International Journal of Molecular Zoology, 2025, Vol.15, No.2, 58-68 http://animalscipublisher.com/index.php/ijmz 59 and reveal fine-scale spatial structure. Structural genomic variation, including insertions, deletions, and duplications, plays a role in the adaptability, and invasiveness of non-model species. In L. fulica, such variation may be associated with traits, like rapid population expansion, environmental tolerance, and resistance to control measures, although these aspects remain understudied, and need to be further explored using advanced genomic tools (Morrison et al., 2015; Vijayan et al., 2022). This study used whole genome sequencing and structural variation analysis to reveal the evolutionary genomics of L. fulica. We combined genomic data with its ecological information and population statistics to figure out, why it is so adapted to the environment, why it is so invasive, and the genetic reasons behind these characteristics. Such a result not only provides a scientific basis for its management, but also enables us to have a more comprehensive understanding of the evolutionary laws of invasive species. 2 Genome Assembly and Annotation of the Giant African Land Snail 2.1 Sequencing strategies and assembly indicators The latest advancements in sequencing technology have enabled high-quality, chromosomal level genome assembly in African land snails, particularly Achatina fulica andAchatina immaculata. In the research of A. fulica, the method of long-read sequencing of Pacific Biosciences (PacBio) combined with Hi-C chromatin conformation capture was adopted, obtaining approximately 101.6 Gb of long-read data, and the final assembly size was 1.85 Gb. This assembly achieved 726 kb of contig N50 and 59.6 Mb of scaffold N50, and 99.32% of the contigs were anchored to 31 chromosomes, indicating that the genome has a high degree of continuity and integrity (Guo et al., 2019). The assembly quality was further verified through BUSCO (Benchmarking Universal Single-Copy Orthologs) assessment and read segment comparison. The results confirmed the high continuity and high integrity of the genome. Similarly, A. immaculata also constructed A chromosomal level reference genome, providing support for robust comparative analysis (Liu et al., 2021). These assembly achievements are of milestone significance. Among them, A. fulica is the first terrestrial mollusk genome to reach this resolution, providing an important resource for evolutionary and ecological research. 2.2 Genome annotation and gene prediction A total of 23 726 protein-coding genes of the A. fulica genome was identified, among which 96.34% obtained functional annotation through homology analysis, and ab initio prediction method (Guo et al., 2019; Toma et al., 2023). The annotation process integrated transcriptome data, protein homology information and structural prediction tools, ensuring the comprehensiveness of gene identification. It is worth noting that, this genome shows an extremely high proportion of repetitive sequences (up to 71%), a feature consistent with the genomes of other large gastropods, and poses unique challenges for assembly and annotation. Functional annotations show that gene families related to carbohydrate and carbohydrate metabolism, mucus biosynthesis, and shell biominalization play an important role, reflecting the ecological adaptability and invasion potential of snails (Toma et al., 2023). The expansion of gene families such as amylase, cellulase and chitinase is related to their vigorous appetite and rapid growth, while the ascorbic acid biosynthesis pathway is associated with shell formation. 2.3 Comparative genomics with related gastropods In comparative genomics analysis, the comparison results of A. fulica, A. immaculata and other mollusks have provided us with many clues about evolutionary events, and adaptation mechanisms. Analyses of macroscopic collinearity, collinearity blocks and Hox gene clusters revealed that, both species of snails experienced a genome-wide replication (WGD) event approximately 70 million years ago (Liu et al., 2021). Some people hold the view that this WGD helped them enhance their ecological adaptability, and also promoted the process of terrestrial biogenesis, especially in the environmental changes, following the Cretaceous-Paleogene mass extinction event.
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