# Composition Diversity and Expression Specificity of the _Tps_ Gene Family among 24 _Ficus_ Species
## 3 Discussion
### Expression Profiles of the FTPS Genes  
By examining the expression profiles of the _FTPSs_, we determined the diversity and complexity of _FTPSs_ expression status in 24 _Ficus_ species. Here, each species had a unique expression profile indicating a highly species-specific expression array of the _FTPS_ genes. However, although we identified six singletons for five species, we showed that the other 33 orthologous _FTPSs_ were shared by at least two species (Figure 1C). This result suggests that the odors emitted by each _Ficus_ species blend compounds of multiple common terpenoids, rather than entirely species-specific volatiles. By comparing the blends of VOCs released from receptive figs of 20 _Ficus_ species, [PERSON] et al. [50] found that a few major compounds such as \(\beta\)-ocimene, germacrene D, and linalool are common among floral fragrances, while the rare compounds are usually present in a very low proportion in the blends. In addition, [PERSON] and [PERSON] [11] showed that (_E_)-\(\beta\)-ocimene was responsible for 41.75% of VOCs in receptive syconora of _F. syconorus_. In this study, we found that at least 10 _FTPSs_ were annotated as myrcene synthases (Table S3) and were highly expressed in multiple species (Figure 1C). For example, _FTPS1_ and _FTPS2_ that encode different myrcene synthases were found in 21 and 19 species, respectively. Given that myrcene is an isomer of ocimenes, the myrcene/ocimene synthases should also produce common chemical compounds during the repetitive phase of male syconia for the _Ficus_ species. In addition, we also found six _FTPSs_ encoding germacrene D synthases were simultaneously expressed in more than 16 species (Figure 1C). In plants, germacrene D, comprising some 300 isomers (C\({}_{15}\)H\({}_{24}\)), has evolved ecological roles in the interaction of the plant with insects [51; 52]. This plant sesquiterpene can specifically activate a major type of antennal receptor neuron of the tobacco budworm moth _Heliothis virescens_[53]. However, whether germacrene D is involved in the interaction of figs and fig wasps remains unclear. In addition, it is worth noting that the distribution and expression intensity of the _FTPSs_ across species do not always correlate with the phylogenetic relationship of the species. Recently, [PERSON] et al. [54] investigated the volatiles emitted by receptive male figs of _F. hirita_ and _F. triloba_, two phylogenetic related species, and found that the two species share 48 VOCs, but the most abundant volatiles differ. Here, we identified 11 homologous _FTPS_ pairs between the two species, but the expression level of each _FTPS_ pair was very different (Figure 1C). These results suggest that the proportion of compounds is more important than the composition itself. However, interestingly, we also found that two distantly related species (_F. pyriformis_ and _F. semicordata_) had highly similar expression profiles of _FTPSs_ (Figure 1C). Within the genus of _Ficus_, species _F. pyriformis_ and _F. semicordata_ belong to different subgenera, _Ficus_ and _Syconorus_, respectively. In this study, the single relevance between the two species is that they were all collected from Thailand. Given that the two species have distinguished morphologies from each other and from the other fig species, sampling and identification errors can be ruled out. We also checked the other genes in the transcriptomes of the two species and found different gene lists and expression profiles, suggesting that the two RNA libraries were not misused or mixed. Previous studies confirm that similar volatile blends of fig species can trigger their evolutionary convergence to attract particular wasp species [55; 56; 57]. In turn, regionally pollinator sharing can produce gene flow between fig species [54; 58]. In _Ficus_, hybridization and introgression can occur not only among fig taxa from the same section but also among taxa from different sections [58].