Plant‐pollinator‐interactions are often highly specialised and may even lead to coevolution. Yet when plants and pollinators coevolve, it is not clear if this will also result in frequent cospeciation. Here we investigate the mutual evolutionary history of South African oil‐collecting Rediviva bees and their Diascia host plants, in which the elongated forelegs of female Rediviva have been suggested to coevolve with the oil‐producing spurs of their Diascia hosts. We found Rediviva foreleg length to be significantly correlated with Diascia spur length (P < 0.05, r = 0.43), suggestive of coevolution. However, as trait correlation could also be due to so‐called pollinator shifts, we tested if cospeciation or pollinator shifts have dominated the evolution of Rediviva–Diascia interactions by analysing previously generated phylogenies in a cophylogenetic framework. Distance‐based cophylogenetic analyses (PARAFIT, PACO) indicated significant congruence of the two phylogenies (P < 0.05). Yet we found that phylogenetic relatedness was correlated with ecological similarity (the spectrum of flower‐visitor interaction partners) only for Diascia but not for Rediviva, suggesting that phylogenetic congruence might be due to phylogenetic tracking by Diascia of Rediviva rather than strict (reciprocal) coevolution. Furthermore, event‐based reconciliation using a parsimony approach (CORE‐PA) revealed only 10‐14 cospeciation events but 53‐57 pollinator shifts. Probabilistic cophylogenetic analyses (COALA) supported this trend (0‐6 cospeciations, 29‐45 pollinator shifts). Our study suggests that diversification of the plant has been largely driven by the bee (phylogenetic tracking, pollinator shifts) but not vice versa. Moreover, our data suggest that, even in coevolving mutualisms, cospeciation events might rarely occur.
Should I stay or should I go? Pollinator shifts rather than cospeciation dominate the evolutionary history of South African Rediviva bees
Year: 2019
