The Historical Speciation of Mauremys Sensu Lato: Ancestral Area Reconstruction and Interspecific Gene Flow Level Assessment Provide New Insights

Genome Evolution and the Future of Phylogenomics of Non-Avian Reptiles

Non-avian reptiles comprise a large proportion of amniote vertebrate diversity, with squamate reptiles-lizards and snakes-recently overtaking birds as the most species-rich tetrapod radiation. Despite displaying an extraordinary diversity of phenotypic and genomic traits, genomic resources in non-avian reptiles have accumulated more slowly than they have in mammals and birds, the remaining amniotes. Here we review the remarkable natural history of non-avian reptiles, with a focus on the physical traits, genomic characteristics, and sequence compositional patterns that comprise key axes of variation across amniotes. We argue that the high evolutionary diversity of non-avian reptiles can fuel a new generation of whole-genome phylogenomic analyses. A survey of phylogenetic investigations in non-avian reptiles shows that sequence capture-based approaches are the most commonly used, with studies of markers known as ultraconserved elements (UCEs) especially well represented. However, many other types of markers exist and are increasingly being mined from genome assemblies in silico, including some with greater information potential than UCEs for certain investigations. We discuss the importance of high-quality genomic resources and methods for bioinformatically extracting a range of marker sets from genome assemblies. Finally, we encourage herpetologists working in genomics, genetics, evolutionary biology, and other fields to work collectively towards building genomic resources for non-avian reptiles, especially squamates, that rival those already in place for mammals and birds. Overall, the development of this cross-amniote phylogenomic tree of life will contribute to illuminate interesting dimensions of biodiversity across non-avian reptiles and broader amniotes.

Chromosome-level genome assembly of the Chinese three-keeled pond turtle (Mauremys reevesii) provides insights into freshwater adaptation

Mauremys reevesii is an endangered freshwater turtle that symbolizes longevity in Chinese culture. Despite its importance, genetic studies of this species remain limited, with no genomic sequence reported to date. Here, we report a high-quality, chromosome-level genomic sequence of M. reevesii obtained using a combination of Nanopore and Hi-C sequencing technologies. The 2.37 Gb M. reevesii genome was assembled from a total of ~226.80 Gb of Nanopore sequencing data. The M. reevesii genome contig N50 is 34.73 Mb, the highest value in published turtle genomes. In total, 18,238 genes were functionally annotated. The contigs were clustered and ordered onto 27 pseudochromosomes covering ~96.55% of the genome assembled with Hi-C data. To explore genome evolution, synteny analysis was performed between M. reevesii (freshwater turtle) and Gopherus evgoodei (terrestrial turtle) genomes. In general, each chromosome of M. reevesii corresponded to one chromosome of Gopherus evgoodei, but some interchromosomal rearrangements occurred between the two species based on the assembled genomes. These interchromosomal rearrangements were further confirmed by mapping of the long-read nanopore data to the assembly. The reconstructed demographic history showed varied effective population size among freshwater, marine and terrestrial turtles. We also discovered expansion of genes related to the innate immune system in M. reevesii that may provide defence against freshwater pathogens. The high-quality genomic sequence provides a valuable genetic resource for further studies of genetics and genome evolution in turtles.

The complete mitochondrial genome of the endangered Assam Roofed Turtle, Pangshura sylhetensis (Testudines: Geoemydidae): Genomic features and phylogeny

The Assam Roofed Turtle, Pangshura sylhetensis is an endangered and least studied species endemic to India and Bangladesh. The present study decodes the first complete mitochondrial genome of P. sylhetensis (16,568 bp) by using next-generation sequencing. The assembly encodes 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), two ribosomal RNAs (rRNAs), and one control region (CR). Most of the genes were encoded on the majority strand, except NADH dehydrogenase subunit 6 (nad6) and eight tRNAs. All PCGs start with an ATG initiation codon, except for Cytochrome oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 5 (nad5), which both start with GTG codon. The study also found the typical cloverleaf secondary structures in most of the predicted tRNA structures, except for serine (trnS1) which lacks of conventional DHU arm and loop. Both Bayesian and maximum-likelihood phylogenetic inference using 13 concatenated PCGs demonstrated strong support for the monophyly of all 52 Testudines species within their respective families and revealed Batagur trivittata as the nearest neighbor of P. sylhetensis. The mitogenomic phylogeny with other amniotes is congruent with previous research, supporting the sister relationship of Testudines and Archosaurians (birds and crocodilians). Additionally, the mitochondrial Gene Order (GO) analysis indicated plesiomorphy with the typical vertebrate GO in most of the Testudines species.

The complete mitochondrial genome of the Cyclemys fusca (Chelonia: Geoemydidae)

The complete mitochondrial genome (mitogenome) of Cyclemys fusca was obtained and characterized in this study. The circular molecule is 16,491 bp in length and contained 13 protein-coding genes (PCGs), two ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and one non-coding region (control region). Its gene arrangement type is identical to the type of most vertebrate. All protein-coding genes initiate with ATG as start codon, except for COI started with GTG. Interestingly, COI and ND6 end up with AGG. The complete mitogenome of C. fusca provides the basic data to research molecular systematics of Geoemydidea.

The complete mitochondrial genome of Geochelone sulcata

The complete mitochondrial genome of Geochelone sulcata was determined using PCR, Long-PCR with length of 16,692 bp. The genome organization, gene order, and base composition was similar to typical vertebrate. Gene content included 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and one control region. Otherwise, the lack of C, as same as in the other species of Testudinidae, was detected in arms of tRNA^Lys gene in G. sulcata. In addition, an extra nucleotide A was discovered in ND3 gene in G. sulcata. The complete mitogenome of G. sulcata provides the basic data to research molecular systematics of Testudinidae.

The complete mitochondrial genome of the Heosemys depressa (Testudines, Geoemydidae)

The complete mitochondrial genome of Heosemys depressa was obtained and characterized in this study. The mitochondrial genome is a circular molecule of 16,773bp in length, and harbours 13 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes, 22 transfer RNA (tRNA) genes, and 1 non-coding D-loop region (control region). Its gene arrangement type is identical to the type of most vertebrate. Phylogenetic analysis suggests that H. depressa is closely related to H. annandalii than to the other species. Our data provide a useful resource for the phylogenetic studies of genus Heosemys.

Complete mitochondrial genome of the Cyclemys pulchristriata (Chelonia: Geoemydidae)

In this study, we obtained complete mitochondrial genome sequence of Cyclemys pulchristriata. The mitochondrial genome reaches a length of 16,527 bp, containing 13 protein-coding genes (PCGs), 22tRNA genes, 2 rRNA genes and 1 control region. All protein-coding genes initiate with ATG as start codon, except for CO1 started with GTG. Most protein-coding genes ended by TAA as stop codon. Interestingly, there is an extra nucleotide A insertion in ND3 gene in C. pulchristriata. This study provides information on the genetic resources of C. pulchristriata that will contribute to protect this species.