Musin Morocco: a Quaternary sequence of intraspecific evolution

Abstract

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.

THE CHANGING PACE OF INSULAR LIFE: 5000 YEARS OF MICROEVOLUTION IN THE ORKNEY VOLE(MICROTUS ARVALIS ORCADENSIS)

“…This suggests that, for M. arvalis at least, body size reduction between fossil and modern specimens has not been a response to long‐term, natural global warming since the LGM (Millien et al ), but rather a more recent anthropogenic phenomenon (Sheridan and Bickford ). A similar trend observed in mice species has been linked with pervasive anthropogenic perturbations—from habitat destruction to climate change (Cassaing et al ; Stoetzel et al )—during very recent times. However, the archaeological record for Mainland Orkney shows size reduction in voles much earlier, between the 4th and 12th centuries AD, suggesting that anthropogenic impacts could have had greater/earlier effects on small mammals in confined/insular environments and/or in higher latitudinal locations.…”

Biogeographic variations in wood mice: testing for the role of morphological variation as a line of least resistance to evolution

“…Rohlf and Marcus 1993;Bookstein 1991;Mitteroecker and Gunz 2009). Such methods, based on landmarks or outline analyses, have been used to tackle many topics regarding rodent evolution: evolutionary patterns along fossil lineages (Renaud et al 1996Piras et al 2009;Stoetzel et al 2013), diversification among species, addressing the respective role of adaptation and neutral evolution (e.g. Cardini 2003;Monteiro et al 2005;Macholan 2006;Michaux et al 2007a); differentiation between populations, investigating the role of environmental variations (Renaud 1999;Fadda and Corti 2001;Michaux 2003, 2007;McGuire 2010;Helvaci et al 2012), processes favoring co--occurrence among species , patterns and route of colonization (Valenzuela--Lamas et al 2011;Siahsarvie et al 2012;Cucchi et al 2013).…”

Shrews of the genus Crocidura from El Harhoura 2 (Témara, Morocco): The contribution of broken specimens to the understanding of Late Pleistocene–Holocene palaeoenvironments in North Africa

“…The impact of human activities and inter-specific competition were likely involved (other murid species arriving in Morocco during Holocene, especially the house mouse around 3000 BP) and seem to have had a stronger influence than climatic changes on the morphological evolution of Mus. It is interesting to note here that despite a clear morphological stability throughout the El Harhoura 2 stratigraphy (no statistical difference between the 8 studied levels), Stoetzel et al (2013) demonstrated a significant relationship between tooth shape (m1 and M1 first DFA axis) and the diversity indices (Shannon and Simpson). This may reflect changes in morphology related to biotic or abiotic environmental changes (e.g.…”

“…In order to classify the archaeological specimens, Discriminant Analyses were performed using modern species found in Morocco today as a reference sample, and a posteriori specific assignations for fossil specimens were performed (Baylac and Friess, 2005;Evin et al, 2013;Stoetzel et al, 2013). Size (logarithm of the centroid size), playing an important role to discriminate white-toothed shrews was included in the analyses in order to optimize the specific classification (Cornette et al, 2015a).…”

“…To relate these faunistic results with palaeobiodiversity a regression with the same pooled results and the Shannon's diversity index (Spellerberg and Fedor, 2003) of this region for this period following Stoetzel et al (2013) was performed. Shannon's diversity index permits to evaluate the palaeobiodiversity of small vertebrate (small mammals, reptiles and amphibians).…”