was little or no information of the relationships among species. This lack of systematics prevented Mayr from basing any of his group designations on sister-species relationships. However, in the past 10 years, detailed molecular phylogenetic studies have been completed for six genera in Mayr’s original list and two others that do not occur in the West Indies. In this paper, we collate these phylogenies and use them to test general predictions from Ernst Mayr’s reconstruction of sea urchin speciation patterns. General predictions across all genera in the study include familiar tenets of allopatric speciation. Testing these predictions with molecular data reveals a considerable concordance with Mayr’s animations but also shows some surprises about the way speciation proceeds in sea urchins.
We compiled molecular data for variation in the mitochondrial cytochrome oxidase I (COI) genes for Mayr’s groups 1 and 2 genera Tripneustes (Lessios et al., 2003a), Eucidaris (Lessios et al., 1999), and Lytechinus (Zigler and Lessios, 2004); group 3 genera Echinometra (McCartney et al., 2000; Landry et al., 2003) and Diadema (Lessios et al., 2003b); and group 4 genera Strongylocentrotus (Biermann et al., 2003), Arbacia (Metz et al., 1998), and Heliocidaris (Zigler et al., 2003). Phylogenetic relationships are taken directly from the original analyses. Data for the gamete recognition molecule bindin are available for six of these eight genera: Tripneustes (Zigler and Lessios, 2003a), Lytechinus (Zigler and Lessios, 2004), Echinometra (Landry et al., 2003; Metz and Palumbi, 1996; McCartney and Lessios, 2004), Strongylocentrotus (Biermann, 1998), Arbacia (Metz et al., 1998), and Heliocidaris (Zigler et al., 2003). In general, phylogenetic relationships at COI and bindin are concordant. Major exceptions are the positions of Lytechinus williamsi and Echinometra insularis in their respective genera (Landry et al., 2003; Zigler and Lessios, 2004). In Strongylocentrotus, we have included the monotypic genera Allocentrotus and Hemicentrotus because phylogenetic analysis places the species in these genera firmly within the genus Strongylocentrotus (Biermann et al., 2003). We used Kimura two-parameter genetic distances based on COI comparisons. In Diadema, combined ATPase 8 and 6 and COI sequences were used. Distances were compiled for sister species (two or more species that split at the tip of a branch or a species that forms an outgroup to a clade of closely related species). Allopatric neighbors are defined as allopatric species that are not separated by an obvious, insurmountable geographic barrier, such as a land mass.
We characterize bindin evolution as “fast” if the nonsynonymous-to-synonymous substitution ratio in at least an ≈100-bp “hotspot” region of the gene is >1 and if there are several codons on which positive selection