Browsing by Author "Guerra, Patricia C."

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    Effects of host plant and maternal feeding experience on population vital rates of a specialized leaf beetle
    (2013) Rios, Rodrigo S.; Cardenas, Maritza; Gonzalez, Kely; Cisternas, Monica F.; Guerra, Patricia C.; Loayza, Andrea P.; Gianoli, Ernesto
    In herbivorous insects, the interaction between adult preference and progeny performance on specific host plants is modified by maternal feeding experience and host plant quality. Ultimately, changes in the strength of this interaction can affect insect population dynamics. In this study, we hypothesized that adult host plant preference influences progeny performance through a maternal feeding experience x host plant interaction, that is, the effect of adult feeding experience on progeny performance will depend on the host plant. Second, that decoupling of the preference-performance relationship due to host switching results in different population vital rates changing population dynamics. An increase in development time and a decrease in body size of individuals in the alternate host should decrease population growth. We tested these hypotheses using two lines of the tortoise beetle Chelymorpha varians Blanchard fed with two hosts (Convolvulus arvensis and Calystegia sepium). Maternal feeding experience treatments were crossed with host plant species, and the offspring's developing time and adult size were measured. The host plant influence on the beetle's population vital rates was tested using stage-structured matrix population models and life table response experiments. Host plant preference affected offspring body size through a host plant effect that contributed to adaptive life history responses only in the better quality host. C. varians' population growth was positive when fed with either host; comparatively, however, C. sepium had a negative effect on growth by reducing all transition probabilities of the life cycle stages of the beetle. Here, we show that individuals of C. varians prefer and perform differently on distinct hosts and that these patterns influence population vital rates in different ways. When beetles prefer the host plant where their progeny performs best, life history responses and life stage transitions lead to higher population growth; otherwise, growth rate decreases.
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    Explaining differential herbivory in sun and shade: the case of Aristotelia chilensis saplings
    (2010) Guerra, Patricia C.; Becerra, Jose; Gianoli, Ernesto
    Differential herbivory in contrasting environments is commonly explained by differences in plant traits. When several plant traits are considered, separate correlation analyses between herbivory and candidate traits are typically conducted. This makes it difficult to discern which trait best explain the herbivory patterns, or to avoid spurious inferences due to correlated characters. Aristotelia chilensis saplings sustain greater herbivory in shaded environments than in open habitats. We measured alkaloids, phenolics, trichomes, leaf thickness and water content in the same plants sampled for herbivory. We conducted a multiple regression analysis to estimate the relationship between herbivory and each plant trait accounting for the effect of correlated traits, thus identifying which trait(s) better explain(s) the differential herbivory on A. chilensis. We also estimated insect abundance in both light environments. Palatability bioassays tested whether leaf consumption by the main herbivore on A. chilensis was consistent with field herbivory patterns. Overall insect abundance was similar in open and shaded environments. While saplings in open environments had thicker leaves, lower leaf water content, and higher concentration of alkaloids and phenolics, no difference in trichome density was detected. The multiple regression analysis showed that leaf thickness was the only trait significantly associated with herbivory. Thicker leaves received less damage by herbivores. Sawfly larvae consumed more leaf tissue when fed on shade leaves. This result is consistent with field herbivory and, together with results of insect abundance, renders unlikely that the differential herbivory in A. chilensis was due to greater herbivory pressure in open habitats.