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ABSTRACT Widely documented in animals, behavioural thermoregulation mitigates negative impacts of climate change. Plants experience especially strong thermal variability but evidence for plant behavioural thermoregulation is limited. Along a montane elevation gradient,Argentina anserinaflowers warm more in alpine populations than at lower elevation. We linked floral temperature with phenotypes to identify warming mechanisms and documented petal movement and pollinator visitation using time‐lapse cameras. High elevation flowers were more cupped, focused light deeper within flowers and were more responsive to air temperature than low; cupping when cold and flattening when warm. At high elevation, a 20° increase in petal angle resulted in a 0.46°C increase in warming. Warming increased pollinator visitation, especially under cooler high elevation temperatures. A plasticity study revealed constitutive elevational differences in petal cupping and stronger temperature‐induced floral plasticity in high elevation populations. Thus, plant populations have evolved different behavioural responses to temperature driving differences in thermoregulatory capacity. 

Abstract The floral microenvironment impacts gametophyte viability and plant–pollinator interactions. Plants employ mechanisms to modify floral temperature, including thermogenesis, absorption of solar radiation, and evaporative cooling. Whether floral thermoregulation impacts reproductive fitness, and how floral morphological variation mediates thermoregulatory capacity are poorly understood.We measured temperature of the floral microenvironment in the field and tested for thermogenesis in the lab in early spring floweringHexastylis arifolia(Aristolochiaceae). We evaluated whether thermoregulatory capacity was associated with floral morphological variation. Finally, we experimentally determined the thermal optimum and tolerance of pollen to assess whether thermoregulation may ameliorate thermal stress to pollen.Pollen germination was optimal near 21 °C, with a 50% tolerance breadth of ~18 °C. In laboratory conditions, flowers exhibited thermogenesis of 1.5–4.8 °C for short intervals within a conserved timeframe (08:00–09:00 h). In the field, temperature inside the floral tube often deviated from ambient – floral interiors were up to 4 °C above ambient when it was cold, but some fell nearly 10 °C below ambient during peak heat. Flowers with smaller openings were cooler and more thermally stable than those with larger openings during peak heat. Thermoregulation maintained a floral microenvironment within the thermal tolerance breadth of pollen.Results suggest thatH. arifoliaflowers have a stronger capacity to cool than to warm, and that narrower floral openings create a distinct floral microenvironment, enhancing floral cooling effects. While deviation of floral temperature from ambient conditions maintains a suitable environment for pollen and suggests an adaptive role of thermoregulation, we discuss adaptive and nonadaptive mechanisms underlying floral warming and cooling. 

Abstract Thermal environments vary widely across species ranges, establishing the potential for local adaptation of thermal performance optima and tolerance. In the absence of local adaptation, selection should favor mechanisms to meet thermal optima. Floral temperature is a major determinant of reproductive success in angiosperms, yet whether gametic thermal performance shows signatures of local adaptation across temperature gradients, and how variation in gametic thermal performance influences floral evolution, is unknown. We characterized flowering season temperatures for the forb, Argentina anserina, at extremes of a 1000 m elevation gradient and generated thermal performance curves for pollen and ovule performance in populations at each extreme. Thermal optima fell between mean and maximum intrafloral temperatures. However, cooler high-elevation populations had ~4 °C greater pollen thermal optima than warmer low-elevation populations, while tolerance breadths did not differ. We then tested whether plants at elevational extremes differentially warmed the floral microenvironment. High-elevation flowers warmed significantly more than low, bringing intrafloral temperatures nearer the pollen optima. A manipulative experiment demonstrated that stronger warming in high elevation was conferred by floral tissues. Elevational divergence in floral warming may be driven, in part, by selection on flowers to meet different thermal demands of the gametophytes. 

Abstract Climate change has influenced species distributions worldwide with upward elevational shifts observed in many systems. Leading range edge populations, like those at upper elevation limits, are crucial for climate change responses but can exhibit low genetic diversity due to founder effects, isolation, or limited outbreeding. These factors can hamper local adaptation at range limits. Using the widespread herb,Argentina anserina, we measured ecological attributes (population density on the landscape, area of population occupancy, and plant and flower density) spanning a 1000 m elevation gradient, with high elevation populations at the range limit. We measured vegetative clonal potential in the greenhouse for populations spanning the gradient. We combined these data with a ddRAD-seq dataset to test the hypotheses that high elevation populations would exhibit ecological and genomic signatures of leading range edge populations. We found that population density on the landscape declined towards the high elevation limit, as is expected towards range edges. However, plant density was elevated within edge populations. In the greenhouse, high elevation plants exhibited stronger clonal potential than low elevation plants, likely explaining increased plant density in the field. Phylogeographic analysis supported more recent colonization of high elevation populations which were also more genetically isolated, had more extreme heterozygote excess and had smaller effective population size than low. Results support that colonization of high elevations was likely accompanied by increased asexuality, contributing to a decline in effective population size. Despite high plant density in leading edge populations, their small effective size, isolation and clonality could constrain adaptive potential.