Diversification and coevolution in brood pollination mutualisms: Windows into the role of biotic interactions in generating biological diversity

Cospeciation is not the dominant driver of plant-pollinator codiversification in specialized pollination systems

This study systematically rejects the long-standing notion of cospeciation as the dominant driver of codiversification between flowering plants and their specialist pollinators. Through cophylogenetic analysis of six classical specialized pollination systems, the research finds that cospeciation events are consistently outnumbered by non-cospeciation events, such as host-switch, duplication, and association losses. The findings support a more dynamic and diffuse codiversification paradigm, highlighting the importance of considering a broader range of evolutionary events in understanding plant-pollinator codiversification. This new understanding is robust across diverse pollination systems and has significant implications for conservation strategies in the face of environmental change.

150 Years of Coevolution Research: Evolution and Ecology of Yucca Moths (Prodoxidae) and Their Hosts

Yucca moths (Tegeticula and Parategeticula) are specialized pollinators of yucca plants, possessing unique, tentacle-like mouthparts used to actively collect pollen and deposit it onto the flowers of their hosts. The moths' larvae feed on the developing seeds and fruit tissue. First described in 1873, the yucca-yucca moth pollination system is now considered the archetypical example of a coevolved intimate mutualism. Research conducted over the past three decades has transformed our understanding of yucca moth diversity and host plant interactions. We summarize the current understanding of the diversity, ecology, and evolution of this group, review evidence for coevolution of the insects and their hosts, and describe how the nature of the interaction varies across evolutionary time and ecological contexts. Finally, we identify unresolved questions and areas for future research.

Phylogenomics illuminates the phylogeny of flower weevils (Curculioninae) and reveals ten independent origins of brood-site pollination mutualism in true weevils

Weevils are an unusually species-rich group of phytophagous insects for which there is increasing evidence of frequent involvement in brood-site pollination. This study examines phylogenetic patterns in the emergence of brood-site pollination mutualism among one of the most speciose beetle groups, the flower weevils (subfamily Curculioninae). We analysed a novel phylogenomic dataset consisting of 214 nuclear loci for 202 weevil species, with a sampling that mainly includes flower weevils as well as representatives of all major lineages of true weevils (Curculionidae). Our phylogenomic analyses establish a uniquely comprehensive phylogenetic framework for Curculioninae and provide new insights into the relationships among lineages of true weevils. Based on this phylogeny, statistical reconstruction of ancestral character states revealed at least 10 independent origins of brood-site pollination in higher weevils through transitions from ancestral associations with reproductive structures in the larval stage. Broadly, our results illuminate the unexpected frequency with which true weevils-typically specialized phytophages and hence antagonists of plants-have evolved mutualistic interactions of ecological significance that are key to both weevil and plant evolutionary fitness and thus a component of their deeply intertwined macroevolutionary success.

Regional Pollination Activity by Moth Migration in Athetis lepigone

Nocturnal moths (Lepidoptera) are important pollinators of a wide range of plant species. Understanding the foraging preferences of these insects is essential for their scientific management. However, this information is lacking for most moth species. The present study was therefore conducted to delineate the host plant feeding and pollination ranges of an agriculturally important nocturnal moth species Athetis lepigone by identifying the pollen species adhering to their bodies during long-distance migration. Pollen grains were dislodged from 1871 A. lepigone migrants captured on Beihuang Island in the Bohai Strait between 2020 and 2021. This region is a key seasonal migration pathway for A. lepigone in northern China. Almost 20% of all moths sampled harbored pollens, providing direct evidences that this moth species may serve as pollinators. Moreover, at least 39 pollen taxa spanning 21 plant families and 31 genera were identified, with a preference for Asteraceae, Amaranthaceae, and Pinaceae. Additionally, the pollen adherence ratios and taxa varied with moth sex, inter-annual changes, and seasonal fluctuations. Most importantly, the pollen taxa were correlated with insect migration stages and indicated that A. lepigone bidirectionally migrates between central China (Shandong, Hebei, and Henan Provinces) and northeastern China (Liaoning Province). Overall, the findings of the present work provide valuable information on the pollination behavior, geographical origins, and pollination regions of A. lepigone moths and could facilitate the design and optimization of efficacious local and regional management strategies for this important insect.

Field sampling of fig pollinator wasps across host species and host developmental phase: Implications for host recognition and specificity

Previous genetic studies of pollinator wasps associated with a community of strangler figs (Ficus subgenus Urostigma, section Americana) in Central Panama suggest that the wasp species exhibit a range in host specificity across their host figs. To better understand factors that might contribute to this observed range of specificity, we used sticky traps to capture fig-pollinating wasp individuals at 13 Ficus species, sampling at different phases of the reproductive cycle of the host figs (e.g., trees with receptive inflorescences, or vegetative trees, bearing only leaves). We also sampled at other tree species, using them as non-Ficus controls. DNA barcoding allowed us to identify the wasps to species and therefore assign their presence and abundance to host fig species and the developmental phase of that individual tree. We found: (1) wasps were only very rarely captured at non-Ficus trees; (2) nonetheless, pollinators were captured often at vegetative individuals of some host species; (3) overwhelmingly, wasp individuals were captured at receptive host fig trees representing the fig species from which they usually emerge. Our results indicate that wasp occurrence is not random either spatially or temporally within the forest and across these hosts, and that wasp specificity is generally high, both at receptive and vegetative host trees. Therefore, in addition to studies that show chemicals produced by receptive fig inflorescences attract pollinator wasps, we suggest that other cues (e.g., chemicals produced by the leaves) can also play a role in host recognition. We discuss our results in the context of recent findings on the role of host shifts in diversification processes in the Ficus genus.

Pollinator and host sharing lead to hybridization and introgression in Panamanian free-standing figs, but not in their pollinator wasps

Obligate pollination mutualisms, in which plant and pollinator lineages depend on each other for reproduction, often exhibit high levels of species specificity. However, cases in which two or more pollinator species share a single host species (host sharing), or two or more host species share a single pollinator species (pollinator sharing), are known to occur in current ecological time. Further, evidence for host switching in evolutionary time is increasingly being recognized in these systems. The degree to which departures from strict specificity differentially affect the potential for hybridization and introgression in the associated host or pollinator is unclear. We addressed this question using genome-wide sequence data from five sympatric Panamanian free-standing fig species (Ficus subgenus Pharmacosycea, section Pharmacosycea) and their six associated fig-pollinator wasp species (Tetrapus). Two of the five fig species, F. glabrata and F. maxima, were found to regularly share pollinators. In these species, ongoing hybridization was demonstrated by the detection of several first-generation (F1) hybrid individuals, and historical introgression was indicated by phylogenetic network analysis. By contrast, although two of the pollinator species regularly share hosts, all six species were genetically distinct and deeply divergent, with no evidence for either hybridization or introgression. This pattern is consistent with results from other obligate pollination mutualisms, suggesting that, in contrast to their host plants, pollinators appear to be reproductively isolated, even when different species of pollinators mate in shared hosts.

Pollinator sharing between reproductively isolated genetic lineages of Silene nutans

High reciprocal pollination specialization leading to pollinator isolation can prevent interspecific pollen transfer and competition for pollinators. Sharing pollinators may induce mating costs, but it may also increase pollination services and pollen dispersal and offer more resources to pollinators, which may be important in case of habitat fragmentation leading to pollination disruption. We estimated pollen dispersal and pollinator isolation or sharing between two reproductively isolated genetic lineages of Silene nutans (Caryophyllaceae), which are rare and occur in parapatry in southern Belgium, forming two edaphic ecotypes. As inter-ecotypic crosses may lead to pollen wastage and inviable progeny, pollinator isolation might have evolved between ecotypes. Silene nutans is mainly pollinated by nocturnal moths, including nursery pollinators, which pollinate and lay their eggs in flowers, and whose caterpillars feed on flowers and seeds. Pollinator assemblages of the two ecotypes are largely unknown and inter-ecotypic pollen flows have never been investigated. Fluorescent powdered dyes were used as pollen analogues to quantify intra- and inter-ecotypic pollen transfers and seeds were germinated to detect chlorotic seedlings resulting from inter-ecotypic pollination. Nocturnal pollinators were observed using infrared cameras on the field, and seed-eating caterpillars were collected and reared to identify nursery pollinator species. No pollinator isolation was found: we detected long-distance (up to 5 km) inter-ecotypic dye transfers and chlorotic seedlings, indicating inter-ecotypic fertilization events. The rare moth Hadena albimacula, a nursery pollinator specialized on S. nutans, was found on both ecotypes, as well as adults visiting flowers (cameras recordings) as seed-eating caterpillars. However, S. nutans populations harbor different abundance and diversity of seed predator communities, including other rare nursery pollinators, suggesting a need for distinct conservation strategies. Our findings demonstrate the efficiency of moths, especially of nursery pollinators, to disperse pollen over long distances in natural landscapes, so to ensure gene flow and population sustainability of the host plant. Seed-predator specificities between the two reproductively isolated genetic lineages of S. nutans, and pollinator sharing instead of pollinator isolation when plants occur in parapatry, suggest that conservation of the host plant is also essential for sustaining (rare) pollinator and seed predator communities.

From monocots to dicots: host shifts in Afrotropical derelomine weevils shed light on the evolution of non-obligatory brood pollination mutualism

Weevils from the tribe Derelomini (Curculionidae: Curculioninae) are specialized brood pollinators engaged in mutualistic relationships with several angiosperm lineages. In brood pollination systems, reproductive plant tissues are used for the development of insect larval stages, whereas adult insects pollinate their plant hosts as a reward. The evolutionary history of derelomines in relationship to their hosts is poorly understood and potentially contrasts with other brood pollination systems, wherein a pollinator lineage is usually associated with a single host plant family. In the case of Afrotropical Derelomini, host records indicate a diverse host repertoire consisting of several families of monocot and dicot plants. In this study, we investigate their phylogenetic relationships, timing of diversification and evolution of host use. Our results suggest that derelomine lineages started their diversification ~40 Mya. Reconstructions of host use evolution support an ancestral association with the monocotyledonous palm family (Arecaceae), followed by several shifts towards other plant families in Afrotropical lineages, especially to dicotyledonous plants from the family Ebenaceae (on the genus Euclea L.). Some level of phylogenetic conservatism of host use is recovered for the lineages associated with either palms or Euclea. Multiple instances of sympatric weevil assemblages on the same plant are also unravelled, corresponding to either single or independent colonization events. Overall, the diversity of hosts colonized and the frequency of sympatric assemblages highlighted in non-obligatory plant–derelomine brood pollination systems contrast with what is generally expected from plant–insect brood pollination systems.

Diversity and species-specificity of brood pollination of leafflower trees (Phyllanthaceae: Glochidion) by leafflower moths (Lepidoptera: Epicephala) in tropical Southeast Asia (Cambodia)

Glochidion (Phyllanthaceae; leafflower trees) is a genus of trees which is widely reported to be pollinated by leafflower moths (Gracillariidae: Epicephala) in temperate and subtropical Asia, Australia, and the Pacific islands. However, the pollination ecology of Glochidion is not well described from tropical Asia, the region where it is most species-rich at both local (≤9 spp.) and regional (~200 spp.) scales. Here we report investigations of pollination biology and species-specificity of five Glochidion species in tropical Southeast Asia (Cambodia). Through nocturnal observations and fruit dissections, we find that at least three and likely five Glochidion species in Cambodia are pollinated by seed-parasitic leafflower moths. We find no evidence that any of these leafflower moths are non-mutualistic parasites, despite known examples of such parasites of this mutualism elsewhere in Asia. While the presence of a single larva in a fruit results in only a fraction of seeds being consumed, the presence of more than one larva per fruit-a frequent occurrence in some species-can result in almost all seeds within the fruit being infested. Multilocus phylogenetic analysis indicates that there are five different minimally monophyletic leafflower moth clades, each of which pollinates a unique Glochidion host species. Our results indicate that in its center of diversity in tropical Asia this system is an obligate pollination mutualism as previously described at the global margins of its distribution. These findings provide insights into the processes that generate and maintain biodiversity and maintain mutualism stability in plant-insect interactions in this biodiversity hotspot.

Genome-wide sequence data show no evidence of hybridization and introgression among pollinator wasps associated with a community of Panamanian strangler figs

The specificity of pollinator host choice influences opportunities for reproductive isolation in their host plants. Similarly, host plants can influence opportunities for reproductive isolation in their pollinators. For example, in the fig and fig wasp mutualism, offspring of fig pollinator wasps mate inside the inflorescence that the mothers pollinate. Although often host specific, multiple fig pollinator species are sometimes associated with the same fig species, potentially enabling hybridization between wasp species. Here, we study the 19 pollinator species (Pegoscapus spp.) associated with an entire community of 16 Panamanian strangler fig species (Ficus subgenus Urostigma, section Americanae) to determine whether the previously documented history of pollinator host switching and current host sharing predicts genetic admixture among the pollinator species, as has been observed in their host figs. Specifically, we use genome‐wide ultraconserved element (UCE) loci to estimate phylogenetic relationships and test for hybridization and introgression among the pollinator species. In all cases, we recover well‐delimited pollinator species that contain high interspecific divergence. Even among pairs of pollinator species that currently reproduce within syconia of shared host fig species, we found no evidence of hybridization or introgression. This is in contrast to their host figs, where hybridization and introgression have been detected within this community, and more generally, within figs worldwide. Consistent with general patterns recovered among other obligate pollination mutualisms (e.g. yucca moths and yuccas), our results suggest that while hybridization and introgression are processes operating within the host plants, these processes are relatively unimportant within their associated insect pollinators.

Evolution of antagonistic and mutualistic traits in the yucca-yucca moth obligate pollination mutualism

Species interactions shape the evolution of traits, life histories and the pattern of speciation. What is less clear is whether certain types of species interaction are more or less likely to lead to phenotypic divergence among species. We used the brood pollination mutualism between yuccas and yucca moths to test how mutualistic (pollination) and antagonistic (oviposition) traits differ in the propensity to increase phenotypic divergence among pollinator moths. We measured traits of the tentacular mouthparts, structures used by females to actively pollinate flowers, as well as ovipositor traits to examine differences in the rate of evolution of these two suites of traits among pollinator species. Morphological analyses revealed two distinct groups of moths based on ovipositor morphology, but no such groupings were identified for tentacle morphology, even for moths that pollinated distantly related yuccas. In addition, ovipositor traits evolved at significantly faster rates than tentacular traits. These results support theoretical work suggesting that antagonism is more likely than mutualism to lead to phenotypic divergence.

A new brood-pollination mutualism between Stellera chamaejasme and flower thrips Frankliniella intonsa

BACKGROUND

Brood pollination mutualism is a special type of plant-pollinator interaction in which adult insects pollinate plants, and the plants provide breeding sites for the insects as a reward. To manifest such a mutualism between Stellera chamaejasme and flower thrips of Frankliniella intonsa, the study tested the mutualistic association of the thrips life cycle with the plant flowering phenology and determined the pollination effectiveness of adult thrips and their relative contribution to the host's fitness by experimental pollinator manipulation.

RESULTS

The adult thrips of F. intonsa, along with some long-tongue Lepidoptera, could serve as efficient pollinators of the host S. chamaejasme. The thrips preferentially foraged half-flowering inflorescences of the plants and oviposited in floral tubes. The floral longevity was 11.8 ± 0.55 (mean ± se) days, which might precisely accommodate the thrips life cycle from spawning to prepupation. The exclusion of adult thrips from foraging flowers led to a significant decrease in the fitness (i.e., seed set) of host plants, with a corresponding reduction in thrips fecundity (i.e., larva no.) in the flowers.

CONCLUSIONS

The thrips of F. intonsa and the host S. chamaejasme mutualistically interact to contribute to each other's fitness such that the thrips pollinate host plants and, as a reward, the plants provide the insects with brooding sites and food, indicating the coevolution of the thrips life cycle and the reproductive traits (e.g., floral longevity and morphology) of S. chamaejasme.

Staying in touch: how highly specialised moth pollinators track host plant phenology in unpredictable climates

Background

For specialised pollinators, the synchrony of plant and pollinator life history is critical to the persistence of pollinator populations. This is even more critical in nursery pollination, where pollinators are obligately dependant on female host plant flowers for oviposition sites. Epicephala moths (Gracillariidae) form highly specialised nursery pollination mutualisms with Phyllanthaceae plants. Several hundred Phyllanthaceae are estimated to be exclusively pollinated by highly specific Epicephala moths, making these mutualisms an outstanding example of plant–insect coevolution. However, there have been no studies of how Epicephala moths synchronise their activity with host plant flowering or persist through periods when flowers are absent. Such knowledge is critical to understanding the ecology and evolutionary stability of these mutualisms. We surveyed multiple populations of both Breynia oblongifolia (Phyllanthaceae) and it’s Epicephala pollinators for over two years to determine their phenology and modelled the environmental factors that underpin their interactions.

Results

The abundance of flowers and fruits was highly variable and strongly linked to local rainfall and photoperiod. Unlike male flowers and fruits, female flowers were present throughout the entire year, including winter. Fruit abundance was a significant predictor of adult Epicephala activity, suggesting that eggs or early instar larvae diapause within dormant female flowers and emerge as fruits mature. Searches of overwintering female flowers confirmed that many contained pollen and diapausing pollinators. We also observed diapause in Epicephala prior to pupation, finding that 12% (9/78) of larvae emerging from fruits in the autumn entered an extended diapause for 38–48 weeks. The remaining autumn emerging larvae pupated directly without diapause, suggesting a possible bet-hedging strategy.

Conclusions

Epicephala appear to use diapause at multiple stages in their lifecycle to survive variable host plant phenology. Furthermore, moth abundance was predicted by the same environmental variables as male flowers, suggesting that moths track flowering through temperature. These adaptations may thereby mitigate against unpredictability in the timing of fruiting and flowering because of variable rainfall. It remains to be seen how widespread egg diapause and pre-pupal diapause may be within Epicephala moths, and, furthermore, to what degree these traits may have facilitated the evolution of these highly diverse mutualisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01889-4.

Unique chemistry associated with diversification in a tightly coupled cycad-thrips obligate pollination mutualism

Cycad cone thermogenesis and its associated volatiles are intimately involved in mediating the behavior of their obligate specialist pollinators. In eastern Australia, thrips in the Cycadothrips chadwicki species complex are the sole pollinators of many Macrozamia cycads. Further, they feed and reproduce entirely in the pollen cones. M. miquelii, found only in the northern range of this genus, is pollinated only by a C. chadwicki cryptic species that is the most distantly related to others in the complex. We examined the volatile profile from M. miquelii pollen and ovulate (receptive and non-receptive) cones to determine how this mediates pollination mechanistically, using GC-MS (gas chromatography-mass spectrometry) and behavioral tests. Monoterpenes comprise the bulk of M. miquelii volatile emissions, as in other Macrozamia species, but we also identified compounds not reported previously in any cycad, including three aliphatic esters (prenyl acetate and two of uncertain identity) and two aliphatic alcohols. The two unknown esters were confirmed as prenyl (3-methylbut-2-enyl) esters of butyric and crotonic ((E))-but-2-enoic) acids after chemical synthesis. Prenyl crotonate is a major component in emissions from pollen and receptive ovulate cones, is essentially absent from non-receptive cones, and has not been reported from any other natural source. In field bioassays, Cycadothrips were attracted only to those volatile treatments containing prenyl crotonate. We discuss M. miquelii cone odorants relative to those of other cycads, especially with respect to prenyl crotonate being a species-specific signal to this northern C. chadwicki cryptic species, and how this system may have diversified.

Why are there not more herbivorous insect species?

Insect species richness is estimated to exceed three million species, of which roughly half is herbivorous. Despite the vast number of species and varied life histories, the proportion of herbivorous species among plant-consuming organisms is lower than it could be due to constraints that impose limits to their diversification. These include ecological factors, such as vague interspecific competition; anatomical and physiological limits, such as neural limits and inability of handling a wide range of plant allelochemicals; phylogenetic constraints, like niche conservatism; and most importantly, a low level of concerted genetic variation necessary to a phyletic conversion. It is suggested that diversification ultimately depends on what we call the intrinsic trend of diversification of the insect genome. In support of the above, we survey the major types of host-specificity, the mechanisms and constraints of host specialization, possible pathways of speciation, and hypotheses concerning insect diversification.

Evaluating insect-host interactions as a driver of species divergence in palm flower weevils

Plants and their specialized flower visitors provide valuable insights into the evolutionary consequences of species interactions. In particular, antagonistic interactions between insects and plants have often been invoked as a major driver of diversification. Here we use a tropical community of palms and their specialized insect flower visitors to test whether antagonisms lead to higher population divergence. Interactions between palms and the insects visiting their flowers range from brood pollination to florivory and commensalism, with the latter being species that feed on decaying-and presumably undefended-plant tissues. We test the role of insect-host interactions in the early stages of diversification of nine species of beetles sharing host plants and geographical ranges by first delimiting cryptic species and then using models of genetic isolation by environment. The degree to which insect populations are structured by the genetic divergence of plant populations varies. A hierarchical model reveals that this variation is largely uncorrelated with the kind of interaction, showing that antagonistic interactions are not associated with higher genetic differentiation. Other aspects of host use that affect plant-associated insects regardless of the outcomes of their interactions, such as sensory biases, are likely more general drivers of insect population divergence.

Morphological and Molecular Perspectives on the Phylogeny, Evolution, and Classification of Weevils (Coleoptera: Curculionoidea): Proceedings from the 2016 International Weevil Meeting

The 2016 International Weevil Meeting was held immediately after the International Congress of Entomology (ICE). It built on the topics and content of the 2016 ICE weevil symposium Phylogeny and Evolution of Weevils (Coleoptera: Curculionoidea): A Symposium in Honor of Dr. Guillermo "Willy” Kuschel. Beyond catalyzing research and collaboration, the meeting was intended to serve as a forum for identifying priorities and goals for those who study weevils. The meeting consisted of 46 invited and contributed lectures, discussion sessions and introductory remarks presented by 23 speakers along with eight contributed research posters. These were organized into three convened sessions, each lasting one day: (1) weevil morphology; (2) weevil fossils, biogeography and host/habitat associations; and (3) molecular phylogenetics and classification of weevils. Some of the topics covered included the 1K Weevils Project, major morphological character systems of adult and larval weevils, weevil morphological terminology, prospects for future morphological character discovery, phylogenetic analysis of morphological character data, the current status of weevil molecular phylogenetics and evolution, resources available for phylogenetic and comparative genomic studies of weevils, the weevil fossil record, weevil biogeography and evolution, weevil host plants, evolutionary development of the weevil rostrum, resources available for weevil identification and the current status of and challenges in weevil classification.

Co-niche construction between hosts and symbionts: ideas and evidence

Symbiosis is a process that can generate evolutionary novelties and can extend the phenotypic niche space of organisms. Symbionts can act together with their hosts to co-construct host organs, within which symbionts are housed. Once established within hosts, symbionts can also influence various aspects of host phenotype, such as resource acquisition, protection from predation by acquisition of toxicity, as well as behaviour. Once symbiosis is established, its fidelity between generations must be ensured. Hosts evolve various mechanisms to screen unwanted symbionts and to facilitate faithful transmission of mutualistic partners between generations. Microbes are the most important symbionts that have influenced plant and animal phenotypes; multicellular organisms engage in developmental symbioses with microbes at many stages in ontogeny. The co-construction of niches may result in composite organisms that are physically nested within each other. While it has been advocated that these composite organisms need new evolutionary theories and perspectives to describe their properties and evolutionary trajectories, it appears that standard evolutionary theories are adequate to explore selection pressures on their composite or individual traits. Recent advances in our understanding of composite organisms open up many important questions regarding the stability and transmission of these units.

Using niche breadth theory to explain generalization in mutualisms

For a mutualism to remain evolutionarily stable, theory predicts that mutualists should limit their associations to high-quality partners. However, most mutualists either simultaneously or sequentially associate with multiple partners that confer the same type of reward. By viewing mutualisms through the lens of niche breadth evolution, we outline how the environment shapes partner availability and relative quality, and ultimately a focal mutualist's partner breadth. We argue that mutualists that associate with multiple partners may have a selective advantage compared to specialists for many reasons, including sampling, complementarity, and portfolio effects, as well as the possibility that broad partner breadth increases breadth along other niche axes. Furthermore, selection for narrow partner breadth is unlikely to be strong when the environment erodes variation in partner quality, reduces the costs of interacting with low-quality partners, spatially structures partner communities, or decreases the strength of mutualism. Thus, we should not be surprised that most mutualists have broad partner breadth, even if it allows for ineffective partners to persist.

Biogeography of mutualistic fungi cultivated by leafcutter ants

Leafcutter ants propagate co-evolving fungi for food. The nearly 50 species of leafcutter ants (Atta, Acromyrmex) range from Argentina to the United States, with the greatest species diversity in southern South America. We elucidate the biogeography of fungi cultivated by leafcutter ants using DNA sequence and microsatellite-marker analyses of 474 cultivars collected across the leafcutter range. Fungal cultivars belong to two clades (Clade-A and Clade-B). The dominant and widespread Clade-A cultivars form three genotype clusters, with their relative prevalence corresponding to southern South America, northern South America, Central and North America. Admixture between Clade-A populations supports genetic exchange within a single species, Leucocoprinus gongylophorus. Some leafcutter species that cut grass as fungicultural substrate are specialized to cultivate Clade-B fungi, whereas leafcutters preferring dicot plants appear specialized on Clade-A fungi. Cultivar sharing between sympatric leafcutter species occurs frequently such that cultivars of Atta are not distinct from those of Acromyrmex. Leafcutters specialized on Clade-B fungi occur only in South America. Diversity of Clade-A fungi is greatest in South America, but minimal in Central and North America. Maximum cultivar diversity in South America is predicted by the Kusnezov-Fowler hypothesis that leafcutter ants originated in subtropical South America and only dicot-specialized leafcutter ants migrated out of South America, but the cultivar diversity becomes also compatible with a recently proposed hypothesis of a Central American origin by postulating that leafcutter ants acquired novel cultivars many times from other nonleafcutter fungus-growing ants during their migrations from Central America across South America. We evaluate these biogeographic hypotheses in the light of estimated dates for the origins of leafcutter ants and their cultivars.

Coevolution with pollinating resin midges led to resin-filled nurseries in the androecia, gynoecia and tepals of Kadsura (Schisandraceae)

Background and Aims

Resin is a defence against herbivores and a floral reward in a few African and South American species whose bee pollinators collect it for nest construction. Here we describe a new role for floral resin from the Asian genus Kadsura (Schisandraceae). Kadsura tepals tightly cover a globe formed by carpels (in females) or near-fused stamens with fleshy connectives (in male flowers of most, but not all species).

Methods

We carried out field observations at four sites in China and used pollinator behavioural assays, chemical analyses and time-calibrated insect and plant phylogenies to investigate the specificity of the interactions and their relationship to floral structure.

Key Results

Nocturnal resin midges ( Resseliella , Cecidomyiidae) walk around on the flowers' sexual organs to oviposit, thereby transferring pollen and wounding tissues. The larvae then develop in resin-filled chambers. Male and female floral scents are dominated by α-pinene, while the resinous exudate is dominated by caryophyllene. As revealed by barcoding of multiple midge larvae per flower species, the mutualisms are species specific and appear to have evolved over the past 6-9 million years.

Conclusions

Resin feeding, not pollen or ovule feeding, by midge larvae explains the abundant Kadsura exudates, highlighting the poorly known world of nocturnal flower-fly interactions.

A Novel, Enigmatic Basal Leafflower Moth Lineage Pollinating a Derived Leafflower Host Illustrates the Dynamics of Host Shifts, Partner Replacement, and Apparent Coadaptation in Intimate Mutualisms

Leafflower plant/leafflower moth brood pollination mutualisms are widespread in the Paleotropics. Leafflower moths pollinate leafflower plants, but their larvae consume a subset of the hosts' seeds. These interactions are highly phylogenetically constrained: six clades of leafflower plants are each associated with a unique clade of leafflower moths (Epicephala). Here, we report a previously unrecognized basal seventh pollinating Epicephala lineage-associated with the highly derived leafflower clade Glochidion-in Asia. Epicephala lanceolaria is a pollinator and seed predator of Glochidion lanceolarium. Phylogenetic inference indicates that the ancestor of E. lanceolaria most likely shifted onto the ancestor of G. lanceolarium and displaced the ancestral allospecific Epicephala pollinator in at least some host populations. The unusual and apparently coadapted aspects of the G. lanceolarium/E. lanceolaria reproductive cycles suggest that plant-pollinator coevolution may have played a role in this displacement and provide insights into the dynamics of host shifts and trait coevolution in this specialized mutualism.