Patterns of morphological evolution in Marmota (Rodentia, Sciuridae): geometric morphometrics of the cranium in the context of marmot phylogeny, ecology and conservation

Abstract

Marmots are of great interest for both sociobiologists studying the evolution of mammal societies and conservationists trying to protect them from extinction. In contrast, their phylogeny and morphological evolution are poorly understood and studied. Recently, a phylogenetic analysis using cytochrome b provided the first reconstruction of marmot evolutionary history and suggested that a high level of sociality evolved at least twice independently in the two proposed marmot subgenera. A morphological analysis of the marmot mandible supported this subgeneric classification and showed interesting, and unexpected, patterns in the evolution of marmot skeletal characters. In the present study we investigated a more complex, and potentially informative structure, the ventral cranium. Geometric morphometric techniques were applied in the first analysis of cranial morphology including all marmot species. Three main phenetic groups were found, which reflect phylogeny (subgenus Petromarmota, and Palaearctic subgenus Marmota) or geographical distribution (Palaearctic vs. Nearctic subgenus Marmota). Convergence in skeletal characters due to size similarities, a common finding in the sciurid skeleton according to traditional morphological analyses, did not occur in the marmot ventral cranium. Despite a genetic distance between Marmota vancouverensis and Marmota caligata similar to that among different populations of the latter species, the Vancouver Island marmot had the most atypical ventral cranium in the subgenus Petromarmota. This finding confirmed results obtained with the mandible, and emphasized the uniqueness of M. vancouverensis and the usefulness of complementing molecular analyses with morphological studies for a thorough characterization of population divergence, and a careful planning of conservation strategies. (C) 2004 The Linnean Society of London

Functional Anatomy of Incisal Biting in <i>Aplodontia rufa</i> and Sciuromorph Rodents – Part 2: Sciuromorphy Is Efficacious for Production of Force at the Incisors

“…Morphometric analyses of the skull and mandible in marmots by Cardini [2003], Cardini and O'Higgins [2004] and Cardini et al [2005] provide interesting insights into phylogenetic patterns of shape changes but no evidence for increased ability to produce forces at the incisors. Cardini and Tongiorgi [2003] studied shape changes in the mandible of Marmota flaviventris during growth and development.…”

Phylogenetic and Environmental Components of Morphological Variation: Skull, Mandible, and Molar Shape in Marmots (Marmota, Rodentia)

“…These skeletal structures were chosen because they are common in the fossil record, where morphology remains crucial for phylogenetic reconstruction, and because their genetics, development, and function differ in ways that could influence their adaptive responses. Marmots were chosen because they have mtDNA sequence divergences that fall within the 5-10% range, and because previous studies found phylogenetic patterning in all three skeletal structures (Cardini 2003; Polly 2003a;Cardini and O'Higgins 2004). We specifically focused on quantitative, geometric morphometric representations of morphology because of current interest in such traits.…”

“…Our specific objectives were as follows: (1) to measure within-and between-population variance in the shape of the ventral cranium, the lateral mandible, and the occlusal surface of the lower molars; (2) to partition the variance among environmental and genetic (i.e., phylogenetic) factors; (3) to assess how well trees based on the morphological data replicate those based on cytochrome b mtDNA sequences; and (4) to evaluate how the genetic, developmental, and functional differences relate to usefulness of each trait for phylogeny reconstruction. Previous morphometric studies have compared skeletal structures Nicola et al 2003;Cardini and O'Higgins 2004), but they did not comparatively assess the contribution of phylogenetic and environmental factors.…”

Cranial morphometric and fine scale genetic variability of two adjacentMastomys natalensis (Rodentia: Muridae) populations

“…Indeed, Patton and Brylski (1987) have shown clearly body size variation in pocket gophers inhabiting alfalfa crops versus natural dry environments, Taylor et al (2005) have underlined significant geographical differences in cranial shape between eastern and western Cape populations of Otomys saundersiae, occupying distinct ecological biomes. Several studies have shown the presence of local population-level differentiation in size and shape variation of molars, skulls and mandibles in mammals (Cardini et al 2003, Cardini and O'Higgins 2004, Polly 2007 Moreover, the significant skull shape variation between populations showed that the morphological patterns evolved in Arvicanthis from Sudan are distinct enough to allow identification of populations (Rahman Abdel 2005). We also know already that African murids are able to vary their diet between seasons which suggests also a remarkable power of adaptation to local conditions in that group (Gliwicz 1987).…”