Evolutionary importance of phenotypic plasticity in aphid-host plant interactions insights from a study of mexican population of Brevicoryne Brassicae
Phenotypic plasticity is a salient characteristic commonly held to be adaptive in aphids in relation to the varying environments constituted by the host plants. Plant´s nutritional quality can influence phenotypic expression of life history and behavioral and morphological traits in aphids. We investigated the extent of morphological plasticity elicited by host plants grown with three different levels of soil nitrogen (optimum level for plant growth (200 ppm), double the optimum level (400 ppm), and one-quarter of the optimum level (50 ppm)). Our study includes the aphid Brevicoryne brassicae and two related sympatric host plants of the genus Brassica in the Highlands of Chiapas, Mexico (B. campestris and B. oleracea). Up to six nymphs of each of several females (clones) were placed in an individual plant of each host species. Each individual aphid was observed over the course of 15 days, starting with the onset of reproduction, and age at first reproduction and total number of offspring produced was recorded in order to calculate the individual's intrinsic rate of increase (rm), as a measure of fitness. Adult aphids were collected and placed in alcohol (70%) and mounted on a micro-slide in order to measure four morphological traits. A principal component analysis was carried out in order to summarize variation of morphological characteristics. Mode and intensity of selection on morphology (the first two principal components, PC) was estimated in each combination of environments (host-nitrogen level) by means of multiple lineal regression (Lande and Arnold, 1983) of relative fitness (rm) as a function the two PCs. The first two PCs explained 89.7% of variation in morphological traits. PC-1 summarizes variation in general size, whereas PC-2 is related to variation in body length in relation to general size. The genotype of the aphid explained a small fraction of variance in morphology independent of host or level of nitrogen where it developed. Furthermore, a general effect of the host plant species on PC-1 was detected. Aphids that developed on B. campestris were, on average, larger than those that developed on B. oleracea. No significant effect of level of soil nitrogen was found on PC-1 and PC-2. None of the interactions among factors (genotype, nitrogen level, and host plant species) was significant. Significant differences in rm (our estimate of fitness) among aphid genotypes were detected. However, no relationship was found between morphology (PC-1 and PC-2) and fitness (rm) within host plants or nitrogen levels. Existence of genetic variation in fitness would predict a process of local (host) adaptation. However, the host race formation could be limited if expressed phenotypic plasticity found is noisy in relation to the environment.
| Main Authors: | , , |
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| Format: | Texto biblioteca |
| Language: | eng |
| Subjects: | Brevicoryne brassicae, Plasticidad fenotípica, Brassica oleracea, Brassica campestris, Plantas huéspedes, Relación insecto-planta, Artfrosur, |
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