Temporal migration affects genetic diversity of biennial plant populations

How do differences in flowering time influence gene flow in populations of a biennial plant species?

Many plants require two or more years to produce flowers, but flowering individuals can be observed every year in natural populations. This is due to “temporal migrants”, that is, individuals flowering at a different time from the majority of their contemporaries. Biennial species are the simplest example of such a phenomenon. The number of temporal migrants will depend upon how heritable flowering time is. In the case of complete heritability, individuals inhabiting a given geographic location are subdivided into biennial mating groups (often referred to as demes) that would never inbreed, i.e. no temporal migrants. In the case in which reproduction time shows a significant environmental component, some individuals from a given mating group may behave, for example, as triennial instead of as biennial, contributing to gene flow between groups.

Biennial organism’s life cycle. (A) Depiction of two geographically separated populations over four years showing parent-offspring inheritance (dashed lines), spatial migration (solid black line), and temporal migration (solid red line). (B) Details on temporal migration showing parent-offspring inheritance (dashed lines) and temporal migration (solid line).

In their new study published in AoBP, Muñoz-Pajares et al. explore the consequences of temporal migration on the genetic diversity of Erysimum mediohispanicum populations. E. mediohispanicum is an endemic but common herb of the Iberian Peninsula exhibiting a biennial habit. The plant can usually grow for 2–3 years as vegetative rosettes before dying after reproduction. Hence, it exhibits variation in age at first reproduction, which is the trait required to generate temporal migrants among mating groups. For the first time, the authors report a U-shape relationship, meaning that intermediate migration rates maximize genetic differences between flowering and non-flowering individuals. This study contributes to unravelling the complexity of processes shaping genetic diversity of natural populations.

This study contributes to the AoBP Special Issue entitled The Ecology And Genetics Of Population Differentiation In Plants.