Divergent natural selection drives the evolution of reproductive isolation in an Australian wildflower

Ecological speciation occurs when reproductive isolation evolves between populations adapting to contrasting environments. A key prediction of this process is that the fitness of hybrids between divergent populations should be reduced in each parental environment as a function of the proportion of local genes they carry, a process resulting in ecologically dependent reproductive isolation (RI). To test this prediction, we use reciprocal transplant experiments between adjacent populations of an Australian wildflower, Senecio lautus, at two locations to distinguish between ecologically dependent and intrinsic genetic reproductive barriers. These barriers can be distinguished by observing the relative fitness of reciprocal backcross hybrids, as they differ in the contribution of genes from either parent while controlling for any intrinsic fitness effects of hybridization. We show ecologically dependent fitness effects in establishment and survival of backcrosses in one transplant experiment, and growth performance in the second transplant experiment. These results suggest natural selection can create strong reproductive barriers that maintain differentiation between populations with the potential to interbreed, and implies a significant role for ecology in the evolutionary divergence of S. lautus.     

Phylogenetic relationships and gene flow between sympatric diploid and tetraploid plants ofDactylis glomerata (Gramineae)

Phylogenetic relationships between sympatric, morphologically indistinguishable diploid and tetraploid plants ofDactylis glomerata L. (Gramineae) in Galicia (Spain) were assessed using allozyme markers for 6 distinct systems. The study exploited recent introduction in Galicia and subsequent hybridization of an alien 4xDactylis subspecies possessing distinct allozymes from those of all the native plants. Opportunities for gene exchanges between the ploidies were estimated from in situ observations of flowering, examination of progenies in 2x/4x natural and experimental crosses, and enzyme analyses. Results show a high genetic similarity between the Galician diploids and tetraploids, which possess peculiar alleles in common. Although the ploidy levels usually have distinct flowering periods, interploidal crosses do occasionally occur. Gene flow is likely much more important from the diploid to the tetraploid level. A good genetic intermixing occurs between the Galician and the alien tetraploid entities which have simultaneous flowering. Autopolyploidization of the diploids followed by various rates of hybridization is proposed as one very probable origin of natural tetraploids inDactylis.     

Surface structure changes of rat adipocytes during lypolysis stimulated by various lypolysis stimulated by various lypolytic agents

A qualitative and quantitative electron microscopic study was performed on rat adipocytes during stimulation of lipolysis by various agents. Scanning electron microscopy of control cells revealed a spherical cell with a textured glycocalyx surface exhibiting small irregular projections. Globular surface evaginations or protrusions measuring 8-18 μM in diameter were seen on cell hemispheres, and there was an average of one protrusion for every two hemispheres examined. Distribution analysis showed that 60 percent of the hemispheres had no protrusions, and 25, 10, and 5 percent of the hemispheres had one, two or three protrusions, respectively. Thin-section and freeze- fracture electron microscopy of the protrusions showed a small triglyceride droplet surrounded by a thin cytoplasmic rim that was continuous with the main cytoplasmic matrix. The glycocalyx coating and plasma membrane extended from the cell surface onto, and over, the protrusion. Scanning microscopy of cells stimulated by lipolytic agents, including epinephrine, adrenocorticotropic hormone, theophylline, and dibutyryl cyclic AMP, revealed a dose-dependent increase in the number of protrusions per cell hemisphere. Maximal concentrations of lipolytic hormones cuase an average 2.5-fold increase in the number of protrusions per hemisphere without changing the average size of the protrusions. Only 40 percent of the stimulated cell hemispheres exhibited no protrusions; over 15 percent of the cells contained three or more; and a number of the protrusions were multilobulate. Insulin prevented the increase in the number of protrusions and the change in distribution caused by the lipolytic hormones but did not prevent the increase caused by theophylline and dibutryl cyclic AMP. The data suggest that the protrusions are a structural feature of the cell and may be related to the lypolytic pathway. These observations may help explain some of the discrepant biochemical data relating to hormonal stimulation of lipolysis.     

Diversification across a heterogeneous landscape

Adaptation to contrasting environments across a heterogeneous landscape favors the formation of ecotypes by promoting ecological divergence. Patterns of fitness variation in the field can show whether natural selection drives local adaptation and ecotype formation. However, to demonstrate a link between ecological divergence and speciation, local adaptation must have consequences for reproductive isolation. Using contrasting ecotypes of an Australian wildflower, Senecio lautus in common garden experiments, hybridization experiments, and reciprocal transplants, we assessed how the environment shapes patterns of adaptation and the consequences of adaptive divergence for reproductive isolation. Local adaptation was strong between ecotypes, but weaker between populations of the same ecotype. F1 hybrids exhibited heterosis, but crosses involving one native parent performed better than those with two foreign parents. In a common garden experiment, F2 hybrids exhibited reduced fitness compared to parentals and F1 hybrids, suggesting that few genetic incompatibilities have accumulated between populations adapted to contrasting environments. Our results show how ecological differences across the landscape have created complex patterns of local adaptation and reproductive isolation, suggesting that divergent natural selection has played a fundamental role in the early stages of species diversification.     

Community structure of lice (Insecta: Phthiraptera) from two sympatric gull species: kelp gull (Larus dominicanus) and Franklin's gull (Larus pipixcan) in Talcahuano, Chile

A total of 1,177 lice of four species were collected from 124 kelp gulls (Larus dominicanus) and 137 lice of the same four species from 60 Franklin's gulls (Larus pipixcan). The louse Saemundssonia lari (O Fabricius) (Phthiraptera: Philopteridae) was the most numerous on both gull species, with infestation rates of 4.9 on kelp gulls and 1.8 on Franklin's gulls. The second most abundant louse was Quadraceps punctatus (Burmeister), with a high infestation rate but low prevalence on kelp gulls; those parameters were much lower among lice from Franklin's gulls. The composition and community structure of the lice were similar on both host species, but not their infestation rates. In addition, the feather mite Zachvatkinia larica Mironov (Acari: Avenzoariidae) is recorded from kelp gulls and Franklin's gulls for the first time, while the gamasid mite Larinyssus sp. is recorded from kelp gulls, also for the first time. The population parameters of all species of ectoparasites are discussed.     

Temperature but not rainfall influences timing of breeding in a desert bird, the trumpeter finch ( Bucanetes githagineus )

Reproductive performance in birds depends on several factors, one of the most important being the time of breeding. Birds try to fit offspring birth and growth to peak vegetative production in order to assure fledgling survival. In arid environments, where weather conditions are often extreme, birds must face unpredictable abiotic conditions. This study uses a border population of the trumpeter finch (Bucanetes githagineus) as a model to test whether climate variables (rainfall and temperature) influence breeding parameters by comparing 2 years with very different weather. The study was carried out in the Tabernas desert (southeastern Spain) in 2004 and 2005. A comparison of laying dates in the 2 years shows a 40-day delay in the date of the first clutch in the coldest year (mean minimum temperature 3°C lower in 2005 than in 2004). However, once the breeding season started, the number of clutches, clutch size, duration of the incubation period, nestling phase, fledgling rates and productivity were similar. One likely explanation for this delay is that low temperatures did not allow the germination of Diplotaxis sp., a plant forming the bulk of the trumpeter finch diet during spring. Its absence could prevent onset of breeding, although other temperature-related factors could also be involved. Although rainfall has frequently been reported as a limiting factor for arid bird species, our 2-year study shows that temperature can also influence the breeding biology of arid bird species, by affecting its timing.     

Development of a biofertilizer based on filamentous nitrogen-fixing cyanobacteria for rice crops in Chile

The purpose of this study was to develop a biofertilizer based on filamentous nitrogen-fixing cyanobacteria selected from rice fields and to generate a technological package compatible with its use for the rice crop in Chile. Thirty-four Chilean rice fields, located between Maule and BioBío regions, were sampled during the 1998/1999 and 1999/2000 growing seasons. A total of 9 species and 3 varieties of cyanobacteria were found, and the nitrogen fixation rate under laboratory conditions was determined for 6 of them. Only 4 were used for the small-scale production of a biofertilizer, which was assayed in field trials. To check the efficiency of the biofertilizer during the rice crop, the nitrogen fixation rates in soil samples were estimated. Additionally, the biofertilizer application efficiency was tested in combination with nitrogen synthetic fertilizer, in rates that were previously established in field trials. Biofertilization allowed a decrease of up to 50% in the use of nitrogen synthetic fertilizer (50 kg N ha⁻¹), resulting in the same grain yield (7.4 t ha⁻¹) and quality in relation to the fertilized control. The use of biofertilizers based on local strains of cyanobacteria shows promise to increase nitrogen use efficiency in rice.     

Suppression mechanisms of COX assembly defects in yeast and human: insights into the COX assembly process

Eukaryotic cytochrome c oxidase (COX) is the terminal enzyme of the mitochondrial respiratory chain. COX is a multimeric enzyme formed by subunits of dual genetic origin whose assembly is intricate and highly regulated. In addition to the structural subunits, a large number of accessory factors are required to build the holoenzyme. The function of these factors is required in all stages of the assembly process. They are relevant to human health because devastating human disorders have been associated with mutations in nuclear genes encoding conserved COX assembly factors. The study of yeast strains and human cell lines from patients carrying mutations in structural subunits and COX assembly factors has been invaluable to attain the current state of knowledge, even if still fragmentary, of the COX assembly process. After the identification of the genes involved, the isolation and characterization of genetic and metabolic suppressors of COX assembly defects, reviewed here, have become a profitable strategy to gain insight into their functions and the pathways in which they operate. Additionally, they have the potential to provide useful information for devising therapeutic approaches to combat human disorders associated with COX deficiency.