Abstract
Cleistogamy (CL) in angiosperms historically has been understudied; however, its co-occurrence with chasmogamy (CH) across many plant species suggests a fitness advantage to maintaining this mixed-mating strategy. Maintenance of mixed-mating has been attributed to reproductive assurance, resource allocation or genetic trade-offs. Our goals were to explore patterns of CH and CL, quantify reproductive contributions measured by fruit production and determine how CL is maintained in the endangered perennial Polygala lewtonii. This species exhibits CH and both above-ground cleistogamy (CL-AG) and below-ground cleistogamy (CL-BG). In monthly censuses from 2008 to 2012, we documented flowering patterns by counting CH flowering stems, CL-AG fruits and CL-BG rhizomes per plant. Monitoring of buds on CH flowering stems in 2004 provided an estimate of CH fruits per plant. Plant excavations in 2005 of CL-BG rhizomes provided an estimate of CL-BG fruits per plant. Floral morphs were temporally separated with CH flowers observed from January to May and CL flowers from June to February. Overall, 17.5 % of plants flowered; most plants expressed CH first in spring months (63.4 %) and the rest initiated CL-AG in fall months. Reproductive output was dominated by CH (median 26 fruits) compared to combined CL (median 3.5 fruits). Annual reproductive effort of CL-AG was positively correlated with plant age while CH had no relation. Our research shows CH as the dominant form of reproductive effort with most individuals expressing CH and through greater reproductive contributions. CL appears limited by plant size or resources based on the positive relationship with plant age. CL dependency on resource availability is common in other species found in dry or low-quality habitats; however, CL contributions in this species are comparatively low. This raises more questions related to energy requirements of both floral morphs, how this affects the production of viable progeny and why CL persists.
Highlights
Mixed-mating in plants can provide a unique fitness advantage through the production of genetically diverse progeny while preserving locally adapted alleles
Reproductive maturity was defined as flowering CH or CL-AG at least once; some plants expressed only a single floral morph
Median age for initiating CH flowers was 23 months compared to 19 months for CL-AG and 29.5 months for CL-BG
Summary
Mixed-mating in plants can provide a unique fitness advantage through the production of genetically diverse progeny while preserving locally adapted alleles. This mixed-mating was once thought to be evolutionarily unstable; multiple reproductive strategies occur frequently in vascular plants, with 42 % of species. CL increases a populations’ susceptibility to genetic drift and inbreeding depression if deleterious alleles cannot be purged (Lloyd 1979; Lande and Schemske 1985) These fitness trade-offs are factors in maintaining a mixed-mating strategy
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