Abstract
Migration is a process with important implications for the genetic structure of populations. However, there is an aspect of migration seldom investigated in plants: migration between temporally isolated groups of individuals within the same geographic population. The genetic implications of temporal migration can be particularly relevant for semelparous organisms, which are those that reproduce only once in a lifetime after a certain period of growth. In this case, reproductive asynchrony in individuals of the same population generates demes of individuals differing in their developmental stage (non-reproductive and reproductive). These demes are connected by temporal migrants, that is, individuals that become annually asynchronous with respect to the rest of individuals of their same deme. Here, we investigated the extent of temporal migration and its effects on temporal genetic structure in the biennial plant Erysimum mediohispanicum. To this end, we conducted two independent complementary approaches. First, we empirically estimated temporal migration rates and temporal genetic structure in four populations of E. mediohispanicum during three consecutive years using nuclear microsatellites markers. Second, we developed a demographic genetic simulation model to assess genetic structure for different migration scenarios differing in temporal migration rates and their occurrence probabilities. We hypothesized that genetic structure decreased with increasing temporal migration rates due to the homogenizing effect of migration. Empirical and modelling results were consistent and indicated a U-shape relationship between genetic structure and temporal migration rates. Overall, they indicated the existence of temporal genetic structure and that such genetic structure indeed decreased with increasing temporal migration rates. However, genetic structure increased again at high temporal migration rates. The results shed light into the effects of reproductive asynchrony on important population genetic parameters. Our study contributes to unravel the complexity of some processes that may account for genetic diversity and genetic structure of natural populations.
Highlights
Population is a concept with several definitions that still generates vivid discussions in biological sciences (Jonckers 1973; Waples and Gaggiotti 2006; Hey 2011)
Empirical and modelling results were consistent and indicated a U-shape relationship between genetic structure and temporal migration rates. They indicated the existence of temporal genetic structure and that such genetic structure decreased with increasing temporal migration rates
The demographic survey conducted on four E. mediohispanicum sites between July 2010 and June 2012 allowed the estimation of temporal migration rates that varied from a low of 15 % to a high of 67 % (Table 1)
Summary
Population is a concept with several definitions that still generates vivid discussions in biological sciences (Jonckers 1973; Waples and Gaggiotti 2006; Hey 2011). We can describe a population as a group of co-occurring, interbreeding individuals that pass their genetic features on to the generation. A common characteristic of any population is that it inexorably exhibits variation in the number of individuals contributing genetically to the generation (i.e. the effective population size). This attribute determines spatio-temporal variation in allele frequency and shapes genetic structure (Wright 1951, 1965; Kimura and Weiss 1964; Rosenberg et al 2002). The role that population dynamics, migration, adaptive variation and genetic drift plays in determining the extent of genetic structure across space (Loveless and Hamrick 1984; Slatkin 1985, 1987; Rosenberg et al 2002; Manel et al 2003; Storfer et al 2007; Dionne et al 2008)
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