Todd S. Campbell

Introduced species as moving targets: changes in body sizes of introduced lizards following experimental introductions and historical invasions

Introduced species usually fail to establish, but when they succeed, may undergo character release and rapid evolutionary divergence in novel environments. We collected brown anoles (Anolis sagrei: Lacertilia: Iguanidae) from a single Florida population and released them onto two ecologically different dredge-spoil islands in central Florida (forested and non-forested) and measured differences in population growth, individual growth, body size, and condition over four years. The population on the non-forested island expanded twice as fast as the forested island population and reached a density of ca. 12,000 lizards ha−1 and a biomass of ca. 43.3 kg ha−1, among the largest values recorded for non-aggregated terrestrial vertebrates. First-year progeny grew larger than their surviving parents on both islands, indicating character release occurred in early stages of both invasions. However, in subsequent years, lizards became larger on the forested island, but smaller on the non-forested island. Body condition declined over time on both islands, but the effect was most dramatic on the non-forested island. Lizards on the forested island had the lowest survival rates and highest tail autotomy frequencies. These results were attributed to differences in abiotic and biotic conditions on the two islands. Brown anoles are generally larger on islands where they have been introduced than on their native Caribbean islands, and are much larger on mainlands than on islands, indicating character release occurred at larger geographic scales as well. Habitat influences the morphology of introduced species possessing the ability to rapidly adapt to local conditions, presenting invasive species managers with ‘moving targets’.

Evaluation of a new technique for marking anurans

Amphibians can be very difficult to mark because of their extraordinary powers of regeneration. Although many amphibian marking techniques have been developed, few meet the rigorous assumptions of capture-mark-recapture models. Also, excessive toe-clipping may affect frog survivorship adversely. We tested the efficacy of a new hybrid marking technique (VIE-C) that combines Visible Implant Elastomer (VIE) and toe-clipping on four species of treefrogs in West-Central Florida. Of the 840 treefrogs recaptured over a 15-month period, only one mark was unreadable. A significantly higher percentage of VIE marks (80%) than toe-clips (55%) remained viable for the duration of the study. On average, toe-clips remained readable for 100 days, and VIE marks remained readable for 112 days. There were no significant species differences in the length of time that either type of mark lasted. The hybrid VIE-C method represents an improvement over either method used alone, but the VIE mark will be more helpful in correctly reading and clarifying toe-clipping errors than will toe-clips be helpful in reading and clarifying VIE marks.

Insights into the Introduction History and Population Genetic Dynamics of the Nile Monitor ( Varanus niloticus ) in Florida

Invasive species are widely recognized as important drivers of the ongoing biodiversity crisis. The US state of Florida is especially susceptible to the proliferation of invasive reptiles, and nonnative lizards currently outnumber native lizard species. At present, there are 3 documented breeding populations of the Nile monitor (Varanus niloticus) in different regions of Southern Florida, and these populations are considered potential dangers to threatened, fossorial endemics, such as burrowing owls, American crocodiles, and gopher tortoises. Nevertheless, at present, both the introduction histories of these populations and the degree to which they are connected by gene flow are not known. To address these issues, we genotyped V. niloticus from Cape Coral, Homestead Air Reserve Base, and West Palm Beach at 17 microsatellite loci and conducted a variety of analyses to assess both intrapopulation genetic diversity, the degree of gene flow between populations, and the most likely introduction scenario. The results of our analyses demonstrate that all 3 populations have limited genetic diversity (mean number of effective alleles across loci in all 3 populations ~ 2.00) and are highly differentiated from one another (G ST = 0.268; G″ST = 0.628). Our results also suggest that these populations resulted from independent introduction events that occurred within the past few decades. Consequently, we advise that wildlife managers focus management efforts on containment of existing populations and intensification of monitoring efforts on potential migration corridors.

Characterization of 14 novel microsatellite loci in the Argentine black and white tegu (Salvator merianae) via 454 pyrosequencing

We have developed 14 novel microsatellite loci for the Argentine black and white tegu ( Salvator merianae), using samples from invasive populations from the US state of Florida. Pyrosequencing was used to identify 3154 potentially amplifiable microsatellite loci and to subsequently develop 14 informative markers. These 14 markers were screened for variation in 40 individuals from Miami-Dade County, Florida. All loci were polymorphic and contained between 2 and 4 alleles per locus (mean ± SE = 2.71 ± 0.24), with observed heterozygosity ranging from 0.00 to 0.88 (mean ± SE = 0.38 ± 0.07). Four of the loci ( Teg4, Teg5, Teg17, Teg19) significantly deviated from Hardy-Weinberg proportions and three of these loci ( Teg4, Teg5, Teg19) showed evidence of null alleles. In addition, there was statistical evidence for genotypic disequilibrium between Teg14and Teg19. BLASTn searches of NCBI’s ‘nr/nt’ database using microsatellite containing 454 fragments as queries were largely uninformative; however, it is likely that some of these markers will be of utility in S. merinae’s native range.

Combining genetic and distributional approaches to sourcing introduced species: a case study on the Nile monitor (Varanus niloticus) in Florida

Three separate breeding populations of the Nile monitor (Varanus niloticus) have been identified in Florida, USA, located in Cape Coral, West Palm Beach and Homestead Air Reserve Base. This large, predatory lizard could have negative effects on Floridas native wildlife. Here, we infer the source of the introduced populations using genetic and statistical approaches, as well as estimate the potential non-native distribution of V. niloticus in North America. We collected genetic data from 25 Florida individuals as well as utilized genetic datasets from reference individuals spanning the full native distribution throughout sub-Saharan Africa. Using occurrence data from the inferred source population and the full species range, we built ecological niche models (ENMs) and projected them onto North America to determine regions with suitable climate. Our results indicated that the introduced populations resulted from three separate introduction events, and all originated from the southern coastal region of West Africa. The ENM built from the West African source population predicted only the southernmost portions of North America to be suitable. Conversely, the model derived from the full species’ range predicted suitable climates across a large portion of the United States. This information can be used to focus management and eradication efforts.

Insights into the introduction history and population genetic dynamics of the Argentine black-and-white tegu (Salvator merianae) in Florida

Invasive species are a major threat to global biodiversity. The US state of Florida is especially susceptible to the spread of exotic reptiles due to its subtropical climate, disturbed habitats, and robust pet trade. The Argentine black-and-white tegu (Salvator merianae) is a large, omnivorous lizard currently established in two different regions of Southern Florida. These two populations pose potential threats to sensitive ground nesting species such as gopher tortoises, American crocodiles, and migratory birds. At present, the introduction histories of these populations and the degree to which they are connected by gene flow are largely unknown. To address these issues, we genotyped S. merianae from Hillsborough and Miami-Dade Counties at ten microsatellite loci to assess intrapopulation genetic diversity, the degree of gene flow between populations, and compare the plausibilities of several potential introduction scenarios. Our results indicate that both populations have low genetic diversity [mean number of effective alleles across loci in both populations = 2.09 and are highly differentiated from each other (GST = 0.170; G″ST = 0.545)]. In addition, our results suggest that these populations underwent a bottleneck event prior to their divergence. We discuss what our results suggest about the histories of Florida’s invasive tegu populations, as well as how they inform ongoing management strategies.