Coevolution




Yüklə 19.31 Kb.
tarix21.04.2016
ölçüsü19.31 Kb.
EEE 311/IB 343

Fall 2003
COEVOLUTION

I. Introduction


Coevolution - mutually induced evolutionary change between two or more species or populations.
- more specifically we think of coevolution as reciprocal evolutionary change in interacting species; the partial coordination of non-mixing gene pools over evolutionary time.
Darwin did not use the term coevolution but he did use coadaptation and thought of it as reciprocal change.
II. 1940's - 1960's - Four Independent Approaches to Study of Reciprocal Evolutionary Change
1. Flor (1942) - gene-for-gene concept
2. Mode's (1958) paper - first explicit mathematical model of coevolution; first to use term coevolution
3. Pimentel (1961) - reciprocal genetic changes could regulate populations of interacting species.
4. Ehrlich and Raven (1964) - used concept of reciprocal change to link adaptation and speciation in interacting species.
- Janzen (1980) - mutually induced evolution must be demonstrated.
- Seigler and Price (1976) - adaptive roles of at least some plant constituents are independent of selection pressure from a plant's enemies.
III. Five Modes of Coevolution
First three do not involve speciation


  1. Gene-for-Gene Coevolution - for each gene causing resistance in a host there is a corresponding (matching) gene for virulence in the parasite or pathogen.

Most coevolution will probably not fit a gene-for-gene hypothesis - most interactions are probably determined polygenically.


Pimentel and Bellotti (1976) - genetic stability (preventing the parasite from overcoming the hosts resistance) among parasite and host is determined by amount of genetic diversity in the host population, ample gene flow between parasite colonies and high selection coefficients on the parasite population from the host population.


  1. Specific Coevolution - where very close coevolution occurs without a gene-

for-gene relationship. Includes close mutualisms and symbioses.

e.g., Acacia cornigera and Pseudomyrmex ferruginea




  1. Guild or Diffuse Coevolution - reciprocal evolutionary change occurs among

groups of species rather than pairs of species. e.g., between pollinators

and flowering plants, some mimicry complexes, frugivorous birds and fleshy-fruited plants.




  1. Diversifying Coevolution - reciprocal evolution between species in which the

interaction causes at least one of the species to become subdivided into two or

more reproductively isolated populations. e.g., pollinators and plants showing extreme reciprocal specialization and those involving hosts and intracellular symbionts




  1. Escape and Radiation Coevolution - differs from other concepts of

coevolution in that it explicitly includes periods during which the interaction

between the taxa does not occur.


Five Steps:
1. plants produce novel secondary compounds through mutation and recombination.
2. The novel chemical compounds reduce the palatability of these plants to insects, and are therefore favored by natural selection.
3. Plants with these new compounds undergo evolutionary radiation into a new adaptive zone in which they are free of their former

herbivores.


4. A novel mutation or recombinant appears in an insect population that permits individuals to overcome the new plant secondary compounds.
5. These insects enter a new adaptive zone and radiate in numbers of species onto the plants containing the novel secondary compounds,

forming a new taxon of herbivores. e.g., Berenbaum 1983


IV. The Geographic Mosaic Theory of Coevolution
View, advanced by John Thompson in his 1994 book entitled "The Coevolutionary Process", that most interactions exhibit an evolutionary dynamic geographic mosaic, formed by the combined interpopulational differences in outcome, adaptation and specialization.
For example, natural selection on the relationship between a pair or group of species may favor directional selection in one population and polymorphism in another. It may favor escalation of antagonism in some environments and reduced antagonism or mutualism in others.
e.g., flower color variation in scarlet gilia (Paige and Whitham 1985) - geographic variation in flower color dependent upon local patterns of pollinator abundance and behavior
e.g., fig wasps and nematode parasites (Herre 1993) - geographic variation dependent upon transmission - vertical transmission favors nematodes that have no effect on the number of offspring produced by their host; horizontal transmission favors nematodes that are more destructive to their hosts.
e.g., antagonistic to mutualistic interactions among populations of scarlet gilia and their ungulate herbivores (Paige, unpublished) - geographic variation dependent upon genetic structure (and possibly densities) of populations.

References

Berenbaum, M. 1983. Coumarins and caterpillars: a case for coevolution. Evolution 37:163- 179.
deWit, P.J.G.M. 1992. Molecular characterization of gene-forgene systems in plant-fungus interactions and the application of avirulence genes in control of plant pathogens. Annual

Review of Phytopathology 30:391-418.


Ehrlich, P.R. and P.H. Raven. 1964. Butterflies and plants: a study in coevolution. Evolution 18:586-608.
Flor, H.H. 1942. Inheritance of pathogenicity in Melampsora lini. Phytopathology 32:653- 669.
Herre, E.A. 1993. Population structure and the evolution of virulence in nematode parasites of fig wasps. Science 259:1442-1445.
Janzen, D.H. 1966. Coevolution of mutualism between ants and acacia in Central America. Evolution 20:249-275.
Janzen, D.H. 1980. When is it coevolution? Evolution 34:611-612.
Kiester, A.R., R. Lande and D.W. Schemske. 1984. Models of coevolution and speciation in plants and their pollinators. The American Naturalist 124:220-243.
Kodric-Brown, A. and J.H. Brown. 1979. Competition between distantly related taxa in the coevolution of plants and pollinators. American Zoologist 19:1115-1127.
Mode, C.J. 1958. A mathematical model for the co-evolution of obligate parasites and their hosts. Evolution 12:158-165.
Paige, K.N. and T.G. Whitham. 1985. Individual and population shifts in flower color by scarlet

gilia: a mechanism for pollinator tracking. Science 227:315-317.


Pimentel, D. 1961. Animal population regulation by the genetic-feedback mechanism. The American Naturalist 95:65-79.
Pimentel, D. and A.C. Bellotti. 1976. Parasite-host population systems and genetic stability. The American Naturalist 110:877-888.
Seigler, D. and P.W. Price. 1976. Secondary compounds in plants: primary functions. The American Naturalist 110:101-105.
Thompson, J.N. 1989. Concepts of coevolution. Trends in Ecology and Evolution 4:179-183.
Thompson, J.N. 1994. The Coevolutionary Process. The University of Chicago Press, Chicago. 376 pp.


Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©azrefs.org 2016
rəhbərliyinə müraciət

    Ana səhifə