COLOR PATTERNS IN RECENT NAUTILUS SPECIES

Recent molecular analyses of modern nautilus populations have yielded highly resolved phylogenies detailing relationships among species (Cambosch et al., 2017). According to these results, Allonautilus is the sister taxon to all other nautilus, which then group according to three geographic areas: the southwest Pacific (e.g., Vanuatu, Fiji, New Caledonia), the Coral Sea (e.g., Papua New Guinea, Eastern Australia), and the Indo-Pacific (e.g., Western Australia, the Philippines, Palau, and Indonesia). Morphological characters have not been incorporated into these studies but it now possible to map the distribution of such characters onto the molecular phylogeny to test for degree of convergence. In the present study, we focus on color patterns in A. scrobiculatus (Papua New Guinea), N. belauensis (Palau), N. macromphalus (New Caledonia), and N. pompilius (Vanuatu, Fiji, and Western Australia). We photographed dozens of mature specimens and broke down several specimens of each species into 4-8 sections each to document the ontogenetic development of the color pattern. We identify five characters based on color patterns in mid-ontogeny, where the differences among species are most clearly expressed: 1) number of stipes on the mid-flanks/whorl; 2) number of stripes on the outer flanks/whorl; 3) width of stripes relative to the interspaces between them on the outer flanks; 4) incidence of branching of stripes on outer flanks; and 5) waviness (irregular margins) of stripes on outer flanks. Although there is some variation in color patterns within species, our preliminary results suggest that color character states are congruent with the molecular phylogeny. Further studies will focus on color tint and intensity, whorl shape, embryonic size, umbilical size, number of septa at maturity, size at maturity, sutural patterns, and ornamentation. Because of the high developmental plasticity in nautilus, we predict that some characters such as adult size and number of septa at maturity will show numerous instances of convergence, as plotted against the molecular tree.