Abstract:

Aims: Survival and reproduction are fundamental traits crucial for maintaining population stability in organisms. Cuticular hydrocarbons serve dual purposes in insects: maintaining water balance and facilitating chemical communication. However, the interplay between adaptation to varying climatic conditions and maintaining reliability in chemical signaling remains poorly understood. This study delves into the sexual dimorphism and seasonal variations in cuticular hydrocarbons of the pollinating fig wasp Ceratosolen gravelyi, which parasitizes the male phase of Ficus semicordata.
Methods: Gas chromatography-mass spectrometry (GC-MS) was employed to analyze the types and concentrations of cuticular hydrocarbons present in female and male adults of C. gravelyi across distinct seasonal periods: rainy, fog-cool, and dry-hot seasons. To elucidate the response mechanism of cuticular hydrocarbons in C. gravelyi to varying seasons, non-metric multidimensional scaling, analysis of similarities, permutational multivariate analysis of variance, and random forest techniques were utilized.
Results: (1) A total of 34 compounds were identified in the cuticular hydrocarbons produced by the pollinator C. gravelyi in F. semicordata, primarily comprising n-alkanes, methylalkanes, olefins, and methylolefins, with carbon chain lengths ranging from C7 and C44. Notably, squalene, 2-Methyloctacosane (2-Me-C28), n-Tetratriacontane (n-C34), n-Hexatriacontane (n-C36), and n-Tetratetracontane (n-C44) emerged as the predominant components, each constituting over 5% of the total composition. (2) Significant qualitative and quantitative differences were observed in the cuticular hydrocarbon profiles between male and female adults of C. gravelyi. Notable contributors to these differences included n-Dotetracontane (n-C42), 17-Pentatriacontene (17-C35:1), 1-Nonacosene (C29:1), 2-Me-C28, and squalene. (3) The cuticular hydrocarbons of both male and female adults exhibited pronounced seasonal variations. During the dry-hot season, there was a notable increase in the proportion of n-alkanes (n-C34, n-C36, and n-C44) and the total absolute content of cuticular hydrocarbons in females. This increase was accompanied by a decrease in the proportion of methylalkanes (2-Me-C28) and methylalkenes (squalene). Conversely, in males, there was an increase in the proportion of methylalkenes, while the proportions of n-alkanes and methylalkanes decreased. However, the total absolute content of cuticular hydrocarbons did not exhibit significant variation in males across seasons.
Conclusion: This study elucidates the sexual dimorphism and seasonal plasticity inherent in the cuticular hydrocarbons of C. gravelyi. Specifically, 2-Me-C28 and squalene emerge as potential candidate sex pheromones facilitating mate recognition among fig wasps. Our findings reveal distinct responses to high temperature and/or dry climate conditions in female and male adults, underscoring the adoption of different adaptive strategies by the two sexes of the pollinator C. gravelyi across seasons. This research sheds light on the chemical adaptation mechanism of fig wasps to varying climatic environments, laying a foundational understanding of the ecological and evolutionary implications of cuticular hydrocarbons. These insights provide a crucial chemical framework for studying the dual traits of insects and unraveling the functional relationship between ecological adaptation and speciation.

Key words: Ficus semicordata, pollinating fig wasp, cuticular hydrocarbons, sexual dimorphism, seasonal adaptability