Sympatric bromeliad species (Pitcairnia spp.) facilitate tests of mechanisms involved in species cohesion and reproductive isolation in Neotropical inselbergs

Abstract

The roles of intra-and interspecific gene flow in speciation and species evolution are topics of great current interest in molecular ecology and evolutionary biology. Recent modelling studies call for new empirical data to test hypotheses arising from the recent shift from a 'whole-genome reproductive isolation' view to a 'genic' view of species and speciation. Particularly scarce (and thus of particular interest) are molecular genetic data on recently radiated, naturally hybridizing species in strongly structured and species-rich environments. Here, we studied four sympatric plant species (Pitcairnia spp.; Bromeliaceae) adapted to Neotropical inselbergs (isolated outcrops resembling habitat 'islands' in tropical rainforests) using nuclear and plastid DNA. Patterns of plastid DNA haplotype sharing and nuclear genomic admixture suggest the presence of both, incomplete lineage sorting and interspecific gene flow over extended periods of time. Integrity and cohesion of inselberg species of Pitcairnia are maintained despite introgression and in the face of extremely low within-species migration rates (N e m < 1 migrant per generation). Cross-evaluation of our genetic data against published pollination experiments indicate that species integrity is maintained by the simultaneous action of multiple prezygotic barriers, including flowering phenology, pollinator isolation and divergent mating systems. Postzygotic Bateson-Dobzhansky-Muller incompatibilities appear to contribute to isolation, as suggested by asymmetric introgression rates of single loci. Our results suggest that incomplete lineage sorting, hybridization and introgression form integral aspects of adaptive radiation in Neotropical inselberg 'archipelagos'. Inselbergs with multiple closely related co-occurring species should be of special interest to students of speciation in mountain systems, and to ongoing conservation programmes in the Atlantic Rainforest biodiversity hotspot.

Floristic and ecological characterization of habitat types on an inselberg in Minas Gerais, southeastern Brazil

“…Alcantarea, Encholirium, Orthophytum, Pitcairnia, Tillandsia and Vriesea). These genera dominate inselberg landscapes in Brazil and some have been the subject of studies of molecular and evolutionary biology (Barbará et al 2007;Palma-Silva et al 2011), which showed that intraspecific gene flow among inselbergs for certain bromeliads is unusually low (PalmaSilva et al 2011), reinforcing the island-like characterization of these outcrops. It is important to note that mat-forming Bromeliaceae possess particular traits to cope with the drought conditions of inselbergs .…”

Development and characterization of microsatellite markers for Vriesea simplex (Bromeliaceae) and cross-amplification in other species of Bromeliaceae

“…The Bromeliaceae is a widely represented angiosperm family in the Neotropics and is an excellent example of adaptive radiation in vascular plants (Benzing, 2000), which provides an excellent model for studying divergence between populations and species (Sarthou et al, 2001;Barbar a et al, 2007a;Palma-Silva et al, 2009), and for understanding the role of gene flow during speciation processes among sympatric plant species (Palma-Silva et al, 2011).…”

Reproduction biology and chloroplast inheritance in Bromeliaceae: a case study in Fosterella (Pitcairnioideae)

“…Flower shape in the hybrids is intermediate between the two parents in each case Reproduction biology and chloroplast inheritance in Fosterella (Pitcairnioideae) between closely related sympatric species. In their work on a group of sympatric Pitcairnia species on inselbergs of the Atlantic rainforest of Brazil, Palma-Silva et al (2011) found that frequent hybridization events occur between sympatric species, but these events did not lead to an intermingling of the species. The fact that integrity and cohesion of these inselberg species are maintained despite introgression was explained with the help of the porous genome concept, according to which species are defined by sets of co-adapted alleles rather than by full reproductive isolation.…”