Gene lineage analysis in populations ofHelianthus niveus andH. petiolaris (Asteraceae)

Helianthus petiolaris andH. niveus are polytypic species which are morphologically distinct at the periphery of their ranges but intergrade in areas of sympatry.Helianthus niveus includes both annual and perennial members, whereasH. petiolaris is strictly annual. Chloroplast DNA and nuclear ribosomal DNA restriction site data were used to reconstruct the evolutionary history of populations of the two species. Cladistic analyses reveal the following: (1) neither species is monophyletic; (2) the annual habit is derived once in this complex; and (3) the region of morphological intergradation appears to be primary in origin. The significance of interbreeding versus common descent in defining species concepts is discussed in relation to the above cladistic analyses.     

THE ORIGIN OF WEST EUROPEAN SUBSPECIES OF HONEYBEES (APIS MELLIFERA): NEW INSIGHTS FROM MICROSATELLITE AND MITOCHONDRIAL DATA

Apis mellifera is composed of three evolutionary branches including mainly African (branch A), western and northern European (branch M), and southeastern European (branch C) populations. The existence of morphological clines extending from the equator to the Polar Circle through Morocco and Spain raised the hypothesis that the branch M originated in Africa. Mitochondrial DNA analysis revealed that branches A and M were characterized by highly diverged lineages implying very remote links between both branches. It also revealed that mtDNA haplotypes from lineages A coexisted with haplotypes M in the Iberian Peninsula and formed a south-north frequency cline, suggesting that this area could be a secondary contact zone between the two branches. By analyzing 11 populations sampled along a France-Spain/Portugal-Morocco-Guinea transect at 8 microsatellite loci and the DraI RFLP of the COI-COII mtDNA marker, we show that Iberian populations do not present any trace of “africanization” and are very similar to French populations when considering microsatellite markers. Therefore, the Iberian Peninsula is not a transition area. The higher haplotype A variability observed in Spanish and Portuguese samples compared to that found in Africa is explained by a higher mutation rate and multiple and recent introductions. Selection appears to be the best explanation to the morphological and allozymic clines and to the diffusion and maintenance of African haplotypes in Spain and Portugal.     

Biogeography of the túngara frog, Physalaemus pustulosus: a molecular perspective

Physalaemus pustulosus, a small leptodactylid frog with South American affinities, ranges across northern South America through Middle America to southern Mexico. To investigate its geographic variation and evolutionary origins, we analysed the presumptive gene products of 14 allozyme loci and sequenced a portion of the mitochondrial COI gene from individuals sampled throughout the distribution. Generally, allozyme dissimilarities and sequence divergences are correlated with each other and with geographic proximity. The greatest discontinuity in genetic variation was found between populations in Middle America vs. South America + Panama. Based on two Bayesian MCMC (Markov chain Monte Carlo) divergence time estimates involving two independent temporal constraints, the timing of the separation of northern and southern túngara frog lineages is significantly older than the time since completion of the current Panama land bridge. P. pustulosus first invaded Middle America from South America about 6-10 million years ago giving rise to the northern lineage. The southern lineage then invaded Panama independently after land bridge completion. Despite millions of years of independent evolution, the multilocus allozyme data revealed that western Panama populations represent a contact zone containing individuals with alleles from both groups present.     

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.     

Recherches sur la phylogénie du genre Saga (Orthoptera: Tettigoniidae): données chromosomiques

L’analyse cytogénétique de quatre espèces européennes de Saginae, dont les caryotypes n’avaient jamais été étudiés, la ré-investigation de celui de Saga pedo (Pallas 1771), la prise en compte des données publiées, et le résultat d’investigations sur le terrain, permettent de proposer une reconstitution de leur phylogénie. Les caryotypes les plus ancestraux semblent être ceux de Saga ornata Burmeister 1839 et de Saga cappadocica Werner 1903, publiés antérieurement, dont tous les autosomes seraient acrocentriques. La fusion de deux paires de leurs chromosomes aboutirait aux caryotypes de Saga natoliae Serville 1839 et de Saga hellenica Kaltenbach 1967, comportant une paire de grands submétacentriques. Ces deux caryotypes se différencient par une inversion péricentrique touchant ces grands chromosomes, probablement chez S. natoliae. Saga campbelli Uvarov 1921 et Saga rammei Kaltenbach 1965, ont acquis une fusion chromosomique de plus et possèdent donc deux paires de grands submétacentriques. Le caryotype de S. rammei détient en plus une particularité de son hétérochromatine. Enfin, le caryotype de S. pedo est tétraploïde, probablement formé de la juxtaposition de deux génomes diploïdes par hybridation. La particularité de l’hétérochromatine de S. rammei se retrouve chez S. pedo sur deux chromosomes différents. Alors que l’on pourrait attendre des quadruplets ou des doublets de chromosomes, il existe une grande diversité de chromosomes en copie unique. Ceci démontre qu’un fort taux de remaniements chromosomiques a modifié le caryotype de S. pedo, postérieurement à son passage à la tétraploïdie. Cette accumulation de remaniements, aboutissant à une forte hétérozygotie, peut s’expliquer par l’absence de filtre méiotique chez cette espèce parthénogénétique. Nos dernières prospections terrain dans le sud des Balkans, nous ont amené à découvrir une zone probable d’intergradation entre Saga pedo et certains taxons sexués affines. L’analyse chromosomique des individus de cette région va sans doute se révéler d’une importance essentielle pour la poursuite de nos recherches.     

A hybrid zone between hydrothermal vent mussels (Bivalvia: Mytilidae) from the Mid-Atlantic Ridge

This study provides the first example of a hybrid zone between animal taxa distributed along the mid-ocean ridge system. We examined the distribution and genetic structure of deep-sea hydrothermal vent mussels (Bivalvia: Mytilidae) along a 2888-km portion of the Mid-Atlantic Ridge between 37 degrees 50' N and 14 degrees 45' N latitude. Mitochondrial DNA (mtDNA), allozymes and multivariate-morphometric evidence discriminated between individuals of a northern species, Bathymodiolus azoricus, and a southern species, B. puteoserpentis, that were separated by an intermediate ridge segment almost devoid of mussels. A small sample of mussels from Broken Spur, a vent locality along this intermediate zone, revealed a mixed population with gene frequencies and morphology that were broadly intermediate to those of the northern and southern species. Multilocus clines in mtDNA and allozyme frequencies were centred over the intermediate zone. We consider intrinsic and extrinsic processes that might limit genetic exchange across this hybrid zone.     

Natural hybridization betweenSaimiri taxa in the Peruvian Amazonia

A wild population situated in the border of the distributions ofSaimiri sciureus macrodon andS. boliviensis peruviensis, in the Peruvian Amazonia, was studied in relation to 22 protein loci. These genetic markers provided indications of secondary intergradation between these two taxa, reinforcing previous morphological and cytogenetic evidences. Continued studies in this region on the hybrids' viability and fertility may be important for decisions related to the taxonomy of this genus.     

Distinguishing between primary and secondary intergradation among morphologically differentiated populations of Anolis marmoratus

Distinguishing between primary and secondary intergradation among differentiated populations, and the relative importance of drift and selection, are persistent problems in evolutionary biology. An historical perspective on population interactions can provide insight into the nature of contacts, and thus help resolve these questions. Continuously distributed populations of Anolis marmoratus from the island of Basse Terre in the Guadeloupean archipelago of the Lesser Antilles show a striking degree of geographic variation in morphology. Initial surveys of mtDNA variation from throughout the Guadeloupean Archipelago revealed one case where levels of sequence difference and phylogenetic relationships of alleles from morphologically differentiated populations from the east coast of Basse Terre were consistent with primary intergradation. In this paper, I examine the genetic population structure of a series of populations spanning this north-south cline in morphological variation to test the hypothesis of primary intergradation. Sequences of the mitochondrial cytochrome-b gene from 50 individuals representing five populations spanning the cline were obtained and fourteen unique haplotypes (differing by 2% or less) were detected. Patterns of nucleotide substitution among haplotypes do not deviate from neutral expectation indicating no effect of selection at the level of mtDNA sequences. Estimates of population structure and gene flow were made using both summary statistics for nucleotide diversity (N_at) and cladistic methods. The results are sensitive to the choice of gene flow model, and this is discussed in detail. Mitochondrial variation in the northern populations may not be at equilibrium, and the phylogeny of alleles is consistent with a recent increase in effective population size. Estimates of nucleotide diversity, gene flow, and the phylogenetic relationships of haplotypes indicate that the southern-most population (representing the extreme of morphological variation along this cline) has been relatively isolated from populations to the north and has experienced a reduced effective population size. The apparent clinal variation between the southern population and the others may therefore reflect secondary contact and introgression rather than primary intergradation.     

Latitudinal,taxonomic, sexual,and insular determinants of size variation in pigtail macaques,Macaca nemestrina

Regression analysis demonstrates that body and skull size are correlated with latitude in Sundaic (Macaca nemestrina nemestrina)and Indochinese (M. n. leonina)pigtail macaques. These two contiguously distributed subspecies are unusual in that they exhibit opposite latitudinal gradients of increasing size— M. n. nemestrinabecomes larger in a southerly direction,while M. n. leoninabecomes larger in a northerly direction in accordance with the usual pattern of ecogeographic variation seen in other sympatric macaques and mammals (Bergmann ’s rule). The difference in clinal size gradients is one more of a series of characters which delineate these two macaques as natural biological populations. However, since the size gradients converge on a narrow zone along the Thai-Malay Peninsula, the use of size as a character to evaluate genetic and morphological intergradation is equivocal when population variation is considered. The third subspecies, the Mentawi Island pigtail (M. n. pagensis),is an endemic,insular isolate differentiated from the Sundaic pigtail from similar latitudes in terms of its small size. Thus, latitude, insularity, and taxonomic differentiation all affect size variation in the pigtail macaques;also,although the data are not definitive, there is the suggestion that the degree of sexual dimorphism may be an additional covariate of latitude and/or body size.