Identifying Differential Gene Expression in Wing Polymorphism of Adult Males of the Largest Water Strider: De novo Transcriptome Assembly for Gigantometra gigas (Hemiptera: Gerridae)

Geomorphic impacts within Red River Fault and island shifting as witnessed by the phylogeography of the largest water strider

Palaeogeological events and climate oscillations profoundly impact the demographics and distributions of small-range species, increasing the extinction risk. The largest water strider worldwide, Gigantometra gigas (Hemiptera: Gerridae), exhibits restricted distributions in Vietnam and southern China. Herein, we generated three genomic datasets (mitogenomes, 146 nuclear protein-coding genes and single nucleotide polymorphisms) with ecological niche modelling (ENM) to explicitly test whether the present-day distribution of G. gigas actually resulted from geographical and climatic effects. We found that the origin of this largest water strider reached the divergence time of the genus within Gerridae, providing a greater opportunity to explore its response to geographic movements. The right-lateral motion of the Red River Fault facilitated the divergence of two phylogeographic lineages, resulting in the "north-south component" genetic pattern in G. gigas. The Hainan and southeast Vietnam populations of the southern linage were completely separated by the Beibu Gulf but exhibited similar genetic compositions, confirming that Hainan had a continental origin and that Hainan Island joined with the Indo-China Peninsula to promote gene exchange among populations. Additionally, we noticed the low genetic diversity but long demographic history of the northern lineage, which displayed population dynamics opposite to those of other organisms. Integrating the demographic changes and ENM findings revealed that suitable habitat contraction and rapid demographic decline during the Last Glacial Maximum (LGM) triggered the low genetic diversity of the northern lineage. Overall, the demographic history of the largest water strider was mainly shaped by geographical features, and first provided evidence from the phylogeographic perspective of aquatic insects to support the hypothesis of Hainan Island shifting.

Analysis of Differentially Expressed Genes of Chrysoperla sinica Related to Flight Capacity by Transcriptome

The lacewing Chrysoperla sinica (Tjeder) is a common natural enemy of many insect pests in China and is frequently employed for biological control programs. Adults make migratory flights after emergence, which reduces their effectiveness as biological control agents. Previously, we proved that 2-d-old unmated females exhibited significantly stronger flight ability than 3-d-old ones. Meanwhile, 3-d-old unmated adults flew significantly longer distances than mated ones. In this study, Illumina RNA sequencing was performed to characterize differentially expressed genes (DEGs) between virgin and mated adults of different ages in a single female strain of C. sinica. In total, 713,563,726 clean reads were obtained and de novo assembled into 109,165 unigenes with an average length of 847 bp (N50 of 1,754 bp), among which 4,382 (4.01%) unigenes matched known proteins. Based on these annotations, many putative transcripts were related to C. sinica's flight capacity and muscle structure, energy supply, growth, development, environmental adaptability, and metabolism of nutritional components and bioactive components. In addition, the differential expression of transcripts between different ages and mating status were analyzed, and DEGs participating in flight capacity and muscles were detected, including glutathione hydrolase, NAD-specific glutamate dehydrogenase, aminopeptidase, and acidic amino acid decarboxylase. The DEGs with functions associated with flight capacity and muscles exhibited higher transcript levels for younger (2 d--old) virgins. This comprehensive C. sinica transcriptomic data provide a foundation for a better understanding of the molecular mechanisms underlying the flight capacity to meet the physiological demands of flight muscles in C. sinica.