Resource Availability Shaped the Female‐Biased Floral Sex Allocation With Plant Size in Andromonoecious Capparis spinosa in Desert

ABSTRACT Although classic models of size‐dependent sex allocation (SDS) generally predict that among animal‐pollinated plants, female allocation increases with individual size, male‐and female‐biased allocation patterns have also been reported. We hypothesized that Capparis spinosa growing in resource‐poor desert habitats would exhibit a female‐biased sex allocation with increasing plant size, and that this pattern would be directly regulated by resource availability, because female function is generally more resource‐demanding to verify this conjecture. We examined SDS patterns at the flowering stage in the andromonoecious desert plant C. spinosa and assessed the role of resource availability in shaping these patterns through resource supplementation and pruning treatments. The results indicated that male plants with a low biomass occurred at low frequencies (0.021–0.051) in seven of the nine assessed populations. Among andromonoecious individuals across the nine populations, with increasing plant size, we recorded increases in the numbers of male and hermaphroditic flowers, the proportion of hermaphroditic flowers, and values of Lloyd's phenotypic gender index. These findings indicate a strong female‐biased sex allocation in C. spinosa plants of larger size. In addition, 2‐year resource manipulation experiments revealed that both the supplementation of water and nutrients and pruning treatments significantly enhanced the proportion of hermaphroditic flowers, thereby indicating that floral sex allocation is directly regulated by resource availability. Our findings in this study highlight the role of resource availability in shaping size‐dependent sex allocation patterns, particularly for plants in resource‐poor desert habitats, and sheds light on the evolution of sexual systems in plants.