The evolution of sex ratio differences and inflorescence architectures in Begonia (Begoniaceae).
OBJECTIVE
A major benefit conferred by monoecy is the ability to alter floral sex ratio in response to selection. In monoecious species that produce flowers of a given sex at set positions on the inflorescence, floral sex ratio may be related to inflorescence architecture. We studied the loci underlying differences in inflorescence architecture between two monoecious Begonia species and related this to floral sex ratios.


METHODS
We performed trait comparisons and quantitative trait locus (QTL) mapping in a segregating backcross population between Central American Begonia plebeja and B. conchifolia. We focused on traits related to inflorescence architecture, sex ratios, and other reproductive traits.


RESULTS
The inflorescence branching pattern of B. conchifolia was more asymmetric than B. plebeja, which in turn affects the floral sex ratio. Colocalizing QTLs of moderate effect influenced both the number of male flowers and the fate decisions of axillary meristems, demonstrating the close link between inflorescence architecture and sex ratio. Additional QTLs were found for stamen number (30% variance explained, VE) and pollen sterility (12.3% VE).


CONCLUSIONS
One way in which Begonia species develop different floral sex ratios is through modifications of their inflorescence architecture. The potential pleiotropic action of QTL on inflorescence branching and floral sex ratios may have major implications for trait evolution and responses to selection. The presence of a single QTL of large effect on stamen number may allow rapid divergence for this key floral trait. We propose candidate loci for stamen number and inflorescence branching for future characterization.
Department of Biology, Syracuse University, 107 College Place, Room 110 LSC, Syracuse, New York 13244 USA.
Alex D
AD
Twyford
Richard A
RA
Ennos
Chris D
CD
White
Mobina Shaukat
MS
Ali
Catherine A
CA
Kidner
D031112:Begoniaceae / Q000033:anatomy & histology / Q000235:genetics* / Q000502:physiology; D005075:Biological Evolution; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D035264:Flowers; D014644:Genetic Variation; D056626:Inflorescence / Q000033:anatomy & histology*; D018519:Meristem; D010641:Phenotype; D011058:Pollen; D040641:Quantitative Trait Loci; D019655:Quantitative Trait, Heritable; D012744:Sex Ratio; D013045:Species Specificity
Begonia conchifolia; Begonia plebeja; Begoniacaeae; floral sex ratio; inflorescence architecture; monoecy; quantitative trait loci (QTL); reproductive biology