杂色蛤仔与菲律宾蛤仔的染色体核型比较及聚类分析OA

The taxonomic relationship between Ruditapes variegatus and Ruditapes philippinarum remains unresolved owing to morphological similarities and classification challenges that require innovative approaches.Karyotype analysis provides essential cytogenetic characters for species delimitation and evolutionary studies.We established the first complete karyotype of R.variegatus and conducted a rigorous comparative analysis with R.philippinarum.Using trochophore larvae,we obtained metaphase chromosomes via optimized protocols involving hypotonic treatment,hot-drop slide preparation,and Giemsa staining.We systematically measured chromosome number,relative length,and arm ratio,determining detailed karyotype formulas,fundamental numbers,and asymmetry indices.We calculated karyotype resemblance-near coefficients and performed comprehensive unweighted pair group method with arithmetic mean cluster analysis,incorporating data from multiple bivalve species to provide a broad taxonomic context and quantitatively assess phylogenetic relationships.Both species shared a diploid number of 2n=38 yet exhibited profoundly different chromosomal architectures.R.variegatus demonstrated pronounced karyotypic asymmetry with a formula of 2n=20m+4sm+14t,NF=62 and an asymmetry index of 37%.Conversely,R.philippinarum displayed remarkable symmetry with a formula of 2n=28m+10sm,NF=76 and 0%asymmetry,which is a configuration rarely observed in bivalves.Further analysis revealed that R.philippinarum had a mean arm ratio of 4.78,which was significantly higher than the 1.47 of R.variegatus.Quantitative evaluation yielded a karyotype resemblance-near coefficient of −0.5156 between species,indicating minimal chromosomal homology and substantial evolutionary divergence.The observed karyotypic divergence from perfect symmetry in R.philippinarum to high asymmetry in R.variegatus suggests different evolutionary trajectories potentially influenced by distinct ecological adaptations,genomic stabilization mechanisms,and chromosomal rearrangement histories.The symmetric metacentric-rich karyotype of R.philippinarum may underlie its phenotypic plasticity,environmental tolerance,and successful global distribution.The asymmetric telocentric-dominated karyotype of R.variegatus may indicate specialized niche adaptation or alternative chromosomal evolutionary pathways.This study establishes the foundational karyotype for R.variegatus and provides decisive cytogenetic evidence for its taxonomic distinction from R.philippinarum,clarifying long-standing systematic uncertainties.Our integrated methodology,which combines classical karyotyping with quantitative similarity indices and phylogenetic clustering,provides an effective framework for resolving complex taxonomic relationships in marine bivalves.These findings significantly advance understanding of chromosomal evolution within the Veneridae family and offer valuable insights for conservation genetics,aquaculture breeding programs,and future phylogenomic studies of commercially important shellfish species.This study contributes substantially to marine biodiversity documentation and provides critical baseline data for the sustainable management of these ecologically and economically valuable clam resources.