Abstract
Populations of dioecious plants commonly exhibit dissimilarities to the equilibrium expectation of a 1:1 sex ratio. Differential expenditure for reproduction between genders is cited as the primary mechanism responsible for a male-biased sex ratio, with increased effects on long-living species, but these mechanisms are still poorly understood. We explore the sex ratio in the endemic gymnosperm Zamia boliviana (Zamiaceae) populations from the Brazilian savanna (the Cerrado). We aim to investigate what the Z. boliviana sex ratio is, and whether population density and ecological correlates lead to variation in the sex proportion among Cerrado habitats. The study was conducted on ten in situ populations of Z. boliviana at sexual maturity (tertiary sex ratio). We estimated the populations’ sex ratio and performed a redundancy analysis to assess the relationship between biotic traits, such as sex ratio, and associated environmental features. Soil texture classes were used to classify the cycad habitats and were expressed in a ternary phase diagram. The results show a significant male-biased sex ratio in seven of the ten populations surveyed. Environmental factors did not explain the redundancy in the reproductive characteristics. However, the cycad occurs in different habitats in their endemic zone. Our study provides new biological data for Z. boliviana, suggesting that the differential reproductive expenditure of sexes in reproduction is governing the mechanisms of sex ratio variation, compared to local environmental factors in this cycad. The pattern of effective sex ratio found here improves our understanding of mechanisms causing biased sex ratios in cycads and other dioecious species from tropical ecosystems.
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Acknowledgements
RS thanks the Instituto Federal de Educação, Ciência e Tecnologia de Mato Grosso for allowing the development of the doctoral thesis in the “Programa de Pós-graduação em Biologia Vegetal, UNESP–Rio Claro.” This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior–Brazil (CAPES)–Finance Code 001, and by the National Council for Scientific and Technological Development (CNPq). The authors thank Pró-Reitoria de Pesquisa–UNICAMP – for the language services provided. LPCM receives a research productivity fellowship from CNPq and the Phenology Lab facilities are supported by the São Paulo Research Foundation (FAPESP) grant to LPCM. GJB is grateful for a postdoctoral fellowship awarded by CAPES/PNPD/UFVJM (Process Number 88887.352134/2019-00). We also thank Juberto Babilônia de Souza (IFMT), Eduardo Guimarães Couto and Maria Hunter of Universidade Federal de Mato Grosso for help with soil identification and interpretation. The authors are grateful to the landowners for allowing access to cycad populations and to Wynand Van Eeden and anonymous reviewers for helpfully improving this manuscript.
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RS and LPCM conceived and designed the study; RS conducted all fieldwork; RS and GJB analyzed and interpreted data. RS wrote the first draft of the manuscript. RS, FP, and LPCM contributed to further versions of the manuscript. All the authors have read and agreed the final content of the manuscript.
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Segalla, R., Pinheiro, F., Barônio, G.J. et al. Male-biased effective sex ratio across populations of the threatened Zamia boliviana (Zamiaceae). Plant Ecol 222, 587–602 (2021). https://doi.org/10.1007/s11258-021-01127-3
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DOI: https://doi.org/10.1007/s11258-021-01127-3