Mating system and the hybridization between self-compatible Phlox cuspidata and self-incompatible Phlox drummondii

Abstract

Mating system can impact the frequency of hybridization and therefore the maintenance of species diversity. I evaluate the effects of weak self-incompatibility (SI) in Phlox cuspidata and SI in Phlox drummondii on mating success within species and on hybridization dynamics between species under controlled conditions. The effects of SI on hybridization frequency were assessed by manipulating the relatedness of conspecific pollen and the relative timing of pollen deposition in mixed-donor interspecific pollinations. Selfing as opposed to outcrossing increased hybridization by 16% in P. cuspidata maternal plants and by 48% in P. drummondii maternal plants because self pollen did not compete as well against heterospecific pollen. The relative timing of conspecific versus heterospecific pollen deposition also impacted hybridization. In self-compatible P. cuspidata, the deposition of self pollen 5 h earlier than heterospecific pollen decreased hybridization by 28%. In self-incompatible P. drummondii, a 5 h delay in the deposition of compatible conspecific pollen increased hybridization by 32%. In this hybrid system, early self-pollination can decrease hybridization (but increase inbreeding) by P. cuspidata maternal plants, and SI may increase hybridization by P. drummondii maternal plants.

Genomic evidence of gene flow during reinforcement in Texas Phlox

“…This is a promising system for future analyses of introgression because of the extensive knowledge about the biogeography of the species (Erbe & Turner ; Levin ; Ruane ) and the strength of reinforcing selection (Hopkins & Rausher , ; Hopkins et al . ).…”

“…Hybrids between P. drummondii and P. cuspidata are observed in the field (Levin 1967(Levin , 1975(Levin , 1985Ferguson et al 1999b;Ruane & Donohue 2008;Ruane 2009) but have high sterility (Ruane & Donohue 2008). Commongarden field experiments indicate that these hybridization events are twice as frequent when P. drummondii has the ancestral light-blue flower colour than when it has the derived dark-red flower colour ), suggesting that prior to flower colour divergence hybridization was more frequent.…”

“…Despite the reduction in hybridization, hybrids can be found in nature (Levin ; Ferguson et al . ; Ruane & Donohue ; Ruane ). Low fertility in hybrids causes selection against hybridization and favours flower colour divergence (Hopkins et al .…”

“…The evolution of flower colour in sympatry decreases hybridization by as much as 50% . Despite the reduction in hybridization, hybrids can be found in nature (Levin 1967;Ferguson et al 1999b;Ruane & Donohue 2008;Ruane 2009). Low fertility in hybrids causes selection against hybridization and favours flower colour divergence .…”

The evolution of intrinsic reproductive isolation in the genus Cakile (Brassicaceae)

“…Thus, the WISO hypothesis predicts RI to be higher when mothers are selfers and fathers are outcrossers, whereas the ‘sink‐provisioning’ hypothesis predicts RI to be lowest under those conditions. Although some support for the WISO hypothesis has been found in species pairs (Brandvain & Haig, and references therein; Ruane, ; Ruhsam et al ., ; Goodwillie & Ness, ; Runquist et al ., ), associations between mating system and early‐stage post‐zygotic RI have yet to be explored in a phylogenetic comparative context or in relation to adaptive divergence.…”