An altitudinal cline in UV floral pattern corresponds with a behavioral change of a generalist pollinator assemblage

Abstract

Spatial variation in pollinator communities or behaviors can underlie floral diversification. Floral traits in the UV spectrum are common and mediate plant-pollinator interactions, but the role of pollinators in driving or maintaining their geographic variation has not been fully explored. We identify an altitudinal cline of increasing relative size of the UV bullseye pattern in Argentina anserina (Rosaceae) flowers, and assess whether pollination context contributes to clinal variation. At four sites that varied in altitude, we document the pollinator assemblage, and pollinator preference and visitation behavior. We then determine how pollinator visits affected pollen receipt and export. Finally, we describe how the functional relationship between UV floral phenotype and pollen receipt changed with altitude. Floral UV bullseye size increased with altitude, which corresponded with a change from a hymenopteran- to a dipteran-dominated pollinator assemblage. While dipteran and hymenopteran preferences for bullseye size were similar, flowers with large bullseyes received more foraging visits than those with small bullseyes at higher altitude. The reverse was observed at the lower altitudes; pollinators approached large-bullseye flowers often but rarely foraged. These differences are expected to affect fitness because foraging visits increased pollen export and receipt. Indeed, when natural variation in bullseye size was considered, it had a stronger effect on pollen receipt than other traits (flower size, display, or color). Plants with larger bullseyes tended to receive more pollen at the highest-altitude site, while those with smaller ones received more pollen at the lowest-altitude site. Results suggest that altitudinal changes in preference and behavior of the overall pollinator assemblage, but not differential preferences of pollinator taxonomic groups, could contribute to clinal variation in a UV floral trait for a generalist-pollinated plant.

Is there a disease‐free halo at species range limits? The codistribution of anther‐smut disease and its host species

“…While cold temperatures have been shown to limit the germination of Microbotryum spores in laboratory conditions (Schäfer, Kemler, Bauer, & Begerow, ), higher temperatures are more often associated with poor disease development (Alexander & Maltby, ) and global distributional studies of Microbtoryum on S. vulgaris and S. acualis have shown higher levels of disease in cooler climates (Abbate & Antonovics, ; Bueker et al., ). Declining pollinator abundance (Kearns, ) and shifts in pollinator community composition (Koski & Ashman, ) at higher elevations may provide a better explanation for the decrease in disease in the two Dianthus species at very high elevations. Indeed, a recent study of anther smut on S. latifolia along a radiation gradient near Chernobyl showed that declines in disease abundance were driven by declining pollinator abundance rather than direct negative effects of radiation on the fungus (Aguileta et al., ).…”

No evidence for adaptation to local rhizobial mutualists in the legume Medicago lupulina

“…Nevertheless, several lines of evidence suggest that adaptation to the local mutualist is a common feature of positive species interactions. Phenotype matching between local plant and pollinator communities is pervasive (Anderson, Johnson, & Anderson, 2009;Gómez, Abdelaziz, Camacho, Muñoz-Pajares, & Perfectti, 2009;Koski & Ashman, 2015), and a recent reciprocal translocation experiment showed that a plant's reproductive success is highest in its local pollinator community (Newman, Manning, & Anderson, 2015). In the classic mutualism between leguminous plants and nitrogen-fixing bacteria, genotype-by-genotype interactions-when fitness depends jointly on the genotypes of both partners-account for a substantial proportion of genetic variation in fitness-related traits within plant populations (Ehinger et al, 2014;Heath, 2010;Heath, Burke, & Stinchcombe, 2012).…”

Reproductive character displacement and environmental filtering shape floral variation between sympatric sister taxa

“…Patterns in the UV spectrum in particular have been shown to be under both pollinator‐mediated (Koski and Ashman ; Peterson et al. ) and abiotic selection, namely by UV irradiance (Koski and Ashman ; Koski and Ashman 2016). For traits like this we predict that the pattern of divergence will depend on the relative strength of selective forces.…”