Abstract
The Spanish dehesas have been severely affected by human activities that date to the prehistoric period and have suffered accelerated decline since the 1980s. Holm oak (Quercus ilex subsp. ballota (Desf.) Samp.) is a key component of this system, and its acorns provide an important food source for wildlife and domesticated livestock. Our earlier work showed structured variation in acorn morphology and biochemistry. Here, we used chloroplast and nuclear microsatellites to detect genetic structure among populations of Q. ilex from the major biogeographic regions of Andalusia. We found high levels of spatial differentiation with chloroplast DNA indicating little seed dispersal among populations. Spatial differentiation was weaker for nuclear DNA, presumably as a result of more widespread pollen dispersal and its larger effective population size. The Baetic Cordillera (Cádiz) population consistently appeared well separated from populations of the northern Sierra Morena, suggesting that the Guadalquivir Valley has played an important role in determining population divergence. This may be, in part, evolutionary, as suggested by chloroplast DNA, and, in part, a result of human-induced population isolation, as Q. ilex has been removed from the Guadalquivir Valley. Evolutionary gene flow rates were greater than contemporary rates, which were limited to unidirectional gene flow from Córdoba to other populations in the Sierra Morena and, surprisingly, to the southern population at Almería. The inconsistency between evolutionary and recent migration rates suggests an effect of anthropogenic activity over the last few generations of Q. ilex.
Highlights
Holm oak (Quercus ilex subsp. ballota (Desf.) Samp.) is the dominant tree species in natural forest ecosystems over large areas of the western Mediterranean Basin and is the distinctive element of the Spanish agrosilvopastoral ecosystem “dehesa”
Our objectives in this research were to (1) determine levels of divergence among populations across Andalusia, (2) estimate differences in migration at an evolutionary and contemporary scale as well as the role of population bottlenecks on genetic diversity among the regions within Andalusia, and (3) assess whether differences in morphological and biochemical traits that we have previously reported are associated with genetic divergence and gene flow within the region
Our results show surprisingly important levels of genetic structure, with chloroplast DNA indicating little gene exchange as a result of seed dispersal among populations
Summary
Holm oak (Quercus ilex subsp. ballota (Desf.) Samp.) is the dominant tree species in natural forest ecosystems over large areas of the western Mediterranean Basin and is the distinctive element of the Spanish agrosilvopastoral ecosystem “dehesa”. Ballota (Desf.) Samp.) is the dominant tree species in natural forest ecosystems over large areas of the western Mediterranean Basin and is the distinctive element of the Spanish agrosilvopastoral ecosystem “dehesa”. Both holm oak natural forest and the dehesa are seriously threatened by several factors, the most important of which are of anthropogenic origin: overexploitation, poor management practices, and fire, as well as diseases and adverse environmental conditions [1]. Q. ilex has become a priority species to achieve these objectives
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