Microsporogenesis in male-sterile and hermaphroditic plants of nine gynodioecious taxa of Hawaiian bidens (Asteraceae)

Microsporogenesis was investigated in hermaphroditic and male-sterile plants in nine gynodioecious taxa of Hawaiian Bidens. Normal microsporogenesis in hermaphrodites and the onset of abortion in male steriles were similar in all taxa and in a hybrid between two gynodioecious species. The early abnormal vacuolation of tapetal cells is the first visible evidence leading to premeiotic abortion of microsporogenesis in male steriles. The sporogenous cells disintegrate rapidly after the vacuolation of the tapetum, resulting in a shrunken, indehiscent anther which is composed of only the epidermal layer with some remnant cells of the endothecium and the connective at anthesis. In hermaphrodites, the tapetal cklls remain dense and undergo karyokinesis to become binucleate during meiosis I. The tapetum becomes plasmodia1 after microspores are released from tetrads and gradually disappears during pollen formation. The genetic factor($ which cause the abortion act with remarkable precision and consistency in all taxa investigated. This suggests that gynodioecy in all Hawaiian Bidens is homologous and the establishment of male sterility in Hawaiian Bidens occurred only once. The spread of the genetic male-sterile factor(s) may be the result of adaptive radiation of the original gynodioecious species or natural interspecific hybridization.link_to_subscribed_fulltex

Mixed mating systems in Hawaiian Bidens (Asteraceae)

Protandry and male sterility promote outcrossing, while self-compatibility and geitonogamy contribute to inbreeding. The combination of these floral mechanisms results in a mixed mating system in all species studied. Outcrossing rates of 15 populations of the 11 species ranged from 0.43-0.88, averaging 0.65. Apparent selfing rates of females ranged from 0-0.25 in 7 gynodioecious populations, suggesting that there is variation in the level of biparental inbreeding among populations. Presence of females increased the level of outcrossing by an average of 9% in gynodioecious populations. Efficiency of gynodioecy as an outcrossing mechanism largely depends on the current outcrossing rate of hermaphrodites, frequency of females, and extent of genetic substructuring in populations. On average, autogamy contributed 4%, geitonogamy contributed 24%, and consanguineous mating contributed 15% to the realized selfing rate (43%) in the hermaphrodites of these species. -from Authorslink_to_subscribed_fulltex

Genetics of gynodioecy in Hawaiian Bidens (Asteraceae)

Inheritance of male sterility in all gynodioecious species of Hawaiian Bidens was investigated by experimental crosses conducted in greenhouses. Both male-sterile individuals and hermaphrodites were segregated in the progenies of openpollinated female and hermaphroditic plants growing in nature. The ratios (H:MS) of 1:0, 1:1, 3:1 were observed in the F1 generations; 3:1 and 15:1 in the F2 generations; and 1:1 and 3:1 in the backcrosses. Thirteen interspecific triple crosses and all quadruple crosses gave MS progenies, indicating a directly allelic relationship among male sterility genes in all gynodioecious species. Based on these results, A digenic-cytoplasmic model was proposed, and the evolution of gynodioecy in Hawaiian Bidens was discussed. © The Oenetical Society of Great Britain.link_to_subscribed_fulltex

Three-dimensional reciprocity of floral morphs in wild flax (Linum suffruticosum): a new twist on heterostyly

• Here, we studied the floral morphology and pollination of the distylous plant Linum suffruticosum (Linaceae) in southern Spain.• We observed a previously unreported form of distyly that involved twisting and bending of styles and stamens during floral development to achieve three-dimensional reciprocity of anthers and stigmas in the long-styled (pin) and short-styled (thrum) morphs. This developmental pattern causes pin pollen to be placed on the underside of pollinating Usiaflies (Bombyliidae), and thrum pollen to be placed on the top of the thorax and abdomen. The pin stigmas contact the flies on the dorsum, apparently picking up predominantly thrum pollen, and the thrum stigmas contact the flies on the ventral surface, apparently picking up predominantly pin pollen.• This form of heterostyly would appear on morphological grounds to be far more efficient in dispersing pollen between compatible morphs than the typical pin–thrum system. If so, this plant fits Darwin’s prediction of efficient pollen flow between heterostylous morphs more closely than anything Darwin himself reported.• Molecular phylogenetic analyses indicate that this form of heterostyly evolved in a lineage that already had typical heterostyly. The analyses also indicate that there have been several independent origins of heterostyly in Linumand at least one reversal to stylar monomorphism

Outcrossing rates and allozyme variation in rayed and rayless morphs of Bidens pilosa

Thirty-four isozyme loci were assayed in 1048 plants from three Hawaiian populations of the autogamous introduced weed Bidens pilosa. Total isozyme gene diversity was very low, 0-049. One population containing only rayless plants was completely monomorphic at all loci except PGI-3, and this locus was nearly fixed. In a large population polymorphic for rayed, rayless, and intermediate plants, two loci showed rare variants and PGI-3 was polymorphic. Allele frequencies at PGI-3 were not significantly different among the floral morphs, but outcrossing rates, measured by progeny tests using PGI-3 as a genetic marker, were significantly higher in the radiate morph (9 per cent) than in the rayless and intermediate morphs (5 per cent). Presumably radiate plants have higher outcrossing rates because they are more attractive to pollinators. © The Genetical Society of Great Britain.link_to_subscribed_fulltex