Plastic Responses Contribute to Explaining Altitudinal and Temporal Variation in Potential Flower Longevity in High Andean Rhodolirion montanum

Abstract

The tendency for flower longevity to increase with altitude is believed by many alpine ecologists to play an important role in compensating for low pollination rates at high altitudes due to cold and variable weather conditions. However, current studies documenting an altitudinal increase in flower longevity in the alpine habitat derive principally from studies on open-pollinated flowers where lower pollinator visitation rates at higher altitudes will tend to lead to flower senescence later in the life-span of a flower in comparison with lower altitudes, and thus could confound the real altitudinal pattern in a species´ potential flower longevity. In a two-year study we tested the hypothesis that a plastic effect of temperature on flower longevity could contribute to an altitudinal increase in potential flower longevity measured in pollinator-excluded flowers in high Andean Rhodolirium montanum Phil. (Amaryllidaceae). Using supplemental warming we investigated whether temperature around flowers plastically affects potential flower longevity. We determined tightly temperature-controlled potential flower longevity and flower height for natural populations on three alpine sites spread over an altitudinal transect from 2350 and 3075 m a.s.l. An experimental increase of 3.1°C around flowers significantly decreased flower longevity indicating a plastic response of flowers to temperature. Flower height in natural populations decreased significantly with altitude. Although temperature negatively affects flower longevity under experimental conditions, we found no evidence that temperature around flowers explains site variation in flower longevity over the altitudinal gradient. In a wetter year, despite a 3.5°C temperature difference around flowers at the extremes of the altitudinal range, flower longevity showed no increase with altitude. However, in a drier year, flower longevity increased significantly with altitude. The emerging picture suggests an increase in flower longevity along the altitudinal gradient is less common for potential flower longevity than for open-pollination flower longevity. Independently of any selection that may occur on potential longevity, plastic responses of flowers to environmental conditions are likely to contribute to altitudinal variation in flower longevity, especially in dry alpine areas. Such plastic responses could push flowers of alpine species towards shorter life-lengths under climate change, with uncertain consequences for successful pollination and plant fitness in a warming world.

Ovule bet‐hedging at high elevation in the South American Andes: Evidence from a phylogenetically controlled multispecies study

“…This constellation of characteristics suggests reduced and less predictable pollination in the upper alpine does not severely limit seed set. In several strongly outcrossing high Andean species, less reliable visitation on higher sites is known to be ameliorated by intrinsically long‐lived flowers of capitula in Asteraceae or more prolonged flower longevity produced by the plastic extension of the flower life span under cooler temperatures and higher soil moisture content allowing more time for the accumulation of scarce pollinator visits (Arroyo et al, ; Arroyo, Dudley, Jespersen, Pacheco, & Cavieres, ; Dudley, Arroyo, & Fernández‐Murillo, ; Medan, ; Pacheco, Dudley, Cabezas, Cavieres, & Arroyo, ; Torres‐Díaz et al, ). Long‐lived flowers have also been implicated in compensating low and stochastic visitation in several other alpine areas (Ai et al, ; Bingham & Orthner, ; Duan, & Liu, ; Pickering, ; Steinacher & Wagner, ; Utelli & Roy, ).…”

Functional role of long-lived flowers in preventing pollen limitation in a high elevation outcrossing species

“…R. montanum is partially self-compatible, strongly herkogamous and mostly outcrossing ( Ladd and Arroyo 2009 ; Pacheco et al 2016 ). Elevational tendencies in potential flower longevity measured in pollinator-excluded flowers have been extensively studied by Pacheco et al (2016) . In more normal years, mean potential flower longevity stands at 8.1 days and does not vary with elevation.…”

“… Ashman et al 2004 ). Long-lived flowers are an intrinsic property of some alpine species ( Steinacher and Wagner 2010 ; Torres-Díaz et al 2011 ; Pacheco et al 2016 ). Although potential flower longevity (measured in pollinator-excluded flowers) does not necessarily increase with elevation in such species, compensation of lower visitation rates at higher elevations can be expected.…”

“…Like many amaryllids (e.g. Arroyo and Dafni 1995 ; Baker et al 2000 ), R. montanum is characterized by large long-lived flowers ( Pacheco et al 2016 ). If flower longevity compensation occurs at higher elevations in R. montanum , levels of seed set should be greater than expected from the depression in visitation rates.…”

One for all and all for one: retention of colour‐unchanged old flowers increases pollinator attraction in a hermaphroditic plant

“…; Pacheco et al . ). Indeed, pollination effectiveness has been broadly associated with a reduction in floral longevity in self‐incompatible species or those with low selfing rates ( e.g .…”