Mating consequences of contrasting hermaphroditic plant sexual systems

Abstract

For hermaphroditic angiosperms with multiple flowers, the sex roles can be exclusively combined in bisexual flowers (monocliny), strictly separated among different flowers (monoecy), or arrayed in mixtures of bisexual flowers with female flowers (gynomonoecy) or male flowers (andromonoecy). The hypothesized benefits favoring the evolution of these contrasting hermaphroditic sexual systems are typically examined individually, usually by assessing success through only one sex role. We tested predictions of most hypotheses experimentally with an andromonoecious species, Anticlea occidentalis (Melanthiaceae), based on the performance of intact plants (andromonoecy) and those with emasculated bisexual flowers (functionally monoecious) or emasculated male flowers (functionally monoclinous with sterile peripheral flowers). Andromonoecy in this species enables efficient, size-dependent resource allocation, emphasizing female function in large plants. Emasculation revealed that anthers in male flowers promote female mating quality (outcrossing rate and mate diversity), whereas anthers in bisexual flowers promote male mating quantity (pollen dispersal distance and probability of any siring success). Thus, different hermaphroditic sexual systems likely evolve to capitalize on suites of benefits, rather than just one, and provide compromises between quantitative and qualitative reproductive components. These compromises apparently maximize an individual's combined genetic contributions through female and male functions, rather than separate contributions through each sex role.

Frequent fires do not affect sexual expression and reproduction in Vachellia caven

“…() conducted on V. caven in different sites and seasons, and those found for the andromonoecious Solanum carolinense (Vallejo‐Marín & Rausher ), Capparis spinosa (Zhang & Tan ) and Anticlea occidentalis (Tomaszewski et al . ) showed the same pattern. Several non‐mutually exclusive mechanisms have been proposed to explain the benefit of female success supplied by increasing male flowers: (i) producing cheaper male flowers saves resources that can be reallocated to seed production (e.g.…”

The dynamic mosaic phenotypes of flowering plants

“…For example, in Sagittaria latifolia (Sarkissian et al ., ) and Anticlea occidentalis (Fig. j; Tomaszewski et al ., ) average production of female and bisexual flowers, respectively, increases with plant size, whereas that of male flowers does not vary.…”

“…Panels (f–j) illustrate qualitatively different flower types within inflorescences, including: (f) female ray flowers (F) and bisexual disc flowers (B, note dark anthers) of Ligularia przewalskii ; (g) small central fertile flowers and large peripheral sterile flowers of Hydrangea serrata ; (h) young yellow flowers with receptive stigmas and polleniferous anthers, and postpollination orange flowers of Lantana camara ; (i) dark fertile flowers and pale sterile flowers of Muscari armeniacum ; and (j) bisexual (B, note projecting styles) and male (M) flowers of Anticlea occidentalis . In addition to their qualitative differences, bisexual and male A. occidentalis flowers differ in size, and bisexual flowers also vary in size with flower position (Tomaszewski et al ., ). Panel (k) illustrates the floral display of Satyrium longicauda , the size of which varies with pollinator visitation owing to pollination sensitivity of floral longevity (Harder & Johnson, ).…”

“…g,i; Morales et al ., ; Park et al ., ), those with hermaphroditic sexual systems involving mixtures of bisexual, female and/or male flowers (Fig. d,j; Diggle, ; Torices et al ., ; Tomaszewski et al ., ), and species with different fruit types (Imbert, ). More common, but less apparent, is quantitative variation among flowers of individual plants (Diggle, ; Herrera, ).…”

“…Many features of mosaic phenotypes implement division of labour, including production of distinct feeding and pollinating anthers within flowers (heteranthery, Vallejo‐Marín et al ., ), segregated presentation of female(‐phase) and male(‐phase) flowers within inflorescences (Fig. c,f; Harder et al ., ; Tomaszewski et al ., ), and production of separate vegetative and reproductive ramets (Charpentier & Stuefer, ).…”