Periodic Reporting for period 5 - COMPCON (Competition under (niche) construction)
Reporting period: 2023-05-01 to 2023-10-31
Interspecific competition is arguably the best interaction to address the how individual trait variation and eco-evolutionary feedbacks shape species distributions and trait evolution, due to its indirect effects on the shared resource. However, a clear understanding of such feedbacks is only possible if each contributing factor can be manipulated independently. With COMPCON, we are addressing address the reciprocal interactions between individual variation, niche width, niche construction and the presence of competitors using a system amenable to anipulation of all these variables. The system is composed of two spider mite species, Tetranychus urticae and T. evansi, that up- and down-regulate plant defences (i.e. negative and positive niche construction, respectively). Mites are colonizing tomato plants with different cadmium concentrations, allowing quantitative variation of available niches. Tomato mutant plants with low defences are used as an environment in which niche construction is not expressed. Individual variation in niche width and niche construction are being measured in isogenic lines. Different combinations of lines will then be used to test how such variation in individual traits affects coexistence and evolution with competitors.
Data generated by COMPCON will strengthen the growing link between Ecology and Evolution, as it will test recent hypotheses concerning how individual variation, niche width, niche construction and competition interact to shape species distributions and trait evolution.
Data generated by COMPCON will strengthen the growing link between Ecology and Evolution, as it will test recent hypotheses concerning how individual variation, niche width, niche construction and competition interact to shape species distributions and trait evolution.
The project aims at understanding the consequences of (a) individual variation for traits associated to competition and to the interaction between mites and plants and (b) evolving with competitors, for trait evolution and the probability of coexistence. In particular, we investigate the consequences of niche construction in spider mites, as one species is able to suppress plant defences, thus making resources available to themselves but also to competitors. So far, we found large variation for the ability of spider mites to suppress plant defences, but less so for their ability to benefit from this suppression. These traits were found not to be correlated, which raises important questions concerning the maintenance of such niche construction.
We also found large variation for intra and interspecific competitive ability, but again no correlation among traits. We are currently investigating whether specific combinations of these traits facilitate coexistence among these competitors, based on theoretical predictions.
Moreover, we found that tomato plants accumulate cadmium and that the response of the two species to this accumulation varies in shape and intensity and is altered by the presence of interspecific competitors. However, the change induced by the presence of the competitor is not in niche location or width, as expected by classical theory, but in the shape of the response.
Furthermore, we performed experimental evolution of spider mites on tomato plants with or without cadmium and with or without competitors, then tested how this evolutionary history affected the probability of coexistence in environments with and/or without cadmium. We found effects of the evolutionary history in some, but not all, cases, and a strong dependence of this effect upon the environment tested. These findings have important consequences for the effect of evolution in species interactions.
Finally, we performed experimental evolution of spider mites on tomato plants in which defences can be induced or suppressed or in plants where defences cannot be altered by spider mites, in presence or absence of competitors. We found that T. evansi, the suppressor, stopped suppressing when (a) evolving on plants where suppression has no effect and (b) evolving on plants with competitors. This suggests that suppression has ecological and physiological costs, a key finding for the understanding of herbivore-plant interactions.
We also found large variation for intra and interspecific competitive ability, but again no correlation among traits. We are currently investigating whether specific combinations of these traits facilitate coexistence among these competitors, based on theoretical predictions.
Moreover, we found that tomato plants accumulate cadmium and that the response of the two species to this accumulation varies in shape and intensity and is altered by the presence of interspecific competitors. However, the change induced by the presence of the competitor is not in niche location or width, as expected by classical theory, but in the shape of the response.
Furthermore, we performed experimental evolution of spider mites on tomato plants with or without cadmium and with or without competitors, then tested how this evolutionary history affected the probability of coexistence in environments with and/or without cadmium. We found effects of the evolutionary history in some, but not all, cases, and a strong dependence of this effect upon the environment tested. These findings have important consequences for the effect of evolution in species interactions.
Finally, we performed experimental evolution of spider mites on tomato plants in which defences can be induced or suppressed or in plants where defences cannot be altered by spider mites, in presence or absence of competitors. We found that T. evansi, the suppressor, stopped suppressing when (a) evolving on plants where suppression has no effect and (b) evolving on plants with competitors. This suggests that suppression has ecological and physiological costs, a key finding for the understanding of herbivore-plant interactions.
The data collected in the experimental evolution may shed light on several key aspects of the evolutionary ecology of competition, namely: does evolving together facilitate coexistence? Does character displacement evolve in response to (co)evolution? Does hormesis evolve? How does adaptation to metal-based defences affect performance in other environments? We aim at performing another measure of these traits at a later generation such as to obtain robust answers to these questions.
We performed comprehensive tests of individual niche variation in the fundamental and the realized niche and their potential correlation. This data set is unique in that (a) few studies have addressed the genetic basis of niche width and (b) none has addressed potential correlations among the fundamental and the realized niche width at the individual level. We will subsequently test how variation in individual niche width affects coexistence.
The data concerning individual variation in niche construction revealed significant variation, which is very exciting. We found that such variation in niche construction led to longer persistence of the weaker competitor. We will performed experimental evolution to test whether the suppression of plant defences is maintained in an environment with cheaters or in which niche construction yields no benefit. We found that spider mites ceased suppressing plant defences in such environments, revealing a high cost of suppression, potentially shedding light on the low prevalence of this strategy in herbivores, despite high benefits.
We performed comprehensive tests of individual niche variation in the fundamental and the realized niche and their potential correlation. This data set is unique in that (a) few studies have addressed the genetic basis of niche width and (b) none has addressed potential correlations among the fundamental and the realized niche width at the individual level. We will subsequently test how variation in individual niche width affects coexistence.
The data concerning individual variation in niche construction revealed significant variation, which is very exciting. We found that such variation in niche construction led to longer persistence of the weaker competitor. We will performed experimental evolution to test whether the suppression of plant defences is maintained in an environment with cheaters or in which niche construction yields no benefit. We found that spider mites ceased suppressing plant defences in such environments, revealing a high cost of suppression, potentially shedding light on the low prevalence of this strategy in herbivores, despite high benefits.