Pollination Mutualism Research Articles

Consequences of Nectar Robbing for Realized Male Function in a Hummingbird-Pollinated Plant

The effects of nectar robbers on plants and their mutualistic pollinators are poorly understood due, in part, to the paucity of studies examining male reproductive success in nectar-robbed plants. Here we measured the effects of a nectar-robbing bumblebee, Bombus occidentalis, on realized male reproductive success (seeds sired) in a hummingbird-pollinated plant, Ipomopsis aggregata. To determine the effects of nectar robbing on paternity, we used a series of experimental populations of plants containing a known allozyme marker. In each population, we experimentally controlled the levels of nectar robbing on each I. aggregata plant by cutting a hole in the corolla with dissecting scissors and removing nectar with a micro-capillary tube. We measured hummingbird-pollinator foraging behavior and fruit and seed production (maternal function) for each plant. We then genotyped seeds for the allozyme marker to determine the number of seeds sired by plants with known levels of robbing. Heavy nectar robbing (> 80% of flowers robbed) significantly reduced the number of seeds sired, as well as the number of seeds produced due to pollinator avoidance of heavily robbed plants. Total plant reproduction, both male and female contributions, were reduced by 50% due to high levels of robbing. To date, no other studies have measured the effects of nectar robbing on realized male function (number of seeds sired). Ours is the first study to demonstrate that robbing can simultaneously decrease realized male reproductive success as well as female reproductive success, and that the effects are incurred indirectly through pollinator avoidance of robbed plants.

CONSEQUENCES OF NECTAR ROBBING FOR REALIZED MALE FUNCTION IN A HUMMINGBIRD-POLLINATED PLANT

The effects of nectar robbers on plants and their mutualistic pollinators are poorly understood due, in part, to the paucity of studies examining male reproductive success in nectar-robbed plants. Here we measured the effects of a nectar-robbing bumblebee, Bombus occidentalis, on realized male reproductive success (seeds sired) in a hummingbird-pollinated plant, Ipomopsis aggregata. To determine the effects of nectar robbing on paternity, we used a series of experimental populations of plants containing a known allozyme marker. In each population, we experimentally controlled the levels of nectar robbing on each I. aggregata plant by cutting a hole in the corolla with dissecting scissors and removing nectar with a micro-capillary tube. We measured hummingbird-pollinator foraging behavior and fruit and seed production (maternal function) for each plant. We then genotyped seeds for the allozyme marker to determine the number of seeds sired by plants with known levels of robbing. Heavy nectar robbing (> 80% of flowers robbed) significantly reduced the number of seeds sired, as well as the number of seeds produced due to pollinator avoidance of heavily robbed plants. Total plant reproduction, both male and female contributions, were reduced by 50% due to high levels of robbing. To date, no other studies have measured the effects of nectar robbing on realized male function (number of seeds sired). Ours is the first study to demonstrate that robbing can simultaneously decrease realized male reproductive success as well as female reproductive success, and that the effects are incurred indirectly through pollinator avoidance of robbed plants.

Pollen dispersal in Yucca filamentosa (Agavaceae): the paradox of self‐pollination behavior by Tegeticula yuccasella (Prodoxidae)

We investigated pollen dispersal in an obligate pollination mutualism between Yucca filamentosa and Tegeticula yuccasella. Yucca moths are the only documented pollinator of yuccas, and moth larvae feed solely on developing yucca seeds. The quality of pollination by a female moth affects larval survival because flowers receiving small amounts of pollen or self-pollen have a high abscission probability, and larvae die in abscised flowers. We tested the prediction that yucca moths primarily perform outcross pollinations by using fluorescent dye to track pollen dispersal in five populations of Y. filamentosa. Dye transfers within plants were common in all populations (mean ± 1 SE, 55 ± 3.0%), indicating that moths frequently deposit self-pollen. Distance of dye transfers ranged from 0 to 50 m, and the mean number of flowering plants between the pollen donor and recipient was 5 (median = 0), suggesting that most pollen was transferred among near neighbors. A multilocus genetic estimate of outcrossing based on seedlings matured from open-pollinated fruits at one site was 94 ± 6% (mean ± 1 SD). We discuss why moths frequently deposit self-pollen to the detriment of their offspring and compare the yucca-yucca moth interaction with other obligate pollinator mutualisms in which neither pollinator nor plant benefit from self-pollination.

Artocarpus (Moraceae)–gall midge pollination mutualism mediated by a male‐flower parasitic fungus

A previously undescribed pollination system involving a monoecious tree species, Artocarpus integer (Moraceae), pollinator gall midges, and fungi is reported from a mixed dipterocarp forest in Sarawak, Borneo. The fungus Choanephora sp. (Choanephoraceae, Mucorales, Zygomycetes) infects male inflorescences of A. integer, and gall midges (Contarinia spp., Cecidomyiinae, Diptera) feed on the fungal mycelia and oviposit on the inflorescence. Their larvae also feed on the mycelia and pupate in the inflorescence. The gall midges are also attracted by female inflorescences lacking mycelia, probably due to a floral fragrance similar to that of male inflorescences. Because of the sticky pollen, dominance of Contarinia spp. in flower visitors, and pollen load observed on Contarinia spp. collected on both male and female inflorescences, Artocarpus integer is thought to be pollinated by the gall midges. Although several pathogenic fungi have been reported to have interactions with pollinators, this is the first report on a pollination mutualism in which a fungus plays an indispensable role. The pollination system described here suggests that we should be more aware of the roles fungi can play in pollinations.

Plant invasions — the role of mutualisms

ABSTRACTMany introduced plant species rely on mutualisms in their new habitats to overcome barriers to establishment and to become naturalized and, in some cases, invasive. Mutualisms involving animalmediated pollination and seed dispersal, and symbioses between plant roots and microbiota often facilitate invasions. The spread of many alien plants, particularly woody ones, depends on pollinator mutualisms. Most alien plants are well served by generalist pollinators (insects and birds), and pollinator limitation does not appear to be a major barrier for the spread of introduced plants (special conditions relating to Ficus and orchids are described). Seeds of many of the most notorious plant invaders are dispersed by animals, mainly birds and mammals. Our review supports the view that tightly coevolved, plant‐vertebrate seed dispersal systems are extremely rare. Vertebrate‐dispersed plants are generally not limited reproductively by the lack of dispersers. Most mycorrhizal plants form associations with arbuscular mycorrhizal fungi which, because of their low specificity, do not seem to play a major role in facilitating or hindering plant invasions (except possibly on remote islands such as the Galapagos which are poor in arbuscular mycorrhizal fungi). The lack of symbionts has, however, been a major barrier for many ectomycorrhizal plants, notably for Pinus spp. in parts of the southern hemisphere. The roles of nitrogen‐fixing associations between legumes and rhizobia and between actinorhizal plants and Frankia spp. in promoting or hindering invasions have been virtually ignored in the invasions literature. Symbionts required to induce nitrogen fixation in many plants are extremely widespread, but intentional introductions of symbionts have altered the invasibility of many, if not most, systems. Some of the world's worst invasive alien species only invaded after the introduction of symbionts. Mutualisms in the new environment sometimes re‐unite the same species that form partnerships in the native range of the plant. Very often, however, different species are involved, emphasizing the diffuse nature of many (most) mutualisms. Mutualisms in new habitats usually duplicate functions or strategies that exist in the natural range of the plant. Occasionally, mutualisms forge totally novel combinations, with profound implications for the behaviour of the introduced plant in the new environment (examples are seed dispersal mutualisms involving wind‐dispersed pines and cockatoos in Australia; and mycorrhizal associations involving plant roots and fungi). Many ecosystems are becoming more susceptible to invasion by introduced plants because: (a) they contain an increasing array of potential mutualistic partners (e.g. generalist frugivores and pollinators, mycorrhizal fungi with wide host ranges, rhizobia strains with infectivity across genera); and (b) conditions conducive for the establishment of various alienalien synergisms are becoming more abundant. Incorporating perspectives on mutualisms in screening protocols will improve (but not perfect) our ability to predict whether a given plant species could invade a particular habitat.

Plant invasions--the role of mutualisms.

Many introduced plant species rely on mutualisms in their new habitats to overcome barriers to establishment and to become naturalized and, in some cases, invasive. Mutualisms involving animal-mediated pollination and seed dispersal, and symbioses between plant roots and microbiota often facilitate invasions. The spread of many alien plants, particularly woody ones, depends on pollinator mutualisms. Most alien plants are well served by generalist pollinators (insects and birds), and pollinator limitation does not appear to be a major barrier for the spread of introduced plants (special conditions relating to Ficus and orchids are described). Seeds of many of the most notorious plant invaders are dispersed by animals, mainly birds and mammals. Our review supports the view that tightly coevolved, plant-vertebrate seed dispersal systems are extremely rare. Vertebrate-dispersed plants are generally not limited reproductively by the lack of dispersers. Most mycorrhizal plants form associations with arbuscular mycorrhizal fungi which, because of their low specificity, do not seem to play a major role in facilitating or hindering plant invasions (except possibly on remote islands such as the Galapagos which are poor in arbuscular mycorrhizal fungi). The lack of symbionts has, however, been a major barrier for many ectomycorrhizal plants, notably for Pinus spp. in parts of the southern hemisphere. The roles of nitrogen-fixing associations between legumes and rhizobia and between actinorhizal plants and Frankia spp. in promoting or hindering invasions have been virtually ignored in the invasions literature. Symbionts required to induce nitrogen fixation in many plants are extremely widespread, but intentional introductions of symbionts have altered the invasibility of many, if not most, systems. Some of the world's worst invasive alien species only invaded after the introduction of symbionts. Mutualisms in the new environment sometimes re-unite the same species that form partnerships in the native range of the plant. Very often, however, different species are involved, emphasizing the diffuse nature of many (most) mutualisms. Mutualisms in new habitats usually duplicate functions or strategies that exist in the natural range of the plant. Occasionally, mutualisms forge totally novel combinations, with profound implications for the behaviour of the introduced plant in the new environment (examples are seed dispersal mutualisms involving wind-dispersed pines and cockatoos in Australia; and mycorrhizal associations involving plant roots and fungi). Many ecosystems are becoming more susceptible to invasion by introduced plants because: (a) they contain an increasing array of potential mutualistic partners (e.g. generalist frugivores and pollinators, mycorrhizal fungi with wide host ranges, rhizobia strains with infectivity across genera); and (b) conditions conductive for the establishment of various alien/alien synergisms are becoming more abundant. Incorporating perspectives on mutualisms in screening protocols will improve (but not perfect) our ability to predict whether a given plant species could invade a particular habitat.

Floral isolation betweenAquilegia formosaandAquilegia pubescens

The acquisition of floral nectar spurs is correlated with increased species diversity across multiple clades. We tested whether variation in nectar spurs influences reproductive isolation and, thus, can potentially promote species diversity using two species of Aquilegia, Aquilegia formosa and Aquilegia pubescens, which form narrow hybrid zones. Floral visitors strongly discriminated between the two species both in natural populations and at mixed-species arrays of individual flowers. Bees and hummingbirds visited flowers of A. formosa at a much greater rate than flowers of A. pubescens. Hawkmoths, however, nearly exclusively visited flowers of A. pubescens. We found that altering the orientation of A. pubescens flowers from upright to pendent, like the flowers of A. formosa, reduced hawkmoth visitation by an order of magnitude. In contrast, shortening the length of the nectar spurs of A. pubescens flowers to a length similar to A. formosa flowers did not affect hawkmoth visitation. However, pollen removal was significantly reduced in flowers with shortened nectar spurs. These data indicate that floral traits promote floral isolation between these species and that specific floral traits affect floral isolation via ethological isolation while others affect floral isolation via mechanical isolation.

Oviposition by mutualistic seed-parasitic pollinators and its effects on annual fitness of single- and multi-flowered host plants.

The balance of intimate relationships between plants and seed-eating pollinators can depend on pollinator behaviour in relation to floral characters, such as flower size and flower number. Here, we examined how pollinator oviposition in relation to these traits affected annual fitness (seed output) of single- and multi-flowered Trollius europaeus along altitudinal gradients in subarctic Sweden and the French Alps. Small flies (Chiastocheta spp.) pollinate T. europaeus and their larvae feed on developing seeds. Assuming that late flowers in multi-flowered plants attracted flies to the earliest flower on the same plant, we expected more eggs and higher seed predation in early multiple flowers than in single flowers. Relative seed predation would thereby increase with flower number. Both in Sweden and the Alps, more eggs were placed on large flowers. Early multiple flowers were slightly larger than single flowers, and about twice the size of secondary flowers. As a result, and possibly combined with the effects of secondary flowers, early multiple flowers attracted more ovipositing flies and experienced relatively higher seed predation. However, this did not generally result in higher seed predation of multi-flowered hosts. Multiple flowers had greater seed output than single flowers at all altitudes, also in the high alpine and subarctic sites, where single flowers were more abundant. We hypothesise that the distribution of multiple flowers generally is enforced by environmental factors, rather than by fly-host plant interactions, because only very rarely (in triple-flowered alpine plants) was seed predation disproportionate, and the relationship skewed to the disadvantage of the host. The outcome of the mutualistic interaction was often similar in alpine and subarctic populations, but the underlying factors were different. Subarctic flowers had high abortion and low predation rates, while alpine flowers experienced the reversed situation. The higher fly abundance in the Alps suggests a more intense mutualistic interaction than in Sweden. Despite varying ecological and environmental conditions at these sites, the mutualistic relationship was generally in balance. However, when it was unbalanced, this could be explained by fly behaviour in response to floral traits, and by differences in fly abundance.

Population Persistence, Pollination Mutualisms, and Figs in Fragmented Tropical Landscapes

Population Persistence, Pollination Mutualisms, and Figs in Fragmented Tropical Landscapes

Population Persistence, Pollination Mutualisms, and Figs in Fragmented Tropical Landscapes

Population Persistence, Pollination Mutualisms, and Figs in Fragmented Tropical Landscapes

HOST SPECIFICITY AND THE GENETIC STRUCTURE OF TWO YUCCA MOTH SPECIES IN A YUCCA HYBRID ZONE.

Host specialization is an important mechanism of diversification among phytophagous insects, especially when they are tightly associated with their hosts. The well-known obligate pollination mutualism between yucca moths and yuccas represent such an association, but the degree of host specificity and modes of specialization in moth evolution is unclear. Here we use molecular tools to test the morphology-based hypothesis that the moths pollinating two yuccas, Yucca baccata and Y. schidigera, are distinct species. Host specificity was assessed in a zone of sympatry where the hosts are known to hybridize. Because the moths are the only pollinators, the plant hybrids are evidence that the moths occasionally perform heterospecific pollination. Nucleotide variation was assessed in a portion of the mitochondrial gene COI, and in an intron within a nuclear lysozyme gene. Moths pollinating Y. baccata and Y. schidigera were inferred to be genetically isolated because there was no overlap in alleles at either locus, and all but one of the moths was found on their native host in the hybrid zone. Moreover, genetic structure was very weak across the range of each moth species: estimates of FST for the lysozyme intron were 0.043 (SE = ± 0.004) and 0.021 (SE = ± 0.006) for the baccata and schidigera pollinators, respectively; estimated FST for COI in the baccata moths was 0.228 (± 0.012), whereas schidigera pollinators were fixed for a single allele. These results reveal a high level of migration among widely separated moth populations. We predict that pollen-mediated gene flow among conspecific yuccas is considerable and hypothesize that geographic separation is a limited barrier both for yuccas and for yucca moths.

The evolution of obligate pollination mutualisms: senita cactus and senita moth.

We report a new obligate pollination mutualism involving the senita cactus, Lophocereus schottii (Cactaceae, Pachyceereae), and the senita moth, Upiga virescens (Pyralidae, Glaphyriinae) in the Sonoran Desert and discuss the evolution of specialized pollination mutualisms. L. schottii is a night-blooming, self-incompatible columnar cactus. Beginning at sunset, its flowers are visited by U. virescens females, which collect pollen on specialized abdominal scales, actively deposit pollen on flower stigmas, and oviposit a single egg on a flower petal. Larvae spend 6 days eating ovules before exiting the fruit and pupating in a cactus branch. Hand-pollination and pollinator exclusion experiments at our study site near Bahia Kino, Sonora, Mexico, revealed that fruit set in L. schottii is likely to be resource limited. About 50% of hand-outcrossed and open-pollinated senita flowers abort by day 6 after flower opening. Results of exclusion experiments indicated that senita moths accounted for 75% of open-pollinated fruit set in 1995 with two species of halictid bees accounting for the remaining fruit set. In 1996, flowers usually closed before sunrise, and senita moths accounted for at least 90% of open-pollinated fruit set. The net outcome of the senita/senita moth interaction is mutualistic, with senita larvae destroying about 30% of the seeds resulting from pollination by senita moths. Comparison of the senita system with the yucca/yucca moth mutualism reveals many similarities, including reduced nectar production, active pollination, and limited seed destruction. The independent evolution of many of the same features in the two systems suggests that a common pathway exists for the evolution of these highly specialized pollination mutualisms. Nocturnal flower opening, self-incompatible breeding systems, and resource-limited fruit production appear to be important during this evolution.

Partial avoidance of female inflorescences of a dioecious fig by their mutualistic pollinating wasps

Every dioecious species of fig is pollinated by a specific wasp that only reproduces within the inflorescences of male trees. Pollinators usually die within the closed urn-shaped inflorescence (fig or syconium) they visit. Thus pollinators that enter female syconia allow seed production but die without reproducing. In a previous study, pollinators of one dioecious fig where male and female trees flower synchronously, Ficus hispida, did not exhibit differential attraction or choice between inflorescences of the two sexes. Here we show that Blastophaga psenes, the pollinator of another dioecious species of different lineage, the common fig (F. carica), significantly avoided female syconia, when we experimentally induce a situation of choice. Paradoxically, choosiness can be demonstrated in F. carica where usually wasps do not face a choice because male and female trees do not flower synchronously. We discuss how the mutualism may be stable despite this discrimination and hypothesize why the two species of fig-pollinators exhibit different behaviour on dioecious figs.

Conflict of interest in a mutualism: documenting the elusive fig wasp–seed trade–off

The generally accepted view that mutualisms represent reciprocal exploitations implies a greater or lesser degree of inherent tension between the partners. This view emphasizes the importance of identifying conflicts of interest between the partners, and then attempting to quantify the effects of factors that influence costs and benefits to each. The natural history of the speciose fig-fig wasp pollination mutualisms permits such measurements. However, previous attempts to document the presumed tensions, which are expected to result in a negative relationship between the production of viable seeds and pollinator wasp offspring, have met with mixed results, casting doubt on the existence of the conflict. Here, we present hierarchical analyses of 929 fruits sampled from 30 crops representing nine species of monoecious New World figs. These analyses control for the confounding influences of variation in (1) pollination intensity (numbers of foundress pollinators); (2) flower number per fruit; and (3) the proportion of those flowers that develop, on seed and wasp production, both among and within crops. We thereby show that a negative relationship between the production of viable seeds and wasps is, in fact, ubiquitous, thus documenting this underlying tension inherent in the mutualism. We suggest that complex interactions of variables that influence costs and benefits are likely to be a general property of most mutualistic systems.

Is there a floral parasite mutualism in cycad pollination? the pollination biology of Encephalartos villosus (Zamiaceae)

Observations and experiments were carried out over 5 yr to distinguish between wind and insect pollination in the cycad Encephalartos villosus Lemaire (Zamiaceae). They were also designed to determine whether a pollination mutualism exists between E. villosus and Antliarhinus zamiae (Thunberg) (Coleoptera: Brentidae), an obligate ovule parasite that routinely parasitizes a large proportion of the ovules. The percentage of fertilized ovules dropped slightly when wind was excluded from the megastrobilus. However, when insects were excluded by either net bags or insecticide there was a substantial decrease in the proportion of fertilized ovules. Five beetle species belonging to four families were found on the strobili at the time of pollination. Using data on the effectiveness of pollen transfer to the receptive ovule, as well as data on abundance and pollen loads, a pollinator importance value (PIV) was determined for each beetle species and a pollinator importance index (PII) was determined for each population. PII values showed that an undescribed weevil (Porthetes sp., Curculionidae) was consistently the most important pollinator. A. zamiae and an undescribed beetle species within the Xenoscelinae (Languriidae) played a minor role in pollination, and their contributions varied from year to year and between populations. Two additional beetle species, Metacucujus goodei Endrödy‐Younga (Boganiidae) and a second species of Xenoscelinae, had very low PII values and probably had little or no effect on pollination. Low PIV scores for A. zamiae were a result of its low numbers on the microstrobilus and the tendency of the beetles to remain on the outside of the megastrobilus. In the interaction between E. villosus and A. zamiae, the cycad does not appear to benefit significantly from a pollination service and I interpret this to mean that the relationship is antagonistic rather than mutualistic. There is, however, a possible mutualism between Porthetes sp. and E. villosus.

Permian Pollen Eating

The Random Samples item “Permian pollen eaters” ([16 May, p. 1035][1]) provides a stimulating account of the discovery by Russian paleobiologists Alexander Rasnitsyn and Valentin Krassilov of identifiable pollen in the guts of Early Permian insects. Paleobotanist William Chaloner is quoted as saying that inadvertent consumption of pollen could explain the occurrence of this pollen. One of the preserved insects is a member of the Synomaloptilidae, ancestral to modern bark lice and a member of a Paleozoic insect clade that was postulated by Rasnitsyn to consume “plants by feeding primarily on their reproductive organs …” ( 1 , p. 27, translated from the Russian). In 1997, Rasnitsyn predicted that these and related taxa possessed head and mouthparts that consumed material nutritionally equivalent to pollen ( 2 , p. 65). It has been known that Late Carboniferous coal-ball permineralizations include fossilized fecal pellet assemblages containing histologically pristine plant tissues, some of which consist entirely of spores, pollen, and associated tissue ([3][2]). And insect consumption of wind-dispersed pollen has been demonstrated repeatedly in such consummate pollenivores as syrphid flies ([4][3]), bees ([5][4]), and other pollenivorous insects ([6][5]). The occurrence of pollen interpreted as wind-dispersed in the guts of Permian insects is thus unlikely to be accidental. A more parsimonious conclusion is that several lineages of Early Permian insects were actively consuming nutritionally rich pollen, regardless of the mode of dispersal. Such a diet was a necessary prelude to pollinator mutualisms between seed plants and insects that occurred subsequently in geologic time ([7][6]). 1. A. P. Rasnitsyn, Tr. Paleontol. Inst. 174 , 1 (1980). 2. \___|, Paleontol. J. 11 , 60 (1977). 3. [↵][7]R. W. Baxendale, Palaeontology 22 , 537 (1979); S. V. Meyen, Z. Geol. Wiss. 12 , 269 (1984). 4. [↵][8]P. Stelleman and A. D. J. Meeuse, Tijd. Entomol. 119 , 15 (1976). 5. [↵][9]J. Pojar, Am. Midl. Natl. 89 , 448 (1973). 6. [↵][10]O. Hagerup, Dan. Vidensk. Sels. Biol. Meddel. 18 (no. 4), 1 (1950). 7. [↵][11]C. C. Labandeira, Ann. Rev. Ecol. Syst. , in press. [1]: /lookup/doi/10.1126/science.276.5315.1035a [2]: #ref-3 [3]: #ref-4 [4]: #ref-5 [5]: #ref-6 [6]: #ref-7 [7]: #xref-ref-3-1 View reference 3 in text [8]: #xref-ref-4-1 View reference 4 in text [9]: #xref-ref-5-1 View reference 5 in text [10]: #xref-ref-6-1 View reference 6 in text [11]: #xref-ref-7-1 View reference 7 in text

The Stability and Persistence of Mutualisms Embedded in Community Interactions

In this paper we argue that two-species models of mutualism may be oversimplifications of the real world that lead to erroneous predictions. We present a four-species model of a pollination mutualism embedded in other types of community interactions. Conclusions derived from two-species models about the destabilizing effect of mutualisms are misleading when applied to the present scenario; although the mutualisms are locally destabilizing, the effect is more than canceled by an increased chance of feasibility. The crucial difference is the interaction of the mutualists with other species in a larger web. Furthermore, community persistence (without unrealistic population explosion), arguably a superior ecological criterion, is greatly enhanced by the presence of mutualisms. Therefore, we predict that mutualisms should be common in the real world, a prediction matching empirial findings and in contrast to the predictions from local stability analysis of basic two-species models. This method of stabilizing a mutualism appears superior in some ways to the often-used method of introducing density dependence in the strength of the mutualism, because it permits obligate mutualisms to exist even at low densities, again matching empirical findings. Lastly, this study is an example of how complex model assemblages can behave qualitatively differently from analogous simpler ones.

Evolution of Pollination and Mutualism in the Yucca Moth Lineage

The obligate pollination mutualisms between yucca moths and yuccas are some of the most obvious cases of coevolution, but the phylogenetic origins and extent of coevolution in these interactions are little understood. Ecological and phylogenetic information from the yucca moth family, Prodoxidae, shows that pollination has evolved at least three times from separate moth behaviors. Passive pollination occurs in Greya during nectarine by one species and during oviposition by two other species. Active pollination among prodoxids has evolved only once, in the yucca moths. Several life-history traits necessary for the evolution of obligate mutualism are common traits within the Prodoxidae, and only active pollination and modified mouthparts appear to have been novel traits in the yucca moths. We use moth and host biology in a phylogenetic framework to establish hypotheses for the evolution of active pollination and reciprocal specialization in the form of functional nectarlessness in yuccas.

Relationship between a mutualist and a parasite of the laurel fig, Ficus microcarpa L.

Since 1986, the sterile populations of the laurel fig, Ficus microcarpa L., in Tunisia have become fertile with the arrival of the species-specific pollinating wasp Parapristina verticillata. However, the invasion in 1992 by one of several species-specific parasitic wasps, Odontofroggatia galili, has changed the parameters of this mutualistic relationship. A fig sample collected at Sfax, Tunisia, was analysed, and randomization of the results showed a highly significant negative correlation between the numbers of wasps and parasites. Moreover, the presence of parasites decreases the fecundity of the figs. The consequences of the competition between O. galili and P. verticillata on this fig – fig pollinator mutualism are discussed.

Pollen Removal and Deposition by Specialist and Generalist Bumblebees in Aconitum septentrionale

Pollen removal and deposition was studied in the specialised pollination mutualism between the perennial, partly self-incompatible, herb Aconitum septentrionale (Ranunculaceae) and the long-tongued specialist bee Bombus consobrinus (Apidae). Aconitum septentrionale was also visited by three less abundant generalist bumblebees. Bombus consobrinus was also visiting a few other plants before and after flowering of A. septentrionale. Workers of specialist and generalist bumblebees removed similar amounts of pollen per visit. Queens of the specialist species removed less than worker bees. Flower visit duration was the same for queens as for workers of the specialist. However, both workers and queens of the specialist made shorter visits and thus removed more pollen per unit time than did the two most frequent generalists. Thus the specialist showed a higher efficiency (net energy gain per unit time) as a harvester than the generalists. The proportion of the total pollen production removed by the specialist was similar to that found in other mutualism studies. The proportion of the variation in amount of pollen left in a flower after a visit that could be explained by the combined effects of total pollen production per flower and flower visit duration was less for B. consobrinus than for the two most frequent generalists and also less than seen in other comparable studies in the literature. Workers of B. consobrinus were the only abundant depositors of pollen in flowers of A. septentrionale. Visit duration to female phased flowers explained most of the variation in number of pollen deposited on stigmas. 1% of total pollen production reached conspecific stigmas. Thus B. consobrinus was the only quantitatively important pollinator of A. septentrionale.