Introgressive hybridization between two non-native apple snails in China: widespread hybridization and homogenization in egg morphology.

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 (EF1α) 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 EF1α clones to design specific primers and established a fast and accurate multiplex polymerase chain reaction (PCR) method for genotyping EF1α. Combined with genotyping P. canaliculata and P. maculata based on mitochondrial COI and nuclear EF1α, 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-EF1α 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. © 2020 Society of Chemical Industry.

Parasitic insect-derived miRNAs modulate host development.

Parasitic wasps produce several factors including venom, polydnaviruses (PDVs) and specialized wasp cells named teratocytes that benefit the survival of offspring by altering the physiology of hosts. However, the underlying molecular mechanisms for the alterations remain unclear. Here we find that the teratocytes of Cotesia vestalis, an endoparasitoid of the diamondback moth Plutella xylostella, and its associated bracovirus (CvBV) can produce miRNAs and deliver the products into the host via different ways. Certain miRNAs in the parasitized host are mainly produced by teratocytes, while the expression level of miRNAs encoded by CvBV can be 100-fold greater in parasitized hosts than non-parasitized ones. We further show that one teratocyte-produced miRNA (Cve-miR-281-3p) and one CvBV-produced miRNA (Cve-miR-novel22-5p-1) arrest host growth by modulating expression of the host ecdysone receptor (EcR). Altogether, our results show the first evidence of cross-species regulation by miRNAs in animal parasitism and their possible function in the alteration of host physiology during parasitism.

Cotesia vestalis teratocytes express a diversity of genes and exhibit novel immune functions in parasitism.

Some endoparasitoid wasps lay eggs that produce cells called teratocytes. In this study, we sequenced and analyzed the transcriptome of teratocytes from the solitary endoparasitoid Cotesia vestalis (Braconidae), which parasitizes larval stage Plutella xylostella (Plutellidae). Results identified many teratocyte transcripts with potential functions in affecting host immune defenses, growth or metabolism. Characterization of teratocyte-secreted venom-like protein 8 (TSVP-8) indicated it inhibits melanization of host hemolymph in vitro, while two predicted anti-microbial peptides (CvT-def 1 and 3) inhibited the growth of bacteria. Results also showed the parasitized hosts lacking teratocytes experienced higher mortality after immune challenge by pathogens than hosts with teratocytes. Taken together, these findings indicate that C. vestalis teratocytes secrete products that alter host immune functions while also producing anti-microbial peptides with functions that help protect the host from infection by other organisms.