Principles of early ontogeny in the rugose corals: a critical review

It has been suggested that septal furrows in the Palaeozoic rugose corals are secondary in comparison both to growth lines and to the septal blades inside calices. The leading role of furrows as an indicator of septal increase is thus questioned. Septa are always grouped in quadrants but their increase is generally towards the cardinal septum. The arrangement of the contratingent minor septa seems to be independent of the increase in septal furrows. Hence, the growth of the polyp's skeleton may have started from an aseptal cup.     

Low specificity and nested subset structure characterize mycorrhizal associations in five closely related species of the genus Orchis

Most orchid species rely on mycorrhizae to complete their life cycle. Despite a growing body of literature identifying orchid mycorrhizal associations, the nature and specificity of the association between orchid species and mycorrhizal fungi remains largely an open question. Nonetheless, better insights into these obligate plant–fungus associations are indispensable for understanding the biology and conservation of orchid populations. To investigate orchid mycorrhizal associations in five species of the genus Orchis (O. anthropophora, O. mascula, O. militaris, O. purpurea, and O. simia), we developed internal transcribed spacer‐based DNA arrays from extensive clone library sequence data sets, enabling rapid and simultaneous detection of a wide range of basidiomycetous mycorrhizal fungi. A low degree of specificity was observed, with two orchid species associating with nine different fungal partners. Phylogenetic analysis revealed that the majority of Orchis mycorrhizal fungi are members of the Tulasnellaceae, but in some plants, members of the Thelephoraceae, Cortinariaceae and Ceratobasidiaceae were also found. In all species except one (O. mascula), individual plants associated with more than one fungus simultaneously, and in some cases, associations with ≥3 mycorrhizal fungi at the same time were identified. Nestedness analysis showed that orchid mycorrhizal associations were significantly nested, suggesting asymmetric specialization and a dense core of interactions created by symmetric interactions between generalist species. Our results add support to the growing literature that multiple associations may be common among orchids. Low specificity or preference for a widespread fungal symbiont may partly explain the wide distribution of the investigated species.     

The clues to species specificity of pollination among Brassicaceae

The Brassica S product of the pollen-signalling S-gene (SP11 for Specificity Pollen, or SCR for S locus Cysteine Rich) has recently been identified as a member of the family of PCPs (Pollen Coat Proteins), a group of small basic proteins. In female plants SRK (S Receptor Kinase) has been demonstrated, among several stigma-expressed S genes, to exclusively control self-pollen rejection. Genes and gene products that are highly related to the sporophytic SI system appear to take part in the control of several stages of pollen-stigma interactions in the Brassicaceae. These genes ensure, in particular, the species specificity of late pollen adhesion. Pollen capture itself is not species specific, since it depends essentially on lipophilic affinities between pollen coatings and waxy pellicles on the stigma. These interactions and their control are reviewed here. Received: 2 August 2000 / Revision accepted: 11 August 2000     

Biogeography of the chaetodontidae: an analysis of allopatry among closely related species

Synopsis A recent survey of chaetodontid osteology has produced a hypothesis of relationships among 22 osteologically distinct genera and subgenera. Fourteen supra-specific taxa have distributions that are Indo-Pacific or larger. Most sister taxa inferred by osteology are broadly sympatric. The basal dichotomy within the large genusChaetodon contrasts monophyletic groups centered in the Atlantic and Indo-Pacific with little overlap. Divergence of Atlantic and Indo-Pacific distributions is correlated with the closing of the Tethys seaway 18–13 million years ago. Distributional data of Burgess (1978) and Allen (1980) are reevaluated in the context of putative species pairs and complexes. Species in nearly two thirds of these complexes (18 of 31) are distributed allopatrically. Eight complexes are examined in more detail. Five of these eight contain at least one peripherically isolated species. Distributions of species in four complexes indicate that previously wide-spread species were cleaved more symmetrically. Sympatric distributions within two species pairs indicate that the more narrowly distributed species in each pair arose through central isolation within a broadly distributed ancestor. The area of central isolation corresponds to the classical center of origin. A new hypothesis of vicariance followed by dispersal may partially explain the diversity gradient so prominently featured in dispersal-oriented tropical marine biogeography.     

Micromechanics and anatomical changes during early ontogeny of two lianescent Aristolochia species

 The mechanical properties of young stems of Aristolochia macrophylla Lam. and Aristolochia brasiliensis Mart. et Zucc. were studied during elongation growth and primary differentiation. Data for the modulus of elasticity, for the viscoelastic behaviour caused by longitudinal tension and for the shear modulus resulting from torsion around a longitudinal axis were related to the underlying structural changes by quantitative analysis of stem anatomy, tissue distribution, ultrastructure, and cell wall biochemistry. The orientation of cellulose microfibrils was determined by light microscopy and small-angle X-ray diffraction, and the lignin content was determined by thioglycolic acid derivatization and spectroscopic quantification. It was demonstrated that the increase in stability during early development is due to the complementary effects of increase in cell wall material, lignification, and cellulose microfibril alignment. A detailed micromechanical model, considering internal prestresses, is proposed to explain the characteristic biphasic stress-strain behaviour as well as the strain-hardening observed. Received: 22 March 1999 / Accepted 9 September 1999     

Typing of four genetic loci discriminates among closely related species of New World Leishmania

All New World Leishmania species can cause cutaneous lesions, while only Leishmania (Viannia) braziliensis has been associated with mucosal metastases. Multilocus enzyme electrophoresis (MLEE) is the optimal standard for species identification but is slow and costly. New methods for species identification are needed to ensure proper identification and therapy. The coding regions of four metabolic enzyme markers in the MLEE typing method: mannose phosphate isomerase (MPI), malate dehydrogenase (MDH), glucose-6-phosphate isomerase (GPI), and 6-phosphogluconate dehydrogenase (6PGD), were analysed from seven species of New World Leishmania isolated from patients with either cutaneous or mucosal lesions to identify specific genetic polymorphisms responsible for the phenotypic variations observed in the MLEE typing scheme. We identified species-specific polymorphisms and determined that a combination of sequencing of the mpi and 6pgd genes was sufficient to differentiate among seven closely related species of New World Leishmania and among isolates of L. braziliensis shown previously to have atypical MLEE patterns. When DNA isolated from 10 cutaneous lesion biopsies were evaluated, the sequence typing method was 100% concordant with the published MLEE/monoclonal antibody identification methods. The identification of species-specific polymorphisms can be used to design a DNA-based test with greater discriminatory power that requires shorter identification times. When the causative agent of the disease is L. braziliensis, this method ensures correct species identification, even when the agent is a genetic variant. Proper identification could facilitate adequate treatment, preventing the onset of the disfiguring mucosal form of the disease.     

Comparative study of pollination biology of two closely related alpine Primula species,namely Primula beesiana and P.bulleyana (Primulaceae)

The comparative pollination biology of a population of Primula beesiana,a population of P.bulleyana,and an overlapping population of these two species in Yulong Shan,Yunnan Province,China,was studied in 2004 and 2005.The results indicate that both P.beesiana and P.bulleyana are typical heterostylous and obligate outcrossing species;the main pollinators of the two species were bees and butterflies.At the sites of all three populations,the main pollinating visitors of the two species showed preference for one...     

A critical evaluation of reproductive barriers between closely related species using DNA markers - a case study in Pinus

Former controlled crosses between twelve Pinus montana var. rostrata (Pinus mugo complex) and eight P. sylvestris clones revealed that only two P. sylvestris had efficiently fertilised P. montana. Two species-diagnostic chloroplast DNA markers were applied to verify the species purity of the parental clones. All maternal P. montana were unambiguously confirmed to belong to the P. mugo complex at both chloroplast DNA marker loci. Six P. sylvestris clones carried the `sylvestris' haplotypes. However, the same two P. sylvestris clones that had efficiently fertilised P. montana displayed the chloroplast haplotypes diagnostic to the P. mugo complex. The patterns of highly polymorphic cpDNA microsatellite markers in parents and offspring ruled out contamination by foreign pollen. We concluded that the two clones successful in the crosses represent fertile hybrids between the two species with P. mugo as the pollen donor. Consequently, DNA markers are proposed for verifying or falsifying the success of artificial fertilisation in general. The existence of crossing barriers between the two Pinus species, meaningful to the postulated natural hybridisation and the evolution of their populations in sympatric stands, was indicated and is newly discussed.     

Evidence of reproductive isolation among closely related sympatric species of Serrasalmus (Ostariophysii, Characidae) from the Upper Madeira River, Amazon, Bolivia

The delimitation of the Serrasalmus species (Characiformes, Serrasalminae) from the Bolivian Amazon (Amazonas, Madeira) was examined using intron length polymorphism assessed by EPIC-PCR. The six pairs of primers provided 16 polymorphic loci across the species of the region and the allelic diversity ranged between two and 10 alleles per locus. For each locus, the lack of departure from Hardy-Weinberg expectations in a large number of the populations analysed and the homogenous distribution of linkage disequilibrium between paralogous loci and loci belonging to different intronic systems provided strong lines of evidence that the 16 amplified loci constituted independent neutral markers. Furthermore, allelic diversity was size-dependent, thereby indicating that insertion-deletions occurred frequently but randomly in introns, and that intron length polymorphism was a valid marker for investigating the systematics of piranhas. EPIC-PCR demonstrated that eight of the nine nominal species of piranha of the Upper Madeira were reproductively isolated and identified a new species that differed from its closest morphological and genetic relatives by seven diagnostic or semi-diagnostic loci. By contrast, no diagnostic or semi-diagnostic locus was found between S. spilopleura and S. eigenmanni , nor were their allelic frequencies different, thereby questioning the validity of their biological species status, at least in the Upper Madeira. This study, which was one of the first applications of EPIC-PCR to a large-scale molecular systematic purpose, demonstrates that it is a rapid, reliable and cost-effective tool for elucidating issues pertaining to fish systematics.