Of mice and the 'Age of Discovery': the complex history of colonization of the Azorean archipelago by the house mouse (Mus musculus) as revealed by mitochondrial DNA variation

The Presence of a Shelter in an Open Field Test Has Differential Effects on the Behavior and Stress Response of Two Mouse Species

The open field test (OFT) is frequently used in research to assess anxiety-like behavior and locomotor activity. Its simple design can lead to the misconception that it is a standardized procedure comparable between laboratories. However, some modifications in the setup can cause changes in behavior. Different species might also react differently to the modifications introduced. There is thus need for a better understanding of the impact of modifications and their value for the species in question. Here, we tested two closely related mouse species, Mus musculus and Mus spretus, in an OFT with and without the presence of a shelter. We assessed mouse exploratory behavior through the analysis of multiple behavioral traits, and stress response through the measurement of circulating cortisol levels. Both species had elevated cortisol levels during the OFT in contrast to control animals which were not exposed to the OFT. While the presence of a shelter in the OFT increased the exploratory behavior in both mouse species, M. spretus, but not M. musculus, showed a reduction in cortisol levels. Also, other measured behaviors show a rather proactive coping strategy of the commensal M. musculus in contrast to a reactive strategy of the non-commensal M. spretus. Our study revealed a strong species-specific influence of the OFT design on the resulting behavior and stress levels of mice, illustrating the importance of OFT designs to account for the characteristics of the species under study. The addition of a shelter might be considered to improve experimental results by promoting animal welfare.

Genetic structure and demographic history of house mice in western Europe inferred using whole-genome sequences

The western house mouse, Mus musculus domesticus, is a human commensal and an outstanding model organism for studying a wide variety of traits and diseases. However, we have few genomic resources for wild mice and only a rudimentary understanding of the demographic history of house mice in Europe. Here, we sequenced 59 whole genomes of mice collected from England, Scotland, Wales, Guernsey, northern France, Italy, Portugal and Spain. We combined this dataset with 24 previously published sequences from southern France, Germany and Iran and compared patterns of population structure and inferred demographic parameters for house mice in western Europe to patterns seen in humans. Principal component and phylogenetic analyses identified three genetic clusters in western European mice. Admixture and f-branch statistics identified historical gene flow between these genetic clusters. Demographic analyses suggest a shared history of population bottlenecks prior to 20 000 years ago. Estimated divergence times between populations of house mice from western Europe ranged from 1500 to 5500 years ago, in general agreement with the zooarchaeological record. These results correspond well with key aspects of contemporary human population structure and the history of migration in western Europe, highlighting the commensal relationship of this important genetic model.

House Mice in the Atlantic Region: Genetic Signals of Their Human Transport

BACKGROUND/OBJECTIVES

The colonization history of house mice reflects the maritime history of humans that passively transported them worldwide. We investigated western house mouse colonization in the Atlantic region through studies of mitochondrial D-loop DNA sequences from modern specimens.

METHODS

We assembled a dataset of 758 haplotypes derived from 2765 mice from 47 countries/oceanic archipelagos (a combination of new and published data). Our maximum likelihood phylogeny recovered five previously identified clades, and we used the haplotype affinities within the phylogeny to infer house mouse colonization history, employing statistical tests and indices. From human history, we predefined four European source areas for mice in the Atlantic region (Northern Europe excluding Scandinavia, Southern Europe, Scandinavia, and Macaronesia) and we investigated the colonization from these source areas to different geographic areas in the Atlantic region.

RESULTS

Our inferences suggest mouse colonization of Scandinavia itself from Northern Europe, and Macaronesia from both Southern Europe and Scandinavia/Germany (the latter likely representing the transport of mice by Vikings). Mice on North Atlantic islands apparently derive primarily from Scandinavia, while for South Atlantic islands, North America, and Sub-Saharan Africa, the clearest source is Northern Europe, although mice on South Atlantic islands also had genetic inputs from Macaronesia and Southern Europe (for Tristan da Cunha). Macaronesia was a stopover for Atlantic voyages, creating an opportunity for mouse infestation. Mice in Latin America also apparently had multiple colonization sources, with a strong Southern European signal but also input from Northern Europe and/or Macaronesia.

CONCLUSIONS

D-loop sequences help discern the broad-scale colonization history of house mice and new perspectives on human history.

Genetic diversity and historical demography of underutilised goat breeds in North-Western Europe

In the last decade, several studies aimed at dissecting the genetic architecture of local small ruminant breeds to discover which variations are involved in the process of adaptation to environmental conditions, a topic that has acquired priority due to climate change. Considering that traditional breeds are a reservoir of such important genetic variation, improving the current knowledge about their genetic diversity and origin is the first step forward in designing sound conservation guidelines. The genetic composition of North-Western European archetypical goat breeds is still poorly exploited. In this study we aimed to fill this gap investigating goat breeds across Ireland and Scandinavia, including also some other potential continental sources of introgression. The PCA and Admixture analyses suggest a well-defined cluster that includes Norwegian and Swedish breeds, while the crossbred Danish landrace is far apart, and there appears to be a close relationship between the Irish and Saanen goats. In addition, both graph representation of historical relationships among populations and f4-ratio statistics suggest a certain degree of gene flow between the Norse and Atlantic landraces. Furthermore, we identify signs of ancient admixture events of Scandinavian origin in the Irish and in the Icelandic goats. The time when these migrations, and consequently the introgression, of Scandinavian-like alleles occurred, can be traced back to the Viking colonisation of these two isles during the Viking Age (793-1066 CE). The demographic analysis indicates a complicated history of these traditional breeds with signatures of bottleneck, inbreeding and crossbreeding with the improved breeds. Despite these recent demographic changes and the historical genetic background shaped by centuries of human-mediated gene flow, most of them maintained their genetic identity, becoming an irreplaceable genetic resource as well as a cultural heritage.

Widespread distribution of rodenticide resistance-conferring mutations in the Vkorc1 gene among house mouse populations in Portuguese Macaronesian islands and Iberian Atlantic areas

Growing evidence of widespread resistance to anticoagulant rodenticides (ARs) in house mice pose significant challenges to pest control efforts. First-generation ARs were introduced in the early 1950s but resistance to these emerged later that decade. Second-generation rodenticides were then developed, with resistance being reported in the late 1970s. Research has linked resistance to ARs with mutations in the Vkorc1 gene, leading to the use of more toxic and environmentally harmful compounds. In this study, 243 tail tips of house mice from mainland Portugal and Southern Spain, the Azores and Madeira archipelagos were analysed for all 3 exons of the Vkorc1 gene. Mutations L128S, Y139C, along with the so-called spretus genotype Vkorc1spr are considered responsible for reduced susceptibility of house mice to ARs. All these sequence variants were broadly detected throughout the sampling regions. Vkorc1spr was the most often recorded among mainland populations, whereas Y139C was nearly ubiquitous among the insular populations. In contrast, L128S was only detected in mainland Portugal and four islands of the Azores archipelago. All first generation ARs such as warfarin and coumatetralyl are deemed ineffective against all Vkorc1 variants identified in this study. Second-generation bromadiolone and difenacoum should also be discarded to control populations carrying Vkorc1spr, Y139C or L128S mutations. Inadequate use of ARs in regions where resistant animals have been found in large proportions will result in the spreading of rodenticide resistance among rodent populations through the positive selection of non-susceptible individuals. Consequently, ineffectiveness of rodent control will increase and potentiate environmental contamination, hazarding non-target wildlife through secondary poisoning. We highlight the need for Vkorc1 screening as a crucial tool in rodent management, aiding in the selection of the most appropriate control/eradication method in order to prevent misuse of these toxic biocides and the spread of rodenticide resistance among house mouse populations.

The demographic history of house mice (Mus musculus domesticus) in eastern North America

The Western European house mouse (Mus musculus domesticus) is a widespread human commensal that has recently been introduced to North America. Its introduction to the Americas is thought to have resulted from the transatlantic movements of Europeans that began in the early 16th century. To study the details of this colonization history, we examine population structure, explore relevant demographic models, and infer the timing of divergence among house mouse populations in the eastern United States using published exome sequences from five North American populations and two European populations. For North American populations of house mice, levels of nucleotide variation were lower, and low-frequency alleles were less common than for European populations. These patterns provide evidence of a mild bottleneck associated with the movement of house mice into North America. Several analyses revealed that one North American population is genetically admixed, which indicates at least two source populations from Europe were independently introduced to eastern North America. Estimated divergence times between North American and German populations ranged between ∼1,000 and 7,000 years ago and overlapped with the estimated divergence time between populations from Germany and France. Demographic models comparing different North American populations revealed that these populations diverged from each other mostly within the last 500 years, consistent with the timing of the arrival of Western European settlers to North America. Together, these results support a recent introduction of Western European house mice to eastern North America, highlighting the effects of human migration and colonization on the spread of an invasive human commensal.

Macaronesia as a Fruitful Arena for Ecology, Evolution, and Conservation Biology

Research in Macaronesia has led to substantial advances in ecology, evolution and conservation biology. We review the scientific developments achieved in this region, and outline promising research avenues enhancing conservation. Some of these discoveries indicate that the Macaronesian flora and fauna are composed of rather young lineages, not Tertiary relicts, predominantly of European origin. Macaronesia also seems to be an important source region for back-colonisation of continental fringe regions on both sides of the Atlantic. This group of archipelagos (Azores, Madeira, Selvagens, Canary Islands, and Cabo Verde) has been crucial to learn about the particularities of macroecological patterns and interaction networks on islands, providing evidence for the development of the General Dynamic Model of oceanic island biogeography and subsequent updates. However, in addition to exceptionally high richness of endemic species, Macaronesia is also home to a growing number of threatened species, along with invasive alien plants and animals. Several innovative conservation and management actions are in place to protect its biodiversity from these and other drivers of global change. The Macaronesian Islands are a well-suited field of study for island ecology and evolution research, mostly due to its special geological layout with 40 islands grouped within five archipelagos differing in geological age, climate and isolation. A large amount of data is now available for several groups of organisms on and around many of these islands. However, continued efforts should be made toward compiling new information on their biodiversity, to pursue various fruitful research avenues and develop appropriate conservation management tools.

Climate change facilitated the early colonization of the Azores Archipelago during medieval times

Humans have made such dramatic and permanent changes to Earth's landscapes that much of it is now substantially and irreversibly altered from its preanthropogenic state. Remote islands, until recently isolated from humans, offer insights into how these landscapes evolved in response to human-induced perturbations. However, little is known about when and how remote systems were colonized because archaeological data and historical records are scarce and incomplete. Here, we use a multiproxy approach to reconstruct the initial colonization and subsequent environmental impacts on the Azores Archipelago. Our reconstructions provide unambiguous evidence for widespread human disturbance of this archipelago starting between 700_-60 ⁺⁵⁰ and 850_-60 ⁺⁶⁰ Common Era (CE), ca. 700 y earlier than historical records suggest the onset of Portuguese settlement of the islands. Settlement proceeded in three phases, during which human pressure on the terrestrial and aquatic ecosystems grew steadily (i.e., through livestock introductions, logging, and fire), resulting in irreversible changes. Our climate models suggest that the initial colonization at the end of the early Middle Ages (500 to 900 CE) occurred in conjunction with anomalous northeasterly winds and warmer Northern Hemisphere temperatures. These climate conditions likely inhibited exploration from southern Europe and facilitated human settlers from the northeast Atlantic. These results are consistent with recent archaeological and genetic data suggesting that the Norse were most likely the earliest settlers on the islands.

Genetic structure in Orkney island mice: isolation promotes morphological diversification

Following human occupation, the house mouse has colonised numerous islands, exposing the species to a wide variety of environments. Such a colonisation process, involving successive founder events and bottlenecks, may either promote random evolution or facilitate adaptation, making the relative importance of adaptive and stochastic processes in insular evolution difficult to assess. Here, we jointly analyse genetic and morphometric variation in the house mice (Mus musculus domesticus) from the Orkney archipelago. Genetic analyses, based on mitochondrial DNA and microsatellites, revealed considerable genetic structure within the archipelago, suggestive of a high degree of isolation and long-lasting stability of the insular populations. Morphometric analyses, based on a quantification of the shape of the first upper molar, revealed considerable differentiation compared to Western European populations, and significant geographic structure in Orkney, largely congruent with the pattern of genetic divergence. Morphological diversification in Orkney followed a Brownian motion model of evolution, suggesting a primary role for random drift over adaptation to local environments. Substantial structuring of human populations in Orkney has recently been demonstrated, mirroring the situation found here in house mice. This synanthropic species may thus constitute a bioproxy of human structure and practices even at a very local scale.

Unforeseen diversity of quails (Galliformes: Phasianidae: Coturnix) in oceanic islands provided by the fossil record of Macaronesia

The original bird fauna of most oceanic islands has been affected by recent extinction processes associated with human arrival and its subsequent impacts. In the volcanic Macaronesian archipelagos (Azores, Madeira, Selvagens, Canary Islands and Cape Verde), in the North Atlantic, the Late Quaternary fossil record indicates that there was formerly a higher avian diversity, including a high number of now extinct endemic species. This assemblage of extinct birds includes endemic insular quails (Galliformes: Phasianidae). In this study, we describe three newly discovered extinct species of quails, two of which inhabited the archipelago of Madeira (Coturnix lignorum sp. nov. from Madeira Island and Coturnix alabrevis sp. nov. from Porto Santo Island) and one from Cape Verde (Coturnix centensis sp. nov.). The fossil record also indicates the presence of additional species of extinct endemic quails on other Macaronesian islands. These birds plus the extinct Canary Island quail (Coturnix gomerae) indicate a high former endemic diversity of this genus in Macaronesia, a feature unique among oceanic archipelagos. Anatomical traits show that the new taxa were flightless ground dwellers, making them vulnerable to human interference, with their extinction being linked to human arrival and subsequent habitat alterations and the introduction of invasive species.

The genomic ancestry, landscape genetics and invasion history of introduced mice in New Zealand

The house mouse (Mus musculus) provides a fascinating system for studying both the genomic basis of reproductive isolation, and the patterns of human-mediated dispersal. New Zealand has a complex history of mouse invasions, and the living descendants of these invaders have genetic ancestry from all three subspecies, although most are primarily descended from M. m. domesticus. We used the GigaMUGA genotyping array (approximately 135 000 loci) to describe the genomic ancestry of 161 mice, sampled from 34 locations from across New Zealand (and one Australian city-Sydney). Of these, two populations, one in the south of the South Island, and one on Chatham Island, showed complete mitochondrial lineage capture, featuring two different lineages of M. m. castaneus mitochondrial DNA but with only M. m. domesticus nuclear ancestry detectable. Mice in the northern and southern parts of the North Island had small traces (approx. 2-3%) of M. m. castaneus nuclear ancestry, and mice in the upper South Island had approximately 7-8% M. m. musculus nuclear ancestry including some Y-chromosomal ancestry-though no detectable M. m. musculus mitochondrial ancestry. This is the most thorough genomic study of introduced populations of house mice yet conducted, and will have relevance to studies of the isolation mechanisms separating subspecies of mice.

Global population divergence and admixture of the brown rat (Rattus norvegicus)

Native to China and Mongolia, the brown rat (Rattus norvegicus) now enjoys a worldwide distribution. While black rats and the house mouse tracked the regional development of human agricultural settlements, brown rats did not appear in Europe until the 1500s, suggesting their range expansion was a response to relatively recent increases in global trade. We inferred the global phylogeography of brown rats using 32 k SNPs, and detected 13 evolutionary clusters within five expansion routes. One cluster arose following a southward expansion into Southeast Asia. Three additional clusters arose from two independent eastward expansions: one expansion from Russia to the Aleutian Archipelago, and a second to western North America. Westward expansion resulted in the colonization of Europe from which subsequent rapid colonization of Africa, the Americas and Australasia occurred, and multiple evolutionary clusters were detected. An astonishing degree of fine-grained clustering between and within sampling sites underscored the extent to which urban heterogeneity shaped genetic structure of commensal rodents. Surprisingly, few individuals were recent migrants, suggesting that recruitment into established populations is limited. Understanding the global population structure of R. norvegicus offers novel perspectives on the forces driving the spread of zoonotic disease, and aids in development of rat eradication programmes.

Genetic structure and invasion history of the house mouse (Mus musculus domesticus) in Senegal, West Africa: a legacy of colonial and contemporary times

Knowledge of the genetic make-up and demographic history of invasive populations is critical to understand invasion mechanisms. Commensal rodents are ideal models to study whether complex invasion histories are typical of introductions involving human activities. The house mouse Mus musculus domesticus is a major invasive synanthropic rodent originating from South-West Asia. It has been largely studied in Europe and on several remote islands, but the genetic structure and invasion history of this taxon have been little investigated in several continental areas, including West Africa. In this study, we focussed on invasive populations of M. m. domesticus in Senegal. In this focal area for European settlers, the distribution area and invasion spread of the house mouse is documented by decades of data on commensal rodent communities. Genetic variation at one mitochondrial locus and 16 nuclear microsatellite markers was analysed from individuals sampled in 36 sites distributed across the country. A combination of phylogeographic and population genetics methods showed that there was a single introduction event on the northern coast of Senegal, from an exogenous (probably West European) source, followed by a secondary introduction from northern Senegal into a coastal site further south. The geographic locations of these introduction sites were consistent with the colonial history of Senegal. Overall, the marked microsatellite genetic structure observed in Senegal, even between sites located close together, revealed a complex interplay of different demographic processes occurring during house mouse spatial expansion, including sequential founder effects and stratified dispersal due to human transport along major roads.