Does the occurance of homostyly necessarily accompany the breakdown of heteromorphic incompatibility systems?

Jing Zhao ^1,2 Kuliku • Laiziti ^1,2* Fangfang Jiao ^1,2 Aiqin Zhang ^1,2* Shuang He ^1,2* Dengfu Ren ^1,2

• ¹ Xinjiang University, Urumqi, China
• ² College of Life Science and Technology, Xinjiang University, Urumqi, China

Heterostyly is a genetic polymorphism that facilitates precise pollen transfer through reciprocal herkogamy. The loss or variation of reciprocal herkogamy is usually accompanied by the breakdown of heteromorphic incompatibility system. Homostyly, which is characterized by self-compatibility and same stigma-anther height is a common floral morph in the variation and evolution of heterostyly.Limonium aureum is a distylous species distributed in the desert of northwest China, in which a floral morph with the same stigma-anther height (H-morph) widely distributed in the natural populations, resembling classical homostyly. It is uncertain whether the occurance of H-morph is also accompanied by the breakdown of heteromorphic incompatibility systems, and what is the relationship between the H-morph and long-styled-/short-styled-morph (L-/S-morph). Thus, we investigated the floral morphs composition and frequency, heterostylous syndrome, pollinators and visiting efficiency in five natural populations of L. aureum. The results showed that all populations were composed of L-, S-and H-morphs, except for ATS population with only H-morph, and there were significant differences in flower size parameters, fruit set, and degree of pollination limitation, while no differences among morphs within population. However, each population demonstrated dimorphic pollen-stigma morphology and a strict heteromorphic incompatibility system, especially ATS population, in which they were compatible between morphs with heteromorphic pollen-stigma morphology, regardless of the reciprocal herkogamy, and vice versa. It is speculated that the H-morph in different populations may be at different stages of heterostylous evolution. The ATS population may be a dimorphic population without reciprocal herkogamy which is in the stage before distyly 2 formation, while the other 4 populations may be dimorphic populations with significant variation in reciprocal herkogamy which is in the stage after distyly formation. The H-morph may be caused by stigma-anther separation shortening of Land S-morph in other 4 populations. These phenomenons that the variation of floral morph is independent of physiological incompatibility breakdown, as well as the coexistence of populations from different origins and evolutionary stages within the same species have been reported for the first time in the Plumbaginaceae.