Sex ratio meiotic drive as a plausible evolutionary mechanism for hybrid male sterility.

Biological diversity on Earth depends on the multiplication of species or speciation, which is the evolution of reproductive isolation such as hybrid sterility between two new species. An unsolved puzzle is the exact mechanism(s) that causes two genomes to diverge from their common ancestor so that some divergent genes no longer function properly in the hybrids. Here we report genetic analyses of divergent genes controlling male fertility and sex ratio in two very young fruitfly species, Drosophila albomicans and D. nasuta. A majority of the genetic divergence for both traits is mapped to the same regions by quantitative trait loci mappings. With introgressions, six major loci are found to contribute to both traits. This genetic colocalization implicates that genes for hybrid male sterility have evolved primarily for controlling sex ratio. We propose that genetic conflicts over sex ratio may operate as a perpetual dynamo for genome divergence. This particular evolutionary mechanism may largely contribute to the rapid evolution of hybrid male sterility and the disproportionate enrichment of its underlying genes on the X chromosome--two patterns widely observed across animals.

Multilocus species tree analyses resolve the ancient radiation of the subtribe Zizaniinae (Poaceae).

The phylogeny of the subtribe Zizaniinae of rice tribe (Oryzeae) has not been well resolved, particularly for the monotypic Hygroryza whose systematic position was inconsistent in previous studies. Here, we used the concatenation approach and coalescent-based species tree methods to reconstruct the phylogeny of Zizaniinae based on sequences of 14 nuclear single-copy loci and concatenated chloroplast fragments. Despite the low resolution of the tree from concatenated data and substantial topological incongruence of individual gene trees, the species trees inferred from three coalescent-based methods were fully concordant and highly supported. Importantly, the genus Hygroryza was consistently recovered with strong support by all coalescent-based methods. Further various phylogenetic analyses indicated that incomplete lineage sorting was the most likely process that generated pervasive discordance among individual gene trees, although hybridization and introgression cannot be excluded completely. Our species tree inferences based on multilocus data successfully resolved the phylogenetic relationships of the Zizaniinae lineages and confirmed that ancient rapid radiation has taken place in the diversification history of Zizaniinae. This study demonstrates that coalescent-based species tree approaches outperformed the concatenation method and could effectively decipher ancient rapid radiations as long as well resolved individual gene trees were sufficiently sampled.

Mechanical properties and acoustic emission characteristics of mixed granite after different numbers of freeze‒thaw cycles.

The mechanical properties of rocks in cold regions undergo significant changes as a result of decades of freeze‒thaw cycles with seasonal variations, which can lead to a series of geological disasters, such as collapse. This study investigates the evolution of the mechanical characteristics and internal progressive damage characteristics of mixed granite under freeze‒thaw cycling and axial loading. By measuring the mass, wave velocity, and uniaxial compressive strength of rock samples and combining these metrics with acoustic emission (AE) characteristics, the physical and mechanical properties and microfracture development of mixed granite after different numbers of freeze‒thaw cycles were investigated. The results indicate that as the number of freeze‒thaw cycles increases, the longitudinal wave velocity, uniaxial compressive strength, and elastic modulus of the mixed granite decrease nonlinearly, while the peak strain gradually increases. Combined with the stress‒strain curve, the AE characteristics can be divided into four stages. As the number of freeze‒thaw cycles increases, the AE cumulative count decreases, and the AE counts of the four stages are different. The low-frequency-high-amplitude signals first increases and then tends to stabilize, and they only appeared in the third and fourth stages. At the same time, the proportion of the low-frequency ratio gradually increases, and the proportion of the high-frequency ratio decreases. In addition, based on the rise time/amplitude (RA) and average frequency (AF) characteristics and failure modes, it was found that the internal crack types of mixed granite transition from shear cracks to tensile cracks, among which tensile cracks play a crucial role in rock failure.

The Arabidopsis LRR-RLK, PXC1, is a regulator of secondary wall formation correlated with the TDIF-PXY/TDR-WOX4 signaling pathway.

BACKGROUND: Although a number of leucine-rich repeat receptor-like kinase-encoding genes (LRR-RLKs) have been identified in plants, a functional role has been determined for only a few. Recent studies have demonstrated that an LRR-RLK, PXY/TDR, is important for the process of secondary vascular development. Other studies have indicated that PXY/TDR is unlikely to be the sole LRR-RLK involved in this complex process. RESULTS: In this study, in silico analyses led to the identification of three Arabidopsis LRR-RLK genes (PXY-correlated; PXC1, 2, 3) with transcript accumulation profiles that correlated strongly with several key regulators of vascular development, including PXY/TDR, HB-8, REV, and CLE41. Expression profiling using qPCR and promoter:reporter lines indicated that all three PXC genes are associated with the vasculature. One in particular, PXC1 (At2g36570), had a strong correlation with PXY/TDR. Shifting pxc1 mutants from long-days to short-days showed that loss of the gene led to a dramatic reduction in secondary wall formation in xylem fibers. Transcript analysis of mutants for a variety of secondary cell wall-associated genes, including PXY/TDR indicated that the pathways mediated by PXC1 connect with those mediated by the TDIF-PXY/TDR-WOX4 system. CONCLUSIONS: The data indicate that the LRR-RLK, PXC1 is involved in secondary cell wall formation in xylem fibers. Whereas further study is needed to identify the ligands and mode of action of the PXC1 protein, it is clear from this work that similarly to the shoot apical meristem (SAM), secondary vascular development requires contributions from a number of LRR-RLKs.

Hydrophilic and Positively Charged Polyvinylidene Fluoride Membranes for Water Treatment with Excellent Anti-Oil and Anti-Biocontamination Properties.

Membrane fouling limits the rapid development of membrane separations. In this study, a blend membrane containing polycationic liquid (P(BVImBr1-co-PEGMA1)) is presented that can improve the antifouling performance of polyvinylidene fluoride (PVDF) membranes. By mixing the polycationic liquid into PVDF, an improved membrane-surface hydrophilicity and enlarged membrane porosity were detected. The water contact angle decreased from 82° to 67°, the porosity enlarged from 7.22% to 89.74%, and the pure water flux improved from 0 to 631.68 L m-2 h-1. The blend membrane surfaces were found to be always positively charged at pH 3~10. By applying the membranes to the filtration of oil/water emulsion and bovine serum albumin (BSA) solution, they showed a very high rejection rate to pollutants in wastewater (99.4% to oil droplets and 85.6% to BSA). The positive membrane surface charge and the increased membrane hydrophilicity resulted in excellent antifouling performance, with the flux recovery rates of the dynamic filtration tests reaching 97.3% and 95.5%, respectively. Moreover, the blend membranes demonstrated very low BSA adhesion and could even kill S. aureus, showing excellent antifouling properties.

Selection on grain shattering genes and rates of rice domestication.

Molecular cloning of major quantitative trait loci (QTLs) responsible for the reduction of rice grain shattering, a hallmark of cereal domestication, provided opportunities for in-depth investigation of domestication processes. Here, we studied nucleotide variation at the shattering loci, sh4 and qSH1, for cultivated rice, Oryza sativa ssp. indica and Oryza sativa ssp. japonica, and the wild progenitors, Oryza nivara andOryza rufipogon. The nonshattering sh4 allele was fixed in all rice cultivars, with levels of sequence polymorphism significantly reduced in both indica and japonica cultivars relative to the wild progenitors. The sh4 phylogeny together with the neutrality tests and coalescent simulations suggested that sh4 had a single origin and was fixed by artificial selection during the domestication of rice. Selection on qSH1 was not detected in indica and remained unclear in japonica. Selection on sh4 could be strong enough to have driven its fixation in a population of cultivated rice within a period of c. 100 yr. The slow fixation of the nonshattering phenotype observed at the archeological sites might be a result of relatively weak selection on mutations other than sh4 in early rice cultivation. The fixation of sh4 could have been achieved later through strong selection for the optimal phenotype.

Multilocus analysis of nucleotide variation and speciation in Oryza officinalis and its close relatives.

Nucleotide variation in 10 unlinked nuclear genes was investigated in species-wide samples of Oryza officinalis and its close relatives (Oryza eichingeri and Oryza rhizomatis). Average estimates of nucleotide diversity were the lowest in O. rhizomatis ((sil) = 0.0038) and the highest in O. eichingeri ((sil) = 0.0057) that is disjunctly distributed in Africa and Sri Lanka. These wild rice species appeared to harbor relatively low levels of nucleotide variation relative to other plant species because the diversity level of O. eichingeri is only 23-46% of those in Zea species and 35% of that in Arabidopsis thaliana. The lower nucleotide diversity in these Oryza species could be best explained by their smaller historic effective population sizes. The speciation model test indicated that O. officinalis and its close relatives might have undergone a process of population contraction since divergence from their ancestor. Incongruent topologies among 10 gene trees, particularly regarding the positions of O. eichingeri and O. rhizomatis accessions might be attributed to lineage sorting arising from ancient polymorphism and hybridization/introgression between the Sri Lankan O. eichingeri and O. rhizomatis. However, the null hypothesis of the isolation model was not rejected for any contrast between taxa, which suggested that no subsequent gene flow shaped the present patterns of nucleotide variation since their divergence and that introgression was not pervasive in this group of species. Our molecular dating provides an approximate divergence time of 0.37 Myr between 2 geographical races of O. eichingeri, much more recent compared with the times of other speciation events in this group (0.63-0.68 Myr). A long-distance dispersal from West Africa to Sri Lanka was more likely to play a role in the disjunct distribution of O. eichingeri.