Sexual Tetramorphism in Thymelaea hirsuta (Thymelaeaceae): Morph Ratios in Open-Pollinated Progeny

Abstract

Natural populations of Thymelaea hirsuta have previously been shown to comprise four distinct sexual morphs: males, females, protogynous individuals, i.e., first female then male, and protandrous individuals, i.e., first male then female. The objective of the present study has been to confirm the genetic basis of this sexual tetramorphism by quantifying morph ratios in the open-pollinated progeny of the four sexual phenotypes growing in a natural population. All four phenotypes were recovered in the progeny of each morpho All observed plants displayed a single sexual phenotype, thus confirming the genetic basis of the tetramorphism. The progeny sex ratios indicate that the genetic determination of sex in this species may be influenced by cytoplasmic factors, while the observed levels offunctional female fertility suggest a near-dioecious system. The evolutionary significance of this tetramorphism as a transitional stage in the evolution of dioecy is discussed.

Mating patterns and pollen dispersal in a heterodichogamous tree, Juglans mandshurica (Juglandaceae)

“…In the second form, flowers of both morphs open simultaneously, but one morph is protandrous and the other is protogynous. Heterodichogamy is phylogenetically widespread (Renner, 2001), occurring in nine orders, 12 families, and 18 genera of flowering plants such as Corylus (Müller, 1875), Juglans (Knuth, 1906; Stout, 1928; Wood, 1934; Gleeson, 1982; Kimura et al ., 2003; Bai et al ., 2006), Carya (Thompson & Romberg, 1985; McCarthy & Quinn, 1990), Acer (Gabriel, 1968; Asai, 2000; Sato, 2002), Grayia (Pendleton et al ., 1988, 2000), Thymelaea (Dommee et al ., 1990, 1995), Alpinia (Li et al ., 2001) and Hernandia (Endress & Lorence, 2004). In these species, the flowering phases of the two mating types are synchronous and reciprocal, so their mating patterns have been characterized as disassortative (Gleeson, 1982; Pendleton et al ., 1988; Dommee et al ., 1990; Kimura et al ., 2003; Bai et al ., 2006).…”

Gynodioecy in the common spindle tree (Euonymus europaeusL.) involves differences in the asymmetry of corolla shapes between sexually differentiated flowers

“…For example, a transition from fully bisexual to purely pistillate flowers within a gradient of individuals differing in the number of active stamens has been identified in populations of Geranium sylvaticum, which typically exhibits a pentameric corolla morphology (Asikainen & Mutikainen, 2003;Asikainen & Mutikainen, 2005). In addition, several co-existing sexual types, including purely unisexual, inconstant unisexual, ambisexual and bisexual individuals, have been reported in Thymelaea hirsuta, a species with tetrameric actinomorphic flowers (Shaltout & El-Keblawy, 1992;Dommée et al, 1995). In these systems, the possible effects of stamen abortion on within-flower corolla asymmetry could be tested in complex settings, which might confirm or disprove the generality of this phenomenon and its developmental explanation.…”

Peer Review #2 of "Gynodioecy in the common spindle tree (Euonymus europaeus L.) involves differences in the asymmetry of corolla shapes between sexually differentiated flowers (v0.1)"

“…For example, a transition from fully bisexual to purely pistillate flowers within a gradient of individuals differing in the number of active stamens has been identified in populations of Geranium sylvaticum, which typically exhibits a pentameric corolla morphology (Asikainen & Mutikainen, 2003;. In addition, several co-existing sexual types, including purely unisexual, inconstant unisexual, ambisexual and bisexual individuals, have been reported in Thymelaea hirsuta, a species with tetrameric actinomorphic flowers (Shaltout & El-Keblawy, 1992;Dommée et al, 1995). In these systems, the possible effects of stamen abortion on within-flower corolla asymmetry could be tested in complex settings, which might confirm or disprove the generality of this phenomenon and its developmental explanation.…”