Protection Mutualisms and the Community: Geographic Variation in an Ant-Plant Symbiosis and the Consequences for Herbivores

Protection mutualisms mediate trophic interactions in many systems, but their effects on the surrounding community are rarely studied. Ant-plant symbioses are classic examples of protection mutualisms: myrmecophytic plants provide nesting space and food for symbiotic ants in exchange for ant defense. Ant defense should thus reduce the abundance of herbivores, but studies of ant-plant symbioses usually measure damage to the plant without quantifying the herbivores themselves. In this study, we investigated whether geographic variation in the quality of ant defense in a symbiotic mutualism between Cordia alliodora trees and Azteca ants was associated with the abundance and species richness of plant herbivore communities. In three tropical-dry-forest sites in Middle America, we found that the density of Azteca ants within trees was negatively associated with the levels of leaf herbivory. At sites where ants were effective tree defenders, tree herbivores were less abundant and herbivore assemblages on trees exhibited lower species richness than at a site where ants were poor defenders. In addition, in a site where ants reduced herbivory, herbivore communities were less abundant and diverse in the presence of ants than in their absence, where as in a site where ants did not reduce herbivory, there were no differences in herbivore abundance or richness between trees with or without ants. We conclude that geographic variation in the quality of ant defense drives variation in myrmecophytic-plant herbivore communities. Moreover, ant-plant protection mutualisms should have important but rarely considered effects on herbivore population dynamics and food-plant specialization

Orthogonal fitness benefits of nitrogen and ants for nitrogen‐limited plants in the presence of herbivores

Predictable effects of resource availability on plant growth‐defense strategies provide a unifying theme in theories of direct anti‐herbivore defense, but it is less clear how resource availability modulates plant indirect defense. Ant‐plant‐hemipteran interactions produce mutualistic trophic cascades when hemipteran‐tending ants reduce total herbivory, and these interactions are a key component of plant indirect defense in most terrestrial ecosystems. Here we conducted an experiment to test how ant‐plant‐hemipteran interactions depend on nitrogen (N) availability by manipulating the presence of ants and aphids under different N fertilization treatments. Ants increased plant flowering success by decreasing the densities of herbivores, and the effects of ants on folivores were positively related to the density of aphids. Unexpectedly, N fertilization produced no changes in plant N concentrations. Plants grown in higher N grew and flowered more, but aphid honeydew chemistry stayed the same, and neither the density of aphids nor the rate of ant attraction per aphid changed with N addition. The positive effects of ants and N addition on plant fitness were thus independent of one another. We conclude that N was the plant’s limiting nutrient and propose that addition of the limiting nutrient is unlikely to alter the strength of mutualistic trophic cascades.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/1/ecy2013_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/2/ecy2013-sup-0002-AppendixS2.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/3/ecy2013-sup-0003-AppendixS3.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/4/ecy2013-sup-0001-AppendixS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/5/ecy2013-sup-0006-AppendixS6.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/6/ecy2013.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/7/ecy2013-sup-0007-AppendixS7.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/8/ecy2013-sup-0004-AppendixS4.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139927/9/ecy2013-sup-0005-AppendixS5.pd

Plant‐derived differences in the composition of aphid honeydew and their effects on colonies of aphid‐tending ants

In plant–ant–hemipteran interactions, ants visit plants to consume the honeydew produced by phloem‐feeding hemipterans. If genetically based differences in plant phloem chemistry change the chemical composition of hemipteran honeydew, then the plant's genetic constitution could have indirect effects on ants via the hemipterans. If such effects change ant behavior, they could feed back to affect the plant itself. We compared the chemical composition of honeydews produced by Aphis nerii aphid clones on two milkweed congeners, Asclepias curassavica and Asclepias incarnata , and we measured the responses of experimental Linepithema humile ant colonies to these honeydews. The compositions of secondary metabolites, sugars, and amino acids differed significantly in the honeydews from the two plant species. Ant colonies feeding on honeydew derived from A. incarnata recruited in higher numbers to artificial diet, maintained higher queen and worker dry weight, and sustained marginally more workers than ants feeding on honeydew derived from A. curassavica . Ants feeding on honeydew from A. incarnata were also more exploratory in behavioral assays than ants feeding from A. curassavica . Despite performing better when feeding on the A. incarnata honeydew, ant workers marginally preferred honeydew from A. curassavica to honeydew from A. incarnata when given a choice. Our results demonstrate that plant congeners can exert strong indirect effects on ant colonies by means of plant‐species‐specific differences in aphid honeydew chemistry. Moreover, these effects changed ant behavior and thus could feed back to affect plant performance in the field. The role of indirect effects in trait evolution remains poorly understood. We show that plant chemical traits indirectly affect ant colony fitness and behavior via direct interactions with aphids. These plant‐derived effects on ant behavior could feed back to affect plant fitness in the field.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109587/1/ece31277.pd

Water Stress Strengthens Mutualism Among Ants, Trees, and Scale Insects

Abiotic environmental variables strongly affect the outcomes of species interactions. For example, mutualistic interactions between species are often stronger when resources are limited. The effect might be indirect: water stress on plants can lead to carbon stress, which could alter carbon-mediated plant mutualisms. In mutualistic ant–plant symbioses, plants host ant colonies that defend them against herbivores. Here we show that the partners\u27 investments in a widespread ant–plant symbiosis increase with water stress across 26 sites along a Mesoamerican precipitation gradient. At lower precipitation levels, Cordia alliodora trees invest more carbon in Azteca ants via phloem-feeding scale insects that provide the ants with sugars, and the ants provide better defense of the carbon-producing leaves. Under water stress, the trees have smaller carbon pools. A model of the carbon trade-offs for the mutualistic partners shows that the observed strategies can arise from the carbon costs of rare but extreme events of herbivory in the rainy season. Thus, water limitation, together with the risk of herbivory, increases the strength of a carbon-based mutualism

The Power of Feminist Judgments?

Recent years have seen the advent of two feminist judgment-writing projects, the Women’s Court of Canada, and the Feminist Judgments Project in England. This article analyses these projects in light of Carol Smart’s feminist critique of law and legal reform and her proposed feminist strategies in Feminism and the Power of Law (1989). At the same time, it reflects on Smart’s arguments 20 years after their first publication and considers the extent to which feminist judgment-writing projects may reinforce or trouble her conclusions. It argues that both of these results are discernible—that while some of Smart’s contentions have proved to be unsustainable, others remain salient and have both inspired and hold important cautions for feminist judgment-writing projects

Case Report Bilateral Vocal Cord Paralysis and Cervicolumbar Radiculopathy as the Presenting Paraneoplastic Manifestations of Small Cell Lung Cancer: A Case Report and Literature Review

Introduction. Bilateral vocal cord paralysis (BVCP) is a potential medical emergency. The Otolaryngologist plays a crucial role in the diagnosis and management of BVCP and must consider a broad differential diagnosis. We present a rare case of BVCP secondary to anti-Hu paraneoplastic syndrome. Case Presentation. A 58-year-old female presented to an Otolaryngology clinic with a history of progressive hoarseness and dysphagia. Flexible nasolaryngoscopy demonstrated BVCP. Cross-sectional imaging of the brain and vagus nerves was negative. An antiparaneoplastic antibody panel was positive for anti-Hu antibodies. This led to an endobronchial biopsy of a paratracheal lymph node, which confirmed the diagnosis of small cell lung cancer. Conclusion. Paraneoplastic neuropathy is a rare cause of BVCP and should be considered when more common pathologies are ruled out. This is the second reported case of BVCP as a presenting symptom of paraneoplastic syndrome secondary to small cell lung cancer

Detection and diversity of a putative novel heterogeneous polymorphic proline-glycine repeat (Pgr) protein in the footrot pathogen Dichelobacter nodosus

Dichelobacter nodosus, a Gram-negative anaerobic bacterium, is the essential causative agent of footrot in sheep. Currently, depending on the clinical presentation in the field, footrot is described as benign or virulent; D. nodosus strains have also been classified as benign or virulent, but this designation is not always consistent with clinical disease. The aim of this study was to determine the diversity of the pgr gene, which encodes a putative proline-glycine repeat protein (Pgr). The pgr gene was present in all 100 isolates of D. nodosus that were examined and, based on sequence analysis had two variants, pgrA and pgrB. In pgrA, there were two coding tandem repeat regions, R1 and R2: different strains had variable numbers of repeats within these regions. The R1 and R2 were absent from pgrB. Both variants were present in strains from Australia, Sweden and the UK, however, only pgrB was detected in isolates from Western Australia. The pgrA gene was detected in D. nodosus from tissue samples from two flocks in the UK with virulent footrot and only pgrB from a flock with no virulent or benign footrot for >10 years. Bioinformatic analysis of the putative PgrA protein indicated that it contained a collagen-like cell surface anchor motif. These results suggest that the pgr gene may be a useful molecular marker for epidemiological studies

Integrating plant carbon dynamics with mutualism ecology

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138937/1/nph13679.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138937/2/nph13679_am.pd

Changes in tree community structure in defaunated forests are not driven only by dispersal limitation

Bushmeat hunting has reduced population sizes of large frugivorous vertebrates throughout the tropics, thereby reducing the dispersal of seeds. This is believed to affect tree population dynamics, and therefore community composition, because the seed dispersal of large-seeded trees depends upon large-bodied vertebrates.We report on a long-running study of the effect of defaunation on a tropical tree community. In three censuses over 11 years, we compared sapling recruitment between a hunted and a nonhunted site, which are nearby and comparable to one another, to determine the extent to which species composition has changed through time following defaunation. We expected to find a reduced abundance of tree species that rely on large frugivores for dispersal at the hunted site and altered community structure as a consequence.Although community composition at the hunted site diverged from that at the nonhunted site, the changes were independent of dispersal syndrome, with no trend toward a decline in species that are dispersed by large, hunted vertebrates. Moreover, the loss of large-bodied dispersers did not generate the changes in tree community composition that we hypothesized. Some species presumed to rely on large-bodied frugivores for dispersal are effectively recruiting despite the absence of their dispersers.Synthesis: The presumption that forests depleted of large-bodied dispersers will experience rapid, directional compositional change is not fully supported by our results. Altered species composition in the sapling layer at the hunted site, however, indicates that defaunation may be connected with changes to the tree community, but that the nature of these changes is not unidirectional as previously assumed. It remains difficult to predict how defaunation will affect tree community composition without a deeper understanding of the driving mechanisms at play

Tree recruitment in an empty forest

To assess how the decimation of large vertebrates by hunting alters recruitment processes in a tropical forest, we compared the sapling cohorts of two structurally and compositionally similar forests in the Rio Manu floodplain in southeastern Peru. Large vertebrates were severely depleted at one site, Boca Manu (BM), whereas the other, Cocha Cashu Biological Station (CC), supported an intact fauna. At both sites we sampled small (1 m tall, ,1 cm dbh) and large (1 cm and ,10 cm dbh) saplings in the central portion of 4-ha plots within which all trees 10 cm dbh were mapped and identified. This design ensured that all conspecific adults within at least 50 m (BM) or 55 m (CC) of any sapling would have known locations. We used the Janzen-Connell model to make five predictions about the sapling cohorts at BM with respect to CC: (1) reduced overall sapling recruitment, (2) increased recruitment of species dispersed by abiotic means, (3) altered relative abundances of species, (4) prominence of large-seeded species among those showing depressed recruitment, and (5) little or no tendency for saplings to cluster closer to adults at BM. Our results affirmed each of these predictions. Interpreted at face value, the evidence suggests that few species are demographically stable at BM and that up to 28% are increasing and 72% decreasing. Loss of dispersal function allows species dispersed abiotically and by small birds and mammals to substitute for those dispersed by large birds and mammals. Although we regard these conclusions as preliminary, over the long run, the observed type of directional change in tree composition is likely to result in biodiversity loss and negative feedbacks on both the animal and plant communities. Our results suggest that the best, and perhaps only, way to prevent compositional change and probable loss of diversity in tropical tree communities is to prohibit hunting