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Evolution of resistance and tolerance to herbivores: testing the trade-off hypothesis.

Kariñho-Betancourt E, Núñez-Farfán J - PeerJ (2015)

Bottom Line: However, we did not detect a negative significant correlation between tolerance and total resistance, or between tolerance and leaf trichome density.Conclusions/Significance.Also, because leaf trichome density reduces damage by herbivores and possess genetic variance in the studied population, its evolution is not constrained.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratorio de Genética Ecológica y Evolución, Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria , México, DF , Mexico.

ABSTRACT
Background. To cope with their natural enemies, plants rely on resistance and tolerance as defensive strategies. Evolution of these strategies among natural population can be constrained by the absence of genetic variation or because of the antagonistic genetic correlation (trade-off) between them. Also, since plant defenses are integrated by several traits, it has been suggested that trade-offs might occur between specific defense traits. Methodology/Principal Findings. We experimentally assessed (1) the presence of genetic variance in tolerance, total resistance, and leaf trichome density as specific defense trait, (2) the extent of natural selection acting on plant defenses, and (3) the relationship between total resistance and leaf trichome density with tolerance to herbivory in the annual herb Datura stramonium. Full-sib families of D. stramonium were either exposed to natural herbivores (control) or protected from them by a systemic insecticide. We detected genetic variance for leaf trichome density, and directional selection acting on this character. However, we did not detect a negative significant correlation between tolerance and total resistance, or between tolerance and leaf trichome density. We argue that low levels of leaf damage by herbivores precluded the detection of a negative genetic correlation between plant defense strategies. Conclusions/Significance. This study provides empirical evidence of the independent evolution of plant defense strategies, and a defensive role of leaf trichomes. The pattern of selection should favor individuals with high trichomes density. Also, because leaf trichome density reduces damage by herbivores and possess genetic variance in the studied population, its evolution is not constrained.

No MeSH data available.


Related in: MedlinePlus

Fitness reaction norms of hypothetical genotypes as a function of damage by herbivores.Genetic variance in reaction norms would be detected when damage is over 10%.
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fig-4: Fitness reaction norms of hypothetical genotypes as a function of damage by herbivores.Genetic variance in reaction norms would be detected when damage is over 10%.

Mentions: In the present study, we did not detect genetic variance for tolerance contrasting with results reported for the same population by Fornoni, Valverde & Núñez-Farfán (2003). A possible explanation is that the low levels of leaf damage recorded in this study (86% of individuals that received leaf damage, experienced less than 10% of loss) prevented the expression of differences in tolerance i.e., lack of genetic variation. Previous evidence indicates that D. stramonium in the same population receives, on average, more damage by herbivores (21.65% ± 0.7; mean ± SE) than the average level recorded in this study. In the Ticuman population, the detection of genetic variance occurred when the damage surpassed 10% of total leaf area (see Fornoni, Valverde & Núñez-Farfán, 2003). Thus, if tolerance is a genotype’s reaction norm of fitness in a damage gradient, differences in the reaction norms (i.e., G × E interaction, implying tolerance) could be detected when damage attains higher values. But at low levels of leaf damage, only part of the reaction norm is apparent in the narrow range of the damage gradient and no differences among genotypes is present (Fig. 4). This fact might possibly preclude the detection of a significant correlation between defensive strategies (or a specific resistance trait). Previous studies have shown how the correlation between resistance and tolerance may vary depending on the biotic environment (e.g., levels of leaf damage due to herbivory). For instance, Fornoni, Valverde & Núñez-Farfán (2003) assessed the correlation between defensive strategies by conducting a reciprocal transplants experiment between two natural populations of D. stramonium. They found that the detection of a trade-off between total resistance and tolerance occurred only for native plants growing in the population with the highest levels of leaf damage (i.e., Ticuman). In contrast, in the population where the average level of leaf damage was lower (i.e., Santo Domingo) no trade-off was detected, suggesting that the amount of leaf damage may restrict the detection of a significant correlation between plant defenses.


Evolution of resistance and tolerance to herbivores: testing the trade-off hypothesis.

Kariñho-Betancourt E, Núñez-Farfán J - PeerJ (2015)

Fitness reaction norms of hypothetical genotypes as a function of damage by herbivores.Genetic variance in reaction norms would be detected when damage is over 10%.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4358663&req=5

fig-4: Fitness reaction norms of hypothetical genotypes as a function of damage by herbivores.Genetic variance in reaction norms would be detected when damage is over 10%.
Mentions: In the present study, we did not detect genetic variance for tolerance contrasting with results reported for the same population by Fornoni, Valverde & Núñez-Farfán (2003). A possible explanation is that the low levels of leaf damage recorded in this study (86% of individuals that received leaf damage, experienced less than 10% of loss) prevented the expression of differences in tolerance i.e., lack of genetic variation. Previous evidence indicates that D. stramonium in the same population receives, on average, more damage by herbivores (21.65% ± 0.7; mean ± SE) than the average level recorded in this study. In the Ticuman population, the detection of genetic variance occurred when the damage surpassed 10% of total leaf area (see Fornoni, Valverde & Núñez-Farfán, 2003). Thus, if tolerance is a genotype’s reaction norm of fitness in a damage gradient, differences in the reaction norms (i.e., G × E interaction, implying tolerance) could be detected when damage attains higher values. But at low levels of leaf damage, only part of the reaction norm is apparent in the narrow range of the damage gradient and no differences among genotypes is present (Fig. 4). This fact might possibly preclude the detection of a significant correlation between defensive strategies (or a specific resistance trait). Previous studies have shown how the correlation between resistance and tolerance may vary depending on the biotic environment (e.g., levels of leaf damage due to herbivory). For instance, Fornoni, Valverde & Núñez-Farfán (2003) assessed the correlation between defensive strategies by conducting a reciprocal transplants experiment between two natural populations of D. stramonium. They found that the detection of a trade-off between total resistance and tolerance occurred only for native plants growing in the population with the highest levels of leaf damage (i.e., Ticuman). In contrast, in the population where the average level of leaf damage was lower (i.e., Santo Domingo) no trade-off was detected, suggesting that the amount of leaf damage may restrict the detection of a significant correlation between plant defenses.

Bottom Line: However, we did not detect a negative significant correlation between tolerance and total resistance, or between tolerance and leaf trichome density.Conclusions/Significance.Also, because leaf trichome density reduces damage by herbivores and possess genetic variance in the studied population, its evolution is not constrained.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratorio de Genética Ecológica y Evolución, Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria , México, DF , Mexico.

ABSTRACT
Background. To cope with their natural enemies, plants rely on resistance and tolerance as defensive strategies. Evolution of these strategies among natural population can be constrained by the absence of genetic variation or because of the antagonistic genetic correlation (trade-off) between them. Also, since plant defenses are integrated by several traits, it has been suggested that trade-offs might occur between specific defense traits. Methodology/Principal Findings. We experimentally assessed (1) the presence of genetic variance in tolerance, total resistance, and leaf trichome density as specific defense trait, (2) the extent of natural selection acting on plant defenses, and (3) the relationship between total resistance and leaf trichome density with tolerance to herbivory in the annual herb Datura stramonium. Full-sib families of D. stramonium were either exposed to natural herbivores (control) or protected from them by a systemic insecticide. We detected genetic variance for leaf trichome density, and directional selection acting on this character. However, we did not detect a negative significant correlation between tolerance and total resistance, or between tolerance and leaf trichome density. We argue that low levels of leaf damage by herbivores precluded the detection of a negative genetic correlation between plant defense strategies. Conclusions/Significance. This study provides empirical evidence of the independent evolution of plant defense strategies, and a defensive role of leaf trichomes. The pattern of selection should favor individuals with high trichomes density. Also, because leaf trichome density reduces damage by herbivores and possess genetic variance in the studied population, its evolution is not constrained.

No MeSH data available.


Related in: MedlinePlus