Genetic differentiation of cryptic species

Abstract

Cryptic species are also known as sibling species. They are present in all kinds of organisms and are often referred to as species complexes, i.e. closely related species that appear as a single species based on morphological characters. The occurrence of cryptic species has posed problems in taxonomy, ecology, control of pests and vectors/carriers of diseases, biodiversity assessment, and other disciplines. The somatic metaphase karyotype has been customarily used in cytotaxonomic studies, and has successfully resolved many cryptic species. Gene-enzyme systems (enzymatic proteins, isoenzymes, allozymes) have been used extensively in earlier days as genetic markers for species delineation (particularly analysis of species complexes), population genetics and phylogenetic reconstruction. Currently, partial DNA nucleotide sequences of a single gene or multiple genes (nuclear and/or mitochondrial genes) are commonly used for determining/resolving cryptic species as well as phylogenetics and phylogeography. This paper discusses selected taxonomic groups of animals in which identification has proven problematic based on morphological characters. The role of genetics in differentiating/resolving cryptic species is illustrated by examples of invertebrates (nematode parasites of the genus Angiostrongylus, tephritid fruit flies of the genus Zeugodacus, Libellulid dragonflies of the genus Orthetrum, stingless bees of the genus Tetragonilla) and vertebrates (murid rats of the genera Leopoldamys and Maxomys, bats of the genus Rhinolophus).