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Genetic Variation of Grassland Species Across an Altitude Gradient
Reference
Hahn, T., Kettle, C.J., Ghazoul, J., Frei, E.R., Matter, P. and Pluess, A.R. 2012. Patterns of genetic variation across altitude in three plant species of semi-dry grasslands. PLoS ONE 7: e41608.

Background
The authors write that "altitudinal gradients comprise an assemblage of environmental, especially climatic, variables which influence the distribution of plant species and, potentially, population genetic variation." And it has consequently been concluded by some that climate change may alter species distributions with the result that, locally, certain species "might become extinct," as per Sala et al. (2000) and Thomas et al. (2004).

The basis for this ominous conclusion, as Hahn et al. describe it, derives from the fact that "habitat suitability typically decreases at the upper edge of the altitudinal range where population size might decline," plus the observation that "in small populations genetic diversity is often reduced and inbreeding may increase (Lynch et al., 1995; Young et al., 1996)," with the result that "low genetic diversity and high inbreeding potentially cause loss of fitness due to fixation of deleterious alleles and inbreeding depression (Ouborg et al., 1991; Lynch et al., 1995; Young et al., 2002), which could affect future population persistence."

What was done
Questioning the generality of this suite of speculations, Hahn et al. investigated patterns of population genetic variation in three common plants of semi-dry grasslands - Briza media, a wind-pollinated grass, and Trifolium montanum and Ranunculus bulbosus, both of which are insect-pollinated herbs - at upper peripheral and lower more central altitudes in the Swiss Alps using the amplified fragment length polymorphism (AFLP) technique.

What was learned
The six Swiss scientists determined that contrary to what many have supposed, altitude has not affected genetic diversity in the grassland species they studied. In fact, they say that their study indicates that "populations at the upper periphery are not genetically depauperate or isolated," and that they thus may be "important populations for migration under climate change."

What it means
Hahn et al. conclude that what they call the "potentially pre-adapted genes" of the three plant species they studied might well "spread easily across altitudes," which would help to prevent their local extinction in a potentially warming world of the future.

References
Lynch, M., Conery, J. and Burger, R. 1995. Mutation accumulation and the extinction of small populations. The American Naturalist 146: 489-518.

Ouborg, N.J., Treuren, R. and Damme, J.M.M. 1991. The significance of genetic erosion in the process of extinction. Oecologia 86: 359-367.

Sala, O.E., Chapin, F.S., Armesto, J.J., Berlow, E., Bloomfield, J., Dirzo, R., Huber-Sanwald, E., Huenneke, L.F., Jackson, R.B., Kinzig, A., Leemans, R., Lodge, D.M., Mooney, H.A., Oesterheld, M., Poff, N.L., Sykes, M.T., Walker, B.H., Walker, M. and Wall, D.H. 2000. Global biodiversity scenarios for the year 2100. Science 287: 1770-1774.

Thomas, C.D., Cameron, A., Green, R.E., Bakkenes, M., Beaumont, L.J., Collingham, Y.C., Barend, F., Erasmus, N., Ferreira de Siqueira, M., Grainger, A., Hannah, L., Hughes, L., Huntley, B., van Jaarsveld, A.S., Midgley, G.F., Miles, L., Ortega-Huerta, M.A., Peterson, A.T., Phillips, O.L. and Williams, S.E. 2004. Extinction risk from climate change. Nature 427: 145-148.

Young, A.G., Boyle, T.J.B. and Brown, A.H.D. 1996. The population genetic consequences of habitat fragmentation for plants. Trends in Ecology and Evolution 11: 413-418.

Young, A.G., Hill, J.H., Murray, B.G. and Peakall, R. 2002. Breeding system, genetic diversity and clonal structure in the sub-alpine forb Rutidosis leiolepis F. Muell. (Asteraceae). Biological Conservation 106: 71-78.

Reviewed 20 February 2013