Competition-driven evolution of organismal complexity

Abstract

Non-uniform rates of morphological evolution and evolutionary increases in organismal complexity, captured in metaphors like “adaptive zones”, “punctuated equilibrium” and “blunderbuss patterns”, require more elaborate explanations than a simple gradual accumulation of mutations. Here we argue that non-uniform evolutionary increases in phenotypic complexity can be caused by a threshold-like response to growing ecological pressures resulting from evolutionary diversification at a given level of complexity. Acquisition of a new phenotypic feature allows an evolving species to escape this pressure but can typically be expected to carry significant physiological costs. Therefore, the ecological pressure should exceed a certain level to make such an acquisition evolutionarily successful. We present a detailed quantitative description of this process using a microevolutionary competition model as an example. The model exhibits sequential increases in phenotypic complexity driven by diversification at existing levels of complexity and a resulting increase in competitive pressure, which can push an evolving species over the barrier of physiological costs of new phenotypic features.

Evolutionary adaptation of high‐diversity communities to changing environments

“…We analyzed the adaptation of 30 saturated systems, properties of which were analyzed previously (Doebeli & Ispolatov, 2017; Ispolatov et al., 2019), to environmental changes of various rates. For all those systems, the environmental change in the form of a moving CCC either forces the system to adapt and converge to a new quasi‐stationary state, or it leads to extinction of the whole community.…”

“…According to our previous studies of macroevolutionary processes (Doebeli & Ispolatov, 2014, 2017; Ispolatov et al., 2019), “complex phenotypes” have smaller populations and lower rates of evolution, which makes adaptation challenging. In these models, evolution under constant environmental conditions results in gradual expansion of phenotypic space, and more complex, higher‐dimensional phenotypes evolve only once diversity in lower dimensions has saturated (Ispolatov et al., 2019). Conversely, changing environments tend to reduce the average number of phenotypic dimensions in biological systems, since less complex species are more likely to survive.…”

“…Thus, such periods of reduction of diversity caused by environmental changes were probably followed by periods of resaturation and resulted in evolution of entirely novel phenotypes. In terms of our model of evolution of complex phenotypes (Doebeli & Ispolatov, 2017; Ispolatov et al., 2019), where species have a choice to diversify in the same phenotypic space or inhabit a new phenotypic dimension, such environmental changes would then likely generate new bouts of rapid diversification leading to saturated communities occupying higher‐dimensional phenotype spaces. We plan to include such dramatic evolutionary events in our future models of evolution of complex phenotypes (Ispolatov et al., 2019).…”

“…We analyzed the adaptation of 30 saturated systems, properties of which were analyzed previously (Doebeli & Ispolatov, 2017;Ispolatov et al, 2019), to environmental changes of various rates.…”

“…Doebeli and Ispolatov (2017) andIspolatov et al (2019), we study a system that can be populated by a varying number of phenotypic species, each defined by its phenotypex = (x 1 , …, x D )Here and in the following all vector notations should have bar above the variable rather than below.…”