Burkholderia species are ancient symbionts of legumes

Burkholderia has only recently been recognized as a potential nitrogen-fixing symbiont of legumes, but we find that the origins of symbiosis in Burkholderia are much deeper than previously suspected. We sampled 143 symbionts from 47 native species of Mimosa across 1800 km in central Brazil and found that 98% were Burkholderia . Gene sequences defined seven distinct and divergent species complexes within the genus Burkholderia . The symbiosis-related genes formed deep Burkholderia -specific clades, each specific to a species complex, implying that these genes diverged over a long period within Burkholderia without substantial horizontal gene transfer between species complexes.     

Isolation and characterization of 15 microsatellite loci in the poplar rust fungus,Melampsora larici‐populina,and cross‐amplification in related species

We developed 15 microsatellite loci in the poplar rust fungus, Melampsora larici‐populina, using two enrichment protocols. Polymorphism of each locus was assessed on a panel of 30 isolates, comprising three subpanels (world, regional and local scales). Thirteen loci were polymorphic with three to eight alleles detected. The 15 loci were also tested on five related Melampsora species, M. allii‐populina, M. medusae f. sp. deltoidae, M. larici‐tremulae, M. rostrupii and M. pinitorqua, and partial or global cross‐amplification events were detected.     

Speciation problems in the Papilio machaon group of butterflies (Lepidoptera: Papilionidae)

Abstract. The taxonomic and genetic relationships between P.machaon rathjensi Warnecke from the west side of southern Arabia and P.machaon muetingi Seyer from the east are discussed, together with suggestions of their relationship to P.machaon saharae Oberthiir from the northern Hejaz, Sinai and desert North Africa. It is concluded that though P.m.rathjensi and P.m.saharae are subspecifically distinct, they are very closely related to each other, and both should be regarded as specifically distinct from the rest of the machaon complex.
The remainder of the machaon complex in its turn presents a somewhat similar problem. Thus P.machaon gorganus Fruhstorfer and P.hospiton Géné are normally regarded as good species, but Fl caterpillars have been found in the wild and the cross can be readily produced in captivity with no upset in the sex ratio. Furthermore, recently we have obtained sparse F2 offspring between the two species.
We therefore suggest that the entire P.machaon complex is in a labile state as regards speciation throughout its range and the relationships between the various forms are not easily expressed through the traditional species and subspecies concepts. Our tentative conclusions are that the status of P.machaon and P.hospiton as distinct species probably remains valid. The saharaelrathjensi complex might be considered distinct from P.machaon using the biological species concept, while their genetics indicate a more conservative approach. However, more important than the exact status of the taxa in question is the fact that the P.machaon complex illustrates evoluton in action, the end result of which cannot be predicted.     

Mechanism of water‐stress induced cavitation in conifers: bordered pit structure and function support the hypothesis of seal capillary‐seeding

Resistance to water‐stress induced cavitation is an important indicator of drought tolerance in woody species and is known to be intimately linked to the anatomy of the xylem. However, the actual mechanical properties of the pit membrane are not well known and the exact mode of air‐seeding by which cavitation occurs is still uncertain. We examined the relationship between cavitation resistance and bordered pit structure and function in 40 coniferous species. Xylem pressure inducing 50% loss of hydraulic conductance (P₅₀, a proxy for cavitation resistance) varied widely among species, from ?2.9 to ?11.3 MPa. The valve effect of the pit membrane, measured as a function of margo flexibility and torus overlap, explained more variation in cavitation‐resistance than simple anatomical traits such as pit membrane, pit aperture or torus size. Highly cavitation resistant species exhibited both a high flexibility of the margo and a large overlap between the torus and the pit aperture, allowing the torus to tightly seal the pit aperture. Our results support the hypothesis of seal capillary‐seeding as the most likely mode of air‐seeding, and suggest that the adhesion of the torus to the pit border may be the main determinant of cavitation resistance in conifers.     

Body shape differentiation at global and local geographic scales in the invasive cichlid Oreochromis mossambicus

The Mozambique tilapia Oreochromis mossambicus (Teleostei, Cichlidae) has been transplanted worldwide during the 20th century, and now belongs to the list of the most invasive species. Using a geometric morphometric approach, we describe body shape differentiation among 15 populations from native (Mozambique) and invaded (New Caledonia and Guadeloupe) ranges. A dominant phylogeographic signal is detected, despite the broad range of environmental conditions at the local scale. This result suggests that phylogeographic background rather than phenotypic plasticity responding to environmental variation constitutes the main factor correlated with shape divergence. This could result from successive founder events that occurred during the process of colonization of new geographic areas, and therefore strongly suggests heritable phenotypic differentiation. In addition, shape changes along a major axis of divergence hypothetically refer to different swimming abilities, possibly related to divergent functional requirements between the native and invaded ranges. Overall, patterns of contemporary shape diversification in O. mossambicus probably result from both phylogenetic constraints and adaptive divergence processes. We show that critically taking into account recent phylogenetic history of populations as a constraint on rapid phenotypic divergence is necessary for an improved view of contemporary evolution. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 369–381.