BACKGROUND: Apple snails from the genus Pomacea have spread widely in paddy fields and other wetlands of southern China since their introduction in the 1980s. Pomacea spp. are commonly identified using mitochondrial COI sequences. However, sequencing the nuclear elongation factor 1-alpha (EF1⊍) gene revealed genetic introgression between field populations of P. canaliculata and P. maculata, which produce surviving hybrids in laboratory crossbreeding experiments. RESULTS: In this study, we sequenced 1054 EF1⊍ clones to design specific primers and established a fast and accurate multiplex polymerase chain reaction (PCR) method for genotyping EF1⊍. Combined with genotyping P. canaliculata and P. maculata based on mitochondrial COI and nuclear EF1⊍, we revealed the genetic introgression patterns of 30 apple snail populations in China. Purebred and hybrid individuals of P. canaliculata were widely distributed, while pure maculata-EF1⊍ type was detected only in a few individuals identified as P. canaliculata based on COI sequences. Each egg clutch had one to three genetic patterns, indicating multiple paternity or segregation in the progeny of hybrids. The higher percentages of hybrids in both wild populations and progeny than the homozygotes indicated a potential heterosis in the apple snail populations. Additionally, egg size and clutch size of the apple snails became homogeneous among the non-native populations exhibiting introgression hybridization. CONCLUSION: Our findings emphasize the value of apple snails as a model to study the mechanisms and impacts of introgressive hybridization on fitness traits.

The production of xylanase (TrxA) byTrichoderma reeseiJL-1 in solid-state fermentation (SSF) was optimized by response surface methodology (RSM). Results revealed that factors of concentration of added ammonium sulfate, and moisture content had significant effect on the TrxA production (P<0.05). The maximum xylanase activity (485.0 U/g U/g dry fermentation product) was obtained at 2.9% the ammonium sulfate by employing wheat bran as the solid substrate, 61.6% moisture content and 59.5-h fermentation, which was close to the predicted one, and was 1.8 times as high as that of the basic medium. The optimum temperature and pH for TrXA activity were 45°C and pH 5.0, respectively. Over 90% of xylanase activity was retained after treatment of the enzyme by preincubation over a pH range of 3.0-5.0 for 1 h at 25°C. TrxA exhibitedKmandVmaxvalues of 1.458mg/mL and 25.316 μmol/min/ml, respectively. In the presences of metal ions such as Mn2+the activity of the enzyme increased. Whereas strong inhibition of the enzyme activity was observed in the presences of Fe3+and Ca2+.