Mono- and bispecific genera are noteworthy compared with multispecies genera because they either may be evolutionarily older or would represent not-yet-diversified young lineages, and being in some cases endemic to specific islands and archipelagoes, they also are of conservation concern. Here, the distribution patterns of the mono- and bispecific genera of freshwater turtles and tortoises and the distribution patterns of island endemics are analyzed, using a database provided by the International Union for Conservation of Nature/Species Survival Commission Tortoise and Freshwater Turtle Specialist Group. The mean number of species per genus varied significantly across biogeographic regions. Twenty-eight genera are monospecific, and 18 are bispecific, accounting for 48.9% of the total genera of tortoises and freshwater turtles worldwide. The Oriental region housed the highest fraction of these genera, followed by the Neotropical and Afrotropical regions. More than 11% of the total number of chelonian species (n = 356) were island endemics, with most species being Neotropical. The majority of the endemic island species occurred in the Galapagos Islands and in Papua New Guinea. The endemism index varied remarkably among the various islands/archipelagoes, with the Philippines being the center of endemism with the minor value of the index and the Galapagos being that with the highest value of the index. Island size was correlated neither with the number of endemic species per island nor with the endemism index of each island, but it was significantly correlated with the total number of species (once the Galapagos were removed from analyses as an outlier). Species belonging to mono- and bispecific genera, as well as island endemic species, were more threatened (as a percentage; in all cases > 65%) than the overall percentage of threatened taxa in freshwater turtles and tortoises worldwide (50.3%).

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