Reproductive systems and crossing potential in three species ofBulbophyllum (Orchidaceae) occurring in Brazilian ‘campo rupestre’ vegetation

Experimental self-, cross- and interspecific pollinations were carried out inBulbophyllum weddellii, B. involutum andB. ipanemense (Orchidaceae). The last two species are closely related, butB. weddellii is somewhat more distant. The three species are self-compatible, with pollination by a vector necessary for fruit formation. In all crossing types, high rates of fruit abortion and formation of seeds without embryos were observed, particularly in interspecific crosses that involvedB. weddellii. Crosses between the more closely relatedB. involutum andB. ipanemense produced fruit formation rates and seed viability similar to those obtained in intraspecific crosses. These results agree with current hypotheses that suggest that interspecific crossing rates reflect phylogenetic proximity. Examination of pollen tube growth and aborted fruits suggests that a series of factors may be involved in the high abortion rate for fruits and large proportion of seeds without embryos. The low interspecific fertility noted forB. weddellii andB. involutum is important in the maintenance of isolation between these species that are sympatric, flower in the same period and share the same pollinators.     

Insect pollination and floral mechanisms in South African species ofSatyrium (Orchidaceae)

The morphologically diverse flowers in the genusSatyrium reflect adaptations to a wide range of pollinators. Several recently discovered pollination systems inSatyrium are described and illustrated here; these include pollination by solitary bees, carrion flies, butterflies and moths. Two basic types of floral mechanism are recognised inSatyrium: (1) Species pollinated by lepidoptera and birds have long floral spurs and plate-like viscidia seated in lateral rostellum notches; these viscidia become attached to the proboscis or bill of the pollinator. (2) Species pollinated by flies and bees have relatively short floral spurs and globose viscidia seated in terminal rostellum notches; these viscidia become attached to the face, thorax or eyes of the pollinator.     

Bird pollination in South African species ofSatyrium (Orchidaceae)

Field observations showed that three South African orchid species,Satyrium carneum, S. coriifolium andS. princeps, are pollinated by sunbirds. Foraging sunbirds insert their bills into the labellum chamber of the flowers and suck nectar from the labellum spurs with their tongues. The column overarches the entrance to the labellum and pollinaria become affixed to the upper mandible of the bill. Birds often attempt to remove pollinaria by rubbing their bills against a branch, but are mostly unsuccessful due to the large plate-like viscidia which attach the pollinaria very firmly to the bill. Other modifications for bird pollination in theseSatyrium species may include the red, carmine or orange colour of the flowers, sturdy inflorescence stems used for perching and large amounts of dilute nectar in the spurs. EachSatyrium species was pollinated by several species of sunbird, and despite some differences in flowering time, occasional hybrids occur at a site whereS. carneum andS. coriifolium share the same sunbird pollinators.     

Pollinator limitation and position dependent fruit set in the high Andean orchidMyrosmodes cochleare (Orchidaceae)

Myrosmodes cochleare is a terrestrial orchid restricted to high elevations of the northern Andes. It is self-compatible but not autogamous. Flowering begins at the apex of the inflorescence, but flower size increases steadily towards the base. Fruit set of selfed flowers was found to increase significantly from the apex to the base of the inflorescence. Open-pollinated fruit set was significantly lower than hand-pollinated fruit set overall, but the highest levels occurred in the middle of the inflorescence. Eumenid wasps and a calliphorid fly were observed to pollinate the flowers, but visits were rare and occurred only during infrequent warm periods.     

Floral evolution and phylogeny in the tribeThelymitreae (Orchidaceae: Neottioideae)

The Australian orchid tribeThelymitreae, composed ofCalochilus, Epiblema, andThelymitra, is unique in theOrchidaceae because of the presence of a mitra or staminodal complex. Evidence from floral structure suggests thatEpiblema andThelymitra are sister genera and thatCalochilus is derived from aThelymitra ancestor. A Gene Pool Vortex model and a hypothetical phylogeny illustrate that introgressive hybridization, allopatry, and long distance dispersal have played a major role in the evolution of the tribe. Pollination and hybridization in the tribe are discussed with major emphasis on floral mimicry.     

Allozymic variation in four Indian species of genusMus: A comparative analysis

The present study focusses on allozyme variation in the commensal house mouseMus musculus, the pygmy field miceM. booduga andM. terricolor, and the spiny mouseM. platythrix. Genetic heterozygosity was estimated using a set of 24 polymorphic biochemical genetic markers. The extent of variability present inM. booduga, M. terricolor andM. platythrix has been compared with that in theM. musculus complex. Levels of allozyme variation at species level indicate thatM. musculus has the maximum heterogeneity, followed byM. booduga andM. terricolor, whileM. platythrix shows comparatively homogeneous genetic make-up. Gene frequency data have been used to trace phylogenetic relationships among these four species.     

Different responses of pollinating bees to size variation and sexual phases in flowers ofCampanula

To examine the response of pollinating bees to size and sexual phases of flowers, we constructed an artificial population ofCampanula having large flower variation and presented it to potentially pollinating bees in nurseries. The pollinating bee groups (halictid, megachilid and bumble bees) responded differentially to both the flower size and to the sexual phases of the flowers. Whereas visitation rate of megachilid bees increased with the flower size, those of halictid bees and bumble bees did not show particular trends; for example, bumble bees visited almost all of the flowers consistently. Visitation frequencies to male-and female-phased flowers were significantly different between megachilids at Tokyo and halictids. This study indicates that pollinator attraction could not solely explain the evolution of the flower size inCampanula, and that other factors such as pollen transfer efficiency, should be considered.     

Variation in the functioning of autonomous self-pollination, pollinator services and floral traits in three Centaurium species

Background and Aims

Reproductive assurance through autonomous selfing is thought to be one of the main advantages of self-fertilization in plants. Floral mechanisms that ensure autonomous seed set are therefore more likely to occur in species that grow in habitats where pollination is scarce and/or unpredictable.

Methods

Emasculation and pollen supplementation experiments were conducted under laboratory conditions to investigate the capacity for, and timing of autonomous selfing in three closely related Centaurium species (Centaurium erythraea, C. littorale and C. pulchellum). In addition, observations of flower visitors were combined with emasculation and pollen addition experiments in natural populations to investigate the degree of pollinator limitation and pollination failure and to assess the extent to which autonomous selfing conferred reproductive assurance.

Results

All three species were capable of autonomous selfing, although this capacity differed significantly between species (index of autonomous selfing 0·55 ± 0·06, 0·68 ± 0·09 and 0·92 ± 0·03 for C. erythraea, C. littorale and C. pulchellum, respectively). The efficiency and timing of autogamous selfing was primarily associated with differences in the degree of herkogamy and dichogamy. The number of floral visitors showed significant interspecific differences, with 1·6 ± 0·6, 5·4 ± 0·6 and 14·5 ± 2·1 floral visitors within a 2 × 2 m² plot per 20-min observation period, for C. pulchellum, C. littorale and C. erythraea, respectively. Concomitantly, pollinator failure was highest in C. pulchellum and lowest in C. erythraea. Nonetheless, all three study species showed very low levels of pollen limitation (index of pollen limitation 0·14 ± 0·03, 0·11 ± 0·03 and 0·09 ± 0·02 for C. erythraea, C. littorale and C. pulchellum, respectively), indicating that autonomous selfing may guarantee reproductive assurance.

Conclusions

These findings show that limited availability of pollinators may select for floral traits and plant mating strategies that lead to a system of reproductive assurance via autonomous selfing.     

Body size variation in baboons: A reconsideration of ecological determinism

Popp (1983) presented an intriguing argument regarding the covariation of body size in baboons and rainfall. However, a reanalysis of the data indicates that “Principle 2” of the model is not supported.     

Reproductive trade-offs in a specialized plant/pollinator system involving Asplundia uncinata Harling (Cyclanthaceae) and a derelomine flower weevil (Coleoptera: Curculionidae)

The reproductive interactions of a specialized plant/pollinator system involving Asplundia uncinata Harling (Cyclanthaceae) and a derelomine flower weevil (Coleoptera: Curculionidae: Derelomini) were studied at La Selva, Costa Rica. The inflorescences of A. uncinata exhibit a suite of cantharophilous characters including a precisely synchronized anthesis, protogyny, thermogenesis, olfactory attraction of visitors via modified staminodes, and narrow interfloral entrances. The weevil pollinators use the inflorescences for feeding, mating, and oviposition. The larvae are detritivorous and develop either in the detaching staminate flowers or, at a more favorable rate, in the rotting infructescences. The rate of infructescence abortion was high and caused by low levels of pollination. Manual pollination treatments yielded significantly higher seed counts than obtained under natural conditions, and furthermore demonstrated the inflorescences' ability to reproduce via geitonogamy. In the longer term, the reproductive benefits of maintaining low levels of pollination may shift away from the weevils and towards the plants via an increase in the size of the pollinator population.     

Intraspecific variation in group size in the blackbuck antelope: the roles of habitat structure and forage at different spatial scales

The main ecological factors that are hypothesized to explain the striking variation in the size of social groups among large herbivores are habitat structure, predation, and forage abundance and distribution; however, their relative roles in wild populations are not well understood. I combined analyses of ecological correlates of spatial variation in group size with analyses of individual behaviour in groups of different sizes to investigate factors maintaining variation in group size in an Indian antelope, the blackbuck Antilope cervicapra. I measured group size, habitat structure, forage, and the occurrence of predators in ten blackbuck populations, and, at a smaller spatial scale, within an intensively studied population. To examine the processes by which these ecological factors influence group size, I used behavioural observations and an experiment to estimate the shape of the relationship between group size and potential costs and benefits to individuals. Group size varied extensively both among and within populations. Analyses of spatial variation in group size suggested that both forage and habitat structure influence group size: large-scale, among-population variation in group size was primarily related to habitat structure, while small-scale, within-population variation was most closely related to forage abundance. Analyses of individual behaviour suggested that larger groups incur greater travel costs while foraging. However, individuals in larger groups appeared to experience greater benefits, namely the earlier detection of a “predator”, a reduction in vigilance, and an increase in the time spent feeding. Overall, these findings suggest that individuals in groups experience a trade-off between predation-related benefits and costs arising from feeding competition. Habitat structure and forage likely influence the nature of this trade-off; thus, variation in these ecological factors may maintain variation in group size. The role of predation pressure and other factors in explaining the remaining variation needs further exploration. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Pollination biology of Eulophia alta (Orchidaceae) in Amazonia: effects of pollinator composition on reproductive success in different populations

Background and Aims

Spatial variation in pollinator composition and abundance is a well-recognized phenomenon. However, a weakness of many studies claiming specificity of plant–pollinator interactions is that they are often restricted to a single locality. The aim of the present study was to investigate pollinator effectiveness of the different flower visitors to the terrestrial orchid Eulophia alta at three different localities and to analyse whether differences in pollinator abundance and composition effect this plant''s reproductive success.

Methods

Natural pollination was observed in vivo, and manipulative experiments were used to study the pollination biology and breeding system of E. alta at three sites near Manaus, Brazil. To gain a better understanding of the underlying mechanisms of pollinator attraction, nectar composition and secretion patterns were also studied, floral scent composition was analysed and a bioassay was conducted.

Key Results

Flower visitors, pollinator composition, pollinia transfer efficiency of particular pollinator species and natural fruit set differed among the investigated populations of E. alta. Flowers were self-compatible, partially autogamous and effectively pollinated by five bee species (four Centris species and Xylocopa muscaria). Visiting insects appeared to imbibe small amounts of hexose-rich nectar. Nectar sugar content was highest on the third day after flower opening. Floral fragrance analyses revealed 42 compounds, of which monoterpenes and benzenoids predominated. A bioassay using floral parts revealed that only floral tissue from the labellum chamber and labellum tip was attractive to flower visitors.

Conclusions

The data suggest that observed differences in reproductive success in the three populations cannot be explained by absolute abundance of pollinators alone. Due to behavioural patterns such as disturbance of effective pollinators on flowers by male Centris varia bees defending territory, pollinia transfer efficiencies of particular pollinator species also vary between study sites and result in differing reproductive success.     

Fruit size in a tropical tree species: variation,preference by birds,and heritability

Ocotea tenera (Lauraceae), an understory bird-dispersed tree, produces single-seeded fruits that vary in diameter from 1.4 to 2.4 cm. Much of the variation within a population at Monteverde, Costa Rica occurred within individual trees. The relative size of fruits produced by different trees remained generally constant over an 11-year period despite slight differences between years in the average size of fruits produced by a given tree.Fruit-eating birds could thus express their preferences for particular fruit size characteristics by choosing among trees that have distinct distributions of fruit diameters, and between individually variable fruits within trees. In a field study of individually marked fruits, birds removed 46.2% of fruits; the rest of the fruits were destroyed by invertebrate (25.3%) and vertebrate (4.3%) pulp-feeders or aborted by the plant after remaining ripe but uneaten for as long as 100 days (24.2%). The four major avian seed dispersers of O. tenera each have gape widths exceeding all but the largest fruits. Birds preferred plants with greater-than-average-sized fruits; within trees, they favored larger fruits, apparently because net pulp mass increases with fruit diameter. Fruits that ripened early in the season were more likely to be removed and were removed more quickly than late-ripening fruits.Based on mother-offspring regressions of mean fruit size, the phenotypic variation in fruit diameter in O. tenera is highly heritable, indicating the potential for an evolutionary response to selection by birds. Nonetheless, directional selection on fruit size or shape is likely to be inconsistent, constrained by genetic correlations, and weak compared to selection on traits like fecundity or phenology.     

Hymenopteran parasitoids and dipteran predators of the invasive aphid Diuraphis noxia after enemy introductions: Temporal variation and implication for future aphid invasions

Shifts in prevalence and abundance of hymenopteran parasitoids and dipteran predators, Diuraphis noxia, and other aphids were measured in the west-central Great Plains of North America, April–September, in 2001 and 2002, corresponding to over a decade after first detection of D. noxia and first release of D. noxia enemies. Significant temporal shifts in enemy species prevalence and diversity were detected in this study and more broadly during an 11 year time span. At any given time, some species were relatively common. One parasitoid had been predominant throughout (Aphelinus albipodus), two had shifted in dominance (Lysiphlebus testaceipes and Diaeretiella rapae), three parasitoids had been detected infrequently (Aphidius avenaphis, Aphidius matricariae, and Aphelinus asychis), one parasitoid was detected in the 1990s but not during 2001 and 2002 (Aphelinus varipes), two predatory flies occurred at occasional significant levels (Leucopis gaimarii and Eupeodes volucris), and two parasitoids may have been minor members of the fauna (Aphidius ervi and Praon yakimanum). Aphid populations detected were usually very low or not detected, precluding estimation of percent parasitism. The best evidence of suppression was observations of parasitoids in the rare case of D. noxia exceeding economic thresholds, which complemented past studies using high aphid densities. The D. noxia enemies detected were primarily endemic or long-time residents derived from previous introductions. This enemy community may provide flexibility in responding to a future aphid invasion, allowing more strategic use of biological control and other pest management approaches.     

Limited genetic variation in Lacerta mixta and its parthenogenetic daughter species: evidence from cytochrome b and ATPase 6 gene DNA sequences

Little mtDNA variation was observed among populations of the bisexual Caucasian rock lizard Lacerta mixta and unisexual L. dahli and L. armeniaca. Three haplotypes were detected in L. mixta and the maximum pairwise difference among the samples was 0.67%. No intra- and interspecific variation was found among populations of either L. armeniaca or L. dahli. Moreover, both unisexual species were identical to one of the three haplotypes of L. mixta. The limited variation in L. mixta is likely the result of bottleneck effect, although the small sample size may also be responsible. The lack of variation in the unisexuals was attributed to the restricted variation among the maternal parents, limited involvement of females in the hybridization, and recent origin. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pollen and nectar as a reward in the basal epidendroid Psilochilus modestus (Orchidaceae: Triphoreae): A study of floral morphology, reproductive biology and pollination strategy

Psilochilus modestus Barb. Rodr. is a basal epidendroid orchid occurring in both the semi-deciduous and Atlantic rain forests of the state of São Paulo, southeastern Brazil. This species presents a perfect flowering synchrony within populations, since all the mature buds of each plant open simultaneously in the morning hours of the same day. These flowers are available only for 1 day and are pollinated by several species of small solitary and social native bees. These bees exploit both pollen and nectar as a reward. The bees collecting pollen promote a higher fruit set and perform mainly self-pollination while those collecting nectar, which are less numerous, are responsible for an increase in cross-pollinations. P. modestus is self-compatible but pollinator dependent. Natural fruit set (open pollination) is low when compared with the numbers obtained under manual self- and cross-pollination. Low fruit set in natural conditions is related to deficient pollen transfer, and pollinator inefficiency seems to be the main factor. Some factors, such as the small amount of nectar produced, the low number of flowers per inflorescence and their availability for 1 day only added to the perfect flowering synchrony seem to be responsible for the increase of cross-pollinations. The offering of both pollen and nectar as a reward can represent a transitional condition in basal Epidendroideae. Based on floral morphology, reward production and pollinator behavior, the relationship of P. modestus with the basal and most derived groups within Orchidaceae is discussed.     

Determinants of reproductive success in voles: space use in relation to food and litter size manipulation

Spacing behaviour of female mammals is suggested to depend on the distribution and abundance of food. In addition, food limitation has been found to constrain the reproductive success of females. However, whether females maximize their reproductive success by adjusting space use in relation to current food availability and reproductive effort (e.g. litter size) has not been experimentally studied. We examined these questions by manipulating simultaneously food resources (control vs. food supplementation) and litter sizes (control vs. plus two pups) of territorial female bank voles (Clethrionomys glareolus) in large outdoor enclosures. Females with supplementary food had smaller home ranges (foraging area) and home range overlaps than control females, whereas litter size manipulation had no effect on space use. In contrast, the size of territory (exclusive area) was not affected by food supplementation or litter size manipulation. As we have previously shown elsewhere, extra food increases the reproductive success of bank vole females in terms of size and proportion of weaned offspring. According to the present data, greater overlap of female home ranges had a negative effect on reproductive success of females, particularly on survival of offspring. We conclude that higher food availability increases the reproductive success of bank vole females, and this effect may be mediated through lower vulnerability of offspring to direct killing and/or detrimental effects from other females in the population. Moreover, it seems that when density of conspecifics is controlled for, home range sizes of females, but not territoriality, is related to food resources in Clethrionomys voles.     

Population and species variation of minisatellite DNA in Plantago

Three Plantago species were surveyed for within- and between-population variation at DNA sequences detected with the M13 minisatellite probe. The levels and patterns of variation detected by this probe correspond to those expected from the mating systems of the species. The highly-selfing species P. major has a relatively low variability of minisatellite sequences within populations and considerable differentiation between populations. The outcrossing species P. lanceolata exhibits higher minisatellite variability within populations and moderate differentiation between populations. P. coronopus, with a mixed mating system, has levels of variation intermediate between P. major and P. lanceolata. The levels of variation within and between populations corresponds, in general, to the levels of allozyme variation determined in an earlier study. Mating system and population structure appear to have a major influence on M13-detected fragment variation.     

Morphological variation in populations of Bletia purpurea (Orchidaceae) and description of the new species B. riparia

Bletia purpurea is the most widespread species in its genus. Morphological variation has been recognized throughout the range of its distribution. In this paper, the morphological variation from 63 populations (583 individuals) ofBletia purpurea is assessed to determine whether more than one species were present. Forty-four quantitative and qualitative characters were examined by univariate analyses and exploratory multivariate analyses. Univariate analyses indicate that quantitative characters such as lateral sepal width, petal. width, lip length, and lip width are significantly different for populations from Acazónica, Mexico. Floral parts in the populations from Acazónica are the smallest among all populations. Qualitative characters such as petals covering the lip midlobe and horizontal lip position are found exclusively in the same populations. We concluded that these populations should be described as a new species,B. riparia. Multivariate analyses indicated that morphological variation among the other populations cannot be ascribed to geographic distribution or ecological factors.