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Human-mediated dispersal of animals often acts to bring populations that have been separated for substantial periods of evolutionary time (e.g. millions of years) in their native range into contact in their introduced range. Whether these taxa successfully interbreed in the introduced range provides information on the strength of reproductive isolation amongst them. The invasive delicate skink (Lampropholis delicata) has been accidentally introduced to Lord Howe Island from four genetically divergent (>2 million years) regions of the species' native range in eastern Australia. We used mitochondrial DNA and microsatellite data to investigate whether the individuals from four of the native-range source regions are interbreeding on Lord Howe Island. Our analyses indicate that intraspecific hybridisation among individuals from all four native-range source regions is occurring. Although there is little evidence for hybrids in the northern end of Lord Howe Island (proportion of hybrids: 0–0.02; n = 31), there is a high proportion of hybrids in the central (0.33–0.69; n = 59) and southern regions (0.38–0.75; n = 8) of the island. Given the strong evidence for interbreeding among all four native-range source regions examined, and the relatively minor morphological, life-history and phenotypic variation among them, we suggest that the delicate skink should continue to be treated as a single, widespread, but variable species. Human-assisted dispersal can act to bring populations that have been separated for millions of years into secondary contact in their introduced range. We demonstrate that interbreeding is occurring amongst individuals from the four genetically divergent (>2 million years) native-range lineages of the delicate skink (Lampropholis delicata) that are present on Lord Howe Island. Our findings indicate that, despite substantial genetic structure across its native range, the delicate skink is a single, widespread, but variable species. Photograph by Sarah Simmonds. [ABSTRACT FROM AUTHOR]

Invasive species are considered one of the greatest threats to native ecosystems, second only to habitat loss and fragmentation. Despite this, the temporal dynamics of invasions are poorly understood, with most studies focusing on a single time point, providing us with only a snapshot of the biology and genetics of the invader. We investigated the invasion of Lord Howe Island by the delicate skink Lampropholis delicata and assessed the introduction history and genetic structure of this species over a 5-year period. Using genetic data taken from 2007, and again in 2011/12, we examined changes in the population genetic structure (whether new haplotypes had been introduced to the island, and shifts in haplotype frequencies) of the species on the island between these two time points. No new haplotypes were introduced to the island between 2007 and 2011/12; however, significant shifts in haplotype frequencies across the island were detected. We conclude that the delicate skink is expanding its range into the southern regions of the island and that the haplotype frequencies on Lord Howe Island are still in a state of highly dynamic flux. Our study highlights the importance of considering invasions as dynamic and studying them in such a way that enable us to better manage their impacts. [ABSTRACT FROM AUTHOR]

Lord Howe Island (LHI) is a remote oceanic island in the south-west Pacific that is World Heritage listed due to its diverse, and largely endemic, biota. A suite of introduced species have colonised the island, resulting in the widespread population declines of many native species. The delicate skink (Lampropholis delicata De Vis) was accidentally introduced to LHI from mainland eastern Australia, but there has been no detailed investigation of its biology on the island, or its potential impact on the native biota. We conducted a detailed study of the distribution and biology of the delicate skink on LHI over a six-year period (2007-12). The delicate skink was introduced to LHI in the 1980s, and rapidly spread across the island. It presently occurs in all 21 low-elevation vegetation communities on LHI. The delicate skink is diurnal on LHI, and displays seasonal variation in activity with a peak in November-December. The delicate skink exhibits sexual dimorphism with females having larger body and abdomen sizes and males having longer and broader heads, although the degree of genetic admixture may influence morphology on LHI. Females reproduce in spring and summer (September-February), with a positive relationship between body size and clutch size. Clutch size ranges from 1 to 7 (mean 3.4) and communal egg nests (11-200+ eggs) are common. Tail loss is common on LHI (55%), but is more frequent in adults and females. We conclude that, based on its distribution and abundance, the delicate skink has the potential to impact the diverse and endemic invertebrate fauna on LHI. [ABSTRACT FROM AUTHOR]