Toward a cohesive understanding of glyphosate resistance evolution in the common morning glory

Transcription

1 Toward a cohesive understanding of glyphosate resistance evolution in the common morning glory Regina Baucom Dept of Ecology and Evolutionary Biology University of Michigan Ann Arbor, MI, USA

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3 Treated area (proportion of planted) Herbicide use on US soybean RoundUp Baucom R.S. and R. Mauricio PNAS

4 RoundUp Resistant Weeds

5 The evolution of herbicide resistance Weed population Evolution in action Susceptible Fitness costs associated with resistance? Multiple mechanisms of resistance across populations? Resistance novel or introduced via gene flow? Resistance diagnosed

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7 Glyphosate, or RoundUp Non-selective postemergence herbicide Accumulates in the apical meristems Inhibits plant aromatic amino acid biosynthesis

8 The evolution of glyphosate resistance in the common morning glory, Ipomoea purpurea Dynamics of resistance evolution within one population Traits that respond to selection Correlated responses to selection The geographic mosaic of herbicide resistance evolution Spatial variation Temporal variation Assessment of neutral genetic variation across the landscape

9 Genetic variation for resistance?

10 Genetic variation for resistance? 50% 84%

11 Additive genetic variation for resistance 50% 84%

12 Additive genetic variation for resistance 50% 84%

13 Artificial selection to create divergent population Crossing design Direction of selection X X X 8 X X X 9 X X X 10 X X X Resistance (2) 11 X X X 12 X X X X X X Bottom 20% Glyphosate Resistant Top 20% Glyphosate Resistant 8 X X X 9 X X X 10 X X X 11 X X X 12 X X X Resistance (2) X X X 8 X X X 9 X X X 10 X X X 11 X X X 12 X X X Control (2)

14 Greenhouse resistance screens Measure response to selection 1. Proportion height of main stem remaining 2. Proportion leaves remaining 6 Selection lines (2) Up, (2) Down, (2) Control 16 Families per selection line 3 replicate seed per family Applied kg ai/hc -1 Phenotyped plants for size before and after spray

15 I. purpurea responds to artificial selection for increased/decreased resistance Change in height Response to direct selection Selection Line χ 2 = 13.94; P <0.001

16 I. purpurea responds to artificial selection for increased/decreased resistance Change in height Response to direct selection Change in leaf number Response to indirect selection Selection Line χ 2 = 13.94; P <0.001 Selection Line χ 2 = 10.35; P <0.005

17 Average number of leaves, pre-herbicide Susceptible selection lines are larger pre-spray: fitness cost? b a a Control lines Resistant lines Susceptible lines

18 Within-population dynamics Genetic variation that responds to artificial selection Correlated changes in size Genetic basis? No evidence for target site variation in the EPSPS locus No evidence for higher expression of EPSPS RNA-seq screen points to increased expression of cytochrome p450 gene, i.e., possible metabolism

19 Resistance at a larger scale? The geographic mosaic of herbicide resistance Are there hotspots of glyphosate resistance across geography? Has resistance increased over time? Does gene flow play a role in glyphosate resistance evolution?

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21 Greenhouse resistance assay 2 experiments in greenhouse 47 populations 6 herbicide rates (0, etc) 2 collection years (2003, 2012) ~9K plants total Planted all as seed Applied herbicide at 6 in height Measured size before herbicide Size 2 weeks post-spray Death

22 Survival Species average ED 50 is close to recommended dose kg a.i./ha (95% CI: ) IN OH VA MWAVE SC NC TN SEAVE SPECIES Treatment (kg ai/ha) Variation across regions for ED 50 value

23 Spatial variation in glyphosate resistance 1.7 kg a.i. hc -1 Survival 0 25% 25 50% 50 75% % 3.4 kg a.i. hc Km 100 Km Population: χ 2 = 81.75, P < State: χ 2 = 10.5, P = 0.01 Population: χ 2 = 0, P = 1 State: χ 2 = 8.6, P = 0.01

24 Survival Populations vary for % survival IN OH VA NC SC TN

25 Spatial autocorrelation of resistance % alive post-spray % dead post-spray Significant, but on local scale (w/in 40miles) I = 0.829; P = No isolation by distance for survival R = 0.02; P = 0.27 Less survival in northern populations compared to southern populations

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27 Survival Resistance has increased over time Χ 2 = 12.45; P < NC9 NC29 NC19 NC10 SC5 TN32 TN1 TN20

28 Survival Resistance has increased over time Χ 2 = 12.45; P < NC9 NC29 NC19 NC10 SC5 TN32 TN1 TN20 W = 18.5; P = 1

29 Survival Resistance has increased over time Χ 2 = 12.45; P < NC9 NC29 NC19 NC10 SC5 TN32 TN1 TN20 W = 84.5; P = 0.01

30 Patterns of gene flow or genetic differentiation? DNA from 35 populations (18 individuals/pop) SSR genotyping using 15 polymorphic loci Hierarchical AMOVA Structure analysis Isolation by distance

31 Significant, but low genetic differentiation among populations Analysis of Molecular Variance Source Df F-statistic F-estimate P Region (MW vs SE) 1 F RT State 5 F SR Population 33 F ST Within Populations 585 F IS Structure analysis IN OH NC SC TN VA K = 3 was most likely clusters from Structure analysis (ln(p(d) = ))

32 Genetic Distance No detectable isolation by distance R = 0.002, P = Ln(Geographic Distance (km))

33 Coordinate 1 PCoA of neutral genetic variation State TN IN VA NC SC * Midwest * OH Survivorship Coordinate 2 Populations do not cluster according to resistance level

34 What is the pattern of resistance evolution in nature? Standing genetic variation & Lineage sorting Resistance present ancestrally Resistance introduced via gene flow All about selection history 100 Km

35 What is the pattern of resistance evolution in nature? Standing genetic variation & Lineage sorting Resistance present ancestrally Resistance introduced via gene flow All about selection history Not likely based on PCoA 100 Km

36 What is the pattern of resistance evolution in nature? Standing genetic variation & Lineage sorting Resistance present ancestrally Resistance introduced via gene flow All about selection history Novel mutations in each population Lack of genetic structure due to recent history of introduction Rapid evolution of resistance locally 100 Km

37 What is the pattern of resistance evolution in nature? Standing genetic variation & Lineage sorting Resistance present ancestrally Resistance introduced via gene flow All about selection history 100 Km Novel mutations in each population Lack of genetic structure due to recent history of introduction Rapid evolution of resistance locally All about selection history Need to identify loci/locus of resistance across geographically separate populations to differentiate alternative hypotheses

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39 Acknowledgements Sara Matthews Adam Kuester Trent Leslie Shu-mei Chang UGA Funding sources: