Extremely Long-Lived Stigmas Allow Extended Cross-Pollination Opportunities in a High Andean Plant

Abstract

High-elevation ecosystems are traditionally viewed as environments in which predominantly autogamous breeding systems should be selected because of the limited pollinator availability. Chaetanthera renifolia (Asteraceae) is an endemic monocarpic triennial herb restricted to a narrow altitudinal range within the high Andes of central Chile (3300–3500 m a.s.l.), just below the vegetation limit. This species displays one of the larger capitulum within the genus. Under the reproductive assurance hypothesis, and considering its short longevity (monocarpic triennial), an autogamous breeding system and low levels of pollen limitation would be predicted for C. renifolia. In contrast, considering its large floral size, a xenogamous breeding system, and significant levels of pollen limitation could be expected. In addition, the increased pollination probability hypothesis predicts prolonged stigma longevity for high alpine plants. We tested these alternative predictions by performing experimental crossings in the field to establish the breeding system and to measure the magnitude of pollen limitation in two populations of C. renifolia. In addition, we measured the stigma longevity in unpollinated and open pollinated capitula, and pollinator visitation rates in the field. We found low levels of self-compatibility and significant levels of pollen limitation in C. renifolia. Pollinator visitation rates were moderate (0.047–0.079 visits per capitulum per 30 min). Although pollinator visitation rate significantly differed between populations, they were not translated into differences in achene output. Finally, C. renifolia stigma longevity of unpollinated plants was extremely long and significantly higher than that of open pollinated plants (26.3±2.8 days vs. 10.1±2.2, respectively), which gives support to the increased pollination probability hypothesis for high-elevation flowering plants. Our results add to a growing number of studies that show that xenogamous breeding systems and mechanisms to increase pollination opportunities can be selected in high-elevation ecosystems.

Context‐dependency of resource allocation trade‐offs highlights constraints to the evolution of floral longevity in a monocarpic herb

“…Whether the patterns related to plasticity of floral longevity and resource allocation shown here are adaptive of course remains to be tested, but is still constructive to consider in light of existing theory for the evolution of floral longevity. In general, because greater longevity may translate into more opportunities for outcrossing (Bingham & Orthner, ; Torres‐Díaz et al ., ), plastic increases in longevity under more favorable abiotic conditions, as seen in other species (Arathi et al ., ; Arroyo et al ., ; Jorgensen & Arathi, ), could be interpreted as adaptive, as long as the resulting increase in overall display does not lead to high levels of geitonogamy (Harder & Barrett, ; Ishii & Sakai, ). By contrast, we found decreased floral longevity under high resources.…”

Plasticity of flower longevity in alpine plants is increased in populations from high elevation compared to low elevation populations

“…Thus, we propose that enhanced flower longevity in high elevation environments is a consistent pattern only at the overall community or genus level, and depends on the species composition. Under environmental conditions that accompany low or unpredictable pollination intensities such as in alpine habitats, flowers with an increased longevity should be favored (Torres-Diaz et al 2011;Marques and Draper 2012), and thus, a shift to species with long-living flowers is likely to occur with increasing elevation (Arroyo et al 2006).…”

Number of conspecifics and reproduction in the invasive plant Eschscholzia californica (Papaveraceae): is there a pollinator‐mediated Allee effect?

“…; Torres‐Díaz et al . ), but mean fruit set is high (80–95%). This suggests either an insufficient sample effort for pollinator visitation or very effective pollinator visits.…”