Mutualisms and Parasitisms

A new host record for Philornis (Diptera, Muscidae)

by Ismael Franz

Mutualism variation in the nodulation response to nitrate

by Amanda Stock

Ecología y evolución de interacciones planta-animal

by Rodrigo Medel

Edited by R. Medel,M. Aizen & R. Zamora. Editorial Universitaria. 399 pp. Spanish

Ecology and evolution of negative and positive interactions in Cactaceae: lessons and pending tasks

by Pablo Guerrero

Interactions Between Gall Midges (Diptera: Cecidomyiidae) and Inflorescences of Piper novae-hollandiae (Piperaceae) In Australia

by Jeff Ollerton

Biased oviposition and biased survival together help resolve a fig-wasp conflict

by Douglas Yu

Hui Wang, Jo Ridley, Derek W. Dunn, Ruiwu Wang, James M. Cook, Douglas W. Yu. Manuscript

We report evidence that helps to resolve competing explanations for stability in the classic fig-wasp mutualism. Fig... more We report evidence that helps to resolve competing explanations for stability in the classic fig-wasp mutualism. Fig trees are pollinated by wasps that lay their eggs in the tree’s ovules. Each wasp larva then develops at the expense of a fig seed. Upon maturity, the female wasps collect pollen and disperse to a new tree, continuing the cycle. Fig fitness is increased by producing both seeds and wasps, whereas short-term wasp fitness increases only with more wasps, thereby leading to a conflict of interests. We show experimentally that wasps exploit the inner layers of ovules first (biased oviposition), which is consistent with optimal-foraging theory. As oviposition increases, seeds in the middle layer are replaced on a one-to-one basis by pollinator offspring. Finally, in the outer layer of ovules, seeds disappear but are only partially replaced by pollinator offspring, which suggests high wasp mortality, perhaps due to plant defences (biased survival). We propose that selection to increase growth rate in inner ovules trades off against survivorship in outer ovules, and since there are more wasp offspring in inner ovules, biased survival is maintained. Our results suggest that both biased oviposition and biased survivorship ensure seed production in figs, thereby stabilising the mutualism. Finally, we report evidence suggesting that fig trees direct more resources to figs with more seeds, and this may help balance seed and wasp production at the level of the tree. Because an equal allocation would appear to favour the fig’s interests, the fig appears to be in control of the mutualism.

How to assemble a beneficial microbiome in three easy steps

by Douglas Yu

Istvan Scheuring and Douglas W. Yu. Manuscript.

There is great interest in explaining how beneficial microbiomes are assembled. An exemplar is the attine ants, which... more There is great interest in explaining how beneficial microbiomes are assembled. An exemplar is the attine ants, which cultivate a fungal garden for food and also host a cuticular microbiome that releases antibiotics to defend the garden from parasites. One explanation posits long-term vertical transmission of Pseudonocardia bacteria, which (somehow) continuously evolve compounds in arms-race fashion against parasites. Alternatively, attines are argued to selectively take up (somehow) multiple, non-coevolved actinobacterial genera from the soil, enabling a multi-drug strategy against parasites. We reconcile these two explanations by showing that when hosts provide high resource levels, interference competition is fuelled, and the recruitment of antibiotic-producing (and resistant) bacteria is thereby favored. This partner-choice mechanism is more likely to work if at least one actinobacterial symbiont is vertically transmitted or has a high immigration rate, providing a key role for Pseudonocardia in the attine symbiosis. Our model can also apply to the very wide range of hosts that house antibiotic-producing microbes, including vertebrates, mollusks, arthropods, corals, and plant rhizospheres.

Arms Race Coevolution: The Local and Geographical Structure of a Host–Parasite Interaction

by Rodrigo Medel

Co-authored with M.A. Mendez, C.G. Ossa & C. Botto-Mahan
Evolution Education & Outreach 2910.

Consideration of complex geographic patterns of mreciprocal adaptation has provided insight into new features of the... more Consideration of complex geographic patterns of mreciprocal adaptation has provided insight into new features of the coevolutionary process. In this paper, we provide mecological, historical, and geographical evidence for coevolution under complex temporal and spatial scenarios that include intermittent selection, species turnover across localities, and a range of trait match/mismatch across populations. Our study focuses on a plant host–parasitic plant interaction endemic to arid and semiarid regions of Chile. The long spines of Chilean cacti have been suggested to evolve under parasite-mediated selection as a first line of defense against the mistletoe Tristerix aphyllus. The mistletoe, in turn, has evolved an extremely long morphological structure that emerges from the seed endosperm (radicle) to reach the host cuticle. When spine length was traced along cactus phylogenies, a significant association between spine length and parasitism was detected, indicating that defensive traits evolved in high correspondence with the presence or absence of parasitism in two cactus lineages. Assessment of spine-radicle matching across populations revealed a potential for coevolution in 50% of interaction pairs. Interestingly, hot spots for coevolution did not distribute at random across sites. On the contrary, interaction pairs showing high matching values occur mostly in the northern distribution of the interaction, suggesting a geographical structure for coevolution in this system. Only three sampled interaction pairs were so mismatched that reciprocal selection could not occur given current trait distributions. Overall, different lines of evidence indicate that arms-race coevolution is an ongoing phenomenon that occurs in the global system of interconnected populations.

Ecology and evolution of negative and positive interactions in Cactaceae: lessons and pending tasks

by Rodrigo Medel

Plant Ecology & Diversity 4: 1-11. 2011
Co-authored with Pablo C. Guerrero, Gastón O. Carvallo, Jafet M. Nassar, Julissa Rojas-Sandoval & Virginia Sanz

The Cactaceae is a diverse and conspicuous Neotropical family that has evolved a wide variety of adaptations during... more The Cactaceae is a diverse and conspicuous Neotropical family that has evolved a wide variety of adaptations during co-evolution with their interacting species. Recent research has indicated complex ecological and evolutionary interactions involving cacti and other organisms. In the framework provided by ecological interactions theory we show four case studies involving cacti: (1) the evolutionary ecology of a mistletoe–cactus parasitism in central Chile; (2) the effect of an exotic grass on the demography of a threatened cactus in Puerto Rico; (3) the herpetochory in the genus Melocactus in Venezuela; and (4) the
role of abiotic and biotic factors on the floral morphology in eight cacti in northern Chile. In addition, we highlight some key aspects that might be useful as guidelines and recommendations for structuring future research and collaborative efforts in cactus biology research; these are related to the development of a cactus interaction database that integrates published information; in invasion biology, aspects that account for eventual detrimental effects of invasive species to cactus diversity; and the role of multi-species interactions such as pollination, seed dispersal and nurse plant associations for the maintenance of cacti and the ecosystem services that they provide.

Olfactive detection of fig wasps as prey by the ant Crematogaster scutellaris (Formicidae; Myrmicinae)

by Welmoed Out

2003, Naturwissenschaften 90 (10), 456-459

In the species-specific and obligate mutualism between the fig (Ficus carica) and its pollinator (the fig wasps... more In the species-specific and obligate mutualism between the fig (Ficus carica) and its pollinator (the fig wasps Blastophaga psenes), a third participant, the ant Crematogaster scutellaris, is a predator of the wasps. Here, we ask how ant workers can rapidly localise such prey, whose availability is limited in time and space. Using a Y-tube olfactometer, we tested ant response to odours emitted by different types of figs (receptive female, ripe female or male figs) and by fig wasps (pollinators or non-pollinators). We demonstrate that ants were significantly attracted only to odours emitted by pollinators, either alone or associated with odours of male figs (releasing wasps). Detection of prey odour by ants is an important trait that can explain their observed high rate of predation on pollinators, and could have important implications on the stability of the fig/fig wasp mutualism.

Effects of vector behavior and host resistance on mistletoe aggregation

by Rodrigo Medel

Co-authored with E. Vergara, A. Silva & M. Kalin
Ecology 2004

Understanding the factors affecting parasite aggregation in natural host populations is one of the central questions... more Understanding the factors affecting parasite aggregation in natural host populations is one of the central questions in parasite ecology. While different biological mechanisms giving rise to aggregation have been documented in the literature, the role of established parasites in vector attraction, and its importance in determining clumped parasite distributions has received less attention. In a two-year field study, we evaluated the importance of a bird vector, Mimus thenca (Mimidae), on the aggregation dynamics of the holoparasitic mistletoe, Tristerix aphyllus, on its cactus host, Echinopsis chilensis. Removal
of T. aphyllus from cacti decreased the number of visits and the time spent by the bird vector, which resulted in a 3.5-fold lower seed deposition of the mistletoe on experimental hosts than on control hosts. Vector preference, however, was not the only factor affecting aggregation in this system. Spine length of the cactus acted as a first line of defense against parasitism, by discouraging bird perching on top of host columns. While heavily parasitized hosts received more seeds than unparasitized hosts, spines counteracted this effect. These results provide field evidence that parasite aggregation results from the balance between vector behavior and host resistance traits.

Spatiotemporal dynamics in variable population interactions with density-dependent interaction coefficients

by Maria-Josefina (chepina) Hernandez

Dynamics of transitions between population interactions: a nonlinear interaction alpha-function defined

by Maria-Josefina (chepina) Hernandez

Variation in the outcome of population interactions: bifurcations and catastrophes

by Maria-Josefina (chepina) Hernandez

Disentangling nature, strength and stability issues in the characterization of population interactions

by Maria-Josefina (chepina) Hernandez

Disentangling nature, strength and stability issues in the characterization of population interactions

by Maria-Josefina (chepina) Hernandez

Overcompensation by plants: herbivore optimization or red herring?

by Gordon Fox

Seed dispersers as disease vectors: bird transmission of mistletoes seeds to plant hosts

by Rodrigo Medel

Co-authored with C. Martinez del Rio, A. Silva and M. Hourdequin
Ecology. 1996.

The relationship between mistletoes and birds has been studied from the perspectives of mutualism and seed dispersal.... more The relationship between mistletoes and birds has been studied from the perspectives of mutualism and seed dispersal. Here, we emphasize the role that avian dispersers play as agents of mistletoe seed transmission to plant hosts. We describe the patterns of transmission of the seeds of Tristerix aphyllus, an endophytic Chilean mistletoe, on two of its columnar cacti hosts (Eulychnia acida and Echinopsis skottsbergii) by the Chilean Mockingbird Mimus thenca. In north-central Chile, these cacti grow in relatively discrete subpopulations on north-facing slopes. We measured variation in seed transmission within 10 subpopulations varying in species composition, host density, parasite density, parasite prevalence (defined as the percentage of hosts infested in a given population), and disperser abundance. Seed transmission was independent of species, but was strongly de- pendent on prior parasitism. Parasitized individuals received seeds much more frequently than expected from their relative abundance. We found no correlation between the density of hosts and seed transmission. We found strong positive correlations, however, between parasite prevalence and seed transmission to both parasitized and nonparasitized hosts. Seed transmission of T. aphyllus seeds by M. thenca appeared to be frequency- rather than density- dependent. Seed transmission was also tightly and positively correlated with the abundance of seed-dispersing birds at each site. Because bird abundance and parasite prevalence were correlated, we conducted path analysis to disentangle their relative effect on seed trans- mission. A model including only the direct effect of bird abundance and the indirect effect of parasite prevalence through bird abundance explained roughly the same variance as a full model including both the direct and indirect effects of bird abundance and prevalence on seed transmission. Apparently, variation in bird abundance was the main determinant of variation in transmission. We suggest that mistletoes, host plants, and the birds that disperse mistletoe seeds are systems well suited for studies of the ecological and evolu- tionary dynamics of disease transmission.

Floral herbivory affects female reproductive success and pollinator visitation in the perennial herb Alstroemeria ligtu (Alstroemeriaceae)

by Rodrigo Medel

Co-authored with C. Botto-Mahan, P.A. Ramirez, C.G. Ossa,
M. Ojeda-Camacho & A.V. Gonzalez
International Journal of Plant Sciences. 2011.

Floral damage can reduce flower attractiveness for pollinator service. However, the reproductive impact of flower... more Floral damage can reduce flower attractiveness for pollinator service. However, the reproductive impact of flower herbivory may be contingent on a petal that is damaged. Flowers having nectar guides are expected to suffer reduction in reproductive success when damage is concentrated on these structures compared to petals less involved in pollinator attraction. In this study, we recorded the reflectance pattern of distinctive yellow
tepals of Alstroemeria ligtu and examined their functional role for pollinator attraction and reproductive success.We quantified the richness and abundance of pollinator species attracted to flowers and estimated fruit set and seed production in flowers subject to (1) nectar guide removal, (2) lateral red tepal removal, and (3) unmanipulated flowers. Results indicate that nectar guide removal reduced pollinator visitation rate but did not affect community-level descriptors such as pollinator species richness and flower diversity. The reduction in visitation rate translated into a reduced fruit set and seed production, hence confirming that nectar guides have a clear functional role in the pollination process. We conclude that the location where damage occurs is a relevant factor for pollinator attraction and subsequent reproductive success in this species, suggesting that nectar guide damage may disrupt fine-tuned plant-pollinator communication systems.

Pollinator-mediated selection on the nectar guide phenotype in the Andean monkey flower, Mimulus luteus

by Rodrigo Medel

Co-authored with C. Botto-Mahan and M.T. Kalin-Arroyo
Ecology. 2003.

Mimulus luteus (Scrophulariaceae) is a perennial herb occurring in the South American Andes that shows a wide... more Mimulus luteus (Scrophulariaceae) is a perennial herb occurring in the South American Andes that shows a wide variation in the size and shape of a red spot on the lower lobe of the yellow flower. We describe the preference of four insects (three bees and one butterfly) and one hummingbird species for floral characters, and estimated the strength, direction, and form of pollinator-mediated selection through female fitness. We applied geometric morphometrics to describe the preference of pollinator species for different guide shapes. Our results revealed striking differences in the floral phenotypes preferred by insects and hummingbirds. Insects visited flowers with corollas 1.25-fold larger and guides 1.72-fold larger than the hummingbird species did. While insects preferred flowers with nectar guides pointing toward the corolla tube, the hummingbird preferred flowers with heartshaped nectar guides. Most of the floral preferences shown by pollinators translated into significant linear and nonlinear selection coefficients. When selection was analyzed on a per-flower basis and for female fitness, corolla size was under positive directional selection, and nectar guide size and shape were under disruptive selection. Because the insect and hummingbird pollinators showed a strong segregation in their daily activity time, we suggest that current disruptive selection on the nectar guide phenotype can result from the differential availability of the rewarding floral variants over a day. Our findings suggest that pollinator-mediated selection favoring extreme phenotypes in M. luteus may not only contribute to high nectar guide variation found in this species, but also can promote divergence of corolla and nectar guide traits.