Geographical pattern of genetic variation in the Robertsonian system of Mus musculus domesticus in central Italy

The Robertsonian (Rb) system of Mus musculus domesticus in central Italy consists of three Rb races (CD, 2 n  = 22; CB, 2 n  = 22; ACR, 2 n  = 24), and additional Rb populations with new metacentrics have recently been reported. The aim of the present paper is to provide insight into the process of house mouse raciation in this area. Here we present new data concerning the geographical distribution of mtDNA haplotypes (control region sequence) in the three Rb races and in the surrounding standard populations. The presence of exclusive clades in all the three Rb races supports the idea of a past fragmentation event and a subsequent period of isolation. However, comparison of mtDNA polymorphism between Rb and standard races, and the shape of the mismatch distribution within the races, does not reveal any clear sign of a strong reduction in population size, at this geographical scale, related to race formation.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 395–405.     

Morphological variation in house mice from the Robertsonian polymorphism area of Barcelona

Morphometric variation in the Robertsonian polymorphism zone of Barcelona of Mus musculus domesticus was studied by geometric morphometrics. This system is characterized by populations of reduced diploid number (2 n  = 27–39) surrounded by standard populations (2 n  = 40). We investigated the morphological variation in mice from this area, as well as the effect of geographical distance and karyotype on this variation. We also investigated the degree of co-variation between the two functional units of the mandible to explore the origin of this system (primary intergradation or secondary contact). The size and shape of the cranium, mandible and scapula were analysed for 226 specimens grouped by population, chromosome number and structural heterozygosity. Size was estimated as the centroid size, and shape was estimated after Procrustes superimposition. No significant differences in size between populations or chromosomal groups were detected. Diploid number, structural heterozygosity and local geographical isolation contributed to the differentiation in shape. Morphological differentiation between standard mice and Robertsonian specimens was observed, suggesting genetic isolation between these groups. Co-variation between the ascending ramus and alveolar region of the mandible was quantified by the trace correlation between landmark subsets of these modules. The trace values showed an ascending trend, correlated with the distance from the centre of the polymorphism area, a pattern consistent with a primary intergradation scenario.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 555–570.     

Chromosomal evolution of the house mouse, Mus musculus domesticus, in the Aeolian Archipelago (Sicily, Italy)

We describe the chromosomal evolution of the metacentric populations of the house mouse, Mus musculus domesticus , which constitute the Robertsonian System of Aeolian Islands (Sicily, Italy). Eighty-nine specimens from all the seven islands that form the Archipelago were cytogenetically examined. The analysis shows the presence of 4 Rb races with a large number of shared metacentric chromosomes: 2 n  = 36 on Panarea, 2 n  = 34 on Alicudi, 2 n  = 26 on Lipari and Stromboli, and a different 2 n  = 26 race on Vulcano. On Salina and Filicudi, the standard karyotype was found. Polymorphism was only found in a population on Panarea Island and this population shares no metacentrics with the other races. The distribution of metacentrics among the races and the comparison between the Aeolian metacentrics and those found in the 97 previously documented metacentric populations allows us to formulate a hypothesis of chromosomal evolution for the Aeolian Robertsonian system. Six of the twelve metacentric chromosomes found in the Aeolian Islands come from localities outside the archipelago. The evolutionary model highlights how the chromosomal races originated inside the Archipelago and involve several factors, such as formation in situ of metacentrics, zonal raciation and, whole arm reciprocal translocation. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 194–202.     

Chromosomal variation in the house mouse

Although the standard karyotype of the western house mouse, Mus musculus domesticus , consists entirely of acrocentric chromosomes, there are 97 distinct 'populations' that are characterized by various combinations of metacentric chromosomes that have arisen by Robertsonian (Rb) fusions and whole-arm reciprocal translocations (WARTs). In this review we discuss the processes behind the origin and fixation of these rearrangements and then present a unified list of all known metacentric populations and evaluate their phylogenetic relationships. Eleven independent phylogeographical 'systems', each consisting of 2–25 metacentric populations, were identified in Scotland, Denmark, Northern Europe–Northern Switzerland, Southern Switzerland, Northern Italy, Croatia, Spain, Central–Southern Italy, Peloponnesus, Mainland Greece and Madeira. There are six isolated metacentric populations that do not belong to any of these systems. To generate phylogenies of the metacentric populations within each system, we determined those outcomes with the fewest steps regarding accumulation of metacentrics by Rb fusions, WARTs and zonal raciation and taking into account geographical proximity. These phylogenies should be viewed as working hypotheses that will be refined with further chromosomal and molecular data and improvements in methods of phylogenetic reconstruction. The list of metacentric populations and our phylogenies are also published electronically and can be accessed at http://www.studenec.ivb.cz/Projects/RobertsonianMice/ .  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 535–563.     

Mitochondrial DNA variation in the western house mouse (Mus musculus domesticus) close to its site of origin: studies in Turkey

In contrast to a substantial inventory of mitochondrial d -loop sequences from the West European part of the range of the western house mouse Mus musculus domesticus , there are few such data from close to the Middle Eastern origin of the subspecies. This paper attempts to rectify this situation, with details of d -loop sequences of 92 mice from 45 localities in Turkey, adding to the six mice from three localities previously studied from that country. The molecular data were found to be consistent with Turkey being close to the site of origin of M. m. domesticus . The 54 Turkish haplotypes were distributed throughout a phylogenetic tree incorporating representative sequences described previously, and there was high nucleotide diversity among the Turkish mice. There was weak genetic structure in Turkey, although haplotypes of the 'Main Turkish Clade', while common over much of Turkey, were absent from Southern Anatolia. Haplotypes of the Main Turkish Clade were also found in western Europe and it is believed that they derived from Turkey, which thus represents one of the source areas for the westwards expansion of M. m. domesticus .  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 473–485.     

Studies on the Robertsonian chromosomal variation of Mus musculus domesticus (Rodentia, Muridae) in Greece

The karyotype of the house mouse, Mus musculus domesticus , was examined in 282 specimens from 44 localities, in an effort to gain better understanding of the Robertsonian (Rb) variation known to exist in Greece. We consider that an Rb system exists in Peloponnisos, southern Greece, distributed in an area that is substantially larger than previously known. It consists of at least three Rb races with 2 n  = 30, 2 n  = 24 and 2 n  = 28, respectively, the last being reported for the first time in this paper and carrying Rb(3.6), Rb(8.12), Rb(10.14), Rb(13.15), Rb(9.16) and Rb(11.17) in a homozygous state. Additional instances of variation in this Rb system include individuals with 2 n  = 31 and 32 of variable Rb constitution and hybrids between the Rb races with 2 n  = 30 and 2 n  = 24. In southern Peloponnisos, Rb(10.14) was found in either a homozygous or a heterozygous state (2 n  = 38 or 39). The relationships among the Rb populations of Peloponnisos are discussed and hypotheses for their evolution are proposed. Rb variation was also recorded in two new locations of eastern Sterea Ellas (2 n  = 28 and 29) and one in Ipiros, north-west Greece (2 n  = 38). These findings corroborate the existence of two separate Rb systems in those two areas. Moreover, among a number of islands surveyed, Rb variation was only found in Kythira island, with Rb(10.14) in a heterozygous state (2 n  = 39). Finally, the typical all-acrocentric karyotype (2 n  = 40) was found in 51 of the animals studied from 13 localities. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 503–513.     

Microsatellite variability in wild populations of the house mouse is not influenced by differences in chromosomal recombination rates

Differences in recombination rates along the chromosomes can influence the evolution of neutral loci via hitchhiking effects. Generally, these effects should be stronger in regions of low recombination than in regions of high recombination. Detailed information on physical and genetic maps in the house mouse now allows an assessment of the correlation between neutral variability and recombination rates at given chromosomal regions. We chose 29 microsatellite loci from chromosomal regions which show differences in recombination rates and tested their variability in samples from five wild populations of Mus musculus musculus and M. m. domesticus . Our results provide no evidence for a correlation between microsatellite variability and recombination rates. This suggests that the high average mutation rate of microsatellites in mammals counterbalances the effects of long-range hitchhiking in the mouse genome.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 629–635.     

Population history and genetic structure of a circumpolar species: the arctic fox

The circumpolar arctic fox Alopex lagopus thrives in cold climates and has a high migration rate involving long-distance movements. Thus, it differs from many temperate taxa that were subjected to cyclical restriction in glacial refugia during the Ice Ages. We investigated population history and genetic structure through mitochondrial control region variation in 191 arctic foxes from throughout the arctic. Several haplotypes had a Holarctic distribution and no phylogeographical structure was found. Furthermore, there was no difference in haplotype diversity between populations inhabiting previously glaciated and unglaciated regions. This suggests current gene flow among the studied populations, with the exception of those in Iceland, which is surrounded by year-round open water. Arctic foxes have often been separated into two ecotypes: 'lemming' and 'coastal'. An analysis of molecular variance suggested particularly high gene flow among populations of the 'lemming' ecotype. This could be explained by their higher migration rate and reduced fitness in migrants between ecotypes. A mismatch analysis indicated a sudden expansion in population size around 118 000 BP, which coincides with the last interglacial. We propose that glacial cycles affected the arctic fox in a way opposite to their effect on temperate species, with interglacials leading to short-term isolation in northern refugia.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 79–89.     

Mitochondrial DNA in the hybrid zone between Mus musculus musculus and Mus musculus domesticus: a comparison of two transects

We studied mtDNA introgression across the contact zone between Mus musculus musculus and M. m. domesticus in two independent transects in the Czech Republic and Bavaria, Germany. A total of 1270 mice from 98 localities in the Czech transect and 456 mice from 41 localities in the Bavarian transect were examined for presence or absence of a Bam HI restriction site in the mt-Nd1 gene. Using this simple mtDNA marker, variants that belonged to the M. m. domesticus lineage (presence of restriction site) could be unequivocally distinguished from those belonging to the M. m. musculus lineage (absence of restriction site). The extent of introgression of mtDNA, three autosomal allozymes and the X chromosome was compared. The introgression of X markers was more limited than was that of the allozymes and mtDNA. In the Czech transect, the centre for the mtDNA cline was shifted about 3.6 km to the west relative to the X chromosome cline, with asymmetric introgression from M. m. musculus to M. m. domesticus . Interestingly, in the Bavarian transect, the centre of the mtDNA cline was shifted about 10.9 km to the east relative to the X chromosome cline, with asymmetric introgression from M. m. domesticus to M. m. musculus, opposite in direction to that observed in the Czech transect.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 363–378.     

Inferences of selection and migration in the Danish house mouse hybrid zone

We analysed the patterns of allele frequency change for ten diagnostic autosomal allozyme loci in the hybrid zone between the house mouse subspecies Mus musculus domesticus and M. m. musculus in central Jutland. After determining the general orientation of the clines of allele frequencies, we analysed the cline shapes along the direction of maximum gradient. Eight of the ten clines are best described by steep central steps with coincident positions and an average width of 8.9 km (support limits 7.6–12.4) flanked by tails of introgression, indicating the existence of a barrier to gene flow and only weak selection on the loci studied. We derived estimates of migration from linkage disequilibrium in the centre of the zone, and by applying isolation by distance methods to microsatellite data from some of these populations. These give concordant estimates of σ =  0.5–0.8 km generation     . The barrier to gene flow is of the order of 20 km (support limits 14–28), and could be explained by selection of a few per cent at 43–120 underdominant loci that reduces the mean fitness in the central populations to 0.45. Some of the clines appear symmetrical, whereas others are strongly asymmetrical, and two loci appear to have escaped the central barrier to gene flow, reflecting the differential action of selection on different parts of the genome. Asymmetry is always in the direction of more introgression into musculus , indicating either a general progression of domesticus into the musculus territory, possibly mediated by differential behaviour, or past movement of the hybrid zone in the opposite direction, impeded by potential geographical barriers to migration in domesticus territory.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 593–616.     

Chloroplast DNA variation in the shrub Justicia areysiana (Acanthaceae) endemic to the monsoon affected coastal mountains of the southern Arabian Peninsula

The monsoon affected mountains of the southern Arabian Peninsula harbour in climatically favoured refugia vegetation elements of palaeo-African origin. To understand better the temporal and spatial differentiation of these refugia, chloroplast variation in Justicia areysiana Deflers (Acanthaceae), a shrub species endemic to the Yemeni and Omani mountains close to the Arabian Sea, was studied using PCR-RFLP and chloroplast microsatellite diversity. Eleven haplotypes were characterized and show a distinct geographical distribution pattern with a deep split between populations from south Yemeni fog oases and those from Hawf Mountains/Dhofar region in east Yemen and south Oman. Very limited haplotype diversity within populations (h_S = 0.15) and a high level of population differentiation (G_ST = 0.81) demonstrate the strong genetic isolation of populations from each other. Past oscillations between humid and arid periods connected with glacial and interglacial episodes in the Pleistocene and Holocene are considered responsible for the observed patterns of genetic variation.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 437–444.     

Conservation genetics of the endangered red deer from Sardinia and Mesola with further remarks on the phylogeography of Cervus elaphus corsicanus

Red deer Cervus elaphus of the endangered populations from Sardinia and Mesola Wood, northern Italy, were analysed for genetic variation at 531 bp of the mitochondrial control region and 12 polymorphic nuclear microsatellite loci. A phylogenetic analysis was conducted including additional data from the literature to gain insight into the phylogeographical origin of the Sardinian subspecies C. e. corsicanus . Microsatellite variation was low in both populations but Sardinia showed comparatively high variability at the control region. Management recommendations are discussed. In particular, the Mesola red deer, the only remaining indigenous Italian population, ought to be managed to increase the effective population size and should be subdivided into two or more populations. As to the phylogeography of the Sardinian population, microsatellite data favoured mainland Italy as the place of origin in that Sardinia and Mesola showed the smallest distance values and were paired together in trees with high bootstrap support. However, the mitochondrial data only partially confirmed this conclusion but showed great similarity between Sardinian and Spanish red deer. Possible explanations for this discrepancy and general limits of mitochondrial sequences in resolving demographic and biogeographical processes of the recent past are discussed.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 691–701.     

Pinus mugo (Pinaceae) in the Abruzzi Mountains: high morphological variation in isolated populations

Thirty-three individuals of Pinus mugo from the Abruzzian Apennines (Italy), the most isolated population of the species, were examined biometrically to verify the range of trait variation and compared with six other populations sampled in the north-eastern part of the species range. Ten needles and ten cones from each individual were measured and quantified on the basis of 31 traits. The interpopulation comparison revealed a close affinity of the Abruzzian population of P. mugo to three of the six other populations. The other three north-eastern populations, one from the Tatra Mountains and two from the Chornokhora Mountains, appeared to be different. This suggests that these populations originated from other Pleistocene centres of occurrence. The intrapopulation variation of the population from the Abruzzian Apennines is comparable with those of all six populations of P. mugo from the Sudety and Carpathian Mountains. These findings support the hypothesis that isolated but locally abundant plant populations do not necessarily show a reduction in variability resulting from isolation.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 309–316.     

Testing for selection on the androgen-binding protein in the Danish mouse hybrid zone

The three peripheral subspecies of the house mouse Mus musculus have fixed specific variants of the androgen-binding protein (ABP) that have been proposed to be part of a recognition mechanism that could participate in sexual isolation between the subspecies. We tested for selection on Abpa by characterizing the pattern of Abpa introgression across a transect of the hybrid zone between M. m. musculus and M. m. domesticus in Jutland. On the musculus side, the cline for Abpa resembled that of a nearly neutral allozyme more than that of strongly selected X and Y chromosome markers. However, the high central step which displaces the tail of introgression of Abpa to higher frequencies was best accounted for by linkage to a locus under strong selection against hybrids. Still, we cannot exclude that this pattern results from weak selection against Abpa in the tail of introgression, which would be compatible with an assortative choice mechanism. On the domesticus side there was little introgression close to the hybrid zone, presumably due to a geographical barrier to migration. However, substantial frequencies of musculus alleles occurred further away, suggesting mixed colonization patterns as well as flow across the hybrid zone.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 447–459.     

Enhanced colour polymorphisms in island populations of the land snail Euhadra peliomphala

Variations in visible genetic polymorphisms are assumed to decrease in populations on small islands because of intense founder effects, genetic drift and inbreeding. However, we have found evidence of a marked enhancement of colour polymorphisms within populations on small oceanic islands that were colonized from the mainland. The source populations on the mainland of the land snail Euhadra peliomphala in four oceanic islands were estimated by phylogenetic analysis of mitochondrial DNA sequences. Diversity of shell colour was higher in the island populations than in the source populations on the mainland. In addition, the shell colour morphs differed not only among populations from different islands but also between the island populations and the source populations on the mainland. By contrast, no mtDNA variations were found in any of the island populations, even though the source populations possessed high mtDNA diversity. Thus, components of colour morphs changed in the island populations after their colonization, and colour polymorphisms are enhanced in these islands despite the loss of genetic variation. The above findings suggest that ecological mechanisms such as morphological release owing to a release from competition may overcome the tendency toward reduced genetic variation in islands to enhance the colour polymorphism.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 417–425.     

The role of salivary androgen-binding protein in reproductive isolation between two subspecies of house mouse: Mus musculus musculus and Mus musculus domesticus

Previous behavioural studies using inbred lines have suggested that the gene ( Abpa ) for the alpha subunit of salivary androgen-binding protein (ABP) plays a role in prezygotic isolation between house mouse Mus musculus subspecies. We tested this hypothesis in animals from wild allopatric (121 individuals from four samples) and parapatric (320 animals from 15 samples) populations sampled on the Czech–Bavarian transect across the hybrid zone between M. m. domesticus and M. m. musculus . The study did not reveal a consistent statistically significant trend of homosubspecific preferences in individual allopatric and parapatric populations. Nonetheless, the whole pattern of preference was skewed toward homosubspecific preference mostly on the M. m. musculus side of the hybrid zone. The pattern of homosubspecific preferences was stronger for the time spent sniffing than it was for the first choice of the signal (the ratio of homosubspecific vs. heterosubspecific preferences for both sexes was 6 : 2 in allopatric and 21 : 9 in parapatric populations, while the same rates were 4 : 4 and 16 : 14 for the first choice). To the extent that Y-maze tests reflect preference under wild conditions, we suggest that this slight preference may not in itself be sufficient to impede gene flow between the two subspecies and thus act as a reproductive barrier. ABP most probably participates in a complex system of subspecies-specific recognition in the hybrid zone, but the picture is far too complex at this time to allow a conclusive evaluation of the importance of this role.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 349–361.     

Assessment of mate preference in the house mouse with reference to investigations on assortative mating

This study analysed patterns of mate choice based on different types of laboratory test, and points out the advantages of combined methods to assess mate preference. We compared dyadic encounters and two-way choice tests involving a pair of mice or their urinary signature. Preference was assessed in males and females of the two European subspecies of the house mouse Mus musculus that share a secondary hybrid zone. A preference was deduced from directional choice or behavioural discrimination in favour of a mouse. Our results show discrepancies between the outcomes of the different types of test, which we discuss in terms of the quality of the stimuli involved, and of physical access to the information carried by those stimuli. Despite variation, our results indicate that M. m. domesticus did not show a preference, but could discriminate between stimuli of the two subspecies and tended to direct sexual behaviour assortatively. In contrast, both male and female M. m. musculus showed positive discrimination and preference for potential mates and signals carried by their own subspecies. Additionally, our results confirm that subspecies informative signals are present in mouse urine and suggest that they may be molecules of low volatility, necessitating contact for preference to be displayed.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 461–471.     

Variation in native pollinators in the absence of honeybees: implications for reproductive success of an Australian generalist-pollinated herb Trachymene incisa (Apiaceae)

Most plants are generalist in terms of pollination, with the potential for significant spatial and temporal variation in their pollinators. Few studies have investigated how variable pollinators are in a generalist pollination system or how this variation affects plant reproduction. We investigated the degree of variation in pollinators and resulting reproductive success among populations of a widespread generalist-pollinated herb, Trachymene incisa (Apiaceae). The European honeybee was unexpectedly absent from the pollinator assemblages, providing the unique opportunity to study the native Australian pollinators. Insect visitation rates and the taxonomic composition of the pollinator assemblage varied significantly across populations, indicating that populations of T. incisa are not equally serviced and are not equally generalist. This highlights that sampling one population would not characterize the extent of species generalization. There was no positive correlation between insect visitation rate and reproductive success, with the Agnes Banks population receiving the highest visitation rate but producing the lowest reproductive output, and the Myall Lakes population receiving the lowest visitation rate and producing the highest seedling emergence. This study shows that variation in pollinators can have measurable effects on populations of generalist-pollinated plants, therefore there is potential for large-scale change in all plant–pollinator interactions.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 479–490.     

Determination of ploidy and nuclear DNA content in populations of Atriplex halimus (Chenopodiaceae)

Nuclear DNA contents were determined by flow cytometry for 20 populations of the perennial C₄ shrub Atriplex halimus L. (Chenopodiaceae) originating from the Mediterranean basin and Fuerteventura (Canary Islands). Two populations were also analysed for chromosome number: one (from Ibiza, Spain), with a 2C nuclear DNA content of 2.40 pg, was shown to be diploid (2 n  = 2 x  = 18), whilst the other (from Sicily, Italy), with 5.11 pg, was tetraploid (2 n  = 2 x  = 36). With respect to nuclear DNA content, two groups of populations were detected, diploids with 2.40–2.44 pg and tetraploids with 4.77–5.13 pg. The diploid populations were mainly from the western Mediterranean (Spain and France) and Fuerteventura, whereas tetraploids were generally, but not exclusively, from more arid areas in North Africa and the eastern Mediterranean. In general, the diploid and tetraploid populations corresponded to the subspecies halimus and schweinfurthii , respectively. For certain populations having morphologies intermediate between those considered typical of these two subspecies, nuclear DNA contents showed them to be tetraploid. There was significant variation in nuclear DNA content among the tetraploid populations, with greater values in the more easterly populations.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 147 , 441−448.