Population differentiation
Microevolutionary processes could be an alternative explanation for the colonization history of L. columnaris in the Afromontane sky islands of West Central Africa. The early split in L. columnarispopulations between the mainland and South Bioko possibly occurred via a founder event and genetic bottleneck or subsequent genetic drift so that South Bioko plastomes are very distinct relative to the other plastome groups. Furthermore, the two early splits (Figure 3) suggest two independent colonization events of L. columnaris on the island. Under this scenario, the colonization history was likely from mainland Cameroon’s old sky islands to the southern young sky islands in Bioko.
This explanation should be developed with population genetic analyses to explore the correlation between geographic distance and genetic differentiation of populations and find which evolutionary forces are responsible for population differentiation in Bioko.