Abstract
BackgroundThe expression of gender in gymnosperms is challenging because the extent of variability in gender segregations in tree crowns and selection pressure of nature can modify the gender through time.MethodsAn in-depth investigation on spatial segregation of genders in tree crowns and sex expression of a total of 500 trees in five different natural populations of Cedrus deodara was carried out and verified the occurrence of subdioecious (co-existence of male, female, and monoecious) genders in C. deodara.ResultsFive different sexual morphs were apparent among the 500 selected individuals as (1) pure male (M): bearing only male strobili in the whole crown with 22.2%; (2) pure female (F): bearing only female strobili in the whole crown with 12.4%; (3) mixed-monoecious (MM): bearing both male and female strobili with 13.6%; (4) predominantly female (PF) with 25.6%; and (5) predominantly male (PM) with 26.2%. The occurrence of multiple sexual morphs resulted from the complex selection pressure, which increased the stability of the populations. The segregation of genders in crown layers deemed to increase the fitness that may be a mechanism for accelerating outcrossing. The results of the study suggest that the subdioecious gender expression in C. deodara is evolved through the monoecy–paradioecy pathway. The production of male strobili revealed non-significant effect of tree sizes whereas a significant effect was observed for the production of female strobili. Our study established that the total pollen and seed outputs in C. deodara changed frequently according to gender expression.ConclusionsThe size of the tree, resource availability, sex allocation, plant architecture, gender segregation in crowns, and habitat conditions are the prominent causes for gender plasticity.
Highlights
The expression of gender in gymnosperms is challenging because the extent of variability in gender segregations in tree crowns and selection pressure of nature can modify the gender through time
Of the 327 monoecious individuals, (i) 206 were categorized in the group of lower crown female (LC: F) and upper crown male (UC: M), (ii) 82 individuals were in the group of lower crown male (LC: M) and upper crown female (UC: F), and (iii) remaining 39 individuals were in the third group of lower crown male (LC: M), upper crown male (UC: M), and middle crown female (MC: F) (Table 1)
Out of 206 individuals of the first group, i.e., lower crown female (LC: F) and upper crown male (UC: M); 93 individuals fell in the subgroup predominantly female (PF), 26 individuals in the predominantly male (PM), and 87 individuals in mixedmonoecious (MM) subgroup
Summary
The expression of gender in gymnosperms is challenging because the extent of variability in gender segregations in tree crowns and selection pressure of nature can modify the gender through time. The plasticity of sex expression in higher plants indicates the existence of different sex-determining factors These variations are the product of a complex interplay of genetics and environmental factors (Lloyd and Bawa 1984; Sarkissian et al 2001). Such gender plasticity is common in monoecious plants because the production of separate male and female flowers enables greater freedom to respond to specific environmental conditions (Sarkissian et al 2001). A comprehensive study on sex expression in monoecious trees is needed to understand (i) the differential return of investment in reproduction relating to both sexes and (ii) the occurrence of frequency of the leaky morphs (intermediate phenotypes between monoecy and dioecy) as compared to the “stable” distinct male and female morphs, which is so far largely unevaluated
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