Genetic divergence and geographic diversification in Nautilus

Abstract

Despite exhaustive investigation of present-day Nautilus, the phylogenetic relationships of the five or six recognized species within this genus remain unclear. Mitochondrial and nuclear DNA sequence data plus a suite of morphological characters are used to investigate phylogenetic relationships. Systematic analysis of the morphological variation fails to characterize described species as independent lineages. However, DNA sequence analysis indicates that there are three geographically distinct clades consisting of western Pacific, eastern Australian/Papua-New Guinean, and western Australian/Indonesian forms. The morphologically and genetically distinct species Nautilus scrobiculatus falls outside the three geographically recognized assemblages. Members of the genus Nautilus also exhibit low levels of sequence divergence. All these data suggest that Nautilus is currently undergoing diversification, which may have begun only several million years ago. These data also suggest that some of the morphological features used to define Nautilus species may simply represent fixed variations in isolated populations within the same species.

The Paleocene cephalopod fauna from Pebble Point, Victoria (Australia) – fulcrum between two Eras

“…New DNA work on Nautilus (Wray et al, 1995;Bonacum et al, 2010) as well as work conducted by one of the authors here (Vandepas et al, in review) has shown that species of Nautilus are, in fact, highly variable, and that rather than the currently "accepted" species Nautilus pompilius (the type species), N. macromphalus, N. stenomphalus, and N. belauensis (with N. repertus also accepted in some quarters), there is now good understanding that along the Great Barrier Reef there is a complete morphological mixture of characters that have been used to separate N. stenomphalus from N. pompilius -and that there is no difference in the COI gene between the morphologically distinct end members of what has been called N. pompilius and N. stenomphalus. In similar fashion, N. belauensis Saunders is now seen as simply a large N. pompilius, as is N. repertus.…”

Molecular genetic analyses of species boundaries in the sea

“…Other genera that have been recently analyzed include Hydrobia (Ponder & Clark, 1988), Stramonita (Liu et al, 1991), Alviniconcha (Denis et al, 1993), Trochus (Borsa & Benzie, 1993), Tectus (Borsa & Benzie, 1993), Austrocochlea (Parsons & Ward, 1994), Drupella (Johnson & Cumming, 1995), Columbella (Oliverio, 1995), Patella (Côrte-Real et al, 1996a,b;Ridgway et al, 1998), Nassarius (Sanjuan et al, 1997), Nucella (Kirby et al, 1997;Marko, 1998), and Dendronotus (Thollesson, 1998). Cephalopods are comparatively less studied, but genera where species boundaries have recently been revised or identified based on genetic analyses include Photololigo (Yeatman & Benzie, 1994), Nautilus (Wray et al, 1995), Sepioteuthis (Izuka et al, 1996) and Illex (Carvalho & Nigmatullin, 1998).…”

“…Consequently, the number of genetic studies that have resulted in the synonymization of species is probably higher for mollusks than most other marine invertebrate phyla. The above-mentioned studies of Donax (Adamkewicz & Harasewych, 1996) and Nautilus (Wray et al, 1995) are but two examples of numerous cases where distinctions between sympatric taxa based on shell morphology were not supported by genetic data. On the other hand, genetic data have also demonstrated that minor differences in shell morphology (or other characters) can sometimes be taxonomically important (e.g.…”

Genetic diversity of isolated populations of Nautilus pompilius (Mollusca, Cephalopoda) in the Great Barrier Reef and Coral Sea

“…The Nautiloidea represent a distinctly monophyletic group, containing the only extant cephalopods with an external shell (Bonnaud et al 2004). The pearly Nautilus (Mollusca, Cephalopoda) is a modern survivor of a previously abundant group of shelled cephalopods and it is a direct descendant of these fossil forms (Woodruff et al 1987;Wray et al 1995;Boyle and Rodhouse 2005). Although often cited as a living fossil (Wells 1986;Davis 1987;Basil et al 2000) genetic studies indicate that current Nautilus species may only have originated between 1 and 5 million years ago (Woodruff et al 1987).…”