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Role of pollinators in prezygotic isolation between calcicolous and silicicolous ecotypes of Silene nutans

par Cornet, Camille
Promoteur Van Rossum, Fabienne ;Noret, Nausicaa
Publication Non publié, 2020-08-25

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Résumé :

Silene nutans is a complex of cryptic species with a wide distribution across Europe. In particular, an eastern (E1) and a western (W1) genetic lineages are strongly differentiated and several barriers to reproduction between them have been demonstrated, including strong hybrid inviability. In southern Belgium, where the E1 and W1 lineages come into secondary contact, they occur on different soils, forming a calcicolous and a silicicolous ecotype, respectively. Given possible mating costs (pollen loss and investment in inviable progeny) involved in inter-ecotypic pollination, pollinator isolation, a prezygotic isolation mechanism, could have evolved between populations of the two ecotypes. Silene nutans is mainly pollinated by nocturnal moths, including nursery pollinators, which pollinate and lay their eggs in flowers, and whose caterpillars feed on the flowers and the seeds. However, the pollinator assemblages of the two ecotypes of S. nutans in southern Belgium are largely unknown and have never been compared.To determine if pollinator isolation represents a barrier to reproduction between the two ecotypes of S. nutans, pollen dispersal between populations was studied using fluorescent powdered dyes as pollen analogues, pollinator assemblages of the two ecotypes were observed using infrared cameras, and nursery pollinators were compared between the two ecotypes by rearing larvae found on the field.Overall, no evidence of pollinator isolation was found, since intra- and inter-ecotypic pollen flows were similar. Moreover, Hadena albimacula, a nursery pollinator specialized on S. nutans in Belgium, was found in the two ecotypes, both with the cameras visiting flowers and as caterpillars found in the field. However, the studied populations differed in their communities of seed predators, including rare nursery pollinators, suggesting a need for distinct conservation strategies.