Mating system shifts a species’ range

Abstract

Understanding the ecological and evolutionary mechanisms that shape a species’ range is an important goal in evolutionary biology. Evidence indicates that mating system is an effective predictor of the global range of native species or naturalized alien plants, but the mechanisms underlying this predictability are not elaborated. Here, we develop a theoretical model to account for the ranges of plants under different mating systems based on migration‐selection processes (an idea proposed by Haldane). The model includes alternation of gametophyte and sporophyte generations in one life cycle and the dispersal of haploid pollen and diploid seeds as vectors for gene flow. We show that the interaction between selfing rates and gametophytic selection determines the role of mating system in shaping a species’ range. Selfing restricts the species’ range under gametophytic selection in nonrandom mating systems, but expands the species’ range under the absence of gametophytic selection in any mating system. Gametophytic selection slightly restricts the species’ range in random mating. Both logarithmic and logistic models of population demography yield similar conclusions in the case of fixed or evolving genetic variance. The theory also helps to explain a broader relationship between mating system and range size following biological invasion or plant naturalization.

The wave of gene advance under diverse systems of mating

“…Adaptive alleles spread from the initial population and move along one-dimensional space. Figure 1 shows the life cycle for each local population that follows the sequence of events: generation of pollen and ovules, pollen flow, selection at the gametophyte stage, mixed mating, seed flow, and selection at the sporophyte stage (Hu et al 2019). The difference from a previous study (Hu et al 2019) lies in that we focus here on the spread of advantageous mutant alleles where traveling waves occur (Fisher 1937).…”

“…Figure 1 shows the life cycle for each local population that follows the sequence of events: generation of pollen and ovules, pollen flow, selection at the gametophyte stage, mixed mating, seed flow, and selection at the sporophyte stage (Hu et al 2019). The difference from a previous study (Hu et al 2019) lies in that we focus here on the spread of advantageous mutant alleles where traveling waves occur (Fisher 1937). A traveling wave is the term given to the processes in which an allele advances at a constant speed while maintaining a constant shape of the distribution of allele frequencies (Shigesada and Kawasaki 1997, p 47).…”

“…MC simulations also confirm that selfing impedes the wave of advance of advantageous alleles. Selfing restricts colonization in the presence of gametophytic selection (Hu et al 2019). For instance, population density exhibits a traveling wave with the largest rate of spread under random mating (Fig.…”

“…For instance, pollen limitation can lead to Allee effects and slow down species invasion (Groom 1998;Davis et al 2004). Mating systems may act as a barrier to gene flow or interact with selection, which naturally influences the wave of advance of advantageous genes, or the species range expansion that could co-evolve with the wave of advance of advantageous genes (Hu et al 2019). Nevertheless, the significance of mating systems in regulating the wave of advance of advantageous genes remains to be elaborated.…”

“…The interaction of mating systems with selection in shaping gene spread can occur in both the gametophyte and sporophyte stages of the life cycle. We recently showed that selfing as a barrier to adaptive gene flow can limit a species range under gametophytic selection (Hu et al 2019). Differences between outcrossing rates could provide a biological basis for pre-mating barriers to both neutral and selective gene flow between genetically related species (Pickup et al 2019).…”