Low Pairwise Distances Research Articles

Species diversity and DNA barcoding of wrasses (Teleostei: Labridae) along the southwest coast of India

Wrasses are among the most interesting and numerically abundant fish families and are widely distributed in deep and coastal marine waters. A survey was undertaken to study the diversity of labrids along the southwest coast of India between December 2020 to January 2022. A total of 98 specimens belonging to the family Labridae were collected during the study period, including nine species classified under five genera. The species included Cheilinus chlorourus, Halichoeres timorensis, Halichoeres marginatus, Halichoeres zeylonicus, Labroides dimidiatus, Stethojulis trilineata, Stethojulis interrupta, Thalassoma lunare and Thalassoma jansenii. The species were identified through morphological studies and DNA barcoding using the mitochondrial cytochrome oxidase I (COI) gene. The analyses aimed to document the morphological and molecular variations of species from different localities. The resultant molecular data were compared with morphological identifications and additional sequence data from GenBank. The results concluded that generated mtDNA sequences of wrasses matched closely with the available sequences in the GenBank. The studied species were nested in clades with the nearest related species with low Pairwise distances. The study recommends stock assessment of the labrids of India, as they are heavily exploited for both as food and ornamental fish species.

Finding a maximum k-club using the k-clique formulation and canonical hypercube cuts

Detecting low-diameter clusters is an important graph-based data mining technique used in social network analysis, bioinformatics and text-mining. Low pairwise distances within a cluster can facilitate fast communication or good reachability between vertices in the cluster. Formally, a subset of vertices that induce a subgraph of diameter at most k is called a k-club. For low values of the parameter k, this model offers a graph-theoretic relaxation of the clique model that formalizes the notion of a low-diameter cluster. Using a combination of graph decomposition and model decomposition techniques, we demonstrate how the fundamental optimization problem of finding a maximum size k-club can be solved optimally on large-scale benchmark instances that are available in the public domain. Our approach circumvents the use of complicated formulations of the maximum k-club problem in favor of a simple relaxation based on necessary conditions, combined with canonical hypercube cuts introduced by Balas and Jeroslow.

Complete mitochondrial genomes of two lenoks, Brachymystax lenok and Brachymystax lenok tsinlingensis

The circular mitochondrial genomes of Brachymystax lenok and B. lenok tsinlingensis are 16,832 and 16,669 bp in length, respectively. The mitogenomes of two lenoks shared common features with those of other teleosts in terms of gene arrangement, base composition, and transfer RNA structures. The two genomes have an overall nucleotide sequence identity of 98.3%. Through the comparisons between the two lenoks, we found their gene arrangement, composition, and sizes are the same, and the A+T content is identical. As with other freshwater salmonids, a T-type mononucleotide microsatellite and various tandem repeats were identified in the control regions of the lenoks. The low pairwise distance (2.1%) inferred from 12 mitochondrial protein-coding genes on heavy strand showed close proximity of B. lenok and B. lenok tsinlingensis.

MOLECULAR INSIGHTS INTO THE BIOGEOGRAPHY AND SPECIES STATUS OF NEW ZEALAND'S ENDEMIC LATRODECTUS SPIDER SPECIES; L. KATIPO AND L. ATRITUS (ARANEAE, THERIDIIDAE)

New Zealand's endemic sand dune Latrodectus widow spider species, L. katipo and L. atritus, possess behavioral and physiological attributes likely to promote dispersal over large distances. Morphological, physiological and behavioral similarities between L. katipo and L. hasselti, an Australian endemic, suggest gene flow may occur across the Tasman Sea. In this study we examine intraspecific and interspecific genetic relationships within the ND1 gene region between L. katipo, L. atritus, L. hasselti and L. hesperus to assess whether the genetic evidence supports current taxonomic species designations. We found low interspecific pairwise distances among L. katipo and L. atritus populations, suggesting either introgression, incomplete lineage sorting, or that the current taxonomic distinction between the two species may be invalid. Parsimony and maximum likelihood analyses were inconclusive as to the rela- tionships between the New Zealand Latrodectus species and the Australian L. hasselti. Low pairwise distances between L. hasselti and the New Zealand widow fauna indicated that L. katipo and L. atritus were not present in New Zealand before the fragmentation of Gondwana.