Research Summary: Nuclear and Chloroplast Microsatellites Show Multiple Introductions in the Worldwide Invasion History of Common Ragweed, Ambrosia artemisiifolia



Ambrosia artemisiifolia is a North American native that has
become one of the most problematic invasive plants in Europe and Asia. We
studied its worldwide population genetic structure, using both nuclear and
chloroplast microsatellite markers and an unprecedented large population
sampling. Our goals were (i) to identify the sources of the invasive
populations; (ii) to assess whether all invasive populations were founded by
multiple introductions, as previously found in France; (iii) to examine how
the introductions have affected the amount and structure of genetic
variation in Europe; (iv) to document how the colonization of Europe
proceeded; (v) to check whether populations exhibit significant heterozygote
deficiencies, as previously observed.

Principal Findings

We found evidence for multiple introductions of A.
, within regions but also within populations in
most parts of its invasive range, leading to high levels of diversity. In
Europe, introductions probably stem from two different regions of the native
area: populations established in Central Europe appear to have originated
from eastern North America, and Eastern European populations from more
western North America. This may result from differential commercial
exchanges between these geographic regions. Our results indicate that the
expansion in Europe mostly occurred through long-distance dispersal,
explaining the absence of isolation by distance and the weak influence of
geography on the genetic structure in this area in contrast to the native
range. Last, we detected significant heterozygote deficiencies in most
populations. This may be explained by partial selfing, biparental inbreeding
and/or a Wahlund effect and further investigation is warranted.


This insight into the sources and pathways of common ragweed expansion may
help to better understand its invasion success and provides baseline data
for future studies on the evolutionary processes involved during range
expansion in novel environments.


Publisher: Public Library of Science

Date Published: 10-March-2011

Author(s): Gaudeul M., Giraud T., Kiss L., Shykoff J.


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