## 3 Discussion
### Niche Dimensions within Sapromyophily: A Closer Look at Scent in Fly-Pollinated Jabrosa Species  
A landmark survey [62] of floral scent variation in fly-pollinated stapelioid milkweeds across southern Africa challenged the notion that sapromyophilous plants use the same, fetid volatiles to attract flies to brood-site deceptive flowers, as it described unexpected variation in compound identity, blend complexity and associated differences in floral color and shape. A more focused analysis of carrion mimicry in the South African orchid _Satyrinum punishment_ Thunb. revealed that variation in flower size and oligosulfide concentration was associated with niche partitioning between sarcophagid and calliphorld flies, which appear to specialize in dead animals of different sizes [90]. Subsequent studies in the same region revealed that flies attracted by scent are filtered as pollinators by non-chemical traits that either restrict access by size (floral guardrails [91]) or encourage landing by simulating the presence of other flies (tepal spots [92]). Similar niche partitioning may be occurring among fly-pollinated Andean _Jabrosa_ species, given observed variation in flower size and morphology, scent composition and the diversity of observed fly visitors [56]. Here we examined the floral scent composition of Andean _Jabrosa_ species for hints of niche dimensionality, by virtue of supplemental GC-MS analyses of cut flowers in smaller headspace chambers. Greenhouse cultivated plants of _J. rotacea_ and _J. sativa_ allowed us to use SPME-GC-MS to analyze scent from whole and dissected flowers. For _J. rotacea_, the oligosaccharides that dominated samples analyzed via thermal desorption (Table S3) were accompanied by other compounds (acetophenone, small aliphatic alcohols, aldehydes and ketones) associated with dehiscing anthers, suggesting pollen as a source tissue [57]. These compounds are characteristic of urine, feces or decaying substances [53; 54], suggesting a more complex brood-site model than rotting meat [93]. For _J. sativa_, SPME-GC-MS revealed a complex series of thioesters formed with C2-C7 acids (Figure S2), one of which was present, along with an aromatic S-compound (2-isopentyl thiophene), in samples collected from unopened flower buds (Table S4). Thioester formation, through esterification of carboxylic acids with methionol, is known to be mediated by cheese-making bacteria such as _Brevibacterium linens_[94]. It is unclear whether floral microbes are responsible for thioester biosynthesis in flowers of _J. sativa_. Thioesters are exceedingly rare in floral scent studies, having only been identified (S-methyl thiolacetate) from bat-pollinated flowers of _Cephalocreus_ Pfeiff. cati [95]. Apart from thioesters, the core _J. sativa_ floral bouquet recovered by all headspace-GC-MS methods used (Tables S3 and S4) included compounds (oligosulfides, indole, p-cresol, 2-ketones and C6-C9 aliphatic aldehydes) that predict a more generalized spectrum of floral visitors, including flies attracted to carrion, dung, hides and urine. This agrees with our field observations that a broad spectrum of saprophilous flies visited the flowers [56]. A total of five \"morpho-species\" from three families (Calliphoridae, Muscidae and Sarcophagidae) pollinated _J. sativa_ flowers. The remaining two fly-pollinated species in our study could not be cultivated, so we performed dose-response sampling with SPE micro traps in remote Andean field sites. In flowers of _J. laciniata_, the presence of oligosaccharides was complemented by generic monoterpenes and a metabolic series of ringed N-compounds with mass spectra suggesting pyrroles and piperidines (Table S3, Figure S2). Common monoterpenes (e.g., terpinolene,-linalool) are known to attract flies (e.g., _Musca domestica_ [PERSON], 1758) that otherwise favor fetid odorants, such as indole [96].