Should I stay or should I go? Pollinator shifts rather than cospeciation dominate the evolutionary history of South African Rediviva bees and their Diascia host plants

Plant–pollinator interactions are often highly specialised, which may be a consequence of co‐evolution. Yet when plants and pollinators co‐evolve, 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. After controlling for phylogenetic nonindependence, we found Rediviva foreleg length to be significantly correlated with Diascia spur length, suggestive of co‐evolution. However, as trait correlation could also be due to pollinator shifts, we tested if cospeciation or pollinator shifts have dominated the evolution of Rediviva–Diascia interactions by analysing phylogenies in a cophylogenetic framework. Distance‐based cophylogenetic analyses (PARAFIT, PACo) indicated significant congruence of the two phylogenies under most conditions. Yet, we found that phylogenetic relatedness was correlated with ecological similarity (the spectrum of partners that each taxon interacted with) 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) co‐evolution. Furthermore, event‐based reconciliation using a parsimony approach (CORE‐PA) on average revealed only 11–13 cospeciation events but 58–80 pollinator shifts. Probabilistic cophylogenetic analyses (COALA) supported this trend (8–29 cospeciations vs. 40 pollinator shifts). Our study suggests that diversification of Diascia has been largely driven by Rediviva (phylogenetic tracking, pollinator shifts) but not vice versa. Moreover, our data suggest that, even in co‐evolving mutualisms, cospeciation events might occur only infrequently.     

Broad-scale latitudinal patterns of genetic diversity among native European and introduced house sparrow (Passer domesticus) populations

Introduced species offer unique opportunities to study evolution in new environments, and some provide opportunities for understanding the mechanisms underlying macroecological patterns. We sought to determine how introduction history impacted genetic diversity and differentiation of the house sparrow (Passer domesticus), one of the most broadly distributed bird species. We screened eight microsatellite loci in 316 individuals from 16 locations in the native and introduced ranges. Significant population structure occurred between native than introduced house sparrows. Introduced house sparrows were distinguished into one North American group and a highly differentiated Kenyan group. Genetic differentiation estimates identified a high magnitude of differentiation between Kenya and all other populations, but demonstrated that European and North American samples were differentiated too. Our results support previous claims that introduced North American populations likely had few source populations, and indicate house sparrows established populations after introduction. Genetic diversity also differed among native, introduced North American, and Kenyan populations with Kenyan birds being least diverse. In some cases, house sparrow populations appeared to maintain or recover genetic diversity relatively rapidly after range expansion (<50 years; Mexico and Panama), but in others (Kenya) the effect of introduction persisted over the same period. In both native and introduced populations, genetic diversity exhibited large-scale geographic patterns, increasing towards the equator. Such patterns of genetic diversity are concordant with two previously described models of genetic diversity, the latitudinal model and the species diversity model.