GEOGRAPHIC CLINES IN GENETIC VARIATION

Transcription

1 GEOGRAPHIC CLINES IN GENETIC VARIATION Gerald Rehfeldt (presented by Albert R. Stage) USDA Forest Service Rocky Mountain Research Station In risk mapping, the primary considerations are the presence of the host tree species, some measure of its density, and the distribution of the pest agent. High-density or overstocked stands are often considered to be of higher risk then stands with lower stocking levels; also important is the climatic stress on the population. This presentation shows how the predictions from a climate model can be converted to variables that may indicate the status of the stress of conifer species and their populations in the western USA and southwestern Canada. Forty-eight monthlies were derived from the basic temperature and precipitation data and fit to geographic surfaces with thin plate splines. These monthlies were then used to describe the clines of genetic variation that exist within species for growth characteristics. The mapping of clinal variation is useful in delineating seed zones and deriving seed transfer guidelines. The reverse image of such maps should indicate where the species would be under stress due to climatic conditions. For this reason, it is recommended that the monthlies and the climatic limits could be useful in risk mapping. 223

2 Rehfeldt INTRODUCTION Genetics research during the last 75 year or so has demonstrated that species of forest trees are composed of populations, each of which is adapted (i.e., physiologically attuned) to only a portion of the environmental gradient inhabited by the species. For most of the widespread species, models exist that describe the clinal variation in genetic responses of populations within species. These models are invariably driven by geographic predictors. But, now that a climate model is available that makes point predictions on the landscape, researchers can directly relate and eventually map genetic responses to climate Genetic variation is displayed along geographic gradients but interpretation is invariably in terms of climate. Out of the files is a geographic cline, Douglas-fir vs. elevation. Geographic variation is acting as a surrogate for climate, which is more difficult to measure. Armed with a climate model we then ready to assess plant-climate relationships. With climate models that provided point predictions we cannot replace the surrogates. In this slide, genetic variation in growth potential measured in a provenance test of populations of Douglas-fir is related to the elevation of the stand in which the seeds were collected.

3 Geographic Clines in Genetic Variation climate surfaces 3006 weather stations Hutchinson s thin plate splines Temperature and precipitation surfaces Algorithms for derived variables Splines for derived variables Predict for DEM grids (1 km) Map with GIS 2. There are 48 surfaces form normalized monthlies weather variables based on temperature and precipitation. climate variables derived from temperature and precipitation monthlies Degree-days > 5 C Degree-days < 0 C Frost-free period Last spring frost First fall frost Growing season degree-days > 5 C Summer-winter temperature differential Date degree-days > 5 C reaches 100 Mean annual temperature Mean annual precipitation Growing season precipitation Mean cold month temperature Minimum cold month temperature Mean warm month temperature Maximum warm month temperature Annual moisture index Summer moisture index All of these variables are of demonstrated importance in plant geography. The model can then be used to predict the climate across the landscape.

4 Rehfeldt This is a map of degree-days>5c. There are nearly 6 million terrestrial pixels in the map, and predicted values of degree days range from 0 to 6700.

5 Geographic Clines in Genetic Variation 5. In this map, we re zooming in from the previous slide on Lewiston, Idaho, Idaho s only seaport. This looks like a map of DEMs, but it s not. This is a map of degree-days that clearly shows the major drainages (Snake, Salmon, Clearwater), the Lewiston-Clarkston valley, and the high mountains. Degree-days range from 2700 to 0 for the pixels in this map. 227

6 Rehfeldt This is the same map of Lewiston that allows some of the topography to show through. Now, these maps are based on a 1 k grid which can be seen in the slides. It s important to know that the climate model itself makes point predictions that are not necessarily tied to the DEMs.

7 Geographic Clines in Genetic Variation 7. Frost-free periods vary from 0 to Negetative degree-days show how severe the winters are.

8 Rehfeldt Then using output from the General Circulation Models and refitting the splines, one can map climates predicted for the future. This map is for degree-days>5 and uses the greenhouse gas scenario (1% increase per year) of the Hadley and Canadian GCMs. Upper left is contemporary climate, upper right is that for the decade beginning in 2030, lower left for the decade beginning in 2060, and lower right for the decade beginning in Range in contemporary values 0 to Range in 2090 will be 0 to 8344.

9 Geographic Clines in Genetic Variation 10. This is the same sequence of illustrations that was used in the previous slide. It shows the effects of global warming on negative degree-days. Notice the effects are expected to be much greater on winter temperatures than on summer temperatures. 231 Degree-days < 0 Contemporary ranges is 0 to 2250, 2090 range would be 0 to 1052.

10 Rehfeldt FFP (frost-free period) current on left, 2090 on right..

11 Geographic Clines in Genetic Variation 12. To me, this one is scary. Global warming, of course, is portrayed as a temperature effect. Yet, the response of plants will be determined by the interaction of temperature with precipitation. This slide compares the contemporary annual moisture index (DD5/MAP) for the contemporary climate (left) with that projected for 2090 (right). 233 AMI (annual moisture index): left is for 2000, right is dd5/map.

12 Rehfeldt Now, armed with the climate model, we re ready to consider biological effects. This slide compares our ability to predict genetic responses of populations with geographic predictors (left) and climate predictors (right). Pinus sylvestris lattitude is a good surrogate for the climate variables.

13 Geographic Clines in Genetic Variation 14. This is a similar comparison for Engelmann spruce. Engelmann spruce elevation is a poor surrogate for the climate effects; in fact, it leads to the wrong interpretation. 235 GOALS assess population differentiation in relation to climate Pinus sylvestris and Larix sibirica Picea engelmannii compare effects of climate change Siberia vs. western USA 15. Studies of genetic responses to climate included researchers from RMRS and the Sukachev Institute of Forest in Krasnoyarsk, Russia. We had these objectives. Only those dealing with USA will be considered here.

14 Rehfeldt GOALS assess population differentiation in relation to climate Pinus sylvestris and Larix sibirica Picea engelmannii compare effects of climate change Siberia vs. western USA Definitions. genecology of Engelmann spruce 295 populations sampling natural distribution 18 blue spruce populations 20 white spruce common garden studies in Idaho 17. The USA example involves Engelmann spruce.

15 Geographic Clines in Genetic Variation 18. This photo was taken in the provenance test conducted at low elevation at the Priest River Experimental Forest. The populations are planted in 10- tree row plots. This means that any differences that are apparent between rows is due to genetic differences between the populations. At this mild site, differences are obvious. 237

16 Rehfeldt This is the high elevation planting site. Growth is less at high elevation, and differences were more difficult to detect.

17 Geographic Clines in Genetic Variation 20. Yet, in studies of genetic variation of western conifers, the best variables for assessing genetic differentiation invariably come from greenhouseshadehouse tests of shoot elongation where precise measurements can be made while controlling extraneous environmental effects (e.g., mosquitoes have a definite effect on the quality of the data). 239

18 Rehfeldt This slide shows different patterns of shoot elongation for spruce populations. Engelmann results genetic differences are obvious genetic differences most pronounced for patterns of shoot elongation winter temperatures drive population differentiation 22. The tests showed these results. They can be displayed by clines in relation to the climate where the seeds were collected.

19 Geographic Clines in Genetic Variation 23. The cline is steepest for the warmest climate and flattens out in the coldest climates. One can then describe clines like this on with regression models. 241

20 Rehfeldt regression models shoot elongation variable start cessation duration rate amount predictors winter temperatures, summer precipitation winter temperatures, summer maximum temperatures winter temperature, summer maximum temperature winter temperatures, summer max temperatures, freezing dates winter temperatures, summer maximum temperatures R Notice that the best predictors for spruce involve winter temperatures the variables that are expected to change the most with global warming. These models, of course, are suited to predicting responses. But to map responses, we need to know the climate at point locations on a map grid. The spline climate model, as shown previously, can be use to estimate the climate of each of the 6 million pixels for all of the climate variables that are important in predicting genetic responses in spruce. Then for each pixel, one can estimate the genetic response for a population growing there as if it had been tested in a common garden. This is what we get:

21 Geographic Clines in Genetic Variation 25. This map says that the duration of shoot elongation for populations from throughout western USA varies from 12 to 400 days. It s nonsense. And, the reason it doesn t make sense is that Engelmann spruce does not grow in all of these pixels. Before we can make sense out of this, we need an estimate of which pixels are climatically suited for the species. 243

22 Rehfeldt mapping distribution of Engelmann spruce 17 climate variables Climatic limits of 295 populations Canonical discriminant analysis of 9 species (1500 observations) First map now a second approximation. 27. This slide shows the results from four different attempts to map the Engelmann distribution. They re pretty good, but all have problems.

23 Geographic Clines in Genetic Variation 28. This map is the consensus of the four on the previous slide. 11% of the 7 million pixels show suitable climate Black Hills error, Colorado hole, Sierra Nevada and so on; remember, this is a climate unite. This map will suffice for this presentation, but one should be aware that we ve now developed statistical approaches that do a much better job. So, we now have a rough species map which gives us a basis for predicting genetic responses to climate. Still, one must remember: 245

24 Rehfeldt 29. Climate might be right but other things are limiting This map is more like it. Continuous variation across landscape, duration from 21 to 9 clines steepest for mildest climates but for the results to be useful to forest managers we need to classify the variation into seed zones or clime types.

25 Geographic Clines in Genetic Variation Climatypes breadth: ± standard error of the mean for t 0.2 for duration of shoot elongation: zone interval (days) 31. Climatype classifications below

26 Rehfeldt Geographic Zones for Duration of Shoot Elongation: all populations occupying pixels of the same color are expected to have a similar duration of shoot elongation when grown in a common garden. Zones are smaller in mild climates and broader in more severe. However, these zones are for only 1 variable. For describing genetic variation in this species, we have 5 variables and all need to be taken into consideration..

27 Geographic Clines in Genetic Variation Engelmann spruce climatypes variable duration of elongation amount of elongation cessation of elongation start of elongation rate of elongation zones All possible combinations of these zones would give 3600!! But, we re lucky. For western USA, there s only

28 Rehfeldt Here they are. This may not be 3600, but it s still a huge number that would be impractical to administer by management. So, when we think about how we got to this point, we realize that there were many sources of error along the way.

29 Geographic Clines in Genetic Variation Sources of error Population effects sampling errors experimental errors Climate data normalization fitting splines Genecology regression models: population effects on climate Mapping DEMs Climate predictions per DEM Raster calculator 35. There were sampling errors, experimental errors, errors in climate estimates, errors in the splines, errors in the DEMs, and errors of prediction all, we hope, are tiny. But, there are many sources of error such that the errors of estimation in delineating seed zones or climatypes can t be quantified. For this reason, one can not assume that the boundaries between these zones are fixed. In fact, 286 climatypes mapped for Englemann spruce are dominated by a few large climatypes. 251

30 Rehfeldt climatype summary statistics total climatypes: 268 climatypes with pixels<10: 30 climatypes with pixels>99: 168 area of 20 largest climatypes: 66% Keep in mind that 100 pixels is approximately equivalent to 1 township or 36 square miles. It s the few large climatypes on which management should concentrate. We can see the large ones as we zoom in: 37. There are 65 climatypes shown here for Idaho and Montana, but 20 account for about 75% of the distribution of spruce.

31 Geographic Clines in Genetic Variation Global Warming Amount Siberia: +6 to +8 C up to +20% (100 mm) ppt western USA: +4 to +5 C up to +17% (130 mm) ppt Effect Siberia: bonanza western USA: disaster 38. So, let s look at global warming: 253

32 Rehfeldt This slide shows a map of the distribution of spruce predicted for the climates of today (upper left), decade of 2030 (upper right), decade of 2060 (lower left), and decade of 2090 (lower right). Obviously, the climates favorable for this species move upwards off the top of the mountains and northward off the top of the map.

33 Geographic Clines in Genetic Variation 40. Here s a gallery of some of the contemporary sites that are expected to have a climate suitable for spruce at the end of the century. It s hard to imagine a orderly migration into such places. 255

34 Rehfeldt This is complicated, but this slide illustrates how populations and, therefore, species will respond to a change in climate. Each of these figures shows genetic response functions for two populations, for lodgepole pine on the left and Scots pine on the right. These results come from provenance tests. They show that populations have a climatic optimium within which growth (and survival is optimum). This is the point at the peak of the respective curves. However, populations differ in growth potential, as shown by the different heights of the curves. They also differ in cold hardiness, and this is illustrated by the differences in thex-axis coordinate of the optimum. And, there is a negative relationship between growth potential of populations and cold hardiness. Together, these characteristics mean that most populations are competitively excluded from their climatic optima. In fact, only one population, the one with the highest sit index growing in the mildest climates, actually occupies its optima. Other populations are relegated to suboptimal conditions and the degree of suboptimality increases as the climate becomes more and more severe. It s the degree of suboptimality that will determine initial responses to global warming. For populations occupying their optima, any warming will be deleterious to growth and survival. But, for populations occupying sites that are colder than their optima, a warming climate will be advantageous. Consequently, for western USA, global warming has disastrous consequences in both the short and long terms. But in Siberia, global warming should be a stimulant to growth and productivity.

35 Geographic Clines in Genetic Variation the time factor Interspecific effects Immigration is slow; extirpation can be fast Result is a temporarily impoverished flora Intraspecific effects Accommodating global warming requires more change per generation than genetic systems can provide Result is a lag in response to change Adjusting to global warming may require natural systems up to 1000 years Scariest part of global warming is the speed not the amount of change 42. When we think about global warming, one tends to concentrate on the amount of warming. But, in historical perspective, the amount of change isn t very much: temperatures fluctuated by about 7C during the Pleistocene. Plants can adjust to this amount of change. The scary part about global warming from the viewpoint of plants is the speed. 257

36 Rehfeldt finale when converted to variables with physiological importance, 4-5 C increase has huge impact -- alter species distributions -- wholesale redistribution of genotypes within species to mitigate the impact, mankind can participate in the evolutionary processes Concluding points about global warming. How does mankind participate? By assisting migration of genotypes to the novel location of their optimal climates. By planting more trees.

37 Geographic Clines in Genetic Variation 44. Maps like this one can provide assistance to the manager. The blue shows the distribution of a climatypes in the contemporary climate. The orange shows the 2030 projected distribution of the climate inhabited by the climatypes, the yellow the 2060 distribution, and the pink the 2090 distribution. For mankind to be participating in the evolutionary process, seeds today could be collected in the blue zone and planted in the orange zone in anticipation of the change in climate. 259

38 Rehfeldt opinion page yes, it s happening no, the GCM s don t quite have it right yes, there is something we can do to mitigate the effects but, it s the cause not the effect that needs attention buy now Siberian or Yukonian estates, sit back, and watch the show Because the cause of the problem is not being addressed, what we can accomplish as individuals is almost nothing compared to the scope of the problem. My suggestion is to buy now while permafrost is still cheap and watch natural history unfold.

39 Geographic Clines in Genetic Variation REFERENCES Rehfeldt, G.E., C.C. Ying, D.L. Spittlehouse, and D.L. Hamilton Genetic responses to climate in Pinus contorta: niche breadth, climate change, and reforestation. Ecological Monographs 69: Rehfeldt, G.E., C.C. Ying, and W.R. Wykoff Physiologic Plasticity, Evolution, and Impacts of a Changing climate on Pinus contorta. Climatic Change 50: Rehfeldt, G.E., Ying CC, Spittlehouse DL, Hamilton DL (1999) Genetic responses to climate in Pinus contorta: niche breadth, climate change, and reforestation. Ecological Monographs 69: Rehfeldt, G.E., N.M. Tchebakova, Y.I. Parfenova, W.R. Wykoff, N.A. Kouzmina, and L.I. Milyutin Intraspecific responses to climate in Pinus sylvestris. Global Change Biology 8: Rehfeldt, G.E. 2004, Inter- and intra-specific variation in Picea engelmannii and its congeneric cohorts: biosystematics, genecology and climate-change. Gen. Tech. Rep. RMRS-GTR-134. Ft Collins, CO: U.S. Department of Agriculture, Forest Service, Rock Mountain Research Station. Rehfeldt, G.E., N.M. Tchebakova, and E. Parfenova Genetic responses to climate and climate change in conifers of the temperate and boreal forests. Recent Advances in Genetics and Breeding 1: Rehfeldt, G.E A spline climate model for western United States. Gen. Tech. Rep. RMRS- GTR. Ft Collins, CO: U.S. Department of Agriculture, Forest Service, Rock Mountain Research Station. In Press. 261

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