Is distyly in subtropical Psychotria brachyceras (Rubiaceae) similar to the general trends observed for the genus?

Abstract

Distyly is a floral polymorphism that promotes cross-pollination through precise pollination. Psychotria is a mostly tropical genus of distylous Rubiaceae. Although widely studied in Brazil, some regions/species are still poorly explored, which hinders the understanding of distyly system along a greater geographical range. Here, we studied a subtropical population of Psychotria brachyceras in southern Brazil. For this, we characterized morphs occurrence, reciprocity of sexual structures, mating and incompatibility systems. In addition, we compared the reciprocity values from other species of the genus based on values gathered from literature to understand how the population behaves. The population showed equal proportions of thrum (short stigma/high anthers) and pin (high stigma/short anthers) morphs. Reciprocity was higher than the average for the genus and inaccuracy values between sexual organs were evenly distributed between the organ types, indicating a trend to typical distyly. Higher fruit set rates in intermorph and open pollination treatments and pollen tube growth observations confirmed that the population has a functional heteromorphic incompatibility system. Psychotria brachyceras showed no signs of distinct traits to typical distylous populations, which seems to ensure reproductive success and distyly maintenance.

Investigating the longstanding mystery of stigma length differences between morphs of distylous plants

“…However, the adaptive significance of these traits has yet to be well understood (Ganders 1979;Dulberger 1992;Barrett 2019). It has been suggested that the longer length of the S-styled stigma may have a compensatory function by increasing its surface area, thus enhancing the capacity to receive pollen grains (Ree 1997;Trevizan et al 2021a). The Sstyled stigma is subject to interference from various factors, including its location below the anthers, its position inside the corolla tube, and physical interference from intrafloral trichomes and the corolla tube walls (Watanabe et al 2014;Costa & Machado 2017).…”

“…Such morphological arrangement is called reciprocal herkogamy: the reciprocal positioning in the sexual structures between distinct morphs. Since morphs are usually self-incompatible (Barrett & Shore 2008;Trevizan et al 2021a), reciprocal herkogamy is thought to favour disassortative (i.e., intermorph) pollen transfer, ensuring outcrossing, minimizing pollen wastage, and enhancing genetic variability in populations (Darwin 1877;Keller et al 2014;Barrett 2019).…”

“…Because of its reverse herkogamy (i.e., stigmas below anthers; Cardoso et al 2018), S-styled morphs may have greater interference from self-pollen, that can fall on stigmas via gravity (Ree 1997;Trevizan et al 2021a). In addition, since the S-styled stigmas are usually inside the corolla in tubular flowers, pollen deposition may be affected by the interference of the corolla wall and hairs (Baker 1958;Watanabe et al 2014).…”

“…In addition, since the S-styled stigmas are usually inside the corolla in tubular flowers, pollen deposition may be affected by the interference of the corolla wall and hairs (Baker 1958;Watanabe et al 2014). Thus, it has been suggested that a longer stigmatic surface may act to compensate for such issues and increase the probability of crosspollen deposition (Ree 1997;Watanabe et al 2014;Trevizan et al 2021a;Trevizan et al 2021b). In agreement, some studies have quantified pollen deposition and showed that S-styled stigmas receive more intermorph pollen grains than L-styled stigmas (Lau & Bosque 2003;Hern andez & Ornelas 2007;Deschepper et al 2018;Jacquemyn et al 2018;Furtado et al 2021).…”

The Bright Side of Psychedelics: Latest Advances and Challenges in Neuropharmacology

“…About 1400 shrubby species that grow in tropical areas around the world belong to the Psychotria genus [ 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 ]. In particular, Psychotria viridis ( Figure 7 A) is a member of the rubiaceae family that grows spontaneously in the humid areas of Central and South America [ 116 ].…”