Data from: Genetic reconstruction of a bullfrog invasion to elucidate vectors of introduction and secondary spread

Reconstructing historical colonization pathways of an invasive species is
critical for uncovering factors that determine invasion success and for
designing management strategies. The American bullfrog (Lithobates
catesbeianus) is endemic to eastern North America, but now has a global
distribution and is considered to be one of the worst invaders in the
world. In Montana, several introduced populations have been reported, but
little is known of their sources and vectors of introduction and secondary
spread. We evaluated the genetic composition of introduced populations at
local (Yellowstone River floodplain) and regional (Montana and Wyoming)
scales in contrast to native range populations. Our objectives were to (1)
estimate the number of introductions, (2) identify probable native
sources, (3) evaluate genetic variation relative to sources, and (4)
characterize properties of local- and regional-scale spread. We sequenced
937 bp of the mitochondrial cytochrome b locus in 395 tadpoles collected
along 100 km of the Yellowstone River, from three additional sites in MT
and a proximate site in WY. Pairwise ΦST revealed high divergence among
nonnative populations, suggesting at least four independent introductions
into MT from diverse sources. Three cyt b haplotypes were identical to
native haplotypes distributed across the Midwest and Great Lakes regions,
and AMOVA confirmed the western native region as a likely source. While
haplotype (Hd = 0.69) and nucleotide diversity (π = 0.005) were low in
introduced bullfrogs, the levels of diversity did not differ significantly
from source populations. In the Yellowstone, two identified haplotypes
implied few introduction vectors and a significant relationship between
genetic and river distance was found. Evidence for multiple invasions and
lack of subsequent regional spread emphasizes the importance of enforcing
legislation prohibiting bullfrog importation and the need for continuing
public education to prevent transport of bullfrogs in MT. More broadly,
this study demonstrates how genetic approaches can reveal key properties
of a biological invasion to inform management strategies.