MtDNA polymorphisms: evolutionary significance in adaptation and speciation of subterranean mole rats

Patterns of mtDNA diversity in subterranean mole rats of the Spalax ehrenbergi superspecies (2n = 52, 54, 58 and 60) were previously studied in the main ranges of the four chromosomal species, and specifically in the 2n = 60 species and its peripheral steppe semi-isolates and desert isolates. In the present study we correlated mtDNA diversity indices, nucleon diversity, h , and nucleotide divergence, π, with physical (climatic), biotic (parasites) and biological (genetical, morphological, physiological and behavioural) factors, showing that mtDNA diversity is structured ecogeographically and biologically. The following significant correlations of mtDNA diversity were indicated with: (i) climatic heterogeneity and unpredictability; (ii) levels of ecto- and endoparasites; and (iii) biological diversities, primarily with physiological diversity associated with the energy budget. Small steppe semi-isolates and desert isolates harbour high levels of mtDNA haplotype diversity, some novel, which may be a prerequisite for future speciation events. We conclude that the ecogeographical and biological correlates, as well as the maintenance of mtDNA polymorphisms in small isolated populations, strongly suggest that mtDNA diversity is not neutral. Diversifying natural selection appears to be an important differentiating factor of mtDNA diversity in the twin evolutionary processes of adaptive radiation and active speciation. We suggest critical experiments to substantiate our conclusions and highlight the contribution of mtDNA diversity to fitness, i.e. to the biological function of mtDNA diversity in the evolutionary process.     

Variations in ribosomal DNA and mitochondrial DNA among chromosomal species of subterranean mole rats

Restriction site variations in nuclear ribosomal DNA (rDNA) spacers and mitochondrial DNA (mtDNA) were examined in several populations of mole rats with variable numbers of chromosomes, which represented the two superspecies Spalax leucodon (2n = 38, 54, or 62) and Spalax ehrenbergi (2n = 52, 54, 58, or 60). Sequence divergence of rDNA spacers between the members of the superspecies was approximately 8%, while the variation within each superspecies was 4% on average. The intrasuperspecies differentiation of rDNA spacers was generally associated with changes in the diploid number of chromosomes. However, substantial divergence (approximately 1.5%) was also detected among populations with the same diploid number of chromosomes. The sequence divergence of mtDNA among haplotypes of S. ehrenbergi was 10% or higher and among haplotypes of S. leucodon it was approximately 12%. By contrast, the range of sequence divergence between superspecies was 7.4%-12%. The large divergence of mtDNAs within each superspecies of mole rats may be explained by the preservation of ancient mtDNA polymorphisms.      

Seismic communication in the blind subterranean mole-rat: patterns of head thumping and of their detection in the Spalax ehrenbergi superspecies in Israel

Patterns of seismic communication and somatosensory responses were studied in four chromosomal species (2n= 52, 54, 58, 60) of blind subterranean mole-rats, belonging to the Spalax ehrenbergi superspecies in Israel. The patterns involved head thumping signals and surface-recorded cerebral potentials evoked by vibrational signals. The patterns correspond to the differences in territory size and population density which characterize the four species. It is suggested that this correspondence is related to the adaptive significance of the seismic communication.     

Phylogeography of the Golden Jackal (Canis aureus) in India

The golden jackal (Canis aureus) is one of the most common and widely distributed carnivores in India but phylogeographic studies on the species have been limited across its range. Recent studies have observed absence of mitochondrial (mt) DNA diversity in European populations while some North African populations of golden jackal were found to carry gray wolf (Canis lupus lupaster) mtDNA lineages. In the present study, we sequenced 440 basepairs (bp) of control region (CR) and 412 bp of cytochrome b (cyt b) gene of mtDNA from 62 golden jackals sampled from India (n = 55), Israel (n = 2) and Bulgaria (n = 5), to obtain a total of eighteen haplotypes, comprising sixteen from India and one each from Israel and Bulgaria. Except for three previously described haplotypes represented by one cyt b and one CR haplotype both from India, and one CR haplotype from Bulgaria, all haplotypes identified in this study are new. Genetic diversity was high in golden jackals compared to that reported for other canids in India. Unlike the paraphyletic status of African conspecifics with the gray wolf, the Indian (and other Eurasian) golden jackal clustered in a distinct but shallow monophyletic clade, displaying no evidence of admixture with sympatric and related gray wolf and domestic dog clades in the region. Phylogeographic analyses indicated no clear pattern of genetic structuring of the golden jackal haplotypes and the median joining network revealed a star-shaped polytomy indicative of recent expansion of the species from India. Indian haplotypes were observed to be interior and thus ancestral compared to haplotypes from Europe and Israel, which were peripheral and hence more derived. Molecular tests for demographic expansion confirmed a recent event of expansion of golden jackals in the Indian subcontinent, which can be traced back ~ 37,000 years ago during the late Pleistocene. Our results suggest that golden jackals have had a potentially longer evolutionary history in India than in other parts of the world, although further sampling from Africa, the Middle East and south-east Asia is needed to test this hypothesis.     

The effect of protein and salt loading on urinary concentrating ability in four chromosomal species of Spalax ehrenbergi

Urinary concentrating ability was tested under protein and salt load in the four chromosomal species of subterranean mole-rats ( Spalax ehrenbergi superspecies) found in Israel. Protein stress induced by a diet of soyabeans supplemented by agar gel, demonstrated a significant increase in urinary osmolarity (UO). In the species living in the driest and warmest region (2n = 60). UO (1423·101 mOsmol/kg) was significantly (P<0·05) higher than in the other three species (2n = 52. 1172·31 mOsmol/kg; 2n = 54, 1160·116 mOsmol kg; and 2n = 58, 1216·145 mOsmol/kg). Upon salt loading this diet with 0·3 mol NaCl, UO increased significantly. However, when the salt load was increased to 0·45 mol NaCl, UO decreased significantly in all but one species (2n = 60) which maintained UO at 1522·65 mOsmol/kg. A decline in UO was attributed to diuresis resulting from a significant increase in urine and sodium excretion. The kidney, of only the xeric ranging species (2n = 60), demonstrated the ability to produce a hyperosmotic urine, in spite of the high salt load. These results might explain the restricted distribution of S. ehrenbergi: the only species (2n = 60) found in an environment rich in succulents and halophyte plants (steppe). This species appears to push speciation and adaptive radiation to the southern limit of its superspecies.     

Genetic polymorphism of urine deoxyribonuclease I isomerases of subterranean mole rats,Spalax ehrenbergi superspecies,in Israel: Ecogeographical patterns and correlates

Genetic polymorphism of urine deoxyribonuclease I (DNase I) of mole rats was analyzed by isoelectric focusing in a thin-layer polyacrylamide gel (IEF-PAGE). One hundred and three subterranean mole rats, comprising 13 populations belonging to the four chromosomal species (2n = 52, 54, 58, 60) of the actively speciating Spalax ehrenbergi superspecies in Israel, were tested. The following results were indicated. (i) Spalax DNase I consisted of 6-12 major isozymes. (ii) Four phenotypes (numbers in parentheses) were 1 (92), 1-2 (5), 1-3 (4), and 2 (1). The decreasing order of genetic diversity, He, in the four species was 0.37, 0.13, 0.10, and 0.0 for 2n = 58, 52, 54, and 60, respectively. (iii) Spearman rank correlations and multiple regression analyses indicated associations of allele frequencies and genetic diversity with climatic and vegetation factors. We concluded that (a) climatic selection, either directly or indirectly through plant (i.e., food resources) diversity, plays an important role in DNase genetic differentiation and (b) no gene flow and introgression occur between the recent derivative of speciation (2n = 60) and its ancestor (2n = 58), suggesting the operation of reproductive isolation between both species despite natural hybridization.     

Karyotype and genetic evolution in speciation of subterranean mole rats of the genus Spalax in Turkey

Karyotype (2fl) and allozymc diversity at 37 gene loci were determined in 69 subterranean mole rats in Turkey belonging to the two superspecies: the ancestor Spalax leucodon ( n = 55; 20 populations) and the descendant S. ehrenbergi ( n = 14; lour populations). We identified remarkable variation of diploid chromosome numbers in the S. leucodon superspecies: 2 n = 38. 40. 50, 54, 60 and 62; and in the S. ehrenbergi superspecies: 2 n = 52, 56 and 58. Genetic diversity indices were low on average in both S. leucodon and S. ehrenbergi superspecies: Allele diversity, A = 1.081 and 1.074; polymorphism, P-5%= 0.077 and 0.068; heterozygosity, H = 0.038 and 0.027; and gene diversity, H, = 0.038 and 0.034, respectively. H ranged from 0 in mesic or semimesic regions to 0.088 in arid Anatolia. We consider the populations with different diploid chromosome numbers, 2 n , as good biological species. Karyotypic diversity may mark extensive ecological speciation. Nei's genetic distances, D (average 0.174, range 0.002 0.422) and ecogeographical criteria suggest that almost each population may represent a different biological species, but critical future testing is necessary to support this claim. Karyotypes and allozymes are nonrandomly distributed across Turkey, displaying remarkable correlations with climatic and biolir factors. Both In and H are significantly correlated with aridity stress (2 n /rainfall, r , =–0.74; P < 0.001), and in our region also with climatic unpredictability. These results support the niche-width genetic variation hypothesis in space and time. Climatic selection in Turkey appears to be a major architect of karyotype and genetic (allozymc) diversity and divergence in mole rat evolution, in both speciation and adaptation.     

Mhc Class II DNA Polymorphisms within and between Chromosomal Species of the Spalax Ehrenbergi Superspecies in Israel

Restriction fragment length polymorphisms (RFLPs) of two major histocompatibility class II genes (P alpha 1 and Q beta) were studied in 13 populations of four chromosomal species (2n = 52, 54, 58 and 60) of the mole rat, Spalax ehrenbergi superspecies in Israel. A substantial frequency of allelic fragments was found in both genes for all populations, including a desert isolate. In the P alpha 1 gene, one allelic fragment is a result of a deletion mutation which is diagnostic of the 2n = 52 chromosomal species. All other ten allelic variants are the result of point mutations. All mutations are located in a short region flanking the 3' end of the gene. Based on Mhc polymorphisms we confirm earlier evidence that gene flow does not occur between the older chromosomal species (2n = 52, 54, 58), and that reproductive isolation decreases, progressively from the oldest to the youngest species (2n = 60).     

Rapid chromosomal evolution in the mesic four‐striped grass rat Rhabdomys dilectus (Rodentia,Muridae) revealed by mtDNA phylogeographic analysis

The mesic four‐striped grass rat Rhabdomys dilectus De Winton, 1897 is distributed in mesic regions of southern and eastern Africa. We carried out a molecular and chromosomal study of the northernmost populations of the species to provide insight into the subspecific boundaries identified within the species and to describe its genetic structure in Eastern Africa. Maximum likelihood, maximum parsimony and neighbour‐joining methods were used to construct phylogenetic relationships among all the haplotypes belonging to the large part of the species range. Times of divergences were estimated assuming a relaxed molecular clock with two calibration points. We identified three well‐supported clades within R. dilectus. One basal clade corresponding to Rhabdomys d. chakae (2n = 48) is found in South Africa. Two additional sister clades corresponding to R. d. dilectus (2n = 48 and 2n = 46) are allopatrically distributed in southern and northern parts of the species range. Genetic divergence among the three clades is relatively high (ranges 4.2–5.7%). A very divergent new karyotype 2n = 38, FNa = 60 was found in two high‐altitude populations on Mt. Meru and Mt. Kilimanjaro. The karyotype differences consist in three Robertsonian fusions and one whole‐arm reciprocal translocation. Interestingly, the mtDNA phylogeny does not match with the diploid numbers. In fact, the 2n = 38 specimens form a monophyletic group within a clade that includes specimens with the 2n = 46 karyotype that appears as paraphyletic. We estimated the new karyotype originated in peripatric condition during the last phases of the Pleistocene. This study confirms the importance of chromosomal analysis in detecting taxonomic units and cryptic diversity in rodents.     

Molecular genetics of Rhabdomys pumilio subspecies boundaries: mtDNA phylogeography and karyotypic analysis by fluorescence in situ hybridization

The phylogeography of the African four-striped mouse, Rhabdomys pumilio, was investigated using complete sequences of the mtDNA cytochrome b gene (1140 bp) and a combination of fluorescence in situ hybridization (FISH) and conventional cytogenetic banding techniques (G- and C-banding). Two cytotypes (2n=46 and 2n=48) were identified by cytogenetic analysis. There is no evidence of diploid number variation within populations, difference in gross chromosome morphology or of subtle interchromosomal rearrangements at levels detected by ZOO-FISH. Analysis of the mtDNA cytochrome b resulted in two major lineages that correspond roughly to the xeric and mesic biotic zones of southern Africa. One mtDNA clade comprises specimens with 2n=48 and the other representatives of two cytotypes (2n=48 and 2n=46). The mean sequence divergence (12%, range 8.3-15.6%) separating the two mtDNA clades is comparable to among-species variation within murid genera suggesting their recognition as distinct species, the prior names for which would be R. dilectus and R. pumilio. Low sequence divergences and the diploid number dichotomy within the mesic lineage support the recognition of two subspecies corresponding to R. d. dilectus (2n=46) and R. d. chakae (2n=48). Our data do not support subspecific delimitation within the nominate, R. pumilio. Molecular dating places cladogenesis of the two putative species at less than five million years, a period characterised by extensive climatic oscillations which are thought to have resulted in habitat fragmentation throughout much of the species range.     

Cytochrome b sequence analysis reveals differential molecular evolution in African mole-rats of the chromosomally hyperdiverse genus Fukomys (Bathyergidae, Rodentia) from the Zambezian region

African mole-rats (Bathyergidae, Rodentia) of the (eu)social genus Fukomys are one of the most speciose mammal genera endemic to Sub-Saharan Africa. Fukomys distributed in the Zambezian phytochorion is characterized by extreme chromosomal variation (2n=40-78). We inferred a molecular phylogeny of Zambezian Fukomys to resolve the interrelationships and the evolutionary history of the known chromosomal races. We sequenced the entire cytochrome b gene (1140bp) for a total of 66 specimens representing 18 karyotypical races from Zambia. An additional 31 sequences were retrieved from GenBank including data on all other chromosomal races. The haplotypes belonging to a small chromosomal race from Salujinga cluster with the Fukomys mechowii (Giant mole-rat) haplotypes. Differential degrees of chromosomal variation are observed among the major mole-rat clades, which is most pertinent when comparing the central Zambezian Fukomys micklemi and the northern Zambezian Fukomys whytei clades. The karyotypically hyper-diverse (12 known chromosomal races) Fukomys micklemi clade shows low levels of cytochrome b sequence divergence. Within the F. whytei clade we find a more conservative pattern of chromosomal diversification (three known chromosomal races) while the levels of sequence divergence are much higher then in the F. micklemi clade. Our results suggest that chromosomal changes may drive phyletic divergence and, eventually, speciation. The observed cladogenetic events during the Plio-Pleistocene within the F. mechowii, F. whytei, F. damarensis and F. micklemi clades appear to coincide with climatically mediated speciation bursts in other savannah dwelling mammals, including hominids. Based on the molecular data presented, combined with morphological and chromosomal data, the taxonomic implication seems to be that Fukomys may contain several (undescribed) cryptic species.     

Speciation and adaptive radiation of subterranean mole rats, Spalax ehrenbergi superspecies, in Jordan

The major initial mechanism of speciation in subterranean blind mole rats, Spalacidae, is chromosomal, primarily through Robertsonian rearrangements. Here we highlight another scenario of chromosomal rearrangement leading to ecological speciation and adaptive radiation apparently initiated by pericentric inversions and genie divergence to different ecologies in mole rats in Jordan. We analysed karyotype, allozyme, size and ecological diversity across the range of mole rats in Jordan from mesic Irbid in the north to xeric Wadi Musa (Petra region) in the south, a transect of 250 km. We examined mole rats for chromosome ( N =71), size ( N =76), and allozyme ( N =67) diversities, encoded by 32 loci, in 12 populations of the Spalax ehrenbetgi superspecies in Jordan. By a combination of chromosome morphology, genetic distance, body size and ecogeography, we identified four new putative biological species. All species (except two animals in Madaba) share 2 n = 60 but vary in chromosome morphology, caused by pericentric inversions and/or centromeric shifts. The 'north Moav' species is karyotypically polymorphic for 2 n (2 n = 60; including locally also two animals with 2 n = 62). The distribution of the four species is associated with ecogeographical different domains and climatic diversity. Genetic diversity indices were low, but like chromosome arms (NFa) were positively correlated with aridity stress. Discriminant analysis correctly classified 91% of the individuals into the four species utilizing combinatorially chromosome, allozyme and size diversities. It is hypothesized that mole rat evolution underground is intimately associated with climatic diversity stress above ground.     

Differentiation of large-scaled redfin Tribolodon hakonensis (Pisces, Cyprinidae) in the Russian part of the range as inferred from the data of karyological analysis and PCR-RFLP analysis of mitochondrial DNA

Considerable differences in karyotypes of Tribolodon hakonensis from Primorye and the rivers of the Sea of Okhotsk drainage were demonstrated. These differences raise doubts that these fishes belong to one species and point to the necessity of more precise definition of the species status of the southern form of T. hakonensis. The karyological evidence is consistent with the data of mtDNA PCR-RFLP analysis on genetic independence of the southern and the northern forma of T. hakonensis. In the northern form of T hakonensis, variation of the chromosomal arm number was revealed. Specifically, the number of chromosomes was constant (2n = 50), whereas the number of chromosomal arms (NF) constituted 88, 92, and 94, which suggests genetic heterogeneity of the northern form. PCR-RFLP analysis of mtDNA showed that haplotypes of northern T. hakonensis split into two groups with 100% support. Based on comparative phylogenetic and karyological analyses of the Tribolodon species, independent divergence of the southern and the northern forms of T. hakonensis was suggested.     

Genealogical concordance and the specific status of Peromyscus sejugis

Peromyscus sejugis, a peripheral isolate of Peromyscus maniculatus, is a threatened taxon endemic to 2 small islands in the Sea of Cortés. Although its insularity makes the specific recognition of P. sejugis inherently problematic, resolution of this problem has important conservation implications. To evaluate the specific validity and evolutionary history of P. sejugis, we compared sequence variation (ND3/ND4L/ND4) in mtDNA for both island populations of P. sejugis with that for 8 populations of P. maniculatus from mainland Baja California. Each island population of P. sejugis had a single haplotype (0.7% sequence divergence), whereas 11 different haplotypes (mean sequence divergence = 0.68%) were obtained for the populations of P. maniculatus. The mean sequence divergence between the populations of the 2 species was 2.0%. Nested clade analysis supports the conclusion that P. sejugis is an insular isolate of P. maniculatus from mainland Baja California. Although our analysis confirms a low level of mtDNA divergence between P. sejugis and P. maniculatus from Baja California, the genealogical concordance of morphological, chromosomal, microsatellite, and mtDNA haplotype distinctiveness supports the conclusion that the 2 island populations of P. sejugis constitute independent evolutionarily significant units and together represent a phylogenetic species distinct from the P. maniculatus from Baja California.     

Variations of molar morphology in the Spalax ehrenbergi superspecies: adaptive and phylogenetic significance

This study compares and contrasts variations of enamel fold pattern on the crowns of the molars of subterranean mole rats ( Spalax ) belonging to two superspecies, S. ehrenbergi and S. leucodon , and involving about 20 chromosomal species, distributed parapatrically and ranging on different soil types. The sample studied involved 397 skulls, subdivided as follows: 280 of S. ehrenbergi from Israel, representing the four chromosomal species 2n = 52, 54, 58 and 60; 59 of S. ehrenbergi from Egypt, Lebanon, Syria, Jordan and Turkey; 58 of S. leucodon from Turkey.
In making the comparisons it was necessary to take into account the marked changes of molar pattern that take place as a result of wear.
There is a reasonably good agreement between differences of molar pattern and genetic and immunological distances. The species in Israel and Egypt form a compact group, clearly differentiated from Turkish leucodon; ehrenbergi from Turkey and Syria are intermediate, in accordance with their geographical distribution.
In Israel, differences associated with soil type are at about the same level as differences between species. Local populations show a higher level of diversity, and in a number of cases neighbouring populations differed significantly, sometimes over very short distances. Population differences within species are generally associated with differences of soil and vegetation, indicating the influence of natural selection. There are also differences across species boundaries, implying a phylogenetic (heritage) effect. The nature of the adaptive link between molar pattern and soil is unknown: possible factors are contamination of the food by soil, and toughness of the food which necessitates changes of enamel fold length to improve grinding efficiency.     

Total body water and adaptive water turnover rate in four chromosomal species of subterranean mole rats of the Spalax ehrenbergi superspecies in Israel

Total body water (TBW) and water turnover rate (WTR) were measured in 24 subterranean mole rats comprising four populations, each belonging to a different chromosomal species of the Spalax ehrenbergi superspecies in Israel. The four species range in different climates: humid-cool (2n = 52); semiarid-cool (2n = 54); humid-warm (2n = 58) and arid-warm (2n = 60). TBW, as a percentage of body weight, measured by tritiated water (HTO), was 72.4%±4–7 in 2n = 52, significantly ( P < 005) higher than the similar estimates 61.7%± 7.2, and 59.4%± 5–3, for 2n = 60 and 58, respectively. A comparison of HTO space, as a percentage of TBW, closely approximated TBW, ranging from 97% to 108%. WTR was high, 218.1 and 230.9 ml/kg^0-75/day in the mesic populations of 2n = 58 and 52, respectively. By contrast, WTR estimates were significantly lower , ( P < 0.001), 150.2 and 148.9 ml/kg^0-75/day in the xeric populations of 2n = 54 and 60, respectively. The biological half-life time, T_1/2, was similar and faster, 32.7 and 27.9 hours in the mesic populations of 2n = 52 and 58, as compared with slower, 47.9 and 40.8 hours in the xeric populations of 2n = 54 and 60, respectively. Urine osmolarity in the most xeric northern Negev steppic population of 2n = 60 (737 ± 45 mmol/kg) was significantly ( P < 0.001) higher than in the other species.
We conclude that adaptive radiation in the Spalax ehrenbergi superspecies involves speciation in semiarid (2n = 54) and arid (2n = 60) climates by physiological adaptations of kidney water conservation, along with multiple morphological, physiological and behavioural syndromes of climatic adaptations to increasing aridity (Nevo, 1986).     

The origin and genetic relationships of the Baikal seal, Phoca sibirica, by restriction analysis of mitochondrial DNA

The origin and genetic relationships of the Baikal seal, Phoca sibirica, were studied by restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA). Using 17 different six-base recognition restriction endonucleases, we examined 98 Baikal seals, and two other related species, the ringed seal, P. hispida, (n=87), and the Caspian seal, P. caspica, (n=94). Analysis revealed the existence of 87 mtDNA haplotypes in the total of 279 specimens. The haplotypes of each species were divided into different clusters on a dendrogram obtained by UPGMA based on haplotype frequency and mtDNA base substitution. No common haplotypes were found among the species examined. The Baikal seal is much more closely related to the ringed seal than the Caspian seal. The amount of divergence suggested that an ancestor of the Baikal seal came down to the lake approximately 0.4 million years ago as was previously indicated by paleontological studies. The seals examined here showed lower variabilities.     

The incomplete history of mitochondrial lineages between two rockfishes, Sebastes longispinis and Sebastes hubbsi (Scorpaeniformes: Scorpaenidae)

The genetic divergence between two closely related rockfishes, Sebastes longispinis and Sebastes hubbsi, was inferred from both mitochondrial DNA (mtDNA) sequence variations and amplified fragment length polymorphism (AFLP) markers. The two species were placed into two distinct clades in a neighbour-joining tree based on the AFLP data, clearly indicating that they represented separate species. Although this evidence, together with a previous morphological study, revealed clear differences between the two species, no obvious clustering of haplotypes by species was detected in the minimum spanning network inferred from sequence variations in the mtDNA control region (c. 500 base pairs). In fact, the significant Φ(ST) estimates indicated only a restriction of gene flow between the two species. Uncorrected pairwise sequence differences in mtDNA between two species were small (1·8% at maximum, on the lower end of the range of control region divergence between previously studied sister species pairs), suggesting their speciation event as having been fairly recent. The incongruent results of AFLP and mtDNA phylogenies suggested incomplete lineage sorting and introgression of mtDNA in the course of the evolution of the two species. Differences in their main distributional ranges and the small level of sequence divergence in mtDNA suggests that speciation and dispersal may have been associated with glacio-eustatic sea level fluctuations between the Japanese Archipelago and the Korean Peninsula during the past 0·4 million years.     

Unequal transmission of mitochondrial haplotypes in natural populations of field mice with XY females (genus Akodon)

In species with fertile XY females, such as South American field mice (genus Akodon), there are two types of mitochondrial DNA (mtDNA), one passing from XX females and one from XY females. The XX mothers pass their mtDNA to their XX daughters. The XY mothers, however, produce both XX and XY daughters. Because of this breeding scheme, the XY mtDNA remains isolated whereas the XX lineage is continuously invaded by XY mtDNA haplotypes. Using a set of recursion equations, I predicted that XY mtDNA haplotypes should rapidly spread through entire populations composed of both XX and XY females. I examined patterns of nucleotide polymorphism and divergence from the mtDNA control region as well as phylogenetic patterns for evidence of an mtDNA sweep. I compared patterns in two sister species, Akodon boliviensis and Akodon azarae, that are composed of 35% and 10% XY females, respectively. Akodon boliviensis XY females are found in all clades of a phylogenetic mtDNA tree consistent with the spread of mtDNA haplotypes. In addition, A. azarae mtDNA haplotypes showed no deviations from neutrality. These results, in combination with high levels of mtDNA nucleotide diversity in XY females, suggest an ancient origin (>10(4) generations) of XY females in both A. boliviensis and A. azarae.     

Extensive hybridization in hawksbill turtles (Eretmochelys imbricata) nesting in Brazil revealed by mtDNA analyses

Bahia state hosts over 90% of hawksbill (Eretmochelys imbricata) nests registered in the main nesting sites monitored by Projeto Tamar-IBAMA in Brazil. The genetic diversity of this hawksbill population (n=119) was assayed through the analyses of 752 bp of the mitochondrial DNA control region in nesting females. Seven distinct haplotypes, defined by 125 polymorphic sites, were found. Most of the individuals (n=67) display four typical hawksbill haplotypes, 50 individuals display two haplotypes characteristic of the loggerhead turtle (Caretta caretta) and two individuals had a haplotype affiliated with the olive ridley (Lepidochelys olivacea). These results demonstrate hybridization between the hawksbills and two species that nest along the Bahia coast. Of special interest is the high occurrence of loggerhead × hawksbill hybrids (42%), which display loggerhead mtDNA haplotypes but are characterized morphologically as hawksbills. The true hawksbill haplotypes present only three variable sites and low genetic diversity values (h=0.358±0.069; π=0.0005±0.0001). The occurrence of several nesting individuals with identical mtDNA from another species may also suggest a long history of introgression between species producing likely F2 or further generation hybrids. Marine turtle hybrids have been previously reported, but the high frequency observed in Bahia is unprecedented. Such introgression may influence evolutionary pathways for all three species, or may introduce novel morphotypes that develop apart from the parental species. The presence of a unique hybrid swarm has profound conservation implications and will significantly influence the development and implementation of appropriate management strategies for these species.