Ruellia subsessilis (Nees) Lindau (Acanthaceae): A species with a sexual reproductive system that responds to different water availability levels

In Ruellia subsessilis the typical cleistogamy (cleistogamous and chasmogamous morphs), which is common in species of this genus, was not observed. Flowering and fruiting of this species are continuous and the selfing flowers are polymorphic. Objective of present study was to analyze the mechanisms of self-pollination in R. subsessilis. In addition, we studied its reproductive phenology, floral biology, breeding system, seed germination and how its sexual reproductive system responds to different water availability levels. The study was conducted with plants of a natural population and others in a greenhouse, under different water availability levels, in southeastern Brazil. The distribution of the reproductive phenophases was seasonal and concentrated in the rainy season. Production of distinct floral morphs could be observed. These different morphs are named ‘reduced chasmogamous morphs’ (RC), in the dry season, and ‘normal chasmogamous morphs’ (NC), which latter develop in the rainy season. The morph production of the cultivated plants was likewise influenced by water availability: RC developed under drought stress and NC in moist soil. Significant differences between morphs were observed in size parameters of the corolla, androecium and gynoecium, and concerning the number of ovules and pollen grains. In both morphs, selfing occurred late (delayed self-pollination), and pre-anthesis cleistogamy (early self-pollination) occurred sporadically in RC. The seeds resulting from self-pollination were more vigorous and germinated faster than those from cross-pollination.     

Florivory increases selfing: an experimental study in the wild strawberry, Fragaria virginiana

Florivores are antagonists that damage flowers, and have direct negative effects on flowering and pollination of the attacked plants. While florivory has mainly been studied for its consequences on seed production or siring success, little is known about its impact on mating systems. Damage to flowers can alter pollinator attraction to the plant and may therefore modify patterns of pollen transfer. However, the consequences of damage for mating systems can take two forms: a decrease in flower number reduces opportunities for intra-inflorescence pollen deposition (geitonogamy), which, in turn, may lead to a decrease in selfing; whereas a decrease in floral display may also reduce overall visitation and thus increase the chances of self-pollination via facilitated or autonomous autogamy. We investigated the effects of damage by a bud-clipping weevil ( Anthonomus signatus ) in Fragaria virginiana in an experimental setting mimicking natural conditions. We found that increased damage led to an increase in selfing, a result consistent with the increased autogamy pathway. We discuss the implications of this finding and evaluate the generality of florivore-mediated mating system expression.     

Mechanisms and evolution of deceptive pollination in orchids

The orchid family is renowned for its enormous diversity of pollination mechanisms and unusually high occurrence of non-rewarding flowers compared to other plant families. The mechanisms of deception in orchids include generalized food deception, food-deceptive floral mimicry, brood-site imitation, shelter imitation, pseudoantagonism, rendezvous attraction and sexual deception. Generalized food deception is the most common mechanism (reported in 38 genera) followed by sexual deception (18 genera). Floral deception in orchids has been intensively studied since Darwin, but the evolution of non-rewarding flowers still presents a major puzzle for evolutionary biology. The two principal hypotheses as to how deception could increase fitness in plants are (i) reallocation of resources associated with reward production to flowering and seed production, and (ii) higher levels of cross-pollination due to pollinators visiting fewer flowers on non-rewarding plants, resulting in more outcrossed progeny and more efficient pollen export. Biologists have also tried to explain why deception is overrepresented in the orchid family. These explanations include: (i) efficient removal and deposition of pollinaria from orchid flowers in a single pollinator visit, thus obviating the need for rewards to entice multiple visits from pollinators; (ii) efficient transport of orchid pollen, thus requiring less reward-induced pollinator constancy; (iii) low-density populations in many orchids, thus limiting the learning of associations of floral phenotypes and rewards by pollinators; (iv) packaging of pollen in pollinaria with limited carry-over from flower to flower, thus increasing the risks of geitonogamous self-pollination when pollinators visit many flowers on rewarding plants. All of these general and orchid-specific hypotheses are difficult to reconcile with the well-established pattern for rewardlessness to result in low pollinator visitation rates and consequently low levels of fruit production. Arguments that deception evolves because rewards are costly are particularly problematic in that small amounts of nectar are unlikely to have a significant effect on the energy budget of orchids, and because reproduction in orchids is often severely pollen-, rather than resource-limited. Several recent experimental studies have shown that deception promotes cross-pollination, but it remains unknown whether actual outcrossing rates are generally higher in deceptive orchids. Our review of the literature shows that there is currently no evidence that deceptive orchids carry higher levels of genetic load (an indirect measure of outcrossing rate) than their rewarding counterparts. Cross-pollination does, however, result in dramatic increases in seed quality in almost all orchids and has the potential to increase pollen export (by reducing pollen discounting). We suggest that floral deception is particularly beneficial, because of its promotion of outcrossing, when pollinators are abundant, but that when pollinators are consistently rare, selection may favour a nectar reward or a shift to autopollination. Given that nectar-rewardlessness is likely to have been the ancestral condition in orchids and yet is evolutionarily labile, more attention will need to be given to explanations as to why deception constitutes an 'evolutionarily stable strategy'.     

The Life Cycle of Rotaliella elatiana N. Sp.: A Tiny Macroalgavorous Foraminifer from the Gulf of Elat1

ABSTRACT. A new foraminiferan species, Rotaliella elatiana n. sp., was isolated in the Gulf of Elat, where it lives in association with a macrophytic green alga, Enteromorpha. The agamont of this tiny new species has a transparent test composed of a bilocular embryonic chamber followed by six to seven trochospirally coiled inflated chambers. The spiral sutures are undulated. The umbilical side has numerous denticules and has radial grooves. The gamont has only one inflated chamber. Rotaliella elatiana has a classical, heterophasic life cycle, with a regular alternation of diploid agamontic phase and haploid gamontic phase. The gamontic phase of the life cycle is exceptionally reduced and the uninucleated gamonts pair immediately after they build their first chamber. A few cases of autogamic reproduction were observed. R. elatiana is a heterocaryotic species; agamonts have one somatic and two to three generative nuclei.     

Adaptive function of duodichogamy: Why do chestnut trees have two pollen emission phases?

Premise

Intersexual mating facilitation in flowering plants has been largely underexplored. Duodichogamy is a rare flowering system in which individual plants flower in the sequence male-female-male. We studied the adaptive advantages of this flowering system using chestnuts (Castanea spp., Fagaceae) as models. These insect-pollinated trees produce many unisexual male catkins responsible for a first staminate phase and a few bisexual catkins responsible for a second staminate phase. We hypothesized that duodichogamy increases female mating success by facilitating pollen deposition on stigmas of the rewardless female flowers through their proximity with attractive male flowers responsible for the minor staminate phase.

Methods

We monitored insect visits to 11 chestnut trees during the entire flowering period and explored reproductive traits of all known duodichogamous species using published evidence.

Results

In chestnuts, insects visited trees more frequently during the first staminate phase but visited female flowers more frequently during the second staminate phase. All 21 animal-pollinated duodichogamous species identified are mass-flowering woody plants at high risk of self-pollination. In 20 of 21 cases, gynoecia (female flower parts) are located close to androecia (male flower parts), typically those responsible for the second minor staminate phase, whereas androecia are often distant from gynoecia.

Conclusions

Our results suggest that duodichogamy increases female mating success by facilitating pollen deposition on stigmas by means of the attractiveness of the associated male flowers while effectively limiting self-pollination.

     

Directed Positioning of Micronuclei in Paramecium tetraurelia with Laser Tweezers: Absence of Detectible Damage After Manipulation

Possible covert damage from the use of the laser optical force trap (laser tweezers) to reposition micronuclei in Paramecium tetraurelia was assessed by measuring proliferation rates and postautogamous survival and mutation rates of cells after laser manipulations. No differences in subsequent daily proliferation rates among laser manipulated and various control classes of cells were seen. Similarly, the rates of postautogamous lethality and of “slow growth mutations” after repositioning of both micronuclei were not different from such rates in unmanipulated controls. In spite of extensive manipulations of micronuclei by the laser tweezers, there is no evidence of any damage induced by these manipulations. The laser tweezers therefore appears to be a tool of benign effect upon living cells, with tremendous potential use in many cell and developmental biological investigations.     

Reproductive ecology of the basal angiosperm Trithuria submersa (Hydatellaceae)

Background and Aims

Trithuria, the sole genus in the family Hydatellaceae, is an important group for understanding early angiosperm evolution because of its sister relationship to the ancient lineage, Nymphaeales (water lilies). Although also aquatic, Trithuria differs from water lilies in that all species are extremely small, and most have an annual life form and grow in seasonal wetlands. Very little is known about their reproductive ecology. This paper reports on reproductive timing, mode of pollination and characteristics of the breeding system of Trithuria submersa in Western Australia.

Methods

Mass collections of open-pollinated plants from different ecological settings were used to characterize the reproductive developmental sequence and natural pollen reception. Hand-pollination, caging and emasculation experiments were used to measure outcross + geitonogamous pollen reception versus autonomous self-pollination in two populations over two field seasons.

Key Results

Natural outcross or geitonogamous pollination was by wind, not by water or insects, but pollen reception was extremely low. Pollen production was very low and pollen release was non-synchronous within populations. The pollen to ovule (P/O) ratio was 23·9, compared with 1569·1 in dioecious Trithuria austinensis. Stigmas became receptive before male phase and remained so until anthers dehisced and autonomous self-pollination occurred. Natural pollen loads are composed primarily of self pollen. Self- and open-pollinated plants had equivalent seed set (both >70 %). Self-pollinated plants produced seed within 17 d.

Conclusions

Autonomous self-pollination and self-fertilization are predominant in T. submersa. The low P/O ratio is not an artefact of small plant size and is inconsistent with long-term pollination by wind. It indicates that T. submersa has evolved a primarily autogamous breeding system. Selfing, along with the effect of small plant size on the speed of reproduction, has enabled T. submersa to colonize marginal ephemeral wetlands in the face of unpredictable pollination.     

RESPONSE TO SELECTION ON AUTOGAMY IN PHLOX

Two cycles of artificial selection were performed to increase autogamous fruiting in two wild populations of the self-incompatible Phlox drummondii, to decrease autogamous fruiting in two wild populations of the self-compatible Phlox cuspidata, and to both increase and decrease autogamous fruiting in a cultivar of P. drummondii which is pseudo-self-compatible. The breeding systems were determined to be genetically quite flexible, independent of inbreeding depression and other genetic phenomena which could hinder a breeding system shift. This is especially true for increasing autogamy. Self-pollen-pistil compatibility seems to be the single character affected by selection. Based on the continuous variation in both autogamy and self-compatibility, we suggest that the change has been due to genes which modify the self-incompatibility reaction rather than to the simple segregation of alleles at the S-locus.     

Morphological Drift Accompanying Nascent Population Differentiation in the Ciliate Euplotes vannus

A rare phenomenon can occur in ciliated protists of the genus Euplotes, which can undergo genetic recombination by the normal outbreeding process of conjugation following mild starvation. Occasionally, the dominant mutation for the autogamy trait arises. Individuals possessing the trait show obligate self-fertilization upon mild starvation. This yields, after normal asexual division, a population of individuals that are reproductively isolated from the parental outbreeding strain. A morphometric analysis of sympatric autogamous and non-autogamous populations of Euplotes vannus from Somalia demonstrates that there has been morphological drift in gross body proportions in the autogamous populations. However, the positional patterns of the locomotory organelles on the ventral surface remain unchanged. The changes in body proportions in the autogamous populations are relevant to the mechanics of the conjugation process, which involves fusion of the oral regions of paired cells belonging to complementary mating types.     

Evidence for Meiosis in the Testate Amoeba Arcella

ABSTRACT. Electron microscopic studies of Arcella vulgaris have revealed a sexual process occurring in cysts. The evidence includes: I) synaplonemal complexes in prophasic nuclei. 2) two consecutive divisions different from vegetative mitosis, 3) degeneration of certain products of these nuclear divisions, and 4) fusion of nuclei indicating karyogamy. The process is apparently autogamy preceded by a two-division meiosis. The testate amoebae can no longer be considered asexual.     

Floral biology of Philippine morphospecies of the grape relative Leea (Leeaceae)

I observed the floral biology of three Leea morphospecies in a Philippine natural forest habitat. The red-flowered morphospecies Leea guineensis limits selfing through synchronized dichogamy, with male and female flowers temporally separated in the same inflorescence, whereas the two morphospecies of the white-flowered Leea indica might be prone to geitonogamous selfing. Light and soil pH are correlated with phenology. In addition to bees and flies, Leea is visited by wasps, butterflies, beetles, bugs and spiders.     

WHOLE- AND PART-FLOWER SELF-POLLINATION IN GLYCINE CLANDESTINA AND G. ARGYREA AND THE EVOLUTION OF AUTOGAMY

The overall rate of self-fertilization can be viewed as the sum of two distinct processes: 1) self-pollination of all ovules in a flower (whole-flower self-pollination); and 2) self-pollination of some of the ovules in a flower, occurring together with outcrossing of the remaining ovules (part-flower self-pollination). In some situations these processes may be equated with different modes of self-pollination. A model of the mating system in which the progeny of separate fruits serve as the unit of observation is presented. The model partitions the overall rate of self-pollination into components attributable to whole- and part-flower selfing. When the mating system is estimated using information on marker genotypes from chasmogamous fruits in two species of Glycine together with the whole- and part-flower selfing model, the results indicate that the chasmogamous flowers in a subalpine population of G. clandestina underwent a significant level of whole-flower selfing, whereas in another, lower elevation population of G. clandestina and in a subtropical population of G. argyrea, they did not. This difference is thought to be related to the contrast in the variability of environmental conditions for insect-mediated pollination between the habitats sampled. In particular, the large component of whole-flower selfing observed in the subalpine population of G. clandestina may be due to self-pollination that is induced during periods unfavorable to insect-mediated pollination. It can be demonstrated that such induced selfing will be selected whenever environmental conditions are such that pollinator activity limits seed set, and moreover that induced selfing can result in the selection of overall levels of self-pollination that are intermediate between 0 and 1. Monte Carlo simulation is employed to show that ignoring the correlation of self-fertilization events that result from whole- and part-flower selfing may lead to biased estimates of mating system parameters.     

Evidence for selective fruit abortion in Banksia spinulosa (Proteaceae)

Fruit set is consistently low in the genus Banksia (Proteaceae). One explanation for low fruit:flower ratios is that excess flowers allow plants to selectively abort inferior progeny thereby increasing the average quality of the seed crop. We examined whether self-pollinated fruits were aborted selectively in a partially self-compatible population of Banksia spinulosa. Inflorescences were divided in half and pollinated with cross pollen on both sides, self pollen on both sides or cross pollen on one side and self pollen on the other. Seed production was reduced significantly by 38% on fully self-pollinated compared to fully cross-pollinated inflorescences, indicating partial self-incompatibility or inbreeding depression. On inflorescences pollinated with both cross and self pollen, selfed seed set was reduced by 63% compared to crossed seed set. On the selfed half of these inflorescences, fewer fruits and seeds were produced, and more fruits had aborted seeds than on randomly selected halves of fully self-pollinated inflorescences. These results suggest that self-fertilized embryos were developed in the absence of outcrossed progeny but were selectively aborted when outcrossed progeny were present on inflorescences. To determine the amount of outcrossing occurring in the study population, outcrossing rates (t) of naturally pollinated plants were examined by electrophoretic assessment of progeny arrays. Values of I did not differ significantly from one, indicating complete outcrossing. High outcrossing, despite the high probability of self pollen receipt under natural conditions, is consistent with the conclusion that selective abortion occurs in B. spinulosa.     

The relationship between floral display size, pollen carryover and geitonogamy in Myosotis colensoi (Kirk) Macbride (Boraginaceae)

The relative amounts of self- and cross-pollen deposited on stigmas depends on both the number of pollinator visits that occur within plants and the amount of pollen carryover. Data collected for Myosotis colensoi (Kirk) Macbride and compiled from a survey of the literature, reveal that pollen carryover is frequently very high (upwards of 80%) and this at least partially relieves some of the effects of geitonogamous pollinator movements. It is suggested that in some cases, selection for traits that confer a high rate of pollen carryover may occur. Aspects of the plant–pollinator interaction that are likely to influence pollen carryover are discussed.     

A new cryptic irritant and cocarcinogen from seeds of Croton sparciflorus

In recent years the genus Croton has been of particular interest following the isolation of 11 different 12,13-diesters of the polyfunctional diterpene phorbol (1a), from the seed oil of Croton tiglium; these compounds represent its toxic, irritant and cocarcinogenic principles [1]. In addition, croton oil contains what is called “cryptic” cocarcinogens of the phorbol-12,13,20-triester type [1]. The structurally related but non-irritant diterpene ester 20-acetoxy-9-hydroxy-13,15-seco-4α-tigliatriene-(1,6,14)-dione-(3,13) [2] and crotofolin A have been isolated from C. rhamnifolius [3] and from C. corylifolious L. [4], respectively.