Fire frequency effects on cleistogamy expression and progeny performance in Cologania broussonetii

Increased fire frequency usually erodes microenvironmental conditions, causing a drastic limitation of edaphic resources. Thus, the production of permanently closed-small flowers (cleistogamous, CL) should increase in sites with high fire frequency as this implies a less expensive reproductive assurance strategy. However, because open, insect-pollinated flowers (chasmogamous, CH) have the potential capacity to outcross via pollinators, CH progeny produced at any site should outperform selfed CL progeny. We evaluate the effect of fire frequency on the relative production of CL/CH flowers and fruits, and their seed set, along with several progeny performance parameters in Cologania broussonetii (Fabaceae), a resprouting herb with dimorphic cleistogamy native to the Chaco Serrano. Fire frequency increased cleistogamy expression, reaching extreme levels in high fire frequency sites. Seed set was similarly high for both CH and CL flowers in the unburned condition, while in burned sites the few developed CH flowers set more seeds than CL flowers. However, progeny performance was similar between CH and CL progeny at each and across all fire frequency conditions. Cleistogamy expression in C. broussonetii is maximized in abiotically degraded frequently burned habitats, although the selfed CL progeny is as successful as potentially outcrossed CH progeny. Fire frequency may decreased floral size and abundance, selecting for autogamous reproduction, which restricts not only the genetic potential of plant populations but also the resources offered to pollinators. At the community level, increased cleistogamy expression may potentially have negative implications for non-cleistogamous, more outcrossing species surviving in frequently burned environments.