Sensory bias and signal detection trade-offs maintain intersexual floral mimicry.

Mimicry is common in interspecies interactions, yet conditions maintaining Batesian mimicry have been primarily tested in predator-prey interactions. In pollination mutualisms, floral mimetic signals thought to dupe animals into pollinating unrewarding flowers are widespread (greater than 32 plant families). Yet whether animals learn to both correctly identify floral models and reject floral mimics and whether these responses are frequency-dependent is not well understood. We tested how learning affected the effectiveness and frequency-dependence of imperfect Batesian mimicry among flowers using the generalist bumblebee, Bombus impatiens, visiting Begonia odorata, a plant species exhibiting intersexual floral mimicry. Unrewarding female flowers are mimics of pollen-rewarding male flowers (models), though mimicry to the human eye is imperfect. Flower-naive bees exhibited a perceptual bias for mimics over models, but rapidly learned to avoid mimics. Surprisingly, altering the frequency of models and mimics only marginally shaped responses by naive bees and by bees experienced with the distribution and frequency of models and mimics. Our results provide evidence both of exploitation by the plant of signal detection trade-offs in bees and of resistance by the bees, via learning, to this exploitation. Critically, we provide experimental evidence that imperfect Batesian mimicry can be adaptive and, in contrast with expectations of signal detection theory, functions largely independently of the model and mimic frequency. This article is part of the theme issue 'Signal detection theory in recognition systems: from evolving models to experimental tests'.

The evolution of sex ratio differences and inflorescence architectures in Begonia (Begoniaceae).

PREMISE OF THE STUDY: A major benefit conferred by monoecy is the ability to alter floral sex ratio in response to selection. In monoecious species that produce flowers of a given sex at set positions on the inflorescence, floral sex ratio may be related to inflorescence architecture. We studied the loci underlying differences in inflorescence architecture between two monoecious Begonia species and related this to floral sex ratios. METHODS: We performed trait comparisons and quantitative trait locus (QTL) mapping in a segregating backcross population between Central American Begonia plebeja and B. conchifolia. We focused on traits related to inflorescence architecture, sex ratios, and other reproductive traits. KEY RESULTS: The inflorescence branching pattern of B. conchifolia was more asymmetric than B. plebeja, which in turn affects the floral sex ratio. Colocalizing QTLs of moderate effect influenced both the number of male flowers and the fate decisions of axillary meristems, demonstrating the close link between inflorescence architecture and sex ratio. Additional QTLs were found for stamen number (30% variance explained, VE) and pollen sterility (12.3% VE). CONCLUSIONS: One way in which Begonia species develop different floral sex ratios is through modifications of their inflorescence architecture. The potential pleiotropic action of QTL on inflorescence branching and floral sex ratios may have major implications for trait evolution and responses to selection. The presence of a single QTL of large effect on stamen number may allow rapid divergence for this key floral trait. We propose candidate loci for stamen number and inflorescence branching for future characterization.

Natural foliar variegation without costs? The case of Begonia.

BACKGROUND AND AIMS: Foliar variegation is recognized as arising from two major mechanisms: leaf structure and pigment-related variegation. Begonia has species with a variety of natural foliar variegation patterns, providing diverse examples of this phenomenon. The aims of this work are to elucidate the mechanisms underlying different foliar variegation patterns in Begonia and to determine their physiological consequences. METHODS: Six species and one cultivar of Begonia were investigated. Light and electron microscopy revealed the leaf structure and ultrastructure of chloroplasts in green and light areas of variegated leaves. Maximum quantum yields of photosystem II were measured by chlorophyll fluorescence. Comparison with a cultivar of Ficus revealed key features distinguishing variegation mechanisms. KEY RESULTS: Intercellular space above the chlorenchyma is the mechanism of variegation in these Begonia. This intercellular space can be located (a) below the adaxial epidermis or (b) below the adaxial water storage tissue (the first report for any taxa), creating light areas on a leaf. In addition, chlorenchyma cell shape and chloroplast distribution within chlorenchyma cells differ between light and green areas. Chloroplasts from both areas showed dense stacking of grana and stroma thylakoid membranes. The maximum quantum yield did not differ significantly between these areas, suggesting minimal loss of function with variegation. However, the absence of chloroplasts in light areas of leaves in the Ficus cultivar led to an extremely low quantum yield. CONCLUSIONS: Variegation in these Begonia is structural, where light areas are created by internal reflection between air spaces and cells in a leaf. Two forms of air space structural variegation occur, distinguished by the location of the air spaces. Both forms may have a common origin in development where dermal tissue becomes loosely connected to mesophyll. Photosynthetic functioning is retained in light areas, and these areas do not include primary veins, potentially limiting the costs of variegation.

How to cheat when you cannot lie? Deceit pollination in Begonia gracilis.

Mimicry between rewarding and non-rewarding flowers within individuals has been accepted as a strategy favored by selection to deceive pollinators. It has been proposed that this mechanism relies on the exploitation of pollinator's sensory biases, but field evidence is still scarce. In this study, we describe the mechanism of deceit pollination in the monoecious herb Begonia gracilis, a species with exposed rewarding structures (pollen) and intersexual mimicry. Specifically, we test the role of mimicry and exploitation of sensory biases on the reproductive success of male (pollination visitation) and female flowers (probability of setting fruits). We show that pollinators' perception of the amount of reward provided by male flowers is influenced by the independent variation in the sizes of the androecium and the perianth. Large rewarding structures and small perianths were preferred by pollinators, suggesting a central role of the relative size of the rewarding structure on pollinators' foraging decisions. Hence, rewarding male flowers cheat pollinators by exploiting their sensory biases, a strategy followed by non-rewarding female flowers. We suggest that intersexual mimicry operates through the functional resemblance of male flowers' deceit strategy. Artificial manipulation of the flowers supports our findings in natural conditions. Overall, we propose that the continuous and independent variation in the size of the perianth and the reproductive organs among male and female flowers could itself be adaptive.

First macrofossil record of Begonia (Begoniaceae).

PREMISE OF THE STUDY: Begonia is the sixth-largest genus of flowering plants, with about 1400-1500 species in 66 sections. Several species are popular with horticulturalists, mainly for their colorful flowers and leaves. However, the evolutionary history of the genus is debated, and until now there has been no macrofossil record. Here, we report on a fossil winged capsule from the Pliocene of Alabama and interpret it as a Begonia fruit, which represents the first convincing macrofossil evidence of the genus. METHODS: Identification required extensive literature and herbarium searches to compare features of the fossil with those of other recognized fossil and extant taxa that have winged fruits. KEY RESULTS: The fossil is identified as a Begonia fruit on the basis of a combination of characters, including the presence of two unequally developed wings, at least one additional inferred wing, details of the wing venation, a prominent marginal vein, a locule opening associated with a wing, and a persistent pedicel. CONCLUSIONS: Although too young to provide a calibration point for molecular divergence-time estimates, this fossil is noteworthy as the first macrofossil record of Begonia. It may represent a species that initially arrived from the south via Mexico after the closing of the Central American Straits. We propose that this fossil should stimulate a reexamination of other unidentified fossil winged fruits, as older records of Begonia may be forthcoming.

[Pharmacognostic studies on Begonia sinensis rhizome].

OBJECTIVE: To establish the characteristic method of rude medicinal material of rhizome of Begonia sinensis. METHOD: The characteristic features of the rhizome were studies by morphological and microscopic observation. RESULTS: The description and transverse features of transverse section of the rhizome were described, and in the powder the microscopic features such as cluster needle crystals, tentacle, ring-thread vessel were found. CONCLUSION: The characteristics can be used to differentiate the rhizome of Begonia sinensis.

Phylogeny of the Cucurbitales based on DNA sequences of nine loci from three genomes: implications for morphological and sexual system evolution.

The Cucurbitales are a clade of rosids with a worldwide distribution and a striking heterogeneity in species diversity among its seven family members: the Anisophylleaceae (29-40 species), Begoniaceae (1400 spp.), Coriariaceae (15 spp.), Corynocarpaceae (6 spp.), Cucurbitaceae (800 spp.), Datiscaceae (2 spp.), and Tetramelaceae (2 spp.). Most Cucurbitales have unisexual flowers, and species are monoecious, dioecious, andromonoecious, or androdioecious. To resolve interfamilial relationships within the order and to polarize morphological character evolution, especially of flower sexual systems, we sequenced nine plastids (atpB, matK, ndhF, rbcL, the trnL-F region, and the rpl20-rps12 spacer), nuclear (18S and 26S rDNA), and mitochondrial (nad1 b/c intron) genes (together approximately 12,000 bp) of 26 representatives of the seven families plus eight outgroup taxa from six other orders of the Eurosids I. Cucurbitales are strongly supported as monophyletic and are closest to Fagales, albeit with moderate support; both together are sister to Rosales. The deepest split in the Cucurbitales is that between the Anisophylleaceae and the remaining families; next is a clade of Corynocarpaceae and Coriariaceae, followed by Cucurbitaceae, which are sister to a clade of Begoniaceae, Datiscaceae, and Tetramelaceae. Based on this topology, stipulate leaves, inferior ovaries, parietal placentation, and one-seeded fruits are inferred as ancestral in Cucurbitales; exstipulate leaves, superior ovaries, apical placentation, and many-seeded fruits evolved within the order. Bisexual flowers are reconstructed as ancestral, but dioecy appears to have evolved already in the common ancestor of Begoniaceae, Cucurbitaceae, Datiscaceae, and Tetramelaceae, and then to have been lost repeatedly in Begoniaceae and Cucurbitaceae. Both instances of androdioecy (Datisca glomerata and Schizopepon bryoniifolius) evolved from dioecious ancestors, corroborating recent hypotheses about androdioecy often evolving from dioecy.