The threat of Peters's Rock Agama (Agama picticauda) to reptile diversity across the Lesser Antilles

Abstract

During the ongoing sixth global extinction wave, island ecosystems are among the most impacted due to a high introduction rate of non-native species (Tershy et al., 2015; Bellard, Cassey, & Blackburn, 2016; Fernández-Palacios et al., 2021). Within one of the global biodiversity hotspots (Myers et al., 2000), the Caribbean Lesser Antilles are known for their high degree of endemism across numerous taxa, including reptiles (e.g., Smith et al., 2004; Losos et al., 2006). However, continuing introductions of non-native species are homogenizing the regional herpetofauna diversity (Capinha, Marcolin, & Reino, 2020), leading to extinctions and loss of functional trait diversity across islands and ecosystems (Kemp, 2023).

The most common terrestrial non-native vertebrates, throughout the Lesser Antilles, are reptiles (Thorpe, 2022). Their interactions with native reptile species have led to local extinctions and continuing declines in both native population sizes and distribution ranges through predation, hybridization, disease transmission, and competition for resources (Daltry, 2022). Multiple non-native species have already spread nearly regionwide, including Gymnophthalmus underwoodi, Hemidactylus mabouia, Indotyphlops braminus, Anolis/Norops sagrei, and Latin American Iguana iguana (Thorpe, 2022; Thibaudier et al., 2023; van den Burg et al., 2023), while others are spreading rapidly (e.g., Hemidactylus frenatus: Thibaudier et al., 2023 and references therein). Importantly, several of these non-native species are known to have been introduced to the Lesser Antilles from non-native populations in Florida (Powell et al., 2011); a pattern we fear is likely to be repeated by Peters's Rock Agama (Agama picticauda), although no established population has yet been reported in the Lesser Antilles.

Agama picticauda is a medium-sized lizard native to sub-Saharan western and central Africa, with both sexual dichromatism and size dimorphism. Adult males have a bright orange head and tail, while females are light brown and can have yellow to orange dorsolateral patches (Fig. 1). The species is diurnally active, has a maximum recorded snout–vent length of 15.7 cm (Krishnan et al., 2019), and can produce up to three clutches annually, each of 5–12 eggs (Blunden & Krysko, 2007; Krysko, Enge, & Moler, 2019). It occupies both horizontal and vertical surfaces from where it uses a sit-and-stalk approach to identify and pursue arthropods (Enge, Krysko, & Talley, 2004) and small vertebrates (Henigan et al., 2019).

In Florida, the first A. picticauda population was found in 1976 (Wilson & Porras, 1983) and it has since extended its range across the state (Enge, Krysko, & Talley, 2004). Recent analyses show high genetic variation within the Florida population due to introductions from different native origins (Nuñez, Krysko, & Avery, 2016). Given populations across its native range occupy different climatic niches (Krishnan et al., 2019), hybridization between populations of differing origins could result in high ecological adaptability (Consuegra et al., 2011), that in turn can increase establishment success when Florida individuals are translocated to other regions. Alarmingly, A. picticauda appears to be spreading to Caribbean islands as sightings are being reported from the Bahamas and Tortola (British Virgin Islands) (observations 139983395 and 89972864, https://www.inaturalist.org/). On Tortola, at least two adults as well as three juveniles have been observed, suggestive of an establishing population (C. Petrovic, pers. obs.). Further research on the status and impacts on the Bahamas is urgently needed, while on Tortola immediate action is necessary to remove the existing population.

Although the native and non-native dietary range and ecology of A. picticauda are poorly studied, when it spreads to the Lesser Antilles, this could have a major impact on numerous native species. There is clear evidence this species preys on smaller lizards. For example, Henigan et al. (2019) dissected a large female that had cannibalized a smaller individual (5 cm snout–vent length) and Florida residents have observed predation of Anolis species (e.g., iNaturalist record 19472282), and a predation attempt on an Ameiva ameiva (J. Wasilewski pers. obs.). These data are highly troubling given many taxa have life stages within these size ranges, while others (or at least one sex) never grow larger. Species of Alinea, Anolis, Bachia, Capitellum, Copeoglossum, Gymnophthalmus, Mabuya, Marisora and Spondylurus would be susceptible to predation, as well as juveniles of Ameiva, Cnemidophorus, Kentropyx and Pholidoscelis: an assemblage of >45 species (Thorpe, 2022). Furthermore, native adult lizards are likely to experience interspecific competition and potential displacement. Although Agama picticauda is mainly reported from urban and suburban environments, suggesting a low impact within intact forests, given the high threat to the Caribbean forests and their transition to (sub)urban areas, it is expected that A. picticauda could become widely distributed. Besides, not all native Lesser Antillean species are limited to forests, as (pet-free) suburban gardens can also act as important habitats or even sanctuaries for critically endangered reptiles (e.g., Debrot, Boman, & Madden, 2013).

Finally, given the abundance of A. picticauda in Florida and the high volume of shipments from Florida to ports throughout the Caribbean, we strongly emphasize the responsibility of state authorities (including border control), as well as transport and shipping providers, to prevent animals from leaving those shores. Florida-based conservationists and alien species experts, with A. picticauda experience, are encouraged to help Lesser Antillean stakeholders and authorities through training and knowledge transfer to tackle this major threat to Caribbean biodiversity.