Against the odds of unusual mtDNA inheritance, introgressive hybridisation and phenotypic plasticity: systematic revision of Korean freshwater gastropods (Semisulcospiridae, Cerithioidea)

Abstract

The systematics of Semisulcospiridae in Korea is critically revised by means of comparative anatomy, including comprehensive review of type material and mitochondrial phylogenetics (sequences of COI and 16S). The family is represented by two genera with different reproductive modes: Semisulcospira Boettger, 1886 is viviparous and contains three species (S. coreana (Martens, 1886), S. gottschei (Martens, 1886) and S. forticosta (Martens, 1886)) while Koreoleptoxis Burch & Jung, 1988 is oviparous and also contains three species (K. globus (Martens, 1886), K. nodifila (Martens, 1886), K. tegulata (Martens, 1894)). Koreanomelania Burch & Jung, 1988 is synonymised with Koreoleptoxis. Species can be distinguished by differences in shell shape and sculpture. They form well-differentiated clusters in the mitochondrial phylogeny, consistently revealing lower intraspecific than interspecific genetic distances. Sequences of Japanese Semisulcospira species fall into three distinct major clades (A–C), rendering Semisulcospira non-monophyletic in the mitochondrial tree. Only a small number of Japanese samples were closely related to the Korean clade (Clade C). The numerically predominant Japanese mitochondrial Clade B exhibited increased lineage divergence and, when translated into amino acids, significantly more amino acid substitutions in comparison with Korean species. I conclude that these Japanese sequences may be paralogous and/or may undergo non-neutral evolution. Hence, they are not suitable for inferring phylogenetic relationships.