Entomological time travel: reconstructing the invasion history of the buckeye butterflies (genus Junonia) from Florida, USA

Abstract

Invasion biology examines the process by which non-native species integrate into new habitats. Three species of buckeye butterflies (genus Junonia) currently occur in Florida, USA, including Junonia coenia (polyphagous and widely distributed), J. neildi (monophagous and restricted to coastal areas), and J. zonalis (polyphagous tropical species restricted to frost-free South Florida). Two species have long been resident in Florida, whereas J. zonalis was first detected in Florida in 1981. Diagnostic morphological and molecular markers exist for determining Junonia with Caribbean ancestry, allowing observation of the invasion and creation of a secondary contact zone over space and time. We developed techniques to quickly, inexpensively, and unambiguously determine mitochondrial genotypes from museum specimens collected in Florida and the Caribbean over the last 150 years. We reconstructed the invasion of J. zonalis as it colonized Florida using 816 Junonia museum specimens from 1866 to 2016, including some of the oldest insect museum specimens ever genotyped. Significant correlations were found between the presence of Caribbean genotypes and latitude, longitude, and time. Junonia zonalis likely colonized Florida from Cuba by the 1930s, followed by hybridization with resident species, with ongoing genetic exchange between Cuba and the Florida Keys. Episodic gene flow between Florida Keys and mainland populations of J. zonalis may also be occurring. Mainland mitochondrial genotypes appear to be more resilient to extreme high and low temperatures than Caribbean genotypes. This time series in Junonia can be used as a model for understanding the process of adaptation required for successful invasion of new habitats.