The west European subspecies of house mouse (Mus musculus domesticus) has gained much of its current widespread distribution through commensalism with humans. This means that the phylogeography of M. m. domesticus should reflect patterns of human movements. We studied restriction fragment length polymorphism (RFLP) and DNA sequence variations in mouse mitochondrial (mt) DNA throughout the British Isles (328 mice from 105 localities, including previously published data). There is a major mtDNA lineage revealed by both RFLP and sequence analyses, which is restricted to the northern and western peripheries of the British Isles, and also occurs in Norway. This distribution of the 'Orkney' lineage fits well with the sphere of influence of the Norwegian Vikings and was probably generated through inadvertent transport by them. To form viable populations, house mice would have required large human settlements such as the Norwegian Vikings founded. The other parts of the British Isles (essentially most of mainland Britain) are characterized by house mice with different mtDNA sequences, some of which are also found in Germany, and which probably reflect both Iron Age movements of people and mice and earlier development of large human settlements. MtDNA studies on house mice have the potential to reveal novel aspects of human history.

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Recent genetic studies have challenged the traditional view that the ancestors of British Celtic people spread from central Europe during the Iron Age and have suggested a much earlier origin for them as part of the human recolonization of Britain at the end of the last glaciation. Here we propose that small mammals provide an analogue to help resolve this controversy. Previous studies have shown that common shrews (Sorex araneus) with particular chromosomal characteristics and water voles (Arvicola terrestris) of a specific mitochondrial (mt) DNA lineage have peripheral western/northern distributions with striking similarities to that of Celtic people. We show that mtDNA lineages of three other small mammal species (bank vole Myodes glareolus, field vole Microtus agrestis and pygmy shrew Sorex minutus) also form a 'Celtic fringe'. We argue that these small mammals most reasonably colonized Britain in a two-phase process following the last glacial maximum (LGM), with climatically driven partial replacement of the first colonists by the second colonists, leaving a peripheral geographical distribution for the first colonists. We suggest that these natural Celtic fringes provide insight into the same phenomenon in humans and support its origin in processes following the end of the LGM.

Genetic markers are often used to examine population history. There is considerable debate about the behaviour of molecular clock rates around the population-species transition. Nevertheless, appropriate calibration is critical to any inference regarding the absolute timing and scale of demographic changes. Here, we use a mitochondrial cytochrome b gene genealogy, based entirely on modern sequences and calibrated from recent geophysical events, to date the post-glacial expansion of the Eurasian field vole (Microtus agrestis), a widespread temperate mammal species. The phylogeographic structure reflects the subsequent expansion of populations that went through bottlenecks at the time of the Younger Dryas (ca 12 000 years BP) rather than the Last Glacial Maximum (LGM, ca 24 000 years BP), which is usually seen as the time when present-day patterns were determined. The nucleotide substitution rate that was estimated here, ca 4 Â 10 27 substitutions/site/year, remains extremely high throughout the relevant time frame. Calibration with similarly high population-based substitution rates, rather than long-term rates derived from species divergence times, will show that post-LGM climatic events generated current phylogeographic structure in many other organisms from temperate latitudes.

There is now considerable evidence for the survival of temperate species within glacial refugia that were situated at relatively high latitudes, notably the Carpathian Basin and Dordogne region in Europe. However, the prevalence of fossil remains in such locations is rarely matched by molecular evidence for their contribution to subsequent geographical and demographic expansion of the species in question. One obstacle to this has been insufficient analysis of modern samples from the relevant areas, in particular the parts of eastern Europe that surround the Carpathian refugium. In the present study, we examine the patterns of variation in mitochondrial DNA of the common vole (Microtus arvalis), obtained from existing museum specimens and from newly-collected samples obtained in this area. We show that common voles from one of six extant mitochondrial DNA lineages have colonized most of the species' range in eastern Europe. We contend that the post-glacial dispersal of this lineage most likely originated from the Carpathian refugium, adding support to the argument that such northern refugia made an important contribution to existing genetic diversity in Europe.

Published information on the diet of Cuvier's beaked whales Ziphius cavirostris (Odontoceti: Ziphiidae) is reviewed and new information on the stomach contents of three animals: two stranded in Galicia (north-west Spain) in February 1990 at A Lanzada, and in February 1995 at Portonovo; and the third stranded in February 1999 in North Uist (Scotland), is presented. The whale stranded in 1990 was a male; the other two were adult females. All animals were >5 m long.  The limited published information on the diet of this species indicates that it feeds primarily on oceanic cephalopods although some authors also found remains of oceanic fish and crustaceans.  Food remains from the three new samples consisted entirely of cephalopod beaks. The Scottish sample set is the largest recorded to date for this species. The prey identified consisted of oceanic cephalopods, mainly squid (Cephalopoda: Teuthoidea). The most frequently occurring species were the squid Teuthowenia megalops, Mastigoteuthis schmidti and Taoniuspavo (for the Galician whale stranded in 1990), Teuthowenia megalops and Histioteuthis reversa (for the second Galician whale) and T. megalops, Gonatus sp. and Taoniuspavo (for the Scottish whale). Other prey included the squid Histioteuthis bonnellii, Histioteuthis arcturi and Todarodes sagittatus as well as Vampiroteuthis infernalis (Cephalopoda: Vampyromorpha), Stauroteuthis syrtensis and Japetella diaphana (Cephalopoda: Octopoda). The squid eaten (estimated from the measurement of the lower beaks) included juvenile and mature individuals of the most important species (Teuthowenia megalops, Gonatus sp.).  The range of species found in the diet of Z. cavirostris is greater than that reported for sperm whales and bottlenosed whales in the north-east Atlantic.

Skulls of odontocetes (toothed whales, including dolphins and porpoises) are typified by directional asymmetry, particularly in elements associated with the airway. Generally, it is assumed this asymmetry is related to biosonar production. However, skull asymmetry may actually be a by-product of selection pressure for an asymmetrically positioned larynx. The odontocete larynx traverses the pharynx and is held permanently in place by a ring of muscle. This allows prey swallowing while remaining underwater without risking water entering the lungs and causing injury or death. However, protrusion of the larynx through the pharynx causes a restriction around which prey must pass to reach the stomach. The larynx and associated hyoid apparatus has, therefore, been shifted to the left to provide a larger right piriform sinus (lateral pharyngeal food channel) for swallowing larger prey items. This asymmetry is reflected in the skull, particularly the dorsal openings of the nares. It is hypothesized that there is a relationship between prey size and skull asymmetry. This relationship was examined in 13 species of odontocete cetaceans from the northeast Atlantic, including four narrow-gaped genera (Mesoplodon, Ziphius, Hyperoodon, and Kogia) and eight wide-gaped genera (Phocoena, Delphinus, Stenella, Lagenorhynchus, Tursiops, Grampus, Globicephala, and Orcinus). Skulls were examined from 183 specimens to assess asymmetry of the anterior choanae. Stomach contents were examined from 294 specimens to assess prey size. Results show there is a significant positive relationship between maximum relative prey size consumed and average asymmetry relative to skull size in odontocete species (wide-gape species: R 2 ¼ 0.642, P ¼ 0.006; narrow-gape species: R 2 ¼ 0.909, P ¼ 0.031).

Phylogeography interprets molecular genetic variation in a spatial and temporal context. Molecular clocks are frequently used to calibrate phylogeographic analyses, however there is mounting evidence that molecular rates decay over the relevant timescales. It is therefore essential that an appropriate rate is determined, consistent with the temporal scale of the specific analysis. This can be achieved by using temporally spaced data such as ancient DNA or by relating the divergence of lineages directly to contemporaneous external events of known time. Here we calibrate a Eurasian field vole (Microtus agrestis) mitochondrial genealogy from the well-established series of post-glacial geophysical changes that led to the formation of the Baltic Sea and the separation of the Scandinavian peninsula from the central European mainland. The field vole exhibits the common phylogeographic pattern of Scandinavian colonization from both the north and the south, however the southernmost of the two relevant lineages appears to have originated in situ on the Scandinavian peninsula, or possibly in the adjacent island of Zealand, around the close of the Younger Dryas. The mitochondrial substitution rate and the timescale for the genealogy are closely consistent with those obtained with a previous calibration, based on the separation of the British Isles from mainland Europe. However the result here is arguably more certain, given the level of confidence that can be placed in one of the central assumptions of the calibration, that field voles could not survive the last glaciation of the southern part of the Scandinavian peninsula. Furthermore, the similarity between the molecular clock rate estimated here and those obtained by sampling heterochronous (ancient) DNA (including that of a congeneric species) suggest that there is little disparity between the measured genetic divergence and the population divergence that is implicit in our land-bridge calibration.