Hybridization and introgression in sympatric and allopatric populations of four oak species.

BACKGROUND: Hybridization and introgression are vital sources of novel genetic variation driving diversification during reticulated evolution. Quercus is an important model clade, having extraordinary diverse and abundant members in the Northern hemisphere, that are used to studying the introgression of species boundaries and adaptive processes. China is the second-largest distribution center of Quercus, but there are limited studies on introgressive hybridization. RESULTS: Here, we screened 17 co-dominant nuclear microsatellite markers to investigate the hybridization and introgression of four oaks (Quercus acutissima, Quercus variabilis, Quercus fabri, and Quercus serrata) in 10 populations. We identified 361 alleles in the four-oak species across 17 loci, and all loci were characterized by high genetic variability (HE = 0.844-0.944) and moderate differentiation (FST = 0.037-0.156) levels. A population differentiation analysis revealed the following: allopatric homologous (FST = 0.064) < sympatric heterogeneous (FST = 0.071) < allopatric heterogeneous (FST = 0.084). A Bayesian admixture analysis determined four types of hybrids (Q. acutissima × Q. variabilis, Q. fabri × Q. serrata, Q. acutissima × Q. fabri, and Q. acutissima × Q. variabilis × Q. fabri) and their asymmetric introgression. Our results revealed that interspecific hybridization is commonly observed within the section Quercus, with members having tendency to hybridize. CONCLUSIONS: Our study determined the basic hybridization and introgression states among the studied four oak species and extended our understanding of the evolutionary role of hybridization. The results provide useful theoretical data for formulating conservation strategies.

Dynamic Response Characteristics of a Sealing Airbag under Different Impact Types and Impact Pressures.

The rapid isolation of the disaster area underground coal mine can effectively prevent the spread of disaster accidents. Rapid sealing of the disaster area can be realized through sealing in the form of an inflatable capsule. The cushioning performance of the inflatable capsule to an explosion shock wave is an important factor affecting sealing reliability. The response process of a small inflatable capsule under an explosion shock wave was studied using the pipeline explosion experimental system to examine the dynamic response characteristics of the coal mine airbag under the impact load. The deformation buffering process of the inflatable and hydrogel capsules was tested by a drop hammer impact test. Results showed that under the action of three explosion impact pressures (0.3, 0.4, and 0.5 MPa), the inflatable capsule could absorb 22% of the impact energy through its deformation and reduce the maximum explosion impact pressure. Moreover, under the impact of falling weight at different heights (20, 30, 40, and 50 cm), the cushioning process of the inflatable and hydrogel capsules absorbed the impact energy through the compression deformation of the capsule, which is the loading stage. When the hammer speed decreased to zero, the deformation and absorbed energy of the capsule were at maximum. The capsule recovered its deformation and converted the absorbed energy into kinetic energy to make the hammer rebound, which is the unloading stage of the capsule. The capsule body realized the absorption and transfer of impact energy through its deformation and completed the energy buffer through the dynamic response process of multiple loading and unloading.

Sympatric genome size variation and hybridization of four oak species as determined by flow cytometry genome size variation and hybridization.

The Quercus species serve as a powerful model for studying introgression in relation to species boundaries and adaptive processes. Coexistence of distant relatives, or lack of coexistence of closely relative oak species, introgression may play a role. In the current study, four closely related oak species were found in Zijinshan, China. We generated a comprehensive genome size (GS) database for 120 individuals of four species using flow cytometry-based approaches. We examined GS variability within and among the species and hybridization events among the four species. The mean GSs of Q. acutissima, Q. variabilis, Q. fabri, and Q. serrata var. brevipetiolata were estimated to be 1.87, 1.92, 1.97, and 1.97 pg, respectively. The intraspecific and interspecific variations of GS observed among the four oak species indicated adaptation to the environment. Hybridization occurred both within and between the sections. A hybrid offspring was produced from Q. fabri and Q. variabilis, which belonged to different sections. The GS evolutionary pattern for hybrid species was expansion. Hybridization between the sections may be affected by habitat disturbance. This study increases our understanding of the evolution of GS in Quercus and will help establish guidelines for the ecological protection of oak trees.

Experimental Study on Thermosensitive Hydrogel Used to Extinguish Class A Fire.

Hydrogels are crosslinked polymers that become fully swollen when placed in aqueous environments. They are widely used in the field of firefighting because they can remarkably increase the viscosity and wettability of water. In this study, a thermosensitive hydrogel used to effectively suppress class A fire was synthesized by using methylcellulose, sodium polyacrylate, and magnesium chloride. The structure, surface activity and viscosity of the hydrogel were characterized. Fire extinguishing performance was evaluated based on small-scale and large-scale experiments. The results showed that a phase transition of the hydrogel occurred when the temperature rose from 50 °C to 80 °C. After the phase transition, the hydrogel showed a higher viscosity and lower surface tension, which was conducive to attach to the surface of the burning material and acting as an effective barrier to isolate oxygen. The small-scale fire extinguishing tests indicated that the concentration of the hydrogel solution has an eminent influence on fire extinguishing performance. The optimum concentration for extinguishing performance was around 6 wt%. The large-scale experiments demonstrated that the fire-extinguishing performance of this thermosensitive hydrogel was superior to the two other commercial water-based fire extinguishing agents, as it prevented re-ignition highly efficiently.