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Simple Summary: This study investigates the genetic structure and population dynamics of invasive bullfrogs in China employing cutting-edge genomic technologies. By analyzing microsatellite loci and single nucleotide polymorphisms (SNPs), the study identifies three distinct genetic subpopulations of bullfrogs and explores their origins and dispersal pathways. Findings reveal the varying degrees of gene flow between the subpopulations and a severe bottleneck effect followed by a rapid population expansion. Comparison with American bullfrog populations highlights the differences in genetic diversity and suggests potential multiple introductions. The introduction and subsequent range expansion of the American bullfrog (Lithobates catesbeianus) is part of a rising trend of troublesome biological invasions happening in China. This detrimental amphibious invasive species has strong adaptability. After its introduction and spread, it established its own ecological niche in many provinces of China, and its range has continued to expand to more areas. Previous studies recorded the introduction time of bullfrogs and calculated the changes in their genetic diversity in China using mitochondria, but the specific introduction route in China is still unknown. Expanding upon previous research, we employed whole-genome scans (utilizing 2b-RAD genomic sequencing) to examine single nucleotide polymorphisms (SNPs) and microsatellites within Lithobates catesbeianus to screen the genomes of these invasive amphibian species from eight Chinese provinces and two U.S. states, including Kansas, where bullfrogs originate. A total of 1,336,475 single nucleotide polymorphic loci and 17 microsatellite loci were used to calculate the genetic diversity of bullfrogs and their migration pathways. Our results suggest that the population in Hunan was the first to be introduced and to spread, and there may have been multiple introductions of subpopulations. Additionally, the genetic diversity of both the SNP and microsatellite loci in the Chinese bullfrog population was lower than that of the US population due to bottleneck effects, but the bullfrogs can adapt and spread rapidly. This study will offer crucial insights for preventing and controlling future introductions into the natural habitats in China. Additionally, it will assist in devising more precise strategies to manage the existing populations and curtail their continued expansion, as well as aim to improve clarity and originality while mitigating plagiarism risk. [ABSTRACT FROM AUTHOR]

In recent years, bullfrog (Lithobates catesbeianus) has become one of the most commercially important amphibians for aquaculture in China, and its annual production has grown rapidly. However, bacterial diseases caused by Citrobacter freundii infection have resulted in enormous economic losses. The present study used RNA sequencing technology to analyze the transcriptomic profile and differentially expressed genes (DEGs) in the bullfrog liver and spleen post C. freundii infection. De novo assembly resulted in the generation of 77,556 L. catesbeianus transcripts, and 49,421 of these genes were successfully annotated to the databases. Overall, 1487 DEGs were identified in the liver group, including 788 upregulated and 709 downregulated DEGs. A total of 799 DEGs, including 311 upregulated and 488 downregulated genes, were detected in the spleen groups. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed significantly enriched pathways, including pathways involved in metabolism and immune responses. The processes in which the DEGs were enriched were those related to metabolic activities, including the lipid metabolism pathway, amino acid pathway, immune‐related pathway, and inflammatory responses. The results of this study provide insight into the response of bullfrogs against C. freundii at the transcriptome level and reveal the mechanism of the immune response against C. freundii. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome of Lithobates catesbeianus (Anura: Ranidae) is sequenced to analyze the gene arrangement. It is a circular molecule of 18,241 bp in length including 37 genes typically found in other frogs. The AT content of the overall base composition of L. catesbeianus is 59.9%. The length of control region is 2783 bp with 66.0% AT content. Protein-coding genes begin with ATG as start codon except except ND1 and ATP6 began with ATA, COI and ND4L with GTG, and ND2 with ATT. COI end with AGG as stop codon, COII and ND6 end with AGA, ND2 end with TAG, ATP8. ND4L. ND5 and Cytb end with TAA, and the other five PCGs end with a incomplete stop codon (a single stop nucleotide T).