## 1 Introduction  
Chemical communication via floral scent plays a central role in attracting pollinators and is considered a key innovation promoting pollinator shifts and diversification in flowering plants [1; 2; 3]. Floral scent combines with non-chemical components of floral display in complex, multi-sensory communication between flowers and their animal visitors [4; 5; 6]. Nevertheless, floral scent itself can be considered as a multichannel signal, and small evolutionary changes in scent composition may open (or close) signal channels for certain flower visitors that directly affect plant fitness [7; 8; 9]. Thus, pollinator olfactory sensory acuity and olfactory learning are important components of the selective environment that shape floral evolution in angiosperms [10; 11; 12]. Flowering plant lineages are quite labile in their scent chemistry in ways that are linked with their evolutionary success [13; 14]. Although some scent compounds are restricted to particular lineages [15; 16], scent composition may be highly variable within a genus [17; 18; 19] or even within a species [20]. The amount of scent emission as well as its chemical composition could change through adaptation to divergent pollinator environments [21] or mating systems [22; 23], the presence of floral enemies [24] or the combined influence of pollinators and herbivores [25]. Thus, scent composition often tracks floral diversification related to shifts in pollination systems and other aspects of floral function [11; 26; 27]. An important aspect in considering the relevance of pollinators as drivers of floral diversification is the context in which diversification is promoted. For example, floral diversification may occur when plants colonize new geographical areas where the local pollinator fauna is depauperate or differs in relation to the source area [28; 29]. Coastal and inland populations of _Diplacus aurantiacus_ (Curtis) Jeps. (Phrymaceae) in southern California, USA, differ in flower color and primary pollinator [30]. Reciprocal transplant experiments showed that hummingbirds preferred red-flowered, coastal plants in both habitats, whereas hawkmoths exclusively visited yellow-flowered, inland plants but only at inland sites [31]. The persistence of floral color differences across a geographic cline, in the face of gene flow between inland and coastal populations, suggests that color differences in \(D\). _aurantiacus_ are adaptive [32]. Studies of floral scent generally assume that phenotypic differences reflect heritable adaptive changes due to pollinator-mediated selection. For example, there are region-specific differences in phenotypic selection on floral scent in _Gymnadenia odoratissima_ (L.) Rich. orchids and _Arum mcalatum_ L. avoids associated with different pollinator assemblages at different altitudes in Switzerland [33] and regions across the Alps in Europe [34], respectively. The inference of heritable adaptive variation in scent was supported by an experimental evolution study using rapid-cycling _Brassica rapa_ L. plants, in which floral scent composition diverged in response to the selective pressures exerted by different pollinator assemblages, in the absence of environmental variation [21]. However, floral scent variation may also be influenced by abiotic environmental factors, such as soil chemistry, ozone or drought [35; 36; 37]. Drought may directly affect scent emission in real time due to phenotypic plasticity, with associated effects on pollinator attraction and behavior [38]. Similarly, temperature and photoperiod shape diel floral emission patterns [39; 40] as well as pollinator flight periods [41]. We expect these environmental factors to combine across altitudes and latitudes, creating local differences in \"pollinator climate\" _sensu_ Grant and Grant [42], such as moth pollination limited by evening temperatures at higher altitude [43].