When the going gets tough, the tough turn female: injury and sex expression in a sex‐changing tree

Abstract

Premise Plant sex is usually fixed, but in rare cases, sex expression is flexible and may be influenced by environmental factors. Theory links female sex expression to better health, but manipulative work involving the experimental change of health via injury is limited, particularly in sexually plastic species. A better understanding of mechanisms influencing shifts in sex is essential to our understanding of life history theory regarding trade‐offs in sex allocation and differential mortality. Methods We investigated the relationship between physiological stress and sex expression in sexually plastic striped maple trees (Acer pensylvanicum) by inflicting damage of various intensities (crown pruning, defoliation, and hydraulic restriction). We then monitored the sex expression of injured and control individuals for 2 years to assess the extent to which injury may cue changes in sex expression. Results We found that severe damage such as full defoliation or severe pruning increased odds of changing sex to female and decreased odds of changing to male. In fact, no pruned male trees flowered male 2 years later, while all males in the control group flowered partially or fully male. After full defoliation, trees had 4.5 times higher odds of flowering female. Not all injury is equal; less‐severe physical trauma did not affect the frequency of sex change to femaleness. Conclusions This work demonstrates that physical trauma in striped maple appears to exhibit a threshold effect in which only the most stressful of physiological cues instigate changes in sex expression, a phenomenon previously unknown, and that damage stress is strongly correlated with switching to femaleness. These findings have implications for population sex ratios and sustainability within an increasing stressful climate regime.

Defence Is a Priority in Female Juveniles and Adults of Taxus baccata L.

“…The higher levels of TPhC in females in both the pot experiment and field study are interesting. Higher levels of defensive substances in female specimens are frequently observed in dioecious plants, confirming that females are better defended than males [5,13,44,[48][49][50]. As in other studies, we did not find a significant effect of environmental conditions (in our case, fertilization) on males or females [51].…”

“…This may be due to the increased nitrogen requirements of males associated with pollen production because of the high nitrogen content of the pollen grains [9,46]. On the other hand, higher carbohydrates levels in female individuals are associated with a greater demand for carbohydrates used in the production of seeds and associated structures, arils in the case of yew [47,48].…”

Gender- and season-related variability in the content of proteins, amino acids, and carbohydrates in Taxus baccata needles of different age

“…After pollination in March, oneyear-old male needles can focus on vegetative function, whereas one-year-old female needles are forced to supply not only vegetative growth of the youngest shoots but also developing embryos and produce seeds and arils as showed, inter alia, by their lower content of insoluble carbohydrates and higher content of soluble carbohydrates in the present study. Female individuals are associated with a greater demand for carbohydrates used in the production of seeds (Wallace andRundel 1979, Blake-Mahmud andStruwe 2020). According to Robakowski et al (2018), although the green parts of the arils are capable of performing photosynthesis, they can cover only a part of the resources used to produce and maintain seeds and red arils.…”

Sex and flowers: testing the resource-dependent selection hypothesis for flower sex allocation

“…Varying light levels could explain the high variation seen in the proportion of male flowers across both the wild population and glasshouse experiment (Dodson 1962;Gregg 1973). Damage by insects and other forms of physical trauma have also been linked to changes in sex expression in flowering (Freeman et al 1980;Korpelainen 1998;Blake-Mahmud and Struwe 2020). As such, the aphids present on some plants during the experiment may also have affected the sex ratio of infested plants.…”