Evolution of reproductive systems in the genus Silene

The genus Silene contains both hermaphrodite, gynodioecious and dioecious species, dioecy being represented in three sections of the genus. To locate the events of change of reproductive systems, we compared ITS sequences of 22 species of Silene chosen throughout the whole genus, and four putative outgroup species. Gynodioecy, which is the most common reproductive system within the genus Silene and in closely related genera such as Saponaria and Dianthus, is proposed to be ancestral in the genus. Dioecy has evolved at least twice: once in the section containing S. latifolia, and once in the clade containing S. otites and S. acaulis ssp. bryoides. Evolution towards hermaphroditism, associated with evolution of selfing has also occurred at least twice, in S. gallica and S. comica.     

Functional Role of Amino-Terminal Serine16 and Serine27 of Gαz in Receptor and Effector Coupling

Abstract: The α subunit of G_z (α_z) harbors two N-terminal serine residues (at positions 16 and 27) that serve as protein kinase C-mediated phosphorylation sites. The cognate residues in the α subunit of G_t1 provide binding surfaces for the β₁ subunit. We used three serine-to-alanine mutants of α_z to investigate the functional importance of the two N-terminal serine residues. Wild-type or mutant α_z was transiently coexpressed with different receptors and adenylyl cyclase isozymes in human embryonic kidney 293 cells, and agonist-dependent regulation of cyclic AMP accumulation was examined in a setting where all endogenous α subunits of G_i were inactivated by pertussis toxin. Replacement of one or both serine residues by alanine did not alter the ability of α_z to interact with δ-opioid, dopamine D₂, or adenosine A₁ receptors. Its capacity to inhibit endogenous and type VI adenylyl cyclases was also unaffected. Functional release of βγ subunits from the mutant α_z subunits was not impaired because they transduced βγ-mediated stimulation of type II adenylyl cyclase. Constitutively active mutants of all four α_z subunits were constructed by the introduction of a Q205L mutation. The activated mutants showed differential abilities to inhibit human choriogonadotropin-mediated cyclic AMP accumulation in luteinizing hormone receptor-transfected cells. Loss of both serine residues, but not either one alone, impaired the receptor-independent inhibition of adenylyl cyclase by the GTPase-deficient mutant. Thus, replacement of the amino-terminal serine residues of α_z has no apparent effect on receptor-mediated responses, but these serine residues may be essential for ensuring transition of α_z into the active conformation.     

Reconstruction of the STS 14 (Australopithecus africanus) pelvis

The study reports a reconstruction of the sacrum in STS 14 based on extrapolation from the measurements of the first two sacral vertebrae of STS 14 and of the angle formed by the anterior surfaces of their vertebral bodies. Reconstruction is based on comparisons of, and extrapolation from, sacra of Pan troglodytes, Homo sapiens, and Australopithecus afarensis. The reconstructed sacrum has an anterior sacral curvature of 39°. The two ossa coxae were also completed by mirror imaging of one side by the other. With the pelvis completely reconstructed, the pelvic dimensions for the antero-posterior (AP) diameters of the pelvic inlet, midpelvis, and pelvic outlet are 85, 68, and 69 mm and the corresponding transverse (TR) diameters are 109, 88, and 103 mm, respectively. The posterior sagittal diameters in the three pelvic planes are small compared to the anterior sagittal diameters. This analysis indicates that the STS 14 pelvis is platypelloid in the three pelvic planes; i.e., all the AP diameters are smaller than the corresponding TR diameters. This makes the STS 14 pelvis similar to that to Al 288-1, save for a less pronounced degree of platypelloidy at the inlet in the former. © 1995 Wiley-Liss, Inc.     

Effect of N,N-Dicyclohexylcarbodiimide on Acetylcholine Release from Torpedo Synaptosomes and Proteoliposomes Reconstituted with the Proteolipid Mediatophore

The mediatophore is a presynaptic membrane protein that has been shown to translocate acetylcholine (ACh) under calcium stimulation when reconstituted into artificial membranes. The mediatophore subunit, a 15-kDa proteolipid, presents a very high sequence homology with the N,N'-dicyclohexylcarbodiimide (DCCD)-binding proteolipid subunit of the vacuolar-type H(+)-ATPase. This prompted us to study the effect of DCCD, a potent blocker of proton translocation, on calcium-dependent ACh release. The present work shows that DCCD has no effect on ACh translocation either from Torpedo synaptosomes or from proteoliposomes reconstituted with purified mediatophore. However, using [14C]DCCD, we were able to demonstrate that the drug does bind to the 15-kDa proteolipid subunit of the mediatophore. These results suggest that although the 15-kDa proteolipid subunits of the mediatophore and the vacuolar H(+)-ATPase may be identical, different domains of these proteins are involved in proton translocation and calcium-dependent ACh release and that the two proteins have a different membrane organization.     

Separation of Linked Markers in Chinese Hamster Cell Hybrids: Mitotic Recombination Is Not Involved

A search for mitotic recombination was carried out using mutant subclones of cultured Chinese hamster ovary cells. Recombination events were sought between the linked loci specifying the enzymes hypoxanthine phosphoribosyl transferase and glucose-6-phosphate dehydrogenase. It was shown by fluctuation analysis that markers at these two loci co-segregate from doubly heterozygous pseudotetraploid hybrid cells more than 90% of the time. The minority class of segregants, which had lost one marker without losing the other, were genetically analyzed to distinguish between the possibilities of mitotic recombination and deletion of chromosomal material. Nine clones in which a linkage disruption had occured were studied, using further cell hybridization and segregation. In three cases, a recessive lethal loss of genetic information was indicated, suggesting the deletion mechanism. In six cases, it was demonstrated that no new linkage relationships had been established concomitant with linkage disruption. Thus, in all nine clones, the evidence indicated that mitotic recombination was not involved in the events that disrupted linkage between these two loci. If mitotic recombination takes place at all in this system, the rate must be less than about 10^-6 per cell per generation.     

Ectopic pairing and evolution of 5S ribosomal RNA genes in the chromosomes of Drosophila funebris

5S ribosomal RNA from Drosophila melanogaster labeled with ¹²⁵I was used to locate the 5S rRNA genes in chromosomes of D. funebris by means of in situ hybridization. Silver grains were observed at three distinct sites, one of which was a recognized reverse repeat. Only one half of the reverse repeat, however, hybridizes with 5S rRNA and the significance of this phenomenon is discussed. A case of ectopic pairing between two different 5S sites in the genome is reported, and the significance of ectopic pairing is considered.The author was a Predoctoral Fellow supported by Grant GM 1974 from the National Institute of General Medical Sciences, National Institutes of Health.Contribution from Oak Ridge National Laboratory, operated by the Union Carbide Corporation for the U.S. Energy Research and Development Administration.     

The disappearance of four leaf leachates in a hard and soft water stream in South Western Ontario,Canada

The disappearance of ‘dissolved’ organic carbon (D. O. C.) leached from maple, aspen, cedar and pine leaves was followed in hard and soft stream water and hard and soft stream water plus sediment. Differences were found in the rates and extent of the disappearance of D. O. C. between the leaves and the water types. These are discussed in relation to the productivity of two extreme stream types.     

Ants impact the composition of the aquatic macroinvertebrate communities of a myrmecophytic tank bromeliad

In an inundated Mexican forest, 89 out of 92 myrmecophytic tank bromeliads (Aechmea bracteata) housed an associated ant colony: 13 sheltered Azteca serica, 43 Dolichoderus bispinosus, and 33 Neoponera villosa. Ant presence has a positive impact on the diversity of the aquatic macroinvertebrate communities (n = 30 bromeliads studied). A Principal Component Analysis (PCA) showed that the presence and the species of ant are not correlated to bromeliad size, quantity of water, number of wells, filtered organic matter or incident radiation. The PCA and a generalized linear model showed that the presence of Azteca serica differed from the presence of the other two ant species or no ants in its effects on the aquatic invertebrate community (more predators). Therefore, both ant presence and species of ant affect the composition of the aquatic macroinvertebrate communities in the tanks of A. bracteata, likely due to ant deposition of feces and other waste in these tanks.     

Facial bristle feather histology and morphology in New Zealand birds: Implications for function

Knowledge of structure in biology may help inform hypotheses about function. Little is known about the histological structure or the function of avian facial bristle feathers. Here we provide information on morphology and histology, with inferences for function, of bristles in five predominantly insectivorous birds from New Zealand. We chose species with differing ecologies, including: brown kiwi (Apteryx mantelli), morepork (Ninox novaezealandae), hihi (Notiomystis cincta), New Zealand robin (Petroica australis), and New Zealand fantail (Rhipidura fuliginosa). Average bristle length corrected for body size was similar across species. Bristles occurred in distinct groups on different parts of the head and upper rictal bristles were generally longest. The lower rictal bristles of the fantail were the longest possessed by that species and were long compared to bristles of other species. Kiwi were the only species with forehead bristles, similar in length to the upper rictal bristles of other species, and the lower rictal bristles of fantails. Herbst corpuscles (vibration and pressure sensitive mechanoreceptors) were found in association with bristle follicles in all species. Nocturnal and hole‐nesting birds had more heavily encapsulated corpuscles than diurnal open‐nesting species. Our results suggest that avian facial bristles generally have a tactile function in both nocturnal and diurnal species, perhaps playing a role in prey handling, gathering information during flight, navigating in nest cavities and on the ground at night and possibly in prey‐detection. These differing roles may help explain the observed differences in capsule thickness of the corpuscles. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc.