Differences in dichogamy and herkogamy contribute to higher selfing in contrasting environments in the annual Blackstonia perfoliata (Gentianaceae)

Background and Aims

The establishment of plant populations in novel environments may generate pronounced shifts in floral traits and plant mating systems, particularly when pollinators are scarce. In this study, floral morphology and mating system functioning are compared between recently established and older populations of the annual plant Blackstonia perfoliata that occur in different pollinator environments.

Methods

Hand-pollination and emasculation experiments were conducted to assess the extent of pollinator-mediated pollen deposition and pollen limitation, and the contribution of autonomous selfing to total seed production. Detailed measurements of key floral traits were performed to compare the flower morphology and mating system functioning between plants from both pollination environments.

Key Results

Pollinator-mediated pollen deposition was about twice as low in the recently colonized and pollinator-poor environment compared with the old and pollinator-rich sites, but total seed set was little affected by any type of pollen limitation. The contribution of autonomous selfing to total seed production was higher in the pollinator-poor sites than in the pollinator-rich sites (index of reproductive assurance = 0·56 and 0·17, respectively), and seed production was only poorly affected by selfing, whereas in the pollinator-rich populations selfing reduced total reproductive output by about 40 % compared with outcross pollination. Plants originating from pollinator-poor environments produced smaller flowers that showed significantly lower levels of dichogamy (i.e. protogyny) and herkogamy. These reductions resulted in a 2-fold higher capacity for autonomous selfing under pollinator-free conditions (index of autonomous selfing = 0·81 and 0·41 in plants originating from the pollinator-poor and pollinator-rich environment, respectively).

Conclusions

The results illustrate that plant populations colonizing novel environments can differ markedly in floral morphology and mating system functioning. Due to a temporal shift in the male phase, the breeding system of B. perfoliata shifted from delayed selfing under pollinator-rich conditions towards competing selfing in recently established populations, providing greater reproductive assurance when pollinators and/or reproductive partners are limited.     

Reproductive ecology of the Qinghai-Tibet Plateau endemic Gentiana straminea (Gentianaceae), a hermaphrodite perennial characterized by herkogamy and dichogamy

The combined occurrence of both herkogamy and dichogamy in a hermaphrodite species has been considered to strongly favour outcrossing. In this study, we investigated in detail the reproductive ecology of Gentiana straminea Maxim. (Gentianaceae), a hermaphrodite perennial endemic to the Qinghai-Tibet Plateau. In a series of observations and experiments over four consecutive years, we examined whether the combination of dichogamy and herkogamy in individual flowers completely prevents geitonogamous pollen transfer in this species. The mode of floral development clearly indicates that autonomous self-pollination is completely avoided through herkogamy and dichogamy in individual flowers. This implication was confirmed by the breeding experiments, since no seed was produced when flowers were isolated. However, this gentian proved to be highly self-compatible when geitonogamous selfing was artificially induced. Many flowers opened simultaneously on individual plants, the ratio of male to female phase flowers was close to 2:1 in each inflorescence at the full anthesis phase, and they were randomly distributed amongst the upper, middle and lower parts of each stem's inflorescence. On average, Bombus sushikini Skorikov, the most frequent visitor and only legitimate pollinator of G. straminea, visited nearly two flowers per inflorescence, and four flowers per plant. Among the pollinators' foraging bouts, the proportions of geitonogamous visits to inflorescences or flowers within an individual plant were 29% and 37%, respectively. Therefore, despite the strict dichogamous and herkogamous characteristics of the individual flowers, geitonogamous selfing might still prevail in G. straminea because of the size of its floral displays and the continuous visiting behavior of B. sushkini.     

Beta SSR loci cross-amplify in five Salsola taxa

We investigated 20 previously developed Beta SSR markers for their utility in the cross-genera amplification of five morphologically distinct invasive tumbleweed (Salsola) taxa. Of these markers, 17 loci had successful amplification within Salsola taxa. Six loci were polymorphic and were useful in confirming the presence of five genetically distinct Salsola taxa.     

Protein methylase II in five taxa from three phyla

Protein methylase II (protein O-methyltransferase, EC 2.1.1.24) was found in Dictyostelium discoideum amoebae, Astacus leptodactylus axonal, Locusta migratoroides neuronal, Torpedo marmorata electroplaque and Bos bovis stratial tissue and compared in both the soluble and particulate fractions. The intrinsic decay data of the methyl groups transferred onto proteins from Dictyostelium and Torpedo tissues were virtually identical. The short term kinetics of the methyl group transfer of all fractions and of all taxa investigated were non-linear and multiphasic. The particulate fractions displayed transient peaks at 1 min, 3 min, or both after the start of the reaction. The methyl group transfer was stimulated by the neurotoxins veratridine (VTx) and inhibited by veratridine plus tetrodotoxin (TTx) (axonal membrane vesicles of Astacus), stimulated transiently and in a biphasic manner by carbamoylcholine and phospholipase A2 (AChR-rich membrane vesicles of Torpedo), and stimulated transiently and biphasically by the adequate chemotactic stimulus cAMP (aggregation competent amoebae of Dictyostelium).     

Aggregation pheromones in five taxa of the Drosophila virilis species group

ABSTRACT. Aggregation pheromones have been demonstrated in the closely related taxa: Drosophila americana americana Spencer, D. a. texana Patterson, D. novamexicana Patterson, and D. lummei Hackman. These pheromones function much as has been reported previously for D. virilis Sturtevant. The compounds are produced by sexually mature males, but both sexes respond in a wind-tunnel olfactometer. In all species except D. lummei , a 21-carbon alkene is an important pheromone component. In D. virilis the hydrocarbon is (Z)-10-heneicosene (Z10–21), but in D. a. americana, D. a. texana and D. novamexicana it is (Z)-9-heneicosene (Z9-21). All these taxa respond best to the heneicosene which they produce. D. lummei possesses no heneicosenes but, curiously, responds well to both Z9-21 and Z10-21. All species possess five male-specific esters which were previously discovered in D. virilis : methyl tiglate, ethyl tiglate, isopropyl tiglate, methyl hexanoate and ethyl hexanoate. Ethyl tiglate is the most abundant in each case. Responses to the esters vary among the taxa, ranging from highly significant in D. lummei , particularly to ethyl tiglate, to not demonstrable in D. a. americana. Variability in ester response has also been demonstrated between two strains of D. virilis. In all cases the crude male-derived pheromone is synergistic with an extract of fermented willow bark, on which oviposition is said to occur.     

An analysis of tooth and body size relationship in five primate taxa.

The strength and the nature of the covariance between tooth and body size was investigated in Homo, Gorilla, Pan, Papio and Colobus. When sexes are combined in each taxon, the correlations are strong enough to compare the allometry coefficients of taxa, and the non-human taxa show a sufficiently strong linear relationship to compute 'interspecific' allometry coefficients. Allometry coefficients for each variable were not uniform among the taxa, and coefficients also differed from one variable to another. Computed 'intra' and 'inter' specific allometry coefficients from these data suggest that canine size will usually scale at a higher level than molar crown area, which is at most isometric, and not positively allometric with respect to body size. The consequence is that larger representatives of a taxon would be expected to combine relatively larger canines with a proportional, or relatively smaller, molar crown area. It is pointed out that these differences do not correspond to those found between 'gracile' and 'robust' australopithecines.     

Inter- and intra-specific variation among five Erythroxylum taxa assessed by AFLP

BACKGROUND: and Aims The four cultivated Erythroxylum taxa (E. coca var. coca, E. novogranatense var. novogranatense, E. coca var. ipadu and E. novogranatense var. truxillense) are indigenous to the Andean region of South America and have been cultivated for folk-medicine and, within the last century, for illicit cocaine production. The objective of this research was to assess the structure of genetic diversity within and among the four cultivated alkaloid-bearing taxa of Erythroxylum in the living collection at Beltsville Agricultural Research Center. METHODS: Amplified fragment length polymorphism (AFLP) fingerprinting was performed in 86 Erythroxylum accessions using a capillary genotyping system. Cluster analysis, multidimensional scaling (MDS) and analysis of molecular variance (AMOVA) were used to assess the pattern and level of genetic variation among and within the taxa. KEY RESULTS: A clear distinction was revealed between E. coca and E. novogranatense. At the intra-specific level, significant differentiation was observed between E. c. var. coca and E. c. var. ipadu, but the differentiation between E. n. var. novogranatense and E. n. var. truxillense was negligible. Erythroxylum c. var. ipadu had a significantly lower amount of diversity than the E. c. var. coca and is genetically different from the E. c. var. ipadu currently under cultivation in Colombia, South America. CONCLUSIONS: There is a heterogeneous genetic structure among the cultivated Erythroxylum taxa where E. coca and E. novogranatense are two independent species. Erythroxylum coca var. coca is most likely the ancestral taxon of E. c. var. ipadu and a founder effect may have occurred as E. c. var. ipadu moved from the eastern Andes in Peru and Bolivia into the lowland Amazonian basin. There is an indication of artificial hybridization in coca grown in Colombia.     

Predator-induced life-history changes and the coexistence of five taxa in a Daphnia species complex

Interspecific hybridization is common in water fleas of the Daphnia galeata species complex (e.g. D. galeata , D. cucullata , D. hyalina and their interspecific hybrids). We studied the effect of fish on the life histories of five taxa of this species complex originating from the Plußsee, northern Germany. Using four clones per taxon, we found that fish kairomones reduce size at birth and size at maturity significantly. For size at maturity larger taxa showed a significantly stronger reaction to fish kairomones than the smaller taxa. With respect to the intrinsic rate of increase, r , we compared two predation regimes (positive size selective and not selective). We found that under the fish predation regime most clones had a higher r when cultured with fish kairomones, leading to a higher r , and a stronger reaction for the smaller taxa. We conclude that fish predation might be an important factor influencing the co-occurrence of Daphnia parental taxa with their hybrids.     

Floral ontogeny of five species ofTalinum and of related taxa (Portulacaceae)

The floral development of five species ofTalinum is studied. Each flower is surrounded by two involucral bracts. The perianth consists of five tepals initiated in a 2/5 phyllotaxis. In all species studied a first whorl of 10–13 stamens is initiated, except inT. napiforme where this whorl is reduced to five stamens. In multistaminate androecia, additional whorls develop centrifugally. InT. paniculatum, T. portulacifolium andT. napiforme the first stamens are initiated in pairs opposite the outer tepals. In several flowers ofT. paniculatum andT. portulacifolium ten stamens are incepted in spiral sequence resembling diplostemony. Similar ontogenetic patterns are present in several species ofPhytolacca. However, within the genusTalinum the ontogenetic pattern of the firstly initiated stamens is not consistent with traditional diplostemony. InT. triangulare the firstly initiated stamens are incepted in sectors on a ring meristem, resembling the early inception in several species ofAnacampseros andPortulaca. The nectaries are associated with the filament bases and can be defined as caducous nectaries of the staminal type. The development of the tricarpellate, syncarpous gynoecium is very similar in all species studied; it is characterised by a leptate carpel-form.     

Flavonol glycosides from Asplenium foreziense and its five related taxa and A. incisum

The flavonoids of Asplenium foreziense, A. fontanum subsp. fontanum and subsp. pseudofontanum, A. obovatum subsp. obovatum var. obovatum and var. protobillotii, A. obovatum subsp. lanceolatum, and A. incisum were isolated and identified for chemotaxonomic survey. A major constituent of all taxa was kaempferol 3-O-gentiobioside. As minor compounds, kaempferol 3,7-O-glycoside and/or kaempferol 3-O-glycoside were found in A. fontanum, A. obovatum and A. foreziense, and kaempferol 3-O-gentiobioside-4'-O-glucoside, kaempferol 3-O-glucoside and quercetin 3-O-diglucoside in A. incisum. It was suggested that A. foreziense, A. fontanum including subsp. pseudofontanum and A. obovatum including subsp. lanceolatum are not only morphologically but also chemotaxonomically related. The East Asian A. incisum was chemically and geographically different from these taxa.     

Physiology of cold hardiness in cocoons of five earthworm taxa (Lumbricidae: Oligochaeta)

Earthworm cocoons are mostly found in the uppermost soil layers and are therefore often exposed to low temperatures during winter. In the present study, cocoons of five taxa of earthworms were investigated for their tolerance to freezing, melting points of cocoon fluids and dehydration of cocoons when exposed to a frozen environment. Embryos of the taxa investigated were freeze intolerant. The melting points of fully hydrated cocoon fluids were high (above –0.3°C) and thermal hysteresis factors were absent. Exposure to a frozen environment caused the cocoons to dehydrate drastically and dehydrated cocoons showed significantly lower super-cooling points than fully hydrated cocoons, reducing the risk of freezing for dehydrated cocoons. It is proposed therefore that the cold-hardiness strategy of the earthworm cocoons is based on dehydration upon exposure to subzero temperatures in the frozen environment. Cocoons of three surface-dwelling taxa, Dendrobaena octaedra, Dendrodrilus rubidus tenuis and Dendrodrilus rubidus norvegicus had lower supercooling points and survived frost exposure better than cocoons of two deeper-dwelling taxa, Aporrectodea caliginosa and Allolobophora chlorotica. One of the investigated taxa, D. r. norvegicus, was collected from a cold alpine habitat. However, it was not more cold hardy than the closely related D. r. tenuis collected from a lowland temperate habitat. D. octaedra was the most cold hardy taxon, its cocoons being able to withstand –8°C for 3 months and –13.5°C for 2 weeks in frozen soil.Abbreviations dw dry weight - fw fresh weight - SCP supercooling point     

Movement-assisted dichogamy in Atamisquea emarginata (Capparaceae)

 Various aspects of the reproductive biology of Atamisquea emarginata Miers ex Hook. et Arn. were studied in a population from Tucumán, northern Argentina. Flowering took place in late (austral) spring to early summer. The creamy white, entomophilous flowers were protandrous and lasted 3.5–4.5 days. A pleasant odor along with nectar and pollen attracted 36 mostly diurnal insect species of which 41.7% were Hymenoptera, 38.9% Lepidoptera and 19.4% Diptera. However, 75% from all recorded species were infrequent, and domestic bees made ca. 94% of all visits. One halictid bee, one sphecid wasp, one myzinid wasp, four small- to medium-sized butterflies and a hawkmoth completed the set of relatively frequent insect visitors. Pollen and stigma were presented in the same place within the flower, but interference was prevented by a movement-assisted, complete dichogamy mechanism in which the bending ability of the gynophore played a fundamental role. This form of dichogamy was previously unknown in the Capparaceae. In comparison with the known species of the closely allied genus Capparis L., A. emarginata has diurnal, smaller, longer-lasting flowers, that offer much smaller nectar amounts, and that attract a rather generalized array of non-hovering visitors, while Capparis behaves as a more crepuscular-biased sphingophile or ornithophile or chiropterophile. Low levels of seed set under bagging indicates dependence on insect visits and are partly congruent with an earlier report of self-incompatibility in A. emarginata. Pollen tubes arrived to ovules in 90.6% of the inspected flowers. Fruit set of open-pollinated flowers was 43.6%–53.7%. Ninety-five percent of all ovules were regularly aborted in each fruiting ovary; thus, each fruit contained 1.2 developed seeds. Full-sized individuals were expected to produce ca. 10,700 potential offspring per year. Received August 19, 2002; accepted October 8, 2002 Published online: February 7, 2003     

Variable herkogamy and autofertility in marginal populations ofGentianella germanica in the Netherlands

Gentianella germanica (Willd.) Börner, a rare plant species, occurs at the margin of its distribution area in the Netherlands. It is found only in isolated patches of chalk grassland surrounded by intensively-used agricultural land. In 1997 and 1998, we investigated the spatial and temporal separation of anthers and stigma in relation to autofertility. We performed our experiments in one large and two small populations to investigate the possible selection against herkogamy and for increased autofertility in marginal populations with pollination limitation. Dichogamy appeared to be very weak and varied within individuals. Homogamous and protandrous flowers were most frequent. Dichogamy is apparently no effective barrier against self-fertilization in this species. Herkogamy varied significantly between individuals and between populations, and plant and flower size were not correlated with anther-stigma separation. Both observations suggest a genetic basis for herkogamy. Autofertility was generally high in all three populations. Only in one small population was a correlation between autofertility and herkogamy found. In this population, most plants had the stigma positioned above the anthers (mean herkogamy +0.8 mm), while in the other two populations the stigma was positioned mainly in between or below the anthers (mean herkogamy ?0.55 mm). In comparison with earlier data from 1991 and 1992, plants in the large population were less herkogamous and more self-fertile in 1998. Since 1993 this population was mown each year one month earlier than usual, leading to dramatic reductions (bottlenecks) in population size. In addition, the early mowing time may have caused a further reduction of the already scarce visitation by pollinating insects. We hypothesize that both adverse conditions may have caused a selection of plants with smaller anther-stigma separation and higher autofertility and thus showing that human influence can have profound effects on the reproductive success and evolution of rare plant species, even if it occurs in the context of nature conservation.     

Evolution of herkogamy and gynodioecy in Moroccan species ofRomulea (Iridaceae)

Herkogamy and gynodioecy were studied in the Moroccan species ofRomulea. Several types of herkogamy are shown to occur in the different species, with each type corresponding to a characteristic perianth size. The degree of differentiation between female and hermaphrodite morphs varies among the different gynodioecious species. Herkogamy is considered to have evolved prior to the development of the gynodioecious condition. An evolutionary interpretation is proposed based on the degree of herkogamy and of gynodioecy in the different species.     

Morphometric stepwise discriminant analysis of the five genetically determined European taxa of the genus Mus

Univariate and multivariate analyses have been performed on skull and mandible measurements for the five biochemically defined groups of the genus Mus in Europe. Four of these taxa occur in Bulgaria; other samples came from France and Israel. This extensive biometrical analysis has allowed us to establish diagnostic keys for these taxa.     

Aspects of reproduction in Pulsatilla pratensis in Norway

Breeding system and pollinator activity were studied in two Norwegian populations of Pulsatilla pratensis : a small outpost population, on Hovedøya in Oslo, and a large population located centrally within the main area of this species in Norway, on Sandøya in Tjøme, Vestfold. One objective was to assess, if possible, the chance of survival of the outpost population. Pulsatilla pratensis is not completely self incompatible, since artificial selfing produced a small amount of seed. However, spontaneous selfing does not occur. Pollination is accomplished by insects, almost exclusively bumble bees ( Bombus spp.). Nectar thievery resulted when the bumble bee inserted its proboscis from outside the flower in between the tepals (base working). A comparison between the two populations indicates that pollinator scarcity at the time of flowering possibly might constitute a limiting factor for recruitment in the outpost population.     

The contact separation force of the fruit burrs from five plant taxa dispersing by epizoochory

Abstract

Many plant diaspores dispersing by epizoochory bear special structures, such as burrs with hooks, which are responsible for the mechanical interlocking with animal fur or feathers. The number, dimensions and distribution of the interlocking structures on the diaspore can strongly vary depending on the plant species. In this study, to evaluate the interlocking ability of distantly related plants having different diaspore morphologies, the contact separation force (CSF) of single burrs was measured in Arctium lappa, Bidens tripartita, Desmodium sp., Uncinia uncinata and Xanthium strumarium. This force is required to separate the single burr from interlocking with the loop. Usually in the experiment, the burr was broken after separation. The CSFs differed significantly, ranging from 7.07 to 820.94?mN, among the five taxa studied. Six morphometrical variables were measured from each burr and the correlations between the CSFs and these morphometrical variables were analyzed. We have shown that (1) the burr length, (2) the diameter of the distal part and (3) the hook span had significant influences on the CSF. The comparison between the CSF and the fruit weight indicated that single burrs of all taxa studied could bear at least 100-fold weight of the diaspore.     

Multiple sex expressions in Cimicifuga simplex: dichogamy destabilizes hermaphroditism

Cimicifuga simplex (Ranunculaceae) has four types of individuals, differing in their sex expression: there are individuals with hermaphroditic, hermaphroditic and male (andromonoecious), only male, or only female flowers. Purely female individuals appear during the early part of the flowering period of the population, and males during the later part. Strong protandry in hermaphroditic flowers causes a shift in functional sex ratio in the population over time. This facilitates the evolution and maintenance of small proportions of unisexual individuals in the population. A hypothesis developed from this case of multiple sex expression predicts dichogamy as a near-universal feature of andro-and gynomonoecious, androdioecious, and gynodioecious species, and also specific temporal distributions for each sex form depending upon the form of dichogamy. Results of tests on large sets of species strongly support the relevance of this hypothesis.     

Discordance of species trees with their most likely gene trees: the case of five taxa

Under a coalescent model for within-species evolution, gene trees may differ from species trees to such an extent that the gene tree topology most likely to evolve along the branches of a species tree can disagree with the species tree topology. Gene tree topologies that are more likely to be produced than the topology that matches that of the species tree are termed anomalous, and the region of branch-length space that gives rise to anomalous gene trees (AGTs) is the anomaly zone. We examine the occurrence of anomalous gene trees for the case of five taxa, the smallest number of taxa for which every species tree topology has a nonempty anomaly zone. Considering all sets of branch lengths that give rise to anomalous gene trees, the largest value possible for the smallest branch length in the species tree is greater in the five-taxon case (0.1934 coalescent time units) than in the previously studied case of four taxa (0.1568). The five-taxon case demonstrates the existence of three phenomena that do not occur in the four-taxon case. First, anomalous gene trees can have the same unlabeled topology as the species tree. Second, the anomaly zone does not necessarily enclose a ball centered at the origin in branch-length space, in which all branches are short. Third, as a branch length increases, it is possible for the number of AGTs to increase rather than decrease or remain constant. These results, which help to describe how the properties of anomalous gene trees increase in complexity as the number of taxa increases, will be useful in formulating strategies for evading the problem of anomalous gene trees during species tree inference from multilocus data.