patterns is used to reconstruct the diet of the extinct endemic Canariomys bravoi Crusafont, Pairó & Petter, 1964 and Canariomys tamarani López-Martínez & López-Jurado, 1987. These two large rodents, respectively, lived on Tenerife and Gran Canaria, the central islands of the Canarian Archipelago. Mandible shape and dental microwear respectively inform us on the volume of vegetal matter and on the presence of grass in the diet. Both Canariomys, which are of similar size, possess relatively similar mandible outlines and microwear patterns. For each species, a diet based on plant materials except grass is the most likely. Such results chime with the similar environments offered by the islands in which the species lived. On the contrary, molar morphology suggests different feeding habits of the two Canariomys. Thus, this suggests a case of mosaic evolution between teeth and mandibles, as well as the likely sensitivity of mandible shape to a combination of ecological and allometric factors. These new data obtained from the fossil record underline the propensity of island endemic mammals to yield surprising examples of phenotypic evolution. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 28–40. [ABSTRACT FROM AUTHOR]

The bank vole experienced a complex history during the Quaternary. Repeated isolation in glacial refugia led to the differentiation of several lineages in less than 300 000 years. We investigated if such a recent differentiation led to a significant divergence of phenotypic characters between European lineages, which might provide insight into processes of intraspecific differentiation. The size and shape of the first and third upper molars, and first lower molar, of bank voles genetically attributed to different lineages were quantified using an outline analysis of their occlusal surface. The three teeth present similar trends of decreasing size towards high latitudes. This trend, the inverse of Bergmann's rule, is interpreted as the result of a balance between metabolic efficiency and food availability, favouring small body size in cold regions. Molar shape appeared to differ between lineages despite genetic evidence of suture zones. A mosaic pattern of evolution between the different teeth was evidenced. The analysis of such phenotypic features appears as a valuable complement to genetic analyses, providing a complementary insight into evolutionary processes, such as selective pressures, that have driven the differentiation of the lineages. It may further allow the integration of the paleontological dimension of the bank vole phylogeographic history. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 681–694. [ABSTRACT FROM AUTHOR]

Within a group of organisms, some morphologies are more readily generated than others due to internal developmental constraints. Such constraints can channel evolutionary changes into directions corresponding to the greatest intraspecific variation. Long term evolutionary outputs, however, depend on the stability of these intraspecific patterns of variation over time and from the interplay between internal constraints and selective regimes. To address these questions, the relationship between the structure of phenotypic variance covariance matrices and direction of morphological evolution was investigated using teeth of fossil rodents. One lineage considered here leads to Stephanomys, a highly specialized genus characterized by a dental pattern supposedly favoring grass eating. Stephanomys evolved in the context of directional selection related to the climatic trend of global cooling causing an increasing proportion of grasslands in southwestern Europe. The initial divergence (up to ∼6.5 royal was channeled along the direction of greatest intraspecific variation, whereas after 6.5 mya, morphological evolution departed from the direction favored by internal constraints. This departure from the "lines of least resistance" was likely the consequence of an environmental degradation causing a selective gradient strong enough to overwhelm the constraints to phenotypic evolution. However, in a context of stabilizing selection, these constraints actually channel evolution, as exemplified by the lineage of Apodemus. This lineage retained a primitive diet and dental pattern over the last 10 myr. Limited morphological changes occurred nevertheless in accordance with the main patterns of intraspecific variation. The importance of these lines of least resistance directing long-term morphological evolution may explain parallel evolution of some dental patterns in murine evolution. [ABSTRACT FROM AUTHOR]

The lava mouseMalpaisomyswas part of Pleistocene and Holocene faunas of the eastern Canary Islands; it became extinct during historical times. In order to evaluate the evolutionary processes of this endemic species, we set out to identify its relationships with possible mainland relatives. Its dental morphology was compared to a set of fossil and modern murine rodents from various phylogenetic groups, characterized by different diets and dental patterns, using a quantitative method based on a Fourier analysis of the outline of the first upper and lower molars. This morphometric analysis identified different evolutionary grades that are independent of the phylogenetic group. The first cluster is associated with primitive, asymmetric dental outlines, the second with intermediate forms linked to a more herbivorous diet. Highly differentiated forms diverge not only from the second cluster but also from each other. Our investigations revealMalpaisomysto have had an intermediate dental pattern, a result which confirms previous palaeoecological interpretations of this taxon. However, conclusions about its closest mainland relative remain tentative. Based on a comparison of dental size and shape, as well as geographical considerations, a possible mainland ancestor could be eitherParaethomys(North-African Pliocene) orOccitanomys(South-western European Pliocene). Such results support the hypothesis of a Pliocene colonization event, in which caseMalpaisomyswould display a normal evolutionary rate in dental size and shape, in spite of the insular context. In contrast, a late colonization by a modern representative of the African fauna would imply exceptionally high evolutionary rates compared to the background morphological evolution and a decrease in size that is unlikely under insular conditions. © 2004 The Linnean Society of London,Zoological Journal of the Linnean Society, 2004,142, 555–572. [ABSTRACT FROM AUTHOR]

Calcidiscus leptoporus is a cosmopolitan coccolithophore species with one of the longest fossil records. A previous morphometric study on coccoliths of C. leptoporus, carried out on a global set of Holocene sediment samples, indicated that temperature might be a significant factor influencing the size distribution of C. leptoporus. In the present study, C. leptoporus morphological variations and dynamics are studied in samples from Hydrostation S time series, near Bermuda, over a 3 year interval (1991 to 1994) with monthly sampling. Calcidiscus leptoporus was present all year round in very low abundances but displayed strong variations through the time-series, both in absolute abundances (maximum 551 cells/l and minimum <10 cells/l) and in morphology. No significant correlation between environmental parameters and C. leptoporus abundances was found. The seasonal dynamics of C. leptoporus, therefore, appears to be the consequence of plankton community interactions and, possibly, of life-cyle. The morphological study of C. leptoporus shows a sharp decrease in size and variability occurring during the spring–summer transition at the onset of water stratification. Our results give no conclusive evidence as to whether C. leptoporus at Hydrostation S consists of an assemblage of different species or ecophenotypes. However, we provide evidence for significant morphological plasticity linked to seasonality and possibly temperature. More importantly, our results show a trend between temperature and morphology opposite to the study of Knappertsbusch et al. (Knappertsbusch et al., 1997) based on Holocene sediments. These results emphasize the necessity of plankton studies in order to interpret patterns observed in sediments. [ABSTRACT FROM PUBLISHER]