Species invasion history influences community evolution in a tri-trophic food web model. Plos One

Abstract Background: Recent experimental studies have demonstrated the importance of invasion history for evolutionary formation of community. However, only few theoretical studies on community evolution have focused on such views

Direct and Indirect Induction of a Compensatory Phenotype that Alleviates the Costs of an Inducible Defense

Organisms often exhibit phenotypic plasticity in multiple traits in response to impending environmental change. Multiple traits phenotypic plasticity is complex syndrome brought on by causal relations in ecological and physiological context. Larvae of the salamander Hynobius retardatus exhibit inducible phenotypic plasticity of two traits, when at risk of predation by dragonfly larvae. One induced phenotype is an adaptive defense behaviour, i.e., stasis at the bottom of water column, directly triggered by the predation risk. Another one is a compensatory phenotype, i.e., enlarged external gills, for an unavoidable cost (hypoxia) associated with the induced defense. We identified two ways by which this compensatory phenotype could be induced. The compensatory phenotype is induced in response to not only the associated hypoxic conditions resulting from the induced defense but also the most primary but indirect cause, presence of the predator

Species Invasion History Influences Community Evolution in a Tri-Trophic Food Web Model

Background: Recent experimental studies have demonstrated the importance of invasion history for evolutionary formation of community. However, only few theoretical studies on community evolution have focused on such views. Methodology and Principal Findings: We used a tri-trophic food web model to analyze the coevolutionary effects of ecological invasions by a mutant and by a predator and/or resource species of a native consumer species community and found that ecological invasions can lead to various evolutionary histories. The invasion of a predator makes multiple evolutionary community histories possible, and the evolutionary history followed can determine both the invasion success of the predator into the native community and the fate of the community. A slight difference in the timing of an ecological invasion can lead to a greatly different fate. In addition, even greatly different community histories can converge as a result of environmental changes such as a predator trait shift or a productivity change. Furthermore, the changes to the evolutionary history may be irreversible. Conclusions and Significance: Our modeling results suggest that the timing of ecological invasion of a species into a focal community can largely change the evolutionary consequences of the community. Our approach based on adaptive dynamics will be a useful tool to understand the effect of invasion history on evolutionary formation of community

Inducible plasticity : optimal waiting time for the development of an inducible phenotype

Qeustion: How does an organism that possesses inducible plasticity determine waiting time before the development of a secondary phenotype is suitable? Model: Maximization of the fitness currency, the survival possibility times the expected amount of remaining energy at terminal time, with respect to waiting time before development of a secondary phenotype. Key assumptions: If the individual develops the inducible secondary phenotype in the secondary environment, death rate is reduced. The development and maintenance of the inducible phenotype incurs a cost. Results: The optimal waiting tiem should be longer under the following conditions: when the inducible phenotype has low effectiveness in improving the survival rate of an organism exposed to the secondary environment; when the cost of development of the secondary phenotype is high; when the time delay required to develop the phenotype is short; or when the total energy that an organism possesses initially is low and fitness will be evaluated far in the future

An interaction-driven cannibalistic reaction norm

s Cannibalism is induced in larval-stage populations of the Hokkaido salamander, Hynobius retardatus, under the control of a cannibalism reaction norm. Here, I examined phenotypic expression under the cannibalism reaction norm, and how the induction of a cannibalistic morph under the norm leads to populational morphological diversification. I conducted a set of experiments in which density was manipulated to be either low or high. In the high-density treatment, the populations become dimorphic with some individuals developing into the cannibal morph type. I performed an exploratory analysis based on geometric morphometrics and showed that shape characteristics differed between not only cannibal and noncannibal morph types in the high-density treatment but also between those morph types and the solitary morph type in the low-density treatment. Size and shape of cannibal and noncannibal individuals were found to be located at either end of a continuum of expression following a unique size-shape integration rule that was different from the rule governing the size and shape variations of the solitary morph type. This result implies that the high-density-driven inducible morphology of an individual is governed by a common integration rule during the development of dimorphism under the control of the cannibalism reaction norm. Phenotypic expression under the cannibalism reaction norm is driven not only by population density but also by social interactions among the members of a population: variation in the populational expression of dimorphism is associated with contingent social interaction events among population members. The induced cannibalistic morph thus reflects not only by contest-type exploitative competition but also interference competition

Multiple inducible defences against multiple predators in the anuran tadpole, Rana pirica

Question: What conditions are required for evolution of predator-specific inducible defences? Hypotheses: (1) Prey organisms distinguish among predators to which they are exposed. (2) Prey individuals with a predator-specific defence must attain higher survivorship than those with a mismatched defensive phenotype. Organisms: Prey, anuran tadpoles (Rana pirica); biting type predator, dragonfly larvae (Aeshna nigroflava); swallowing type predator, salamander larvae (Hynobius retardatus). Methods: Rana pirica tadpoles were exposed to the predator signal in close proximity to or remote from the dragonfly larvae or the salamander larvae to determine whether the tadpoles develop predator-specific morphologies and whether they utilize predator-specific signals in the induction process. We conducted predation trials to determine whether the tadpoles with induced phenotypes were more resistant to the attack in the corresponding predator environment. Results: Rana pirica tadpoles developed predator-specific morphologies in response to exposure to two different types of predator. The tadpoles discriminated between the predators . that is, different signals were required to develop the specific phenotypes in the induction process. The survival rate of tadpoles of specific phenotypes was higher than that of tadpoles of mismatched or non-induced phenotypes when exposed to predation by the corresponding predators

Evolution of the maturation rate collapses competitive coexistence

Most theoretical studies on character displacement and the coexistence of competing species have focused attention on the evolution of competitive traits driven by inter-specific competition. We investigated the evolution of the maturation rate which is not directly related to competition and trades off with the birth rate and how it influences competitive outcomes. Evolution may result in the superior competitor becoming extinct if, initially, the inferior competitor has a lower, and the superior one a higher, maturation rate at the coexistence equilibrium. This counterintuitive result is explained by an explosive increase in the adult population of the inferior competitor as a result of the more rapid evolution of its maturation rate, which is caused by differences in the intensity and direction of selection on the maturation rates of the two species and in their adult densities, which are related to differences in their life histories. Thus, a life history trait trade-off with a competitive trait may cause a competitive ecological coexistence to collapse

Geographic variation in a predator-induced defense and its genetic basis

Predator-induced morphological defenses are a well-known form of phenotypic plasticity, but we continue to have a limited understanding of geographic variation in these responses and its genetic basis. Here we examine genetic variation and geographic differentiation in the inducible defenses of tadpoles (Rana pirica) in response to predatory salamander larvae (Hynobius retardatus). To do so, we crossed male and female frogs from a “mainland” Japanese island having predaceous salamanders and a more isolated island not having predaceous salamanders and raised resulting offspring in the presence and absence of H. retardatus. Mainland tadpoles exhibited a higher capacity to express the inducible morphology (a more bulgy body) than those from the predator-free island, and expression of the bulgy morph in mainland–island hybrids produced phenotypes that were intermediate to those produced by pure crosses. In addition, parental sex had no effect on expression of the bulgy morph. Our results support the hypothesis that geographic variation in inducible defenses is linked to the additive effects of autosomal alleles that are shaped by differences in historical exposure to the inducing predator