4.2 A complete loss of sex under extreme warming
Despite that clonal plants usually retain two reproductive modes –
sexual seed reproduction and asexual vegetative propagation, a loss of
sex has been widely recognized in the evolutionary process of clonal
plants (Eckert, 2002). Two prior studies have found that warming reduced
the sexual reproduction of P. crispus in the measurement of
inflorescence number (Xu et al., 2020; Yan et al., 2021). Although
inflorescence can indicate sexual reproduction, fruits or seeds are more
directly correlated with plant fitness (Wang et al., 2021b). In the
present study, we found a rare complete loss of sex under extreme
warming as warming blocked the production of fruit sets for three
populations, which corresponds to the second hypothesis. During the
experimental process, inflorescence has also been observed. However, no
fruit sets formed in the warming treatments. The major pollination mode
for P. crispus is hydrophilous (Guo & Huang, 1999). High water
temperature likely damaged the pollen viability, which led to the
failure in the seed formation (Rang et al., 2011). Santamarı́a &
Hootsmans (1998) also found that the seed production of the submerged
plant, Ruppia drepanensis was blocked when the water temperature
exceeds 30 ℃. Therefore, a probable explanation for the complete loss of
sex is that extreme warming disrupted the pollen viability.