Larger hybrid clutch size could drive regional displacement of native Iguana populations across the Lesser Antilles

Native Iguana populations across the Caribbean Lesser Antilles are being replaced by non-native green iguanas (NNGI) once these establish themselves, leading to eventual extinction. Despite this knowledge, and much effort towards NNGI removal and prevention of incursions, the underlying mechanisms of the observed genetic swamping are poorly understood. Previous studies show that larger clutch size is a key reproductive trait of mainland as opposed to insular lizard populations. Higher clutch size in NNGI and their progeny could be a driver in the genetic swamping of insular Iguana populations. We collected data on snout-vent length, tail length, clutch size and genetics opportunistically during an eradication program of hybrid and NNGIs on the island of Saba, home to a native Iguana Iguana population. Data of native and hybrid iguanas from Saba were combined with similar published data from native insular and mainland Iguana populations. Generalized linear modeling revealed that climatic variables could not explain differences in clutch size, in contrast to genetic origins. Our preliminary results show that hybrid iguanas lay significantly more eggs (~40%) than similar-sized native Saba iguanas. Therefore, we suggest that higher hybrid clutch size may be a contributing factor hastening the genetic swamping and declines in native Iguana populations across the Lesser Antilles. Further study is needed to clarify and better understand the drivers of the rapid genetic swamping and loss of Antillean iguana diversity, which should also focus on Iguana delicatissima and utilize genomic approaches to pinpoint genes under selection.