ABSTRACT
A deeper exploration of the causes of variation in variability seems worthwhile. If we see a population of organisms with a limited distribution and low variabilitylike the coelacanth, Latimeria chalumnae Smith, 1939-it is easy to accept that this is a single species (Casane & Laurenti, 2013). By contrast, the relationships among the highly mobile, fast swimming, predatory tuna, genus Thunnus, have been a longstanding phylogenetic problem. The Atlantic Tuna (Thunnus thynnus (Linnaeus, 1758)) and Pacic Tuna (Thunnus orientalis (Temminck & Schlegel, 1844)) are so closely related that they have alternatively been considered species, or subspecies, and there is evidence for hybridisation, shown in high levels of mitochondrial introgression, between these and other congeneric species (Kitagawa et al., 2000; Díaz-Arce et al., 2016). In the terrestrial realm, the Venus Flytrap, Dionaea muscipula Ellis, has a small native range in the southeastern United States and a distinctive morphology and lifestyle. But another group of North American carnivorous plants is much more widespread and morphologically variable, the Trumpet Pitcher Sarracenia purpurea Linnaeus. Although a number of putative subspecies or varieties of S. purpurea have been named, the variety of pitcher shape and colour seems to simply reect the changing environment from Florida to Northern Canada rather than diverging lineages of pitcher plants (Ellison et al., 2004; Ellison & Gotelli, 2009). In a species that is variable and extends over a very large range, does broad variation represent one diverse lineage with individuals that respond to their local conditions, or does that variation mask multiple lineages that have not been recognised as separate species? All species could be placed somewhere on a spectrum of condence in their species assessment, and neither the clearly dened, nor the very fuzzy, is the exception or the rule.
