Historical biogeography of Mediterranean trout

Complete sequencing of the mitochondrial control region was used to describe phylogenetic relationships of brown trout populations (Salmo trutta) in the Mediterranean river basins of Iberia and to review the historical biogeography of trout from the Mediterranean regions. Phylogenetic relationships among trout lineages suggested that the Danubian one is the most ancestral, in accordance with the eastern origin of most of the European freshwater fish species. Nested-clade and mismatch analyses suggested that the present distribution of haplotypes of the Adriatic and Mediterranean lineages resulted from population expansions originated, respectively, from central and western Europe, which favoured extensive secondary contacts between lineages. Reduced diversity detected within 50% of the analysed populations and large intrabasin differentiation indicated restricted gene flow in post-glacial periods.     

Genetic polymorphism at the cytochrome oxidase I gene in mediterranean populations of Batrocera Oleae (Diptera: Tephritidae)

The tephritid Bactrocera oleae (Gmelin) is a harmful pest of olive crops that cause important agricultural and economic losses in the Mediterranean area where 90% of the world olive trees are cultivated. The knowledge of the genetic diversity in insect pest species populations is critical for decisions concerning appropriate control management strategies. In the present work, the genetic variability within and among 7 populations ‐five from Spain, one from Italy and one from Tunisia‐, was assessed by sequencing 1151 bp of the COI gene. A total of 21 haplotypes were observed. The intraspecific diversity was high, particularly in the Spanish populations (haplotype and nucleotide diversity 0.84 and 0.00137, respectively). However, the genetic differentiation among the populations was low in the case of Spanish ones (Fst between 0 and 0.041), and higher –and statistically significant– when comparing with the Italian and Tunisian samples. The haplotypes distribution and the PCoA analysis show three clear groups of populations: Spanish, Italian and Tunisian. The results might indicate the length of time elapsed since B. oleae became established in the Mediterranean region, the large effective sizes expected of its populations and the high gene flow among Iberian populations. The information could be relevant for integrated control programmes coordination.     

Global population genetic structure and male-mediated gene flow in the green sea turtle (Chelonia mydas): analysis of microsatellite loci

We assessed the degree of population subdivision among global populations of green sea turtles, Chelonia mydas, using four microsatellite loci. Previously, a single-copy nuclear DNA study indicated significant male-mediated gene flow among populations alternately fixed for different mitochondrial DNA haplotypes and that genetic divergence between populations in the Atlantic and Pacific Oceans was more common than subdivisions among populations within ocean basins. Even so, overall levels of variation at single-copy loci were low and inferences were limited. Here, the markedly more variable microsatellite loci confirm the presence of male-mediated gene flow among populations within ocean basins. This analysis generally confirms the genetic divergence between the Atlantic and Pacific. As with the previous study, phylogenetic analyses of genetic distances based on the microsatellite loci indicate a close genetic relationship among eastern Atlantic and Indian Ocean populations. Unlike the single-copy study, however, the results here cannot be attributed to an artifact of general low variability and likely represent recent or ongoing migration between ocean basins. Sequence analyses of regions flanking the microsatellite repeat reveal considerable amounts of cryptic variation and homoplasy and significantly aid in our understanding of population connectivity. Assessment of the allele frequency distributions indicates that at least some of the loci may not be evolving by the stepwise mutation model.     

Long-term changes in population genetic features of a rapidly expanding marine invader: implication for invasion success

Large blooms of Rhopilema nomadica, a highly venomous rhizostamatid scyphozoan species introduced to the Mediterranean through the Suez Canal, have become ubiquitous in the summer and winter months along the Israeli coasts since the mid-1980s. This species has since spread across the eastern Mediterranean and was sighted as far west as Tunisia and Sardinia. For the past 12 years, we have studied changes in the mitochondrial COI haplotypes diversity of R. nomadica to investigate small scale fluctuactions of genetic diversity and to reveal possible genetic structuring of the fast spreading invader in the Eastern Mediterranean. The 1091 COI sequences analysed, revealed a highly diverse population displaying 89 haplotypes, 46 of which appeared as singletons, low frequency haplotypes. All the specimens analysed throughout the period belong to a single unstructured population. Though lacking data from the source population in the Red Sea, the high within-population diversity and the high diversity of COI haplotypes support the hypothesis of multiple introductions events, or an open corridor with a continuous influx of propagules. Tajima’s D and Fu’s Fst negative values and the increased numbers of COI singletons from early to late sampling periods, have verified that the Israeli population is characterized by a rapid expanding population. Further research is needed for the evaluation of COI diversity and patterns in R. nomadica populations across the eastern Mediterranean Sea and Red Sea, as well as any correlation of the high variability between COI locus and phenotypic diversity.

     

Genetic differentiation among North Atlantic killer whale populations

Population genetic structure of North Atlantic killer whale samples was resolved from differences in allele frequencies of 17 microsatellite loci, mtDNA control region haplotype frequencies and for a subset of samples, using complete mitogenome sequences. Three significantly differentiated populations were identified. Differentiation based on microsatellite allele frequencies was greater between the two allopatric populations than between the two pairs of partially sympatric populations. Spatial clustering of individuals within each of these populations overlaps with the distribution of particular prey resources: herring, mackerel and tuna, which each population has been seen predating. Phylogenetic analyses using complete mitogenomes suggested two populations could have resulted from single founding events and subsequent matrilineal expansion. The third population, which was sampled at lower latitudes and lower density, consisted of maternal lineages from three highly divergent clades. Pairwise population differentiation was greater for estimates based on mtDNA control region haplotype frequencies than for estimates based on microsatellite allele frequencies, and there were no mitogenome haplotypes shared among populations. This suggests low or no female migration and that gene flow was primarily male mediated when populations spatially and temporally overlap. These results demonstrate that genetic differentiation can arise through resource specialization in the absence of physical barriers to gene flow.     

Genetic variation at twentythree microsatellite loci in sixteen human populations

We have analysed genetic variation at 23 microsatellite loci in a global sample of 16 ethnically and geographically diverse human populations. On the basis of their ancestral heritage and geographic locations, the studied populations can be divided into five major groups, viz. African, Caucasian, Asian Mongoloid, American Indian and Pacific Islander. With respect to the distribution of alleles at the 23 loci, large variability exists among the examined populations. However, with the exception of the American Indians and the Pacific Islanders, populations within a continental group show a greater degree of similarity. Phylogenetic analyses based on allele frequencies at the examined loci show that the first split of the present-day human populations had occurred between the Africans and all of the non-African populations, lending support to an African origin of modern human populations. Gene diversity analyses show that the coefficient of gene diversity estimated from the 23 loci is, in general, larger for populations that have remained isolated and probably of smaller effective sizes, such as the American Indians and the Pacific Islanders. These analyses also demonstrate that the component of total gene diversity, which is attributed to variation between groups of populations, is significantly larger than that among populations within each group. The empirical data presented in this work and their analyses reaffirm that evolutionary histories and the extent of genetic variation among human populations can be studied using microsatellite loci.     

Deep phylogeographic divergence and cytonuclear discordance in the grasshopper Oedaleus decorus

The grasshopper Oedaleus decorus is a thermophilic insect with a large, mostly south-Palaearctic distribution range, stretching from the Mediterranean regions in Europe to Central-Asia and China. In this study, we analyzed the extent of phylogenetic divergence and the recent evolutionary history of the species based on 274 specimens from 26 localities across the distribution range in Europe. Phylogenetic relationships were determined using sequences of two mitochondrial loci (ctr, ND2) with neighbour-joining and Bayesian methods. Additionally, genetic differentiation was analyzed based on mitochondrial DNA and 11 microsatellite markers using F-statistics, model-free multivariate and model-based Bayesian clustering approaches. Phylogenetic analyses detected consistently two highly divergent, allopatrically distributed lineages within O. decorus. The divergence among these Western and Eastern lineages meeting in the region of the Alps was similar to the divergence of each lineage to the sister species O. asiaticus. Genetic differentiation for ctr was extremely high between Western and Eastern grasshopper populations (F(ct)=0.95). Microsatellite markers detected much lower but nevertheless very significant genetic structure among population samples. The nuclear data also demonstrated a case of cytonuclear discordance because the affiliation with mitochondrial lineages was incongruent in Northern Italy. Taken together these results provide evidence of an ancient separation within Oedaleus and either historical introgression of mtDNA among lineages and/or ongoing sex-specific gene flow in this grasshopper. Our study stresses the importance of multilocus approaches for unravelling the history and status of taxa of uncertain evolutionary divergence.     

Autosomal, mitochondrial, and Y chromosome DNA variation in Finland: evidence for a male-specific bottleneck

The high prevalence of rare genetic diseases in Finland has been attributed to a founder effect some 2,000 years ago. However, this hypothesis has not been supported from mtDNA sequence and autosomal microsatellite data which indicate high levels of gene diversity. Here we have identified genetic evidence for a population bottleneck by examining variable microsatellite loci on the nonrecombining portion of Y chromosomes from Finland and four populations from Europe and the Americas. Sequence data from segment I of the control region (HVS-1) of mtDNA (360 bases) and 20 autosomal dinucleotide repeat markers were also analyzed. Partitions of genetic variance within and between populations revealed significant levels of Y-chromosome differentiation between populations. Phylogenetic and diversity analyses revealed divergent Finnish Y-haplotype clades and significantly lower Y-haplotype diversity among Finns as compared to other populations. Surprisingly, Finnish Y-haplotype diversity was even lower than the Native American populations. These results provide support for the Finnish bottleneck hypothesis. Evidence for two separate founding Finnish Y-chromosome lineages was also observed from the Y-chromosome phylogeny. A limited number of closely related founding males may have contributed to the low number of paternal lineages in the Finnish population. In contrast, high levels of genetic diversity for mtDNA and autosomal STRs may be the result of sex-biased gene flow and recent immigration to urban areas from established internal isolates within Finland.     

The Effect of Pleistocene Climate Fluctuations on Distribution of European Abalone (<Emphasis Type="Italic">Haliotis tuberculata</Emphasis>), Revealed by Combined Mitochondrial and Nuclear Marker Analyses

The genetic differentiation among the populations of the European abalone Haliotis tuberculata was investigated using different markers to better understand the evolutionary history and exchanges between populations. Three markers were used: mitochondrial cytochrome oxidase I (COI), the sperm lysin nuclear gene, and eight nuclear microsatellites. These markers present different characteristics concerning mutation rate and inheritance, which provided complementary information about abalone history and gene diversity. Genetic diversity and relationships among subspecies were calculated from a sample of approximately 500 individuals, collected from 17 different locations in the north-eastern Atlantic Ocean, Macaronesia, and Mediterranean Sea. COI marker was used to explore the phylogeny of the species with a network analysis and two phylogenetic methods. The analysis revealed 18 major haplotypes grouped into two distinct clades with a pairwise sequence divergence up to 3.5 %. These clades do not correspond to subspecies but revealed many contacts along Atlantic coast during the Pleistocene interglaciations. The sperm lysin gene analysis separated two different subtaxa: one associated to Macaronesian islands, and the other to all other populations. Moreover, a small population of the northern subtaxon was isolated in the Adriatic Sea—probably before the separation of the two lineages—and evolved independently. Microsatellites were analyzed by different genetics methods, including the Bayesian clustering method and migration patterns analysis. It revealed genetically distinct microsatellite patterns among populations from Mediterranean Sea, Brittany and Normandy, Morocco, and Canary and Balearic islands. Gene flow is asymmetric among the regions; the Azores and the Canary Islands are particularly isolated and have low effective population sizes. Our results support the hypothesis that climate changes since the Pleistocene glaciations have played a major role in the geographic distribution of the European abalone. Traces of these events related to maternal inheritance were shown on COI marker.     

Genetic structure and colonization processes in European populations of the common vole, Microtus arvalis

The level of genetic differentiation within and between evolutionary lineages of the common vole (Microtus arvalis) in Europe was examined by analyzing mitochondrial sequences from the control region (mtDNA) and 12 nuclear microsatellite loci (nucDNA) for 338 voles from 18 populations. The distribution of evolutionary lineages and the affinity of populations to lineages were determined with additional sequence data from the mitochondrial cytochrome b gene. Our analyses demonstrated very high levels of differentiation between populations (overall FST: mtDNA 70%; nucDNA 17%). The affinity of populations to evolutionary lineages was strongly reflected in mtDNA but not in nucDNA variation. Patterns of genetic structure for both markers visualized in synthetic genetic maps suggest a postglacial range expansion of the species into the Alps, as well as a potentially more ancient colonization from the northeast to the southwest of Europe. This expansion is supported by estimates for the divergence times between evolutionary lineages and within the western European lineage, which predate the last glacial maximum (LGM). Furthermore, all measures of genetic diversity within populations increased significantly with longitude and showed a trend toward increase with latitude. We conclude that the detected patterns are difficult to explain only by range expansions from separate LGM refugia close to the Mediterranean. This suggests that some M. arvalis populations persisted during the LGM in suitable habitat further north and that the gradients in genetic diversity may represent traces of a more ancient colonization of Europe by the species.     

淮河克氏原螯虾种群遗传结构

克氏原螯虾（Procambarus clarkii）是广泛分布于我国淡水水域的外来入侵物种,对其种群遗传结构的研究有助于了解种群扩散过程。本文测定了淮河流域自然水体中9个地理种群共151个野生克氏原螯虾线粒体COⅠ序列,获得624 bp的有效基因片段,共定义了25个单倍型。AMOVA分析结果表明,淮河流域的克氏原螯虾种群内的变异占主导地位,单倍型多样性和核苷酸多样性均为中等水平,各地理种群间平均遗传差异较小（F_st=0.078）,遗传差异不显著。系统发生树并没有按地理位置形成对应族群,表明克氏原螯虾各地理种群间存在明显的基因流,各地理种群间没有形成明显的种群遗传分化。     

Contrasting patterns of mitochondrial and microsatellite population structure in fragmented populations of greater prairie-chickens

Greater prairie-chickens (Tympanuchus cupido pinnatus) were once found throughout the tallgrass prairie of midwestern North America but over the last century these prairies have been lost or fragmented by human land use. As a consequence, many current populations of prairie-chickens have become isolated and small. This fragmentation of populations is expected to lead to reductions in genetic variation as a result of random genetic drift and a decrease in gene flow. As expected, we found that genetic variation at both microsatellite DNA and mitochondrial DNA (mtDNA) markers was reduced in smaller populations, particularly in Wisconsin. There was relatively little range-wide geographical structure (FST) when we examined mtDNA haplotypes but there was a significant positive relationship between genetic (FST) and geographical distance (isolation by distance). In contrast, microsatellite DNA loci revealed significant geographical structure (FST) and a weak effect of isolation by distance throughout the range. These patterns were much stronger when populations with reduced levels of genetic variability (Wisconsin) were removed from the analyses. This suggests that the effects of genetic drift were stronger than gene flow at microsatellite loci, whereas these forces were in range-wide equilibrium at mtDNA markers. These differences between the two molecular markers may be explained by a larger effective population size (Ne) for mtDNA, which is expected in species such as prairie-chickens that have female-biased dispersal and high levels of polygyny. Our results suggest that historic populations of prairie-chickens were once interconnected by gene flow but current populations are now isolated. Thus, maintaining gene flow may be important for the long-term persistence of prairie-chicken populations.     

Genetic structure of continental and island populations of the Mediterranean endemic Cyclamen balearicum (Primulaceae)

Cyclamen balearicum is a self-compatible perennial herb endemic to the western Mediterranean Basin. This species occurs in five geographically isolated terrestrial islands in southern France and on four Balearic islands. In this study, we compare genetic variability and differentiation within and among 11 terrestrial island populations and 17 true island populations. Of nine readable enzyme loci, five were polymorphic in both terrestrial and true islands. F statistics showed a significant heterozygote deficiency in all populations, probably due to high levels of autonomous selfing, restricted gene flow, and subsequent genetic drift. Genetic diversity was higher in terrestrial islands than on the Balearic islands, suggesting that the Balearic islands were colonized when they were in contact with the continent. Population differentiation was greater among terrestrial islands (Fst = 0.417 and Gst = 0.344) than among true islands (Fst = 0.112 and Gst = 0.093). Furthermore, differentiation among populations on the Basses Cévennes terrestrial island was greater (Fst = 0.254) than among populations on the true island of Mallorca (Fst = 0.163). The greater genetic differentiation among terrestrial islands could have been caused by genetic bottlenecks associated with changes in climate and human land use that may have reduced population sizes more severely in terrestrial islands in southern France than on the Balearic islands.     

Phylogeography of the montane caddisfly Drusus discolor: evidence for multiple refugia and periglacial survival

We studied the genetic population structure and phylogeography of the montane caddisfly Drusus discolor across its entire range in central and southern Europe. The species is restricted to mountain regions and exhibits an insular distribution across the major mountain ranges. Mitochondrial sequence data (COI) of 254 individuals from the entire species range is analysed to reveal population genetic structure. The data show little molecular variation within populations and regions, but distinct genetic differentiation between mountain ranges. Most populations are significantly differentiated based on F(ST) and exact tests of population differentiation and most haplotypes are unique to a single mountain range. Phylogenetic analyses reveal deep divergence between geographically isolated lineages. Combined, these results suggest that past fragmentation is the prominent process structuring the populations across Europe. We use tests of selective neutrality and mismatch distributions, to study the demographic population history of regions with haplotype overlap. The high level of genetic differentiation between mountain ranges and estimates of demographic history provide evidence for the existence of multiple glacial refugia, including several in central Europe. The study shows that these aquatic organisms reacted differently to Pleistocene cooling than many terrestrial species. They persisted in numerous refugia over multiple glacial cycles, allowing many local endemic clades to form.     

Genetic variability in natural populations of Arabidopsis thaliana in northern Europe

Ten populations of the model plant Arabidopsis thaliana were collected along a north-south gradient in Norway and screened for microsatellite polymorphisms in 25 loci and variability in quantitative traits. Overall, the average levels of genetic diversity were found to be relatively high in these populations, compared to previously published surveys of within population variability. Six of the populations were polymorphic at microsatellite loci, resulting in an overall proportion of polymorphic loci of 18%, and a relatively high gene diversity for a selfing species (HE = 0.06). Of the overall variability, 12% was found within populations. Two of six polymorphic populations contained heterozygous individuals. Both FST and phylogenetic analyses showed no correlation between geographical and genetic distances. Haplotypic diversity patterns suggested postglacial colonization of Scandinavia from a number of different sources. Heritable variation was observed for many of the studied quantitative traits, with all populations showing variability in at least some traits, even populations with no microsatellite variability. There was a positive association between variability in quantitative traits and microsatellites within populations. Several quantitative traits exhibited QST values significantly less than FST, suggesting that selection may be acting to retard differentiation for these traits.     

Intraspecific genetic structure,divergence and high rates of clonality in an amphi‐Atlantic starfish

Intraspecific genetic diversity and divergence have a large influence on the adaption and evolutionary potential of species. The widely distributed starfish, Coscinasterias tenuispina, combines sexual reproduction with asexual reproduction via fission. Here we analyse the phylogeography of this starfish to reveal historical and contemporary processes driving its intraspecific genetic divergence. We further consider whether asexual reproduction is the most important method of propagation throughout the distribution range of this species. Our study included 326 individuals from 16 populations, covering most of the species’ distribution range. A total of 12 nuclear microsatellite loci and sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene were analysed. COI and microsatellites were clustered in two isolated lineages: one found along the southwestern Atlantic and the other along the northeastern Atlantic and Mediterranean Sea. This suggests the existence of two different evolutionary units. Marine barriers along the European coast would be responsible for population clustering: the Almeria–Oran Front that limits the entrance of migrants from the Atlantic to the Mediterranean, and the Siculo‐Tunisian strait that divides the two Mediterranean basins. The presence of identical genotypes was detected in all populations, although two monoclonal populations were found in two sites where annual mean temperatures and minimum values were the lowest. Our results based on microsatellite loci showed that intrapopulation genetic diversity was significantly affected by clonality whereas it had lower effect for the global phylogeography of the species, although still some impact on populations’ genetic divergence could be observed between some populations.     

Genetic structure of the star sea squirt, Botryllus schlosseri, introduced in southern European harbours

The introduction of new genetic variants or species is often caused by maritime transport between harbours. Botryllus schlosseri is a cosmopolitan ascidian species that is found in both harbours and open shore habitats. In order to determine the influence of ship traffic on the genetic structure and phylogeography of B. schlosseri in southern Europe, we analyzed the variability of a fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI). We sampled seven Atlanto-Mediterranean harbour populations and three open-shore populations. In addition, we sequenced some colonies from the US-Atlantic coast and from other Mediterranean localities to perform phylogenetic analyses. Although the number of polymorphic sites recorded (25.8%) was within the range observed in other population studies based on ascidian COI sequences, the haplotypic diversity (16 haplotypes out of 181 sequences) was much lower. Moreover, a lack of intermediate haplotypes was observed. This pattern of high nucleotide diversity and low haplotype diversity was consistent with introduction events of a few divergent haplotypes. We found a strong genetic structure in the study populations. Gene flow was only appreciable between some harbour populations. Harbour- and open-shore populations were well differentiated, although there was no evidence for isolation by distance. A nested clade analysis pointed to long-distance colonization, possibly coupled with subsequent fragmentation, as the underlying process. Our results suggest that B. schlosseri entered the study area via harbour-hopping, possibly through recurrent introduction events. The haplotypes from North America and most of the European ones were grouped in the same phylogenetic clade. This suggests occasional gene flow between both continents, probably through ship transport.     

Overlapping patterns of morphometric and genetic differentiation in the Mediterranean goby Pomatoschistus tortonesei Miller, 1968 (Perciformes, Gobiidae) in Tunisian lagoons

The genetic and morphological variations of Pomatoschistus tortonesei Miller, 1968 were studied in samples collected from three Tunisian lagoons. The morphological analysis included 18 morphometric measurements and was based on linear discriminant analysis (LDA), whereas the genetic analysis was based on the 16S-rRNA and COI mitochondrial genes. Both analyses differentiated the populations and demonstrated consistently a well-supported differentiation between the western Mediterranean samples (Bizerta and Tunis South lagoons) and the eastern Mediterranean sample (El Bibane lagoon). The observed differentiation could be explained in terms of the geographic isolation of the various populations and the influence of environmental factors, which differ greatly between the different sites. The molecular results revealed that the populations are characterised by unique haplotypes which are well defined in relation to limited gene flow and restricted dispersal abilities. Additionally, it seems that local selective pressures have modelled biometrical variation. Morphological results can reflect a differential habitat use revealed in the cephalic features and a different response to hydrodynamic constraints developed in dissimilar dorsal and pelvic fin lengths.     

Genetic diversity of three donkey populations in the Croatian coastal region

Genetic variation in three Croatian donkey populations, Istrian (IS), North Adriatic (NA) and Littoral-Dinaric (LD), was analysed using eight microsatellite loci and by sequence and SSCP analysis of the proximal portion of the mtDNA D-loop region. The analysis of microsatellite loci revealed observed heterozygosities in the range of 0.37 (MPZ002 in LD) to 0.85 (AHT21 in LD) and polymorphic information content values in the range of 0.36 (MPZ002 in NA) to 0.78 (AHT21 in LD). The overall probability of exclusion was 0.991. Two populations (IS and NA) were closely related (Fst=0.0034), whereas genetic distances between IS and LD (Fst=0.021) and NA and LD (Fst=0.027) were higher. Using AMOVA, 97.6% of the total genetic variance was portioned within populations, while 2.7% was portioned between the Littoral-Dinaric population and the Istrian/North Adriatic population group. Sequencing of the proximal part of the mtDNA D-loop region revealed 36 polymorphic sites representing 19 haplotypes which clustered into three haplotype groups (Y, W, Ws). Only the Y haplotype was found in the IS population which is characterized by a large body size. Haplotypes W and Ws were found in the NA and LD populations which include smaller animals. All three haplotypes were found in the LD population, indicating sporadic migration events from the IS into LD donkey population.     

Reduced female gene flow in the European flat oyster Ostrea edulis

The geographical structure of 15 natural populations of the flat oyster (Ostrea edulis L.) was assessed by single-strand conformation polymorphism (SSCP) of a 313-base-pair (bp) fragment of the mitochondrial 12S-rRNA gene. Fourteen haplotypes were observed, with one being dominant in the Mediterranean samples and another one in the Atlantic populations. The geographically extreme populations sampled in Norway and the Black Sea appeared differentiated by exhibiting the dominance of a third group of haplotypes. The results were compared to available microsatellite data at five loci. The Atlantic/Mediterranean differentiation pattern was qualitatively the same with both types of markers, confirming an isolation-by-distance pattern. The average mitochondrial haplotypic diversity displayed a high among populations variance, reflecting small effective population size in some locations. Additionally, a 10-fold quantitative difference was observed in Fst between the mitochondrial and the nuclear genomes, which could be due to an unbalanced sex ratio or sex-biased differential reproductive success between males and females (or both).