DISENTANGLING THE MECHANISMS OF ECOLOGICAL SPECIATION IN SYMPATRIC PALM SPECIES

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How species originate and diverge from their progenitor is one of the key questions in biology. Divergence resulting from geographical isolation is a well-known driving force of speciation, but in theory populations could also diverge into separate species in the absence of geographical isolation, a mechanism generally referred to as speciation with gene flow. Documented cases with very high initial gene flow remain rare. Savolainen et al. provided compelling evidence for in situ speciation in a case study of two species of palm in the genus Howea, H. forsteriana and H. belmoreana, strictly endemic to the minute Lord Howe Island (LHI) in the Tasman Sea. Although this case study is viewed by many as probably one of the most convincing examples of sympatric speciation to date, it has still been hotly debated. Speciation in the face of high gene flow would occur most readily when ecological traits under divergent selection (e.g. soil preference or foraging behaviour) and traits associated with assortative mating (e.g. flowering time or body size) are correlated genetically. The two Howea palm species have distinct peaks of flowering time and have contrasting distributions related to substrate preferences: H. belmoreana is restricted to the older volcanic rocks, whereas H. forsteriana grows predominantly on calcareous soils but also on volcanic soils in disturbed sites. Given these features, a scenario for ecological speciation has been proposed. However, although ecological speciation is thought to be a major generator of biodiversity, the genetic basis behind this process is still poorly understood. Here, building on our previous research, we will determine the mechanisms of reproductive isolation in the evolution of sympatric Howea palms and identify the genes underlying speciation.