Báo cáo khoa học: "Genetics of oak species and the spectre of global climate change"

Chia sẻ: Nguyễn Minh Thắng | Ngày: | Loại File: PDF | Số trang:5

Thêm vào BST

Báo xấu

67
lượt xem 2
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: Genetics of oak species and the spectre of global climate change....

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Báo cáo khoa học: "Genetics of oak species and the spectre of global climate change"

Final address Genetics of oak species and the spectre of global climate change FT Ledig Institute of Forest Genetics, Pacific Southwest Research Station, USDA Forest Service, PO Box 245, Berkeley, CA 94701, USA Summary — Information on the population genetics of oaks is important in designing conservation strategies. If the threat of global warming materializes as projected, it will be necessary to actively in- tervene to conserve the genetic resources of oaks and other wildland plants. What has been learned about the genetic structure of oak species and gene flow within and among species will guide sam- pling efforts and the management of in situ reserves. However, it will be necessary to provide a backup for natural reserves by propagating oaks ex situ in provenance tests, clone banks or tissue cuiture. climate change / population genetics / conservation Résumé — Génétique des chênes et le spectre du changement climatique. L’information rela- tive à la génétique des populations des chênes est un préalable nécessaire à l’adoption d’une straté- gie de conservation de ces espèces. Si la menace du réchauffement global se concrétise, des me- sures concrètes devront être prises pour sauvegarder les ressources génétiques des chênes et d’autres espèces sauvages. Les connaissances acquises à propos de la structure génétique des chênes et des flux géniques à l’intérieur et entre espèces seront valorisées dans l’échantillonnage et la gestion in situ des réserves. En outre il sera sans doute nécessaire d’attribuer des moyens com- plémentaires à cette conservation en multipliant ex situ les chênes en tests de provenances, banques de clones ou par la culture in vitro. changement climatique / génétique des populations / conservation in his reference to the Strasbourg In closing the IUFRO Symposium on warming the Genetics of Oak Species,I would like Conference of 1990. He stressed the im- to draw a connection between what we portance of genetic resources in an era of have learned about the population biology environmental change. However, we gen- of oaks and the dilemma of conservation erally failed to follow Mr Chevalier’s lead in the face of global warming. and largely neglected the implications of our research to the management of genet- In his welcoming address, B Chevalier, ic resources threatened by global warm- Sous-Directeur des Forêts au Ministère de ing. l’Agriculture, introduced the topic of global
the rich genetic resources that Kevin Nixon (Davis and Zabin- Recently, two groups described in Mexico may find a place in ski, 1992; Botkin, 1991) modeled the effect the southern United States or Europe, if of a 2.5 °C change on the ranges of some North American forest trees. Though no Mexican species can adjust to the longer, oaks were included in their simulations, northern photoperiods. Davis and Zabinski (1992) did model the However, the situation may be even effect of climate change on the range of than the ecologists have projected. worse another Fagaceae, American beech (Fa- None of them has taken genetic variation gus grandifolia Ehrh). An increase in mean into account. Their models suggest that annual temperature of 2.5 °C will eliminate beech and other species can survive in the beech from most of its range in the south- northern United States and Canada after ern and central United States (fig 1). the projected changes, but they assume Changes in forest composition will occur that every individual throughout the present very rapidly, in less than 50 years, as pro- range has identical environmental toler- jected by Botkin et al (1991) forest growth ances and limitations. As geneticists, we simulator. know that is not so. What might survive in the northern United States after global Where will the genetic resources come from to replace the species lost as a result warming of 2.5 °C are not beech trees of climate change? Perhaps, southern adapted to the current environment, but beech that presently grow at the southern species can be moved north. Mark Cog- limit of their range. Therefore,I expect gleshall may no longer have to worry about winter injury to his southern red oak widespread forest decline throughout the (Quercus falcata Michx) in Indiana. And range.
It is likely that some trees will survive. al systems of in situ reserves; ie, no sys- The great genic diversity of most of our tem of ex situ conservation. In the United forest species argues for the existence of States, as Kim Steiner told us, very few im- variants preadapted to the new condi- provement programs have adequately inte- tions. A wealth of experience has demon- grated gene conservation into their opera- strated that, on any reasonable test site, tions. even the most maladapted provenance No institutional mechanism exists for will harbor a few tolerant individuals. Nev- the maintenance of seedbanks and prove- ertheless, a severe reduction in numbers nance tests past the tenure of the scien- is to be expected and, coupled with demo- tists who initiated them. Howard Kriebel graphic chance, is likely to lead to local provided cases in point. With the exception extirpations. Alexis Ducousso pointed out of his provenance test of red oak (Quercus that oaks are strongly outcrossing. A dras- rubra L), there were only 2 other old, oak tic reduction in numbers is likely to in- provenance tests in the United States; crease inbreeding, reducing seed set and Scott Pauley established a test of northern increasing the probability of reproductive red oak and Roland Schoenike established failure. a test of southern red oak. Both were lost In the Holocene and in earlier post- when Pauley and Schoenike died. When a glacial eras, oaks contended with change scientist in the United States installs ambi- by migration to new habitat. That is not tious tests, there is no provision for its con- possible in today’s world. Migration corri- tinuity or even for archiving the records. dors are closed by human-imposed Therefore, it was encouraging to hear Jo- barriers; ie, agricultural fields and urban chen Kleinschmitt emphasize the need to development. Furthermore, the projected provide for continuity when he told us changes in the next century will be much about his extensive tests of pedunculate too rapid to be accommodated by migra- (Q robur L) and sessile (Q petraea (Matt) tion. The clustered pattern of chloroplast Liebl) oaks. genomes found by Alexis Ducousso and Storage of seed is not a viable long- his colleagues underscores the limited dis- option for ex situ conservation of term persal capacity of acorns. oaks. However, the success in clonal prop- Therefore, we must be prepared to agation and tissue culture reported by provenances as well as import new move Vladimir Chalupa, Jorg Jorgensen, and species if worst-case projections are real- others offered hope that genetic resources ized. If we are to move materials, we need can be preserved in clone banks. to provide for the conservation of ge- With that as preamble, let’s turn our at- netic resources now. Genetic resources for tention to population genetics. Why do we, breeding are not my main concern. I am as forest geneticists, establish provenance more concerned about conservation of trials, uniform garden studies, reciprocal the genetic diversity necessary to restore transplant experiments? So we can map healthy ecosystems. In situ conservation is clinal or ecotypic. If patterns of variation the best strategy because it allows for the — the patterns are regular, we interpolate to evolutionary dynamics necessary to main- pinpoint the area of desirable seed sourc- tain viable communities. But what do we es. Or we identify distinct populations do in case of catastrophic loss of the re- which it may be prudent to conserve, either serves or an environment that changes too in situ or ex situ. We seek patterns be- permit evolutionary adaptation? rapidly to cause we cannot test every population. A We have back up to present nation- no our
pattern emerging from isozyme studies in model for management of forest genetic conifers is north-south trend of increas- resources? Do they suggest that long-term a ing heterozygosity (Ledig, 1987). Does a evolutionary success is favored by diversi- pattern like that exist in oaks? Antoine ty and an open recombination system?I Kremer suggested that it might. However, believe that is what Gerhard Muller-Starck in species not forced south by glaciation, implied. such as the California oaks (Q agrifolia Of course, many questions still remain Nee, Q douglasii Hook and Arn and Q gar- about the population genetics of oaks, as ryana Dougl ex Hook) that Larry Riggs de- well as other forest trees. For example, we scribed, no such patterns should exist. In have not obtained a good consensus on Europe also, although affected by glacia- the importance of selection in the short- tion, patterns may be especially difficult to term. Antoine Kremer invoked selection to define because of the impacts of ancient explain an increase in heterozygosity with cultures. age of northern red oak naturalized in What else does population genetics tell France. Oak decline may provide an even us? It tells us how to manage species to better opportunity to document selection. reduce inbreeding, the appropriate size for Studies of oak decline in the United States reserves, and the most efficient sampling have revealed that both white and red oak scheme for conservation or breeding. From populations are divided into 2 groups: Victoria Sork we learned that white oak those that suffered drastic decline after (Q alba L) and northern red oak from the 1951 and those that did not. Are these midwestern United States may grow in groups genetically different? Is selection patches of related trees. This may suggest occurring? how we should thin a stand to reduce in- To conclude, change is inevitable, breeding or how to sample for conserva- whether it is decline resulting from intro- tion or testing purposes. duced disease, global warming induced by Others who spoke at the symposium human activities, or part of a natural cycle used isozyme studies to measure gene beyond our making or control. Can we pre- flow between taxa. Roberto Bacilieri serve the present genetic structure of our found that gene flow between intraspecif- oak forests? No! But we are changing the ic populations of European oaks was 100 environment so rapidly that oak forests are times higher than gene flow between Eu- certain to suffer genetic erosion biotype — rope’s 2 problem taxa, sessile and pedun- compounding the threats to depletion — culate oak. However, Rémy Petit found productivity and forest health... unless we that rDNA gave estimates of gene flow 10 are prepared to learn more about the ge- times greater than that indicated by iso- netics of forest populations and then man- zymes. This is disturbing, and we need age them to maintain diversity. We must more work with DNA markers, as Kornel prepare to move genetic materials and Berg told us. We must develop probes for track changing environments. restriction fragment length polymor- I have doubts that genetic improvement phisms, which will certainly be a more of oaks is a sound economic investment in random set of markers than isozymes. the United States, but an oak insurance And we need comparisons using the policy is! Studies of population biology may RAPD technology. tell us how to build a lifeboat- an ark, if Studies of hybridization may be espe- you wish. And for that, society is usually cially valuable. Do the oaks provide a willing to pay.
Global REFERENCES Warming and Biological Diversity (Pe- RL, Lovejoy TJ, eds), Yale Univ Press, ters New Haven Botkin DB, Woodby DA, Nisbet RA (1991) Kirt- FT (1987) Genetic structure and the con- Ledig land’s warbler habitats: a possible early indica- servation of California’s endemic and near tor of climatic warming. Biol Conserv 56, 63-78 endemic conifers. In: Conservation and Man- Davis MB, Zabinski C (1992) Changes in geo- agement of Rare and Endangered Plants graphical range resulting from greenhouse (Elias TS, ed) California Native Plant Society, warming: effects on biodiversity in forests. In: Sacramento, 587-594