1. Does allochronic isolation of three sympatric lineages result in
niche partitioning?
Niche partitioning in three sympatric lineages of
the sunflower maggot fly (Strauzia longipennis)
• The sunflower maggot fly (genus Strauzia) is a phytophagous insect that
parasitizes sunflowers and other plants in the family Asteraceae.
• Many Strauzia species and lineages are found throughout Iowa and the
Midwest (1).
• The species Strauzia longipennis is in the process of diverging into three
separate lineages (S. longipennis var. longipennis, S. longipennis var.
vittigera and S. longipennis var. longitudinalis) (2).
• All three lineages share the same host plant (Helianthus tuberosus), but
maintain low levels of gene flow (2).
• Reproductive isolation between divergent lineages creates barriers to gene
flow (3). The three Strauzia lineages have been found to have significantly
different emergence times, indicating that allochronic isolation contributes
to the maintenance of reproductive isolation (4).
• Geographic and ecological overlap among these three recently diverged
lineages make them ideal for studying the evolution of reproductive barriers
in the early stages of speciation.
REFERENCES
1) Stolzfus WB (1988). The Taxonomy and Biology of Strauzia (Diptera: Tephritidae). Journal of the Iowa
Academy of Sciences 95:117-126.
2) Forbes AA, Kelly PH, Middleton KA, Condon MA (2013). Genetically differentiated races and
speciation-with-gene-flow in the sunflower maggot, Strauzia longipennis. Evolutionary Ecology
27:1017–1032.
3) Matsubayashi, KW and Katakura, H (2009). Contribution of multiple isolating barriers to reproductive
isolation between a pair of phytophagous ladybird beetles. Evolution 63:2563-80.
4) Hippee AC. Elnes ME, Armenta JS, Condon MA, Forbes AA . Divergence before the host shift?
Prezygotic reproductive isolation among three varieties of a specialist fly on a single host plant. In
Review.
→ Figure 1. Topology of a Bayesian tree of the
COI mitochondrial gene for all Strauzia species,
showing relationships of the three lineages.
Known host plants are listed in parentheses.
• Oviposition is most frequent in the top 25% of the plant. Statistical
significance was determined using the chi-square test, with a chi-square
score of 258.06, df=1, P < 0.00001.
• Evidence supports hypothesis 1 because:
1) the difference between the two mean oviposition locations is not
significant, and
2) all three lineages of S. longipennis selected the top region of the plant for
ovipostion.
• Plant growth and eclosion timing results in niche partitioning between
lineages of S. longipennis.
• Complete fly observations and integrate additional oviposition data.
• Include plant height information to further analyze oviposition data.
• Continue fly observations and increase sample sizes of all three fly groups.
• Look at how fly lineages interact with non-native host plants.
• Complete microsatellite work, distinguishing Vittigera and Longitudinalis
females.
• Dissect plant stems to locate eggs/larvae. Rear larvae through pupation to
adult flies to evaluate post-zygotic barriers to reproductive isolation.
Figure 2. Map of collection
sites near the Iowa City area.
Figure 6. Graph representing the mean
oviposition location for Vittigera-Longitudinalis and
Longipennis flies.
Heather A. Widmayer1, Kyle J. Woods1, Elana R. Becker, Emily A. Reasoner, Alaine C. Hippee, and Andrew A. Forbes
Department of Biology, The University of Iowa
1Equal contributors to this poster
BACKGROUND
METHODS
Hypothesis 1:
All three fly species lay eggs in the
same part of the plant during different
peak times. As the plant grows, eggs
end up in different locations in the
stem.
Hypothesis 2:
Each fly species chooses a different
area of the plant to oviposit.
RESEARCH QUESTION RESULTS
CONCLUSIONS
FUTURE DIRECTIONS
ACKNOWLEDGMENTS
Live Collections
• Collected pupae and live flies from H. tuberosus at sites in the Iowa City
area in the fall of 2014 and the summer of 2015.
• Morphologically identified flies by markings on thorax and wing patterns.
• Female S. longipennis var. vittigera and S. longipennis var. longitudinalis
lineages are morphologically identical and can only be identified
genetically. Grouped as 1) S. longipennis var. vittigera and S. longipennis
var. longitudinalis (Vittigera-Longitudinalis) and 2) S. longipennis var.
longipennis (Longipennis).
• Maintained flies in individual cups for identification, host plant association,
and mating data.
• Formed mating pairs and observed mating behavior daily.
Fly Behavior/Plant Observations
• H. tuberosus plants grown from seed in the Biology Greenhouse
• Observed daily ovipositing behavior of mated females on H. tuberosus
plants of various heights and node count
Table 1. Table illustrating the oviposition frequency for Vittigera-Longitudinalis and
Longipennis. 0-0.25, 0.26-0.5, 0.51-0.75, and 0.76-1 divide the plant into quarters with
0 being the top of the stem and 1 being the base.
Figure 3. Illustration showing sites A
and B are in the same nodes relative
to the top of the plant.
• The mean oviposition
locations for Vittigera-
Longitudinalis and
Longipennis are not
significantly different, at
0.1985 and 0.1810
respectively.
• Statistical significance
determined using a t-test.
• Mean calculated using:
1. Standardized nodes:
Oviposition Location
Total Number of Nodes
2. Average of first five
oviposition sites per fly
Figure 4. Illustration showing
oviposition sites A, B, and C are in
different nodes. Photo: Strauzia fly
Figure 5. Dot plot of days when adults of each lineage eclosed in the lab during 2014.
Highlighted regions indicate the time during which 95% of eclosions occurred. Different
letters denote significant differences between lineages within the same year
Thank you to Ray Talent, Akash Bhalerao, and the Biology Greenhouse staff
for assistance with growing and maintaining our plants. Research supported
by NSF DEB-1415617 to AAF and NSF DEB-1314482 to AAF.
ALLOCHRONIC ISOLATION
• Found evidence of significantly different emergence times for each of
the S. longipennis lineages (4).
• Allochronic isolation contributes to reproductive isolation between
lineages (4).