Las plantas parásitas representan aproximadam e n t e u n 1 % d e l t o t a l d e l a s e s p e c i e s angiospermas, con más de 3.000 especies distribuidas en 16 familias (Kuijt 1969, Musselman & Press 1995). La mayor parte de los estudios efectuados sobre plantas parásitas se han focalizado en la ecología de la frugivoría y dispersión de las semillas (e.g.,

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to International Journal of Plant Sciences.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.

Recent studies have revealed that binding of annexin I to phospholipids induces the formation of a second phospholipid binding site. It is shown that the N terminus on the concave side of membrane-bound annexin I is cleaved much faster by trypsin or cathepsin than the N terminus of the free protein. The reactivity of the unique disulfide bond located near the concave face was similarly increased by membrane binding. These results demonstrate that Ca(2+)-dependent membrane binding induces a conformational change on the concave side of the annexin I molecule and support the notion that this face of the molecule may contribute to the formation of the secondary membrane-binding site.

Parasites can reduce host fitness through short‐term mortality, complete or partial castration, or slight reductions in host fecundity. Hosts may reduce reproductive effort as an adaptive strategy to tolerate parasitism. However, host fitness reduction may be unrelated to host adaptation but represent a pathological side‐effect of infection. The present study evaluates experimentally the direct and indirect impact of the protozoan parasite Trypanosoma cruzi on the investment of female kissing bugs in reproductive tissue. The presence of the parasite decreases gonad weight but this effect disappears when body size is included as covariate. To examine in more detail the set of causal relationships involved, a structural equation modelling analysis is performed using body size, moulting time and nutrition as predictor variables on gonad weight in the presence and absence of the protozoan. The results obtained indicate that, irrespective of the pathway and status of infection, female kissing bugs showing a slow development tend to have lighter gonads. On the other hand, the importance of blood ingestion for gonad weight is dependent on body size and contingent on the status of infection. Uninfected individuals tend to invest more in reproductive tissue when ingesting more blood during their ontogeny, and the opposite situation is observed for infected insects. These results indicate that gonad weight reduction in T.cruzi‐infected Mepraia spinolai (Porter, 1934) is a consequence of nutrition curtailment and body size reduction rather than an adaptive strategy to cope with infection.

Summary1. Phylogenetic conservatism of tolerance to freezing temperatures has been cited to explain the tendency of plant lineages to grow in similar climates. However, there is little information about whether or not freezing resistance is conserved across phylogenies, and whether conservatism of physiological traits could explain conservatism of realized climatic niches. Here, we compared the phylogenetical lability of realized climatic niche, foliar freezing resistance and four morphological leaf traits that are generally considered to be adaptations to frost resistance in the Chilean species of Myrceugenia, which grows in a wide range of habitats. 2. We estimated the predicted niche occupancy profiles with respect to minimum temperature (minT) of all species. We measured foliar freezing resistance (using chlorophyll fluorescence), leaf size, leaf mass per area (LMA), stomatal and trichome densities of 10 individuals per species. Finally, we estimated phylogenetic signal, and we performed independent contrast analyses among all variables. 3. We found that both foliar freezing resistance and minT were subject to a significant phylogenetic signal, but the former had a stronger signal. We also detected a significant, but weak correlation between them (r = 0.49, P one tail = 0.04). Morphological traits evolved independent of any phylogenetic effect. 4. Synthesis. Our results show that freezing resistance evolved in association with temperature niche, but with some delay that could result from phylogenetic inertia. Our results also show that morphological leaf traits are more labile than realized climatic niche and frost tolerance and that the formers probably evolved in association with microhabitat preferences.

We report the "Northern 2n=38-40, modifi cation 1" race from three localities of the Liolaemus monticola complex in Chile that appears to be chromosomally and geographical intermediate between two previously described "Northern 2n=38-40" and "Multiple Fission, 2n=40-44 (MF)" races. This race retains the same "Northern" chromosomal features, but differs by being both polymorphic for an enlarged chromosome pair 6 and for a pericentric inversion in chromosome pair 7; these rearrangements are present in the "MF" race. At the population cytogenetics level, the mean proportion of polymorphic chromosomes in the "Northern, mod 1" race is relatively high and intermediate between the Northern" and "MF" races, while the chromosome "alleles" in the "Northern, mod 1" race deviate from the Hardy-Weinberg ratio higher than the aforementioned races. The Roger's distance between samples are in concordance with the chromosome races and the proposals barriers (The Colorado river and the Juncal river). The lowest chromosome "alleles" fl ux values (Nm) are between the chromosomal races, suggesting a low chromosomal introgression. These population cytogenetics patterns, plus the origin of the chromosomal rearrangements, and the recombination patterns resulting from chromosomal heterozygosity are compared with the situation of other populations of the "Northern" and the "MF" races previously described. We discuss the possible "Northern, mod 1" hybrid status in the evolution of this complex in central Chile.KEYWORDS: hybridization, Liolaemus monticola, "Northern modifi cation 1, 2n = 38-40" chromosomal race, population cytogenetics. RESUMENReportamos la citogenética poblacional de la raza "Norte 2n=38-40, modifi cada 1" para tres localidades del complejo de Liolaemus monticola en Chile, que resulta ser cromosómica y geográfi camente intermedia entre dos razas previamente descritas la "Norte, 2n=38-40" y la "Múltiple Fisiones, 2n=40-44 (MF)". Esta raza, retiene las mismas características cromosómicas de la raza "Norte", pero difi ere de ésta dada la condición polimórfi ca para un cromosoma alargado del par 6 y una inversión pericéntrica del par cromosómico 7, rearreglos que están presentes en la raza "MF". A nivel citogenético poblacional, la proporción promedio de los cromosomas polimórfi cos en la raza "Northern, mod 1" is relativamente alta e intermedia entre las razas "Norte" y "MF", en tanto los "alelos" cromosómicos de la raza "Norte, mod 1" se desvían grandemente de los valores Hardy-Weinberg comparados a las razas antes mencionadas. Las distancias de Roger entre las muestra concuerdan con las razas cromosómicas y con las barreras propuestas (El Río Colorado y El Río Juncal). Los valores más bajos de fl ujo ("alelos") cromosómico (Nm) se encuentran entre las razas cromosómicas, sugerentes de una baja introgresión. Estos patrones de citogenética poblacional, más el origen de los rearreglos cromosómicos y de los patrones de recombinación resultantes de la heterocigosidad cromosómica son comparados con la situación que prese...

We report some aspects of the floral biology of Echinopsis chiloensis ssp. chiloensis in a population near to the northern limit of its distribution. Anthesis is strictly diurnal and flowers remain open during 492 min on the average. Echinopsis chiloensis is self-incompatible. Flower longevity, nectar production along day, and floral visitors indicate that this population fits well to a diurnal insect pollination syndrome. These results contrast with a previous report indicating nocturnal anthesis and mixed mellitophylous-sphingophylous pollination syndrome in populations near to the southern limit of the distribution range. We suggest that the pollination syndrome of E. chiloensis is a labile rather than fixed condition that may depend on the abiotic characteristics and geographical location of the population under assessment. KEYWORDS:Flower longevity, nectar production, pollination syndrome, flower adaptation. RESUMENDocumentamos algunos aspectos de la biología floral de Echinopsis chiloensis ssp. chiloensis en una población del límite norte de su rango de distribución. La antesis es estrictamente diurna y las flores permanecen abiertas durante 492 min en promedio. La especie es auto incompatible. La longevidad floral, la marcha de néctar y los registros de polinizadores indican que la población de E. chiloensis se ajusta bien a un síndrome de polinización por insectos diurnos, lo cual contrasta con la antesis nocturna y el síndrome mixto melitófilo-esfingófilo descrito en poblaciones del límite sur de la distribución de la especie. Sugerimos que el síndrome de polinización de E. chiloensis es lábil y no fijo, siendo dependiente de la población bajo estudio y de su ubicación geográfica.

The maintenance of sexuality is a puzzling phenomenon in evolutionary biology. Many universal hypotheses have been proposed to explain the prevalence of sex despite its costs, but it has been hypothesized that sex could be also retained by lineage‐specific mechanisms that would confer some short‐term advantage. Aphids are good models to study the maintenance of sex because they exhibit coexistence of both sexual and asexual populations within the same species and because they invade a large variety of ecosystems. Sex in aphids is thought to be maintained because only sexually produced eggs can persist in cold climates, but whether sex is obligate or facultative depending on climatic conditions remains to be elucidated. In this study, we have inferred the reproductive mode of introduced populations of the pea aphid Acyrthosiphon pisum in Chile along a climatic gradient using phenotypic assays and genetic‐based criteria to test the ecological short‐term advantage of sex in cold environments. Our results showed a latitudinal trend in the reproductive mode of Chilean pea aphid population from obligate parthenogenesis in the north to an intermediate life cycle producing both parthenogenetic and sexual progeny in the southernmost locality, where harsh winters are usual. These findings are congruent with the hypothesis of the ecological short‐term advantage of sex in aphids.