Effects of nectar robbing on pollinator behavior and plant reproductive success of Pitcairnia angustifolia (Bromeliaceae)

Nectar robbers may have direct and indirect effects on plant reproductive success but the presence of nectar robbing is not proof of negative fitness effects. We combined census data and field experiments to disentangle the complex effects of nectar robbing on nectar production rates, pollinator behavior, pollen export, and female reproductive success of Pitcairnia angustifolia. Under natural conditions flowers were visited by four different animal species including a robber‐like pollinator and a secondary robber. Natural levels of nectar robbing ranged from 40 to 100%. Natural variation in nectar robbing was not associated with fruit set in any year whereas seed set was weakly positively associated for 1 year only. Artificial nectar robbing did not increase nectar production or concentration, did not affect the behavior of long‐billed hummingbirds, and when faced with artificially robbed flowers, these visitors behaved as secondary nectar robbers. The number of stigmas within a patch that received pollen dye analogs and the average distance traveled by these analogs were not significantly different between robbing treatments (robbed flowers versus unrobbed flowers), but the maximum distance traveled by these pollen analogs was higher when nectar robbing was not prevented. Overall, the proportion of robbed flowers on an inflorescence had a neutral effect to a weak positive effect on the reproduction of individual plants (i.e. positive association between nectar robbing and fruit set in 2002) even when it clearly changed the behavior of its most efficient pollinator potentially increasing the frequency of nectar robbing within a plant.     

The effects of a bumble bee nectar robber on plant reproductive success and pollinator behavior

Interactions between a plant species (Corydalis caseana), a bumble bee nectar robber (Bombus occidentalis), and a bumble bee pollinator (B. appositus) were studied. There were no significant differences between naturally robbed and unrobbed flowers in fruit set or mean seed set per fruit. Plots of C. caseana plants were subjected to treatments of robbing and no robbing using commercially available colonies of B. occidentalis. Robbers did not pollinate the flowers. Pollinator behavior was observed to determine (1) the number of bees attracted to each plot, (2) the number of inflorescences visited in a plot, (3) the number of flowers visited on each inflorescence, and (4) the distance flown between inflorescences. There were no significant differences in the number of inflorescences visited per bee or the number of flowers visited per inflorescence per bee when robbed and unrobbed treatments were compared. Of the parameters measured, only distance flown between inflorescences differed in the robbed and the unrobbed treatments. Bees flew significantly further between inflorescences in the robbed plots than in the unrobbed plots. The results indicate that the nectar robbers have no negative effect on fruit set or seed set in C. caseana and that they may cause increased pollen flow distances by changing the behavior of the pollinator.     

Interglacial genetic diversification of Moussonia deppeana (Gesneriaceae), a hummingbird‐pollinated,cloud forest shrub in northern Mesoamerica

Recent empirical work on cloud forest‐adapted species supports the role of both old divergences across major geographical areas and more recent divergences attributed to Pleistocene climate changes. The shrub Moussonia deppeana is distributed in northern Mesoamerica, with geographically disjunct populations. Based on sampling throughout the species range and employing plastid and nuclear markers, we (i) test whether the fragmented distribution is correlated with main evolutionary lineages, (ii) reconstruct its phylogeographical history to infer the history of cloud forest in northern Mesoamerica and (iii) evaluate a set of refugia/vicariance scenarios for the region and demographic patterns of the populations whose ranges expanded and tracked cloud forest conditions during the Last Glacial Maximum. We found a deep evolutionary split in M. deppeana about 6–3 Ma, which could be consistent with a Pliocene divergence. Comparison of variation in plastid and nuclear markers revealed several lineages mostly congruent with their isolated geographical distribution and restricted gene flow among groups. Results of species distribution modelling and coalescent simulations fit a model of multiple refugia diverging during interglacial cycles. The demographic history of M. deppeana is not consistent with an expanding–contracting cloud forest archipelago model during the Last Glacial Maximum. Instead, our data suggest that populations persisted across the geographical range throughout the glacial cycles, and experienced isolation and divergence during interglacial periods.     

The effect of hummingbird flower mites on nectar availability of two sympatric Heliconia species in a Brazilian Atlantic forest

BACKGROUND AND AIMS: Hummingbird flower mites feed and reproduce in flowers of host plants pollinated by hummingbirds, and use the nostrils and bill of the hummingbird to move from plant to plant. These mites compete with the pollinator for the nectar produced by flowers. An investigation was made of the relationship between the pattern of nectar production and the effects of hummingbird flower mites in the flowers of two sympatric species of Heliconia (Heliconiaceae). METHODS: Nectar production was sampled by carrying out two experiments: 2-hour intervals and accumulated nectar. Flowers with and without mites were used in both experiments. KEY RESULTS: Exclusion of mites increased nectar production, especially in accumulated daily production (a maximum of 49 % more nectar). Both Heliconia species had the same pattern of nectar production: a high concentration in the morning, which was progressively reduced as the day passed. This pattern of nectar production coincides with the behaviour of the pollinator, which makes more frequent visits in the morning, as observed in a previous study. CONCLUSIONS: The results suggest that the impact of mites on nectar availability of Heliconia is more important with regard to total volume of nectar produced irrespective of flower longevity. A high variation among individuals in nectar produced in the populations was also observed. Hummingbird flower mites strongly affect availability of nectar for hummingbirds.     

Testing non-additive effects of nectar-robbing ants and hummingbird pollination on the reproductive success of a parasitic plant

Nectar robbing may have an indirect negative effect on plant reproduction by discouraging legitimate pollinator species from visiting robbed flowers. In this study, we set up a 2 × 2 factorial design with nectar-robbing ants and hummingbird pollination to test for non-additive effects on fruit set, seed mass, and seed germination of the leafless mistletoe Tristerix aphyllus (Loranthaceae). Even though ants caused conspicuous damage at the base of the floral tubes, nectar availability was reduced by only 8 % in the presence of ants. The green-backed firecrown Sephanoides sephaniodes was insensitive to the presence of ants. Rather, the bird responded to flower number and the presence or the absence of damage, but not to the extent of damage within inflorescences. As hummingbirds were largely insensitive to variation in nectar robbing, the interaction ant × hummingbird had no effect on plant-reproductive success. Thus, the factorial experiment did not provide evidence for indirect negative effects of nectar robbing on plant reproduction. These results suggest that indirect effects of nectar robbers on pollinator behaviour may occur under a more restricted set of conditions than those previously considered. We suggest that the low amount of nectar removed by nectar-robbing ants was insufficient for hummingbirds to avoid robbed flowers, which restricted the potential for non-additive effects.     

The impact of flower-dwelling predators on host plant reproductive success

Flowers attract insects and so are commonly exploited as foraging sites by sit-and-wait predators. Such predators can be costly to their host plant by consuming pollinators. However, sit-and-wait predators are often prey generalists that also consume plant antagonists such as herbivores, nectar robbers and granivores, so may also provide benefits to their host plant. Here we present a simple, but general, model that provides novel predictions about how costs and benefits interact in different ecological circumstances. The model predicts that the ecological conditions in which flower-dwelling predators are found can generate either net benefits to their host plants, net costs to their host plants, or can have no effect on the fitness of their host plants. The net effect is influenced by the relative densities of mutualists and antagonists. The flower-dwelling predator has a strong positive effect on the plant if both the pollinators and the granivores are at high density. Further, the range of density combinations that yield a positive net outcome for the plant increases if the performance of pollinators is negatively density dependent, if the predator is only moderately effective at influencing flower visitor rates by its potential prey, and if pollinators are very effective. If plants of a given species find themselves consistently in conditions where they benefit from the presence of a predator then we predict that natural selection could favour the evolution of plant traits that increase the likelihood of predator recruitment and retention, especially where plants are served by highly effective pollinators.     

Distribution patterns of hummingbird flower mites (Gamasida: Ascidae) in relation to floral availability on Heliconia inflorescences

I analyzed the dispersion patterns of ascid mites (Gamasida:Ascidae) on inflorescences of Heliconia trinidatis in relationto the temporal and spatial distribution of open flowers. Openflowers last only a few hours and are the locations of foodas well as the sole sites from which mites disperse on visitinghummingbirds. All inflorescences were inhabited by populationsof nectarivorous Rhinoseius trinitatis and omnivorous Lasioseiuselegants. All demographic groups of R. trinitatis were associatedstrongly with bracts bearing open flowers on the day of inflorescencecollection or with bracts that would have had an open floweron the day after collection. For L. elegans, only larval distributioncoincided with open flowers. Laboratory observations demonstratedthat mites move throughout an inflorescence at night and preferentiallyaggregate where the next flower will open. Mites enter flowersimmediately at, or just before, anthesis, and unerringly exitopen flowers well in advance of floral abscission. Hummingbirdflower mites exhibit a variety of behavioral adaptations, indicatingextraordinary sensitivity to the physiological and biochemicalnuances of their host inflorescences.     

Phoretic dispersal on bumblebees by bromeliad flower mites (Mesostigmata, Melicharidae)

Nectarivorous flower mites (Mesostigmata: Melicharidae) live mostly on hummingbird-pollinated plants in the New World. We observed Proctolaelaps sp. living on Neoregelia johannis (Bromeliaceae) in a coastal rain forest site in south-eastern Brazil. Flower anthesis of this bromeliad lasted a single day. We recorded mites moving into, feeding from, presumably mating and reproducing, and exiting bromeliad flowers within just a single day. We observed three ant species predating flower mites on bromeliads. The main visitor was the bumblebee Bombus morio, which always landed on the inflorescence to access nectar inside the bromeliad flowers. We found Proctolaelaps sp. mites on 47% of 38 bumblebees inspected, with each Bombus hosting 2 mites on average; only adults and mostly female mites (93%) usually found on the bumblebees’ gula region of the head. This is the first study to document nectarivorous flower mites living on a melittophilous host plant using bumblebees for phoretic dispersal.     

Influence of plant reproductive systems on the evolution of hummingbird pollination

Many hummingbird‐pollinated plant species evolved from bee‐pollinated ancestors independently in many different habitats in North and South America. The mechanisms leading to these transitions are not completely understood. We conducted pollination and germination experiments and analyzed additional reproductive traits in three sister species pairs of which one species is bee‐ and the other hummingbird‐pollinated. All hummingbird‐pollinated species showed higher seed set and germination rates in cross‐pollinated than in self‐pollinated flowers. In the self‐compatible, bee‐pollinated sister species this difference did not exist. As expected, seed set and germination rate were higher after cross‐pollination in the largely self‐incompatible genus Penstemon independently of the pollination syndrome. However, the bird‐pollinated species produce only half of the amount of ovules and pollen grains per flower compared to the bee‐pollinated sister species. This indicates that hummingbird pollination is much more efficient in self‐incompatible populations because hummingbirds waste less pollen and provide higher outcrossing rates. Therefore, hummingbird pollination is less resource costly. Overall, we suggest that hummingbirds may increase the reproductive success compared to bees, influencing the evolution of hummingbird pollination in ecosystems with diverse bee assemblages.     

Two different and sublethal isolates of Nosema lymantriae (Microsporidia) reduce the reproductive success of their host,Lymantria dispar

We examined the effects of two microsporidian isolates of Nosema lymantriae (Germany isolate; Schweinfurt isolate) on the reproductive success of Lymantria dispar L. All possible mating combinations were tested. Both isolates affected the fecundity of infected females and the hatch of neonates. The infection of female L. dispar with either isolate resulted in a higher proportion of non-viable eggs; the survival of neonates during egg stage was not affected. When L. dispar larvae were infected with N. lymantriae [Germany] the number of eggs per egg mass decreased between 24 and 61%. When both adults were infected, the hatch rate decreased to 26%. While the infection of the male or the female host with the Germany isolate affected the number of eggs per egg mass and the hatch of progeny, we did not find a significant effect when male hosts were infected with the Schweinfurt isolate; only infection of the female L. dispar resulted in a reduction of the number of eggs per egg mass between 26 and 37%.     

壬基酚暴露对斑马鱼求偶行为与繁殖成功率的影响

壬基酚(NP)是普遍存在于水生生态系统中的一种环境内分泌干扰物。研究了不同浓度下(0,0.1,1,10,50,100μg/L)NP暴露对斑马鱼(Daniorerio)求偶行为与繁殖成功率的影响。结果表明,NP暴露对斑马鱼求偶行为与繁殖成功率影响显著,100μg/LNP暴露显著减少斑马鱼求偶时间、降低产卵量与受精率(P(0.05)。斑马鱼产卵量与求偶总时间、平均每次求偶时间、长于5s的求偶时间显著正相关(P(0.05),与求偶频率不相关(P=0.951)。NP暴露可能通过影响斑马鱼求偶时间,进而影响产卵量。斑马鱼求偶时间有望作为评估水体NP污染有效的生物标记。     

Parasite-related pairing success in an intermediate host, Caecidotea intermedius (Isopoda): effects of male behavior and reproductive physiology

The acanthocephalan parasite Acanthocephalus dirus develops from the egg to the cystacanth stage inside the freshwater isopod Caecidotea intermedius. We have shown previously that cystacanth-infected male C. intermedius are less likely to initiate mating attempts with females than uninfected males in competitive situations. Here, we used a field-based experiment to examine whether cystacanth-infected males were also less likely to initiate mating attempts with females in noncompetitive situations. We found that infected males were less responsive to females than uninfected males, and we propose that the cystacanth-related change in male mating behavior is mediated by a change in the mating response of males to females rather than male-male competition. We then examined whether cystacanth-related changes in reproductive function, i.e., sperm content and fertilization ability, could explain this variation in male mating behavior. We found that cystacanth-infected males contained both developing and mature sperm and fertilized as many eggs as uninfected males. Thus, we propose that changes in reproductive function are unlikely to explain cystacanth-related variation in male mating behavior in C. intermedius.     

Effects of nectar concentration and flower depth on flower handling efficiency of bumble bees

Summary Fluid viscosity only affected ingestion rates of bumble bees (Bombus) for solutions greater than 35–40% sucrose (mass of solute per mass of solution). This contrasts with previously published models based on fluid dynamics which predicted continuous depression of ingestion rates with increasing viscosity. Individual bees maintained constant lapping rates regardless of sucrose concentration (up to at least 70%). The decline in ingestion rates at higher concentrations apparently resulted from the tongue not contacting liquid long enough to become saturated due to reduced capillary flow. Increasing flower depth similarly decreased the volume of liquid ingested per lap, and did not affect lapping rate. Morphologically dissimilar bees drank at different rates because glossa length affects lapping rate and volume ingested per lap, and body mass affects lapping rate. An additional species-specific component to lapping rate also influenced ingestion rates. Deviations from a regression model derived to explain ingestion rates as a function of glossa length, body mass, flower depth and liquid viscosity suggest mechanistic and behavioralaspects to flower probing time. Because of the relation between ingestion rate and liquid viscosity, the sucrose concentration maximizing a bee's rate of net energy uptake should lie between 50–65%, depending primarily on specific conditions of nectar volume, inflorescence size and flight time between inflorescences.     

Pollinators shift to nectar robbers when florivory occurs,with effects on reproductive success in Iris bulleyana (Iridaceae)

• Studies have indicated that florivory and nectar robbing may reduce reproductive success of host plants. However, whether and how these effects might interact when plants are simultaneously attacked by both florivores and nectar robbers still needs further investigation.
• We used Iris bulleyana to detect the interactions among florivory, nectar robbing and pollination, and moreover, their effects on plant reproductive success. Field investigations and hand‐pollination treatments were conducted on two experimental plots from a natural population, in which Experimental plot was protected from florivores and Control plot was not manipulated.
• The flower calyx was bitten by sawflies to consume the nectary, and three bumblebee species were pollinators. In addition, the short‐tongued pollinator, Bombus friseanus, was the only robber when there was a hole made by a sawfly. The bumblebee had significantly shortened flower handling time when robbing, as compared to legitimate visits. Pollinator visitation and seed production decreased significantly in damaged flowers. However, seed production per flower after supplementary hand‐pollination did not differ significantly between damaged and undamaged flowers. Compared to the Experimental plot, bumblebees visited fewer flowers per plant in a foraging bout in the Control plot.
• The flowers damaged by florivory allowed B. friseanus to shift to a nectar robber. Florivory and nectar robbing collectively decreased plant reproductive success by consuming nectar resources, which may reduce attractiveness to pollinators of the damaged flowers. However, the changes in pollinator behaviour might be beneficial to the plant by reducing the risk of geitonogamous mating.

     

Effects of population size, seed predation and plant size on male and female reproductive success in Vincetoxicum hirundinaria (Asclepiadaceae)

Here we present the results of a study on the effects of population size, seed predation, and plant size on male and female reproductive success in ten Vincetoxicum hirundinaria populations in southwestern Finland. We investigated male reproductive success by recording pollinia removal, and studying pollen quality and quantity. Pod and seed production, and the number of ovules per ovary were counted to estimate female reproductive success. Both pollen quality and pollinia removal were higher in small V. hirundinaria populations compared to large populations. In contrast, the quantity of pollen was higher in large populations than in small populations. Pod initiation was higher in large populations. However, large populations had higher abortion rates and proportionally fewer intact pods. Plant size did not affect male reproductive success whereas pod and seed production correlated positively with plant size, although only in large populations. Population size had no clear impact on seed predation intensities. Variation was, however, observed among populations. Larger plant individuals suffered from an increased risk of being attacked only in two populations. This correlation was not clearly attributed to plant population size. The results of this study suggest that reproductive success in V. hirundinaria may be highly variable and this variation is to some extent explained by population size. Further, population size affected male and female reproductive success differently.     

Effects of indiscriminate foraging by tropical hummingbirds on pollination and plant reproductive success: experiments with two tropical treelets (Rubiaceae)

Summary In cloud forest at Monteverde, Costa Rica, two common treelets (Palicourea lasiorrachis and Cephaelis elata, both Rubiaceae) depend simultaneously on one hummingbird population (Lampornis calolaema) for pollination. Both species are distylous and self-incompatible. In laboratory experiments, we examined possible effects of indiscriminate foraging by hummingbirds among flowers of both species, as observed in the field, on pollination of Palicourea. In each of 35 trials, captive L. calolaema probed 2 flowers from pin plants of Palicourea followed by 20 thrum flowers of the same species, with either 0, 2, or 10 Cephaelis flowers intervening. We assessed pollen transfer by staining and counting pin pollen tubes growing in thrum styles; counts of 0, 1, or 2 pollen tubes relate directly to seed output (0, 1, or 2 seeds per fruit, respectively). Intervening Cephaelis flowers sharply reduced pollen receipt by thrum flowers of Palicourea and reduced some aspects of pollen dispersal from pins as well, thereby curtailing maternal and paternal reproductive potential of Palicourea. Such effects of interspecific pollen loss on reproductive output may lead to strong competition among some, though not all, combinations of plant species pollinated by L. calolaema or of other plant combinations that share animal pollinators.