The Evolution of Dicliny in Schiedea (Caryophyllaceae), an Endemic Hawaiian Genus

Abstract The evolution of dioecy was studied in Schiedea (Caryophyllaceae), a genus endemic to the Hawaiian Islands. Eight of the 22 species are diclinous, possessing gynodioecious, subdioecious, or dioecious breeding systems. A biogeographic analysis of the genus indicates that the ancestor of Schiedea colonized early in the history of the Hawaiian Islands. Subsequently, hermaphroditic species appear to have engaged in inter-island colonization more frequently than diclinous species. For this reason, single-island endemism and dicliny are more common on the older Hawaiian Islands. Strong inbreeding depression was detected in three species of Schiedea , indicating that genetic factors have played a role in the evolution of dicliny. Depending on the level of natural selfing, the expression of inbreeding depressioin may have favored the outcrossed progeny of rare females in populations, and eventually the evolution of dioecy. In contrast to evidence for inbreeding depression, there was very little evidence that resource allocation, sex lability, or habitat partitioning have played an important role in the evolution of dioecy. In subdioecious S. globosa hermaphrodites were largely male in function, and in gynodioecious S. salicaria females and hermaphrodites were equivalent in nearly all aspects of female function that could be measured. Variation in breeding systems in Schiedea and the closely related Alsinidendron may result from the past history of population bottlenecks that have resulted in varying levels of inbreeding depression.     

Lateral plasma membrane compartmentalization links protein function and turnover

Biological membranes organize their proteins and lipids into nano‐ and microscale patterns. In the yeast plasma membrane (PM), constituents segregate into a large number of distinct domains. However, whether and how this intricate patchwork contributes to biological functions at the PM is still poorly understood. Here, we reveal an elaborate interplay between PM compartmentalization, physiological function, and endocytic turnover. Using the methionine permease Mup1 as model system, we demonstrate that this transporter segregates into PM clusters. Clustering requires sphingolipids, the tetraspanner protein Nce102, and signaling through TORC2. Importantly, we show that during substrate transport, a simple conformational change in Mup1 mediates rapid relocation into a unique disperse network at the PM. Clustered Mup1 is protected from turnover, whereas relocated Mup1 actively recruits the endocytic machinery thereby initiating its own turnover. Our findings suggest that lateral compartmentalization provides an important regulatory link between function and turnover of PM proteins.     

Primal-size neural circuits in meta-periodic interaction

Experimental observations of simultaneous activity in large cortical areas have seemed to justify a large network approach in early studies of neural information codes and memory capacity. This approach has overlooked, however, the segregated nature of cortical structure and functionality. Employing graph-theoretic results, we show that, given the estimated number of neurons in the human brain, there are only a few primal sizes that can be attributed to neural circuits under probabilistically sparse connectivity. The significance of this finding is that neural circuits of relatively small primal sizes in cyclic interaction, implied by inhibitory interneuron potentiation and excitatory inter-circuit potentiation, generate relatively long non-repetitious sequences of asynchronous primal-length periods. The meta-periodic nature of such circuit interaction translates into meta-periodic firing-rate dynamics, representing cortical information. It is finally shown that interacting neural circuits of primal sizes 7 or less exhaust most of the capacity of the human brain, with relatively little room to spare for circuits of larger primal sizes. This also appears to ratify experimental findings on the human working memory capacity.     

Effects of soil properties and clonal growth on the apparent sex ratio of the flowering stems of the dioecious clonal shrub Aucuba japonica var. borealis growing in an evergreen coniferous secondary forest

In dioecious plants, the frequencies of flowering stems in each sex produced through clonal growth provide important information on the potential for reproductive success in the populations. However, apart from the light environment in their habitat, the factors affecting the flowering of each sex have not been well documented in shrub species that can maintain their populations in shady environments. In this research, we investigated seven soil variables and the flowering of stems of Aucuba japonica var. borealis in patches of this dioecious clonal shrub with different apparent stem sex ratios in an evergreen coniferous secondary forest with a shady forest floor. Of the 53 patches examined, 52 contained stems with flowers. Flowering stem ratios exhibited a positive relationship with available soil phosphate but a marginal negative relationship with exchangeable magnesium, whereas soil water content was associated with a female-biased flowering sex ratio. Stem density tended to be negatively related to flowering stem ratios in patches containing stems with female flowers but not males. While the results demonstrate that abundant amounts of certain nutrients and moisture in soils promote the production of flowers and/or a bias toward femaleness in patches, it is suggested that antagonistic effects of cations in the soil can inhibit the flowering of both sexes. In addition, the trade-off between sexual reproduction and clonal propagation in the females may amplify the variations in flowering in the population.     

Landscape-scale sexual segregation in the dry season distribution and resource utilization of elephants in Kruger National Park, South Africa

This study compared the dry season distribution of elephant bull groups and mixed herds and the resources driving these distributions within Kruger National Park, South Africa. It is important to understand what resources drive the distribution of elephants as this may be of relevance to understanding and managing their impact. It is also important to distinguish between resource use by bull groups and mixed herds because their impact on the habitat may differ. Our results indicated that sexual segregation, both in space and in resource selection, did occur in Kruger Park. Bulls roamed more widely in the park, and although their distribution and resource use overlapped with mixed herds, they also occurred in areas that mixed herds apparently did not, or could not, utilize in the dry season. This gave rise to areas used exclusively by bulls but no areas used exclusively by mixed herds. Lower collective feeding requirements as a result of smaller group size, wider habitat tolerance, and increased mobility as a result of bigger body size, as well as conflict avoidance with musth bulls in areas with mixed herds, might have been some of the reasons for bull groups roaming more widely and for the establishment of separate bull areas. Rivers were an important resource driving both the distribution of the mixed herds and bull groups, but with the mixed herds occurring closer to these resource hot spots than the bull groups. Tree cover proved important for mixed herds, probably because of the importance of shade and the higher nutritional requirements of the smaller-sized cows and calves. Artificial waterholes might have opened up previously unutilized areas for bulls in the dry season, especially on the grassy basaltic plains in the north of the park. However, the distribution of the mixed herds suggested that they did not occur in higher densities in areas surrounding waterholes.     

Genetic mapping of sterile genes with epistasis in backcross designs

The mapping of sterile genes is an essential issue, which should be solved for the investigation of sterility mechanism in wide hybridization of plants. However, the methods formerly developed cannot address the problem of mapping sterile loci with epistasis. In this study, we developed a new method to map sterile genes with epistasis in wide hybridizations of plants using a backcross design. The maximum likelihood method was used to estimate the parameters of recombination fractions and effects of sterile genes, and the convergent results of these parameters were obtained using the expectation maximization (EM) algorithm. The application and efficiency of this method were tested and demonstrated by a set of simulated data and real data analysis. Results from the simulation experiments showed that the method works well for simultaneously estimating the positions and effects of sterile genes, as well as the epistasis between sterile genes. A real data set of a backcross (BC) population from an interspecific hybrid between cultivated rice, Oryza sativa, and its wild African relative, Oryza longistaminata, was analyzed using the new method. Five sterile genes were detected on the chromosomes of 1, 3, 6, 8 and 10, and significant epistatic effects were found among the four pairs of sterile genes.     

The synaptic basis of activity-dependent eye-specific competition

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Chromosome Segregation and Peptidoglycan Remodeling Are Coordinated at a Highly Stabilized Septal Pore to Maintain Bacterial Spore Development

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