Range Expansion and Dispersal Traits of Green Treefrogs (Hyla cinerea)
Since the 1980s, there has been rapid and ongoing hypothesized climate-related range expansion in native Green Treefrogs (Hyla cinerea) northward and eastward in Illinois, Kentucky, and Indiana, United States. Because anuran leg length is positively correlated with locomotor function, longer legs have been shown to facilitate dispersal of invasive anuran populations undergoing biological invasion. These recent range-expansion populations of H. cinerea provide an ideal opportunity to test if a native frog species exhibits similar changes in dispersal-related traits to those found in invasive species. We tested if individuals on the front end of this expansion exhibit significant differences in femur length when compared with frogs collected from the historical-range distribution. We predicted that frogs found at the expansion edge would have longer femur lengths than their counterparts located in historical parts of the range. We found that relative to snout–vent length (SVL), the femur lengths (FL) of H. cinerea from expanded ranges were on average significantly larger than those of frogs from the historical range. This suggests that native expanded-range populations of this species have undergone changes in FL. Rapid shifts in morphological traits of a native species, H. cinerea, in expanded-range populations, appear to mimic morphological trade-offs observed for invasive species of anurans.ABSTRACT
Map (left panel) showing the current range of Green Treefrogs (Hyla cinerea) (gray area; USGS, 2018) and counties from Alabama, Kentucky, and Illinois, United States in which H. cinerea were sampled. Inset (right) depicts counties in which expanded-range (diagonal lines; n = 5) and historical (solid fill; n = 10) sites were sampled.
Relative femur length (quantified as ratios of FL/SVL) of male Green Treefrogs (Hyla cinerea) from historical- and expanded-range locations. Relative femur length was pooled within Alabama, Kentucky, and Illinois. Box plots represent medians (lines), interquartile ranges (boxes), ranges excluding outliers (whiskers), outliers (dots), and indications of significant differences (letters).
Relative femur length (quantified as ratios of FL/SVL) of male Green Treefrogs (Hyla cinerea) measured from historical (Historical-1) range populations in Alabama (AL), historical (Historical-2) populations in Kentucky (KY) and Illinois (IL), and expanded-range populations in Kentucky (KY) and Illinois (IL). Box plots represent the medians (lines), interquartile ranges (boxes), ranges excluding outliers (whiskers), outliers (dots), and indications of significant differences (letters).
Relative femur length (quantified as ratios of FL/SVL) of male Green Treefrogs (Hyla cinerea) from all counties in Alabama (AL), Illinois (IL), and Kentucky (KY) that were sampled for this study. The date of occurrence of frogs in these counties becomes progressively more recent from left to right. Box plots represent medians (lines), interquartile ranges (boxes), ranges excluding outliers (whiskers), and outliers (dots).
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