“50 years Annals of Forest Science”: Fifty years of genetic studies: what to make of the large amounts of variation found within populations?

Determining the sources and role of intra-specific genetic variation is a classical focus of evolutionary biology (Mitchell-Olds et al. 2007). Ever since the beginning of population genetic studies in forest trees, the observation of high levels of within-stand phenotypic and, later, molecular diversity has been a commonplace. In these sessile and long-lived organisms, the maintenance of adaptive genetic and phenotypic diversity within populations seems of paramount importance, because the environment is likely to change within their life span (Petit and Hampe 2006).
Phenotype diversity has been recurrently reported in forest trees (Borghetti et al. 1988; Cornelius 1994; Aitken et al. 1996; Howe et al. 2003; Wightman et al. 2008; O’Reilly-Wapstra et al. 2013); variability in life history traits (in particular, phenology) and adaptation to stress have consistently been a major subject in forestry. Such studies have typically focussed on variation at the regional or species range level, in relation to large-scale environmental (mostly climatic) gradients (Savolainen et al. 2007; Alberto et al. 2013). Examples abound in several tree species: to quote only a few, we may mention studies on oak bud burst (Ducousso et al. 1996), poplar leaf phenology (Hall et al. 2007), spruce bud burst and bud set (Mimura and Aitken 2010), Scots pine bud burst and frost resistance (Hurme et al. 2000) and growth performance in Spanish cedar (Navarro et al. 2004). The question of the adaptive relevance of clinal genetic variation was explicitly addressed in most such studies or underlay their experimental setup. The amount of genetically based trait variance due to differentiation between populations, as measured by Q ST (Spitze 1993; Prout and Barker 1993), varies from moderate to high depending on the trait; nevertheless, a substantial portion of variance is explained by family differences within populations, as Q ST is generally far smaller than one (see review for forest trees in Latta 2004). At the molecular level, intra-population variance for nuclear loci generally accounts for around 95 % of total variance, as observed by Hamrick and Godt (1990) and largely confirmed by all subsequent studies (see review in Petit et al. 2005). Early molecular marker-based studies reported, in addition to large amounts of intra-population diversity, significant fine-scale spatial genetic structure (FSGS) in several species; the first such study was performed by Brunel and Rodolphe (1985) in Picea abies, followed by a steady stream of publications ever since. Processes leading to the establishment of FSGS have been studied in detail in trees, and modelling of such processes has often been carried out by tree population geneticists (Hardy and Vekemans 1999; Smouse et al. 2001; Sagnard et al. 2007). Such detailed knowledge of FSGS has mainly insisted on neutral processes: it was implicitly assumed that genetic variation was a marker for tracing individual relatedness, not for adaptive processes, and the question of whether within-stand genetic variation may have any adaptive meaning was only seldom asked (but see, e.g. Epperson 1992). This was reasonable, given the nature of the markers used (almost always putatively neutral), but ignored growing evidence of quantitative trait aggregation within populations (e.g. Nanos et al. 2004).


Scotti I, González-Martínez S, Budde K, Lalagüe H 2015. Fifty years of genetic studies: what to make of the large amounts of variation found within populations? Ann. For. Sci.: 1-7. 10.1007/s13595-015-0471-z.

Link to full paper.

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