Morphological diversity of two phylogeographic lineages of Arctic grayling (<i>Thymallus arcticus</i>) in Alberta

Biodiversity is declining globally, necessitating conservation strategies that protect genetic and phenotypic diversity within species. In North America, Arctic grayling ( Thymallus arcticus (Pallas, 1776)) exhibit substantial mitochondrial DNA divergence corresponding to two phylogeographic lineages termed Nahanni and Beringia. However, phenotypic variation has not been widely explored and there has been no direct comparison between the two lineages. This study examined morphological variation between these lineages in Alberta and whether observed variability was associated with sex. Morphology of T. arcticus was investigated using two approaches after assigning fish to a lineage based on their mitochondrial DNA haplotype. Geometric morphometric techniques were used to assess body shape differences between the two lineages and sex considering 16 two-dimensional landmarks. Twelve meristic characters were also enumerated and compared. Subtle yet significant differences in body shape and three meristic traits (lateral line scales, branched pelvic rays, and pyloric caeca) were identified, with body shape analysis resulting in 95% accuracy in lineage assignment. Body shape was also influenced by sex, corroborating evidence of sexual dimorphism in T. arcticus. These results support potential classification of the lineages as evolutionary significant units worthy of independent protection.