Differential reward in “male” versus “female” pollen of functionally dioecious Solanum

Abstract

Premise: Five to six percent of angiosperm species exhibit a dioecious sexual system, with unisexual "male" or "female" flowers borne on separate plants. The consequent need for inter-individual pollen exchange is a special challenge for taxa where pollen is the sole pollinator reward. Dioecious Australian Solanum assure visits from pollenforaging bees via production of inaperturate pollen in functionally female (morphologically bisexual) flowers. Biochemical composition of pollen from Australian Solanum has not been assessed nor compared to porate pollen from staminate flowers to reveal whether these flowers differ in their pollinator reward potential. Methods: Porate pollen from male flowers and inaperturate pollen from functionally female flowers of two functionally dioecious Australian species were compared for protein and amino acid content. We also assessed pollen from bisexual and staminate flowers of a closely related andromonoecious species, in which all pollen is porate, as a comparison across co-occurring sexual systems. Results: In both functionally dioecious species, porate pollen grains from staminate flowers had significantly higher levels of proteins and amino acids than inaperturate pollen grains from functionally female flowers. Levels of proteins and amino acids were highest in bisexual and staminate flowers of the andromonoecious species. Conclusions: Higher levels of proteins and amino acids in porate pollen of "male" flowers in our functionally dioecious Solanum species suggests a greater nutritive reward for bees foraging on "male" plants than for those foraging on functionally "female" plants. Greater reward in porate pollen (including andromonoecious species) may be connected to the potential to generate a pollen tube.

Sex-driven neighborhood effects on herbivory in the dioecious Mediterranean palm Chamaerops humilis L.

“…Besides male palms had twice as many inflorescences as females in one of our study populations, male inflorescences usually produce more flowers per inflorescence than do female inflorescences (Herrera 1989b ). (b) Male inflorescences and flowers often offer higher nutritional qualities as well as higher rewards, such as rich nitrogen content in pollen, compared to females (Cornelissen and Stiling 2005 ; McCall and Irwin 2006 ; Barrett and Hough 2012 ; Ndem-Galbert et al 2021 ). (c) Male inflorescences may be less defended than female inflorescences.…”

“…These individuals evolved a sexual dimorphism with divergent attributes, especially in reproduction and defense (Bawa 1980 ; Barrett and Hough 2012 ). For example, reproductive traits, such as flower size, number of flowers, nectar secretion, or nutrient content, often differ markedly between sexes (Barrett and Hough 2012 ; Vega-Frutis et al 2013 ; Ndem-Galbert et al 2021 ; Calaça et al 2022 ). Also to ensure successful reproduction, female plants are thought to invest more in defensive mechanisms than males (Cornelissen and Stiling 2005 ; Cepeda-Cornejo and Dirzo 2010 ; Tsuji and Sota 2010 ; Avila-Sakar and Romanow 2012 ).…”

Solanum scalarium (Solanaceae), a newly-described dioecious bush tomato from Judbarra/Gregory National Park, Northern Territory, Australia

“…Pollination biology of the species is unknown, but, like other Australian congeners, the flowers are likely buzz pollinated by bees in the genera Xylocopa and Amegilla ( Apidae ; see Anderson and Symon 1988 ; Switzer et al 2016 ) and likely to present high levels of pollen nutritional reward – although with slightly differential rewards available to pollen foragers from male versus functionally female flowers ( Ndem-Galbert et al 2021 ). A small set ( N = 10) of ex situ hand pollinations conducted for this study showed that inaperturate pollen produced by functionally female flowers does not lead to fruit set when used to pollinate other females.…”

Morphological trait evolution inSolanum(Solanaceae): Evolutionary lability of key taxonomic characters

“…Sexual system (sensu Cardoso & al., 2018) has been used in Solanum taxonomy (Symon, 1970, 1979b; Levine & Anderson, 1986; Whalen & Costich, 1986; Anderson & Symon, 1989; Knapp & al., 1998; Dupont & Olesen, 2006; Anderson & al., 2015; Ndem‐Galbert & al., 2021), and varies from cosexual (i.e., hermaphroditic) to various degrees of andromonoecy and dioecy. Inflorescence position, determined by variation in fusion of inflorescence and sympodial stem axes in Solanum (Danert, 1958), has also been used to define some clades (Knapp, 2002b; Bohs, 2005) and position varies from terminal, internodal, axillary, leaf‐opposed or along spur‐shoots.…”

“…Sexual system (sensu Cardoso & al., 2018) has been used in Solanum taxonomy (Symon, 1970(Symon, , 1979bLevine & Anderson, 1986;Whalen & Costich, 1986;Anderson & Symon, 1989;Knapp & al., 1998;Dupont & Olesen, 2006;Anderson & al., 2015;Ndem-Galbert & al., 2021), and varies from cosexual (i.e., hermaphroditic) to various degrees of andromonoecy and dioecy. Inflorescence position, determined…”