Complex range expansion and selective regime in the introduced Florida cane toad.

Area of Science:

• Ecology
• Evolutionary Biology
• Genetics

Background:

• Introduced species offer insights into range expansion processes.
• The cane toad (Rhinella marina) is a model for invasion studies, but its relative, Rhinella horribilis, in Florida is less understood.
• Florida's climate is colder than the native range of Rhinella horribilis.

Purpose of the Study:

• Investigate the introduction history of Rhinella horribilis in Florida.
• Characterize population structure, genetic diversity, and adaptation.
• Identify climate-associated genetic variants and explore potential evolution of dispersal.

Main Methods:

• Sequencing of 280 individuals using double-digest restriction-associated DNAseq (ddRAD).
• Testing introduction hypotheses (single vs. multiple events).
• Analyzing population structure, genetic diversity, gene flow, and climate-associated genetic variants using redundancy analyses.
• Assessing morphological traits (limb length) for dispersal evolution.

Main Results:

• Evidence supports a single introduction event for Rhinella horribilis in Florida.
• Complex range expansion observed with range-wide gene flow and lack of isolation by distance or environment.
• No evidence of a dispersal phenotype at the range edge.
• Selection identified related to precipitation, temperature, and urbanization gradients.
• Climate-associated genetic variants suggest adaptation to the temperate environment.

Conclusions:

• Range-wide gene flow is crucial for maintaining genetic diversity and adaptive capacity in invasive populations.
• Rhinella horribilis successfully adapts to and establishes in Florida's temperate environment due to genetic diversity and gene flow.
• The study highlights the importance of introduction history and ongoing gene flow in invasive species success.