Conservation Concerns

The rediscovery of the endemic Clarión Nightsnake highlights the importance of focused biodiversity surveys and the concern of the Islas Revillagigedo for active conservation management. Properly identifying species numbers and occurrences are first steps in conservation efforts of documenting biodiversity and quantifying extinction events [2]. Recently, several classification schemes have been proposed to the causes and significance of “extinctions” followed by rediscoveries [6], [30]. The case of the Clarión Nightsnake represents a unique scenario better described as “lost” and rediscovered [5], which falls under a combination of current classifications and several possible reasons for why it has gone undetected for so many decades. It nearly fits the “type specimen” criteria of Scheffers et al. [6], where a specimen hasn’t been seen since the type specimen was collected, which is the case for the Clarión Nightsnake. However, there are several reasons that make it different and why it has gone undetected for so long.

First, the Clarión Nightsnake was never declared extinct under any criteria [6], [30], but instead was dismissed as a locality error after not being seen for two decades [12]. Secondly, Isla Clarión is very remote and is only accessible through military escort, therefore biologists do not frequently visit the island. Further, Hypsiglena is not a commonly studied species (i.e. not much attention is given to this taxonomic group), and its secretive, nocturnal behavior makes it difficult to detect even when active efforts are made in general herpetofaunal surveys [9]. Therefore, the case of the missing Clarión Nightsnake involves all four of the socio-ecological factors proposed [30]. Nevertheless, its rediscovery is meaningful and noteworthy because we observed what appears to be a viable population, rather than a dwindling one, which is often the case in recent rediscoveries [5]. Finally, based on multiple lines of evidence we recognized this lineage as a distinct species, fitting the “genetic rediscovery” type of Scheffers et al. [6], such that where a subspecies was lost, a species was found. Though we revealed a potentially viable population by observing nearly a dozen individuals over a two-week period, the remoteness of this fragile island ecosystem makes it particularly susceptible to invasive species, thus warranting conservation management and protection for the Clarión Nightsnake.

The Islas Revillagigedo are small group of seamount islands that rose independently from fracture zones along the eastern edge of the Pacific Plate of North America. Often compared to the Galápagos [13], [31], their remoteness and isolation encourage evolution and speciation in plant and animal colonists. Isla Clarión is the oldest island in the group (Pliocene) and it is the furthest from the mainland, ∼1100 km west of Manzanillo, Colima, México. In 1994, the Islas Revillagigedo were designated a biosphere reserve by the Mexican government because of the large number of endemic plants and animals [32]. This archipelago is also considered an area of diversity and endemism for Mexican herpetofauna on the basis of discrepancy analysis, which compares the location of high biological richness areas with the locations of protected areas [33]. Invasive species threaten faunal components of these islands, including direct predation by feral cats on birds [32], [34]–[35] and lizards [36] on Isla Socorro. Introduced pigs, sheep, and rabbits have caused major changes in vegetation on these islands [31], [37], particularly the near obliteration of cactus on Isla Clarión [31].

Prior to this study, the terrestrial reptile fauna of the Islas Revillagigedo was thought to consist of two endemic lizards, Urosaurus auriculatus on Isla Socorro, U. clarionensis, and an endemic snake Masticophis anthonyi also on Isla Clarión. Our confirmation of Hypsiglena unaocularus on Isla Clarión identifies an additional endemic snake and truly represents a rediscovery. This is not simply the case of elevating a known inhabitant to the specific-level, as is the case for H. catalinae on Isla Santa Catalina. Hypsiglena had not been observed on Isla Clarión prior to 1936, and was essentially lost to the scientific community until now [13]–[14]. We recommend future conservation management strategies incorporate our new discovery. Efforts should be made to prevent additional introductions of invasive species. The introduction of feral cats on Isla Clarión would be devastating to the reptile community, perhaps even more so than on Isla Socorro because of the much smaller size of Isla Clarión. Although we did not observe any stomach contents or predation events by H. unaocularus, lizards are known to make up a large part of the diet of mainland Hypsiglena [38]. Therefore, U. clarionensis probably constitutes the major food source for H. unaocularus, but it is also possible that the remarkably large crickets on Isla Clarión [39] make up part of their diet as well. The introduction of feral cats could pose a double threat to H. unaocularus, not only by direct predation but also by affecting the main food source. Efforts should also be made to continue the eradication of current invasive species and to restore the island’s natural vegetation. Future studies should also be conducted to directly monitor H. unaocularus. We know very little about the abundance, distribution, and ecology of H. unaocularus, and its role in this fragile ecosystem.

Morphological data, geography, and phylogenetic analyses of genetic data reveal that the Clarión population represents a distinct species–H. unaocularus [11]. This species belongs to a clade with two other species of Hypsiglena; one from Isla Santa Catalina (H. catalinae), and a newly identified species from the Sonora–Sinaloa border in México (“H. sp. nov. 2″). Most importantly, we bring the presence of these species–that were otherwise unknown–to the attention of managers and conservation biologists currently monitoring vertebrates in these areas. The recognition of the Isla Santa Catalina population at the specific-level makes this H. catalinae another island endemic. Isla Santa Catalina contains at least eight other endemic reptile species [40]. The Rio Fuerte drainage and Alamos area near the Sonora–Sinaloa state border in México is also an area of biological interest, it represents a major transition zone between the Sonoran Desert, the Sinaloan Thornscrub, and Tropical Deciduous Forest biomes [27]–[28], [41]. Therefore, this area represents a major contact zone for many species groups [42] and contains at least one additional recently identified endemic reptile species, the Rio Fuerte Beaded Lizard Heloderma exasperatum [43]. The species identified in this study should be considered “endemics” to checklists of these areas and should be included in conservation management strategies to maintain biodiversity in these unique regions.