Carezza Botto-Mahan

POLLINATOR-MEDIATED SELECTION ON THE NECTAR GUIDE PHENOTYPE IN THE ANDEAN MONKEY FLOWER, MIMULUS LUTEUS

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 heart-shaped 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.

DNA evidence of Trypanosoma cruzi in the Chilean wild vector Mepraia spinolai (Hemiptera: Reduviidae).

Molecular evidence showed 46.2% of Trypanosoma cruzi infection in Mepraia spinolai insects from North-Central Chile, which is significantly higher than previous reports of up to 26% by microscopic observation. Our results show similar infection levels among nymphal stages, ranging from 38.3 to 54.1%, indicating that younger nymphs could be as important as older ones in parasite transmission. A cautionary note must be stressed to indicate the potential role of M. spinolai in transmitting T. cruzi in country areas due to the high infection level detected by molecular analysis.

Floral Herbivory Affects Female Reproductive Success and Pollinator Visitation in the Perennial Herb Alstroemeria ligtu (Alstroemeriaceae)

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.

Nonadditive effects of flower damage and hummingbird pollination on the fecundity of Mimulus luteus

Flower herbivory and pollination have been described as interactive processes that influence each other in their effects on plant reproductive success. Few studies, however, have so far examined their joint effects in natural populations. In this paper we evaluate the influence of flower damage and pollination by the hummingbird Oreotrochilus leucopleurus on the fecundity of the Andean monkey flower Mimulus luteus. We performed a 2×2 factorial experiment, with artificial clipping of lower petals and selective exclusion of the hummingbird as main factors. In spite of the relatively low proportion (27.5%) of the variance in seed production accounted for by the full factorial model, artificial damage and hummingbird exclusion, as well as their interaction, were highly significant, indicating nonadditive effects of factors on plant fecundity. In the presence of hummingbirds, undamaged flowers had a seed production that was 1.7-fold higher than for damaged flowers, suggesting that the effect of flower damage on female reproductive success occurs probably as a consequence of hummingbird discrimination against damaged corollas. This result indicates that the impact of flower herbivory on plant fecundity was contingent on the presence or absence of hummingbirds, suggesting that pollinators may indirectly select for undamaged and probably resistant flower phenotypes. A second interaction effect revealed that undamaged flowers produced 78.5% more seeds in the absence of rather than in the presence of O. leucopleurus, raising the question of the ecological mechanism involved. We suggest that the strong territorial behavior exhibited by the bee Centris nigerrima may confine the foraging activities of the remaining bee species to safe sites within exclosures. Overall, our results provide evidence that hummingbird pollination and flower herbivory have interdependent effects on M. luteus fecundity, which indicates that it will be difficult to predict their ecological and evolutionary consequences unless interactions are analyzed in an integrated form.

Historia natural cuantitativa de una relación parásito-hospedero: el sistema Tristerix-cactáceas en Chile semiárido

Presentamos informacion cuantitativa de la historia natural de la relacion parasito-hospedero constituida por el muerdago holoparasito Tristerix aphyllus (Loranthaceae) y sus hospederos cactaceas. Mas especificamente, indagamos en los determinantes historicos y biogeograficos de la interaccion y cuantificamos la autoecologia de la biologia floral, polinizacion, dispersion y parasitismo en este sistema. El impacto del parasitismo sobre la evolucion de sistemas defensivos en las cactaceas hospederas es considerado tanto a nivel intraespecifico como interespecifico, tomando en cuenta el potencial para seleccion mediada por parasitos y la estructura geografica de la interaccion. Finalmente, sugerimos futuras avenidas de investigacion en este sistema que incluyen los topicos de: (i) evolucion de la virulencia, (ii) estructuracion de la interaccion en mosaico geografico y, (iii) pruebas historicas de adaptacion. Estos aspectos permitiran adquirir un mayor conocimiento de la sutileza ecologica y de la evolucion de esta especial interaccion en los sistemas naturales de Chile semiarido

Molecular Epidemiology of Chagas Disease in the Wild Transmission Cycle: The Evaluation in the Sylvatic Vector Mepraia spinolai from an Endemic Area of Chile

The sylvatic transmission cycle of Chagas disease in Chile is composed of wild mammals and insects of the genus Mepraia. We determined infection rates and Trypanosoma cruzi genotypes in Mepraia spinolai. We collected 227 insects from two ecologically contrasting areas to assess T. cruzi infection. Polymerase chain reaction (PCR)-amplified minicircle DNAs were characterized by Southern blot and hybridization tests with genotype-specific probes. Infection in insects from the more fertile area was almost 2-fold higher than in the poorer area. The genotype TCI was the most prevalent and other genotypes such as TCIIb, TCIId, and TCIIe were found at lower rates. The areas differed in their genotype distribution but not in their genotype diversity. We suggest that the difference in abundance and richness of mammals between the areas may be producing the detected infection levels in vectors. Our results are compared with those reported for mammals from the same area.

Abundance of Mepraia spinolai in a Periurban zone of Chile.

Mepraia spinolai is a silvatic species of Triatominae which prefers microhabitats near to or in rock piles. It is also able to maintain similar or higher size populations near houses. The density of bugs in quarries near Santiago, Chile, differed within microhabitats and varied significantly within sites according to season. M. spinolai was not found in sites characterized by human perturbation of quarries. Our results confirm M. spinolai as a silvatic triatomine whose importance as a vector of Chagas disease will depend on contact with humans. This could occur if the habitats where populations of this species are found become exploited for the building of urban areas.

Field tests of carbon dioxide and conspecifics as baits for Mepraiaspinolai, wild vector of Chagas disease

In spite of extensive evidence showing an association between host stimuli and insect finding behaviour, the importance of carbon dioxide in attracting Triatominae is not entirely understood. We assessed the potential of conspecific individuals and CO2 in attracting free-ranging individuals of Mepraia spinolai in a Chilean semiarid locality. While the presence of conspecific individuals had no effect on the triatomine behaviour, solid CO2-baited traps were more effective in attracting M. spinolai than control (empty) traps. We conclude that CO2 trapping is an effective field technique for M. spinolai detection and potential control.

Trypanosoma cruzi infection in the sylvatic kissing bug Mepraia gajardoi from the Chilean Southern Pacific Ocean coast.

The Southern Pacific Ocean coast has been traditionally considered a non-active transmission area for Chagas disease. In this report, we show evidence of Trypanosoma cruzi infection in the sylvatic kissing bug Mepraia gajardoi from the northern Chilean coast.

Temporal variation of Trypanosoma cruzi infection in native mammals in Chile.

In the present study, we compared Trypanosoma cruzi infection in four native mammals from a hyperendemic area of Chagas disease in Chile for two different periods to assess the occurrence of interannual variation (1999-2000 vs. 2005-2006). Parasite detection in mammals is performed by polymerase chain reaction assays and confirmed by Southern blot analysis and hybridization test with a universal probe. Results showed significant differences in the levels of T. cruzi infection between the compared periods. We suggest that the major El Niño event occurred in 1997-1998, a large-scale global climatic fluctuation, could be indirectly explaining the extremely high T. cruzi infection in 1999-2000 by means of a time-lag response of the wild transmission cycle of Chagas disease in semiarid Chile after the irruption of small rodent populations.