Abstract
The Amazonian coast has several unique geological characteristics resulting from the interaction between drainage pattern of the Amazon River and the Atlantic Ocean. It is one of the most extensive and sedimentologically dynamic regions of the world, with a large number of continental islands mostly formed less than 10,000 years ago. The natural distribution of the cane toad (Rhinella marina), one of the world’s most successful invasive species, in this complex Amazonian system provides an intriguing model for the investigation of the effects of isolation or the combined effects of isolation and habitat dynamic changes on patterns of genetic variability and population differentiation. We used nine fast-evolving microsatellite loci to contrast patterns of genetic variability in six coastal (three mainlands and three islands) populations of the cane toad near the mouth of the Amazon River. Results from Bayesian multilocus clustering approach and Discriminant Analyses of Principal Component were congruent in showing that each island population was genetically differentiated from the mainland populations. All FST values obtained from all pairwise comparisons were significant, ranging from 0.048 to 0.186. Estimates of both recent and historical gene flow were not significantly different from zero across all population pairs, except the two mainland populations inhabiting continuous habitats. Patterns of population differentiation, with a high level of population substructure and absence/restricted gene flow, suggested that island populations of R. marina are likely isolated since the Holocene sea-level rise. However, considering the similar levels of genetic variability found in both island and mainland populations, it is reliable to assume that they were also isolated for longer periods. Given the genetic uniqueness of each cane toad population, together with the high natural vulnerability of the coastal regions and intense human pressures, we suggest that these populations should be treated as discrete units for conservation management purposes.
Highlights
The Amazonian coastline is a highly dynamic natural system that changes continuously in response to a variety of phenomena that differ considerably in timing and duration, such as Holocene sea level rises, tectonic activities and hydrologic dynamics, including drainage, sedimentation and erosion patterns [1, 2]
All microsatellites were highly polymorphic across the six populations analyzed, and the number of alleles ranged from 6 to 19 (RM2) with a mean of 11.8 alleles per locus
The relative abundance of information on the natural history of this species has mostly been collected in exotic areas, whereas few data are available from its natural range [43]
Summary
The Amazonian coastline is a highly dynamic natural system that changes continuously in response to a variety of phenomena that differ considerably in timing and duration, such as Holocene sea level rises, tectonic activities and hydrologic dynamics, including drainage, sedimentation and erosion patterns [1, 2]. Pleistocene and Middle Holocene is generally considered to be the main event that originated the continental islands by separation from the adjacent mainland [6,7,8]. These continental islands, comparative to oceanic ones, tend to be younger and to present distinct evolutionary patterns due to their formation from vicariance, rather than colonization or founding event in novel environmental conditions such as in oceanic islands. Island populations are often small and isolated with reduced effective population size, being more vulnerable to stochastic genetic processes and environmental changes [17, 18]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
