Hybridization and crossability in Caiophora (Loasaceae subfam. Loasoideae): Are interfertile species and inbred populations results of a recent radiation?

Abstract

Interspecific hybridization is considered a possible mechanism of plant diversification. The Andes are a hotspot of biodiversity, but hybridization in Andean taxa has so far not been investigated intensively. The current study investigates crossability in Caiophora (Loasaceae subfam. Loasoideae) by experimental interspecific hybridization of seven different species. Hand pollination was undertaken, developing fruits counted, thousand (seed) grain weights, and seed viability were examined. Cross pollination led to some fruit set in 36 of the 37 different combinations. Overall fruit set was virtually identical irrespective of the combination of parental plants. Mean germination rates were much higher in hybrid seeds, indicating a marked heterosis effect and the possible presence of an inbreeding depression in the source populations: In experimental hybridization the divergent taxa of Caiophora behave like isolated, inbred populations of a single species. Allopatry and different habitat preferences seem to be the key factors keeping the (interfertile) taxa of Caiophora apart in the apparent absence of both postmating isolating mechanisms and obvious isolating mechanisms in phenology and floral biology. Interspecific hybrids reported from the wild appear to be the result of secondary contact due to human impact.

New insights into the phylogenetic relationships, character evolution, and phytogeographic patterns of Calceolaria (Calceolariaceae)

“…Most Calceolaria species have a narrow distribution or are endemic to single valleys of the Andean mountain range, so rapid allopatric differentiation may have taken place. Similarly, previous studies of two Andean genera ( Hughes and Eastwood, 2006 ;Ackermann et al, 2008 ) also reported an extraordinary rate of speciation, resulting in a large number of geographically isolated but closely related species, a phenomenon referred to as an island radiation on a continental scale.…”

“…It has been proposed that diversifi cation of pollinating animals, concurrent with the topographical and environmental changes resulting from the uplift of the Andes, could have promoted diversifi cation of the fl ora (e.g., Ezcurra, 2002 ;Kay et al, 2005 ;Hughes and Eastwood, 2006 ;Smith and Baum, 2006;Ackermann et al, 2008 ). It has been proposed that diversifi cation of pollinating animals, concurrent with the topographical and environmental changes resulting from the uplift of the Andes, could have promoted diversifi cation of the fl ora (e.g., Ezcurra, 2002 ;Kay et al, 2005 ;Hughes and Eastwood, 2006 ;Smith and Baum, 2006;Ackermann et al, 2008 ).…”

Maintenance of species integrity in the context of a recent radiation: the case ofJamesbrittenia(Scrophulariaceae: Limoselleae) in southern Africa

“…Similar patterns are also observed in Andean plant radiations, with species in both the Iochrominae clade of Solanaceae (crown age = 4.56 Mya; S€ arkinen et al, 2013) and the genus Caiophora C.Presl. (crown age unknown) crossing readily to produce viable offspring (Smith & Baum, 2007;Ackermann et al, 2008). The implication of these patterns is that the development of strong post-zygotic isolation typically requires divergence intervals of at least 6 Myr, and that the question of whether plant species represent reproductively independent entities, corresponding to biological species (Rieseberg, Wood & Baack, 2006), depends on evolutionary context, including divergence time.…”

“…Importantly, as an early Pliocene origin would identify these radiations as being similar in age to those triggered by Andean uplift (Hughes & Atchison, ), the weak post‐zygotic isolation, which is a common feature of Andean plant lineages (e.g. Smith & Baum, ; Ackermann et al ., ), should be a feature of this system also.…”

Genetic admixture and lineage separation in a southern Andean plant

“…Hybridization has been frequently documented in the southern Andes (e.g. Fuchsia : Berry 1982 ; Discaria : Tortosa 1983 ) but there are few works that explore its evolutionary relevance in this region ( Calceolaria : Sérsic et al 2001 ; Caiophora : Ackermann et al 2008 ; Nothofagus : Acosta and Premoli 2010 ; Soliani et al 2012 ). A better understanding of natural hybrids between Escallonia species will elucidate taxonomic problems in the genus and will provide new hypotheses on its evolution.…”