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Transcribed Image Text: Royal
Botanical
Society of
Belgium
An experimentally introduced population of Brassica rapa (Brassicaceae). 2. Rapid
evolution of phenotypic traits
Author(s): Michael R. Sekor and Steven J. Franks
Source: Plant Ecology and Evolution, 2018, Vol. 151, No. 3 (2018), pp. 293-302
Published by: Royal Botanical Society of Belgium and the Botanic Garden Meise
Stable URL: https://www.jstor.org/stable/44945392
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Plant Ecology and Evolution 151 (3): 293-302, 2018
https://doi.org/10.5091/plecevo.2018.1401
PLANT
BACOLOGY
PA
REGULAR PAPER
An experimentally introduced population of Brassica rapa
(Brassicaceae). 2. Rapid evolution of phenotypic traits
Michael R. Sekor & Steven J. Franks¹2
'Louis Calder Biological Field Station, Department of Biological Sciences, Fordham University, Armonk, NY, 10504, USA
Department of Biological Sciences, Fordham University, Bronx, NY, 10458, USA
*Author for correspondence: msekor@fordham.edu
Background and aims - Introduced populations can potentially experience strong selection and rapid
evolution. While some retrospective studies have shown rapid evolution in introduced populations in the
past, few have directly tested for and characterized evolution as it occurs. Here we use an experimental
introduction to directly observe and quantify evolution of multiple traits in a plant population introduced
to a novel environment.
Methods - We experimentally introduced seeds of the annual plant Brassica rapa L. (Brassicaceae) from
a location in southern California into multiple replicated plots in New York. We allowed the populations to
naturally evolve for 3 years. Following the resurrection approach, we compared ancestors and descendants
planted in common garden conditions in New York in multiple phenotypic traits.
Key results - Within only three generations, there was significant evolution of several morphological,
phenological, and fitness traits, as well as substantial variation among traits. Despite selection for larger size
during the three years following introduction, there was evolution of smaller size, earlier flowering time,
and shorter duration of flowering. Although there were rapid evolutionary changes in traits, descendants did
not have greater fitness t n ancestors in New York, dicating a lack of ev for adaptive
least over the timeframe of the study.
at
Conclusions - This study found rapid evolution of several morphological and phenological traits, including
smaller plant size and shorter time to flowering, following introduction, confirming that evolution can
rapidly occur during the early stages of colonization. Many traits evolved in the opposite direction predicted
from phenotypic selection analysis, which suggests that the resurrection approach can reveal unanticipated
evolutionary changes and can be very useful for studying contemporary evolution.
Key words - Rapid evolution, plants, resurrection approach, morphology, flowering time, Brassica rapa,
experimental introduction, introduced species.
INTRODUCTION
& Ian 2015). Despite these examples evolution could no
Transcribed Image Text: INTRODUCTION
While once thought to be a slow process, there is now sub-
stantial evidence that rapid evolution in natural populations
can occur over contemporary timescales (Thompson 2013).
Evolution appears to be particularly rapid in cases where
there is a mismatch between organisms and their environ-
ments (Carroll et al. 2014), as can occur with anthropogen-
ic environmental changes (Palumbi 2001) such as climatic
changes (Levitan 2003) or pesticides (Whalon et al. 2008).
Thus especially strong selection and rapid evolution is ex-
pected for populations introduced to novel environments.
Indeed, prior research provides evidence of rapid evolution
in introduced populations of invasive species (Maron et al.
2004, Ridley & Ellstrand 2010, Novy et al. 2013, Colautti
All rights reserved. © 2018 Meise Botanic Garden and Royal Botanical Society of Belgium
ISSN: 2032-3913 (print)-2032-3921 (online)
Pl. Ecol. Evol. 151 (3), 2018
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Table 1 -Summary of environmental variables in the source and introduced environment.
Source Environment
California
33.661
-117.851
State
Latitude
Longitude
Climate type
Soil type
Vegetation type
Growing season dates
Average high/low temp in January
Average high/low temp in July
Average precipitation in January
Average precipitation in July
& Lau 2015). Despite these examples, evolution could po-
tentially be limited in introduced populations due to fac-
tors such as genetic bottlenecks (Barrett 1991, Van Buskirk
& Willi 2006, Dlugosch & Parker 2008, Bell & Gonzalez
2009), trade-offs (Blows & Hoffmann 2005, Walsh & Blows
2009), or genetic correlations that oppose selection (Etterson
& Shaw 2001). Thus it remains unclear to what extent rapid
adaptive evolution occurs in introduced populations.
Detailed information on the rates of evolution of differ-
ent traits in introduced populations is scarce because much
of the prior research in this area has been indirect, coming
from populations that have already been introduced and
established. Previous studies have used techniques such as
population genetic analyses (Dlugosch et al. 2015), quantita-
Mediterranean
Clay loam
Mediterranean Coastal Scrub
December-April
18°C/9°C
26°C/19°C
7 cm
0.6 cm
tive genetic analyses (Franks et al. 2008b, 2012), or recipro-
cal transplants (Maron et al. 2004, Ridley & Ellstrand 2010,
Novy et al. 2013, Colautti & Lau 2015) to retrospectively
indirectly infer past evolution, rather than directly capturing
evolution in action. In contrast, experimental introductions
provide the opportunity to directly observe evolution as it
occurs (Walsh & Reznick 2011), and allow a focus on the
early stages of introduction and colonization not possible in
studies where the introduced species is already established.
Experimental introductions of taxa to a new environment
have been used to study evolution and colonization success
in a variety of animals (Reznick et al. 1997, Herrel et al.
2008, Forsman et al. 2012, Gotanda & Hendry 2014, Stuart
et al. 2014, Gordon et al. 2015), but examples of experimen-
tal introductions to examine evolution in plants appears to
be surprisingly lacking (Campbell et al. 2006, Hovick et al.
2012). Experimental introductions are particularly powerful
for studying evolution in introduced species when combined
with the resurrection approach (Franks et al. 2008a). In the
parumaction cannonch ancestor obtained from stored neon
Introduced Environment
New York
41.127
-73.731
Temperate
Loam
Eastern Deciduous Forest
April-September
4°C/-5°C
28°C/19°C
5 cm
10 cm
mizuna) and artificially selected lines (e.g. Fast Plants) of
B. rapa, and populations have become feral or naturalized.
This species was chosen due to its demonstrated ability to
rapidly evolve in response to artificial (Williams & Hill 1986,
Agren & Schemske 1994) and natural (Franks et al. 2007)
selection. Franks et al. (2007) documented the evolution of
earlier flowering time in populations of B. rapa following a
five-year drought in southern California. The derived pheno-
types were able to flower at a smaller size, demonstrating a
flexible relationship between size and flowering (Franks &
Weis 2008).
This study examines evolution directly following coloni-
zation in an experimentally introduced population of Bras-
sica rapa. In May 2011, seeds from a population in Southern
California were introduced to ten replicated plots in Armonk,
New York. These sites are separated by 4500 km from their
locality of origin and differ from this in many characteristics,
including climate, soil type and species composition (table
1). We thus expect that the introduced population would ex-
marianna strona calactiva anacon The intenduoad monula