Genotype networks shed light on evolutionary constraints

Abstract

An evolutionary constraint is a bias or limitation in phenotypic variation that a biological system produces. One can distinguish physicochemical, selective, genetic and developmental causes of such constraints. Here, I discuss these causes in three classes of system that bring forth many phenotypic traits and evolutionary innovations: regulatory circuits, macromolecules and metabolic networks. In these systems, genotypes with the same phenotype form large genotype networks that extend throughout a vast genotype space. Such genotype networks can help unify different causes of evolutionary constraints. They can show that these causes ultimately emerge from the process of development; that is, how phenotypes form from genotypes. Furthermore, they can explain important consequences of constraints, such as punctuated stasis and canalization. An evolutionary constraint is a bias or limitation in phenotypic variation that a biological system produces. One can distinguish physicochemical, selective, genetic and developmental causes of such constraints. Here, I discuss these causes in three classes of systems that bring forth many phenotypic traits and evolutionary innovations: regulatory circuits, macromolecules and metabolic networks. In these systems, genotypes with the same phenotype form large genotype networks that extend throughout a vast genotype space. Such genotype networks can help unify different causes of evolutionary constraints. They can show that these causes ultimately emerge from the process of development: that is, how phenotypes form from genotypes. Furthermore, they can explain important consequences of constraints, such as punctuated stasis and canalization. Evolutionary constraintsNo organism or species can produce every conceivable kind of phenotypic variation. This limitation is encapsulated in the notion of constraints on phenotypic evolution [1]. An evolutionary constraint is a bias or limitation in phenotypic variation that a biological system produces. Extreme examples include the absence of photosynthesis in higher animals, the general lack of teeth in the lower jaw of frogs, the absence of palm trees in cold climates and the absence of birds that give birth to live young instead of to eggs [1,2]. In these examples, a trait is completely absent. More subtle constraints manifest themselves as correlations among different characters. A paradigmatic case is allometric scaling [2]. Here, the value of one quantitative trait constrains that of another, typically via a specific nonlinear relationship, For example, metabolic rate is proportional to body mass m raised to approximately three quarter power (m 0.75 ) across many differentIt is not hard to see that constraints can influence the spectrum of evolutionary adaptations and innovations that are accessible to living things. For this reason, questions about the causes and consequences of constrained evolution have attracted much attention [1,[4][5][6][7][8][9][10]. There are multiple kinds and causes of phenotypic constraints (Box 1),...

Clades reach highest morphological disparity early in their evolution

“…The hypothesis of increasing developmental constraint predicts that the increasing complexity and interdependence of ontogenetic processes with evolutionary time effectively lock down the potential for subsequent morphological innovation (14,(61)(62)(63)(64)(65). Such mechanisms purportedly explain why bodyplans become invariant and inflexible with time, although mechanisms by which these constraints may be lifted have been posited (66). Notable examples are the tetrapod pentadactyl limb [early tetrapods explored a range of higher digit numbers (67)], the seven cervical vertebrae of all mammals except sloths and manatees [otherwise invariant from mice to giraffes (68)] and the diagnostic head segmentation of arthropod subphyla [Cambrian genera explored numerous alternatives with relative freedom (14,69)].…”

Strain Variation in the Transcriptome of the Dengue Fever Vector,Aedes aegypti

“…Importantly, a key component of a model organism is the ability to use information gathered from transcriptomics from one strain to make inferences about other strains within the species. This information then can be used in studies that test possible interactions among genotypic variation, transcriptional regulation, and environmental factors (Wagner 2011). …”

Ecological patterns of morphological variation in Italian populations of Romulea bulbocodium (Iridaceae)

“…and by Frignani and Iiriti (2008) to distinguish R. bocchierii Frignani & Iiriti from closely related species including R. bulbocodium. This might be explained by two hypotheses: (i) the characters are genetically constrained (see Wagner, 2011), but the local environment in which they develop may also affect them to a considerable degree; (ii) the character state present also influence whether a plant occurs in IM versus CC and the habitat preferences can be part of the same speciation process that is more complete between R. bulbocodium and R. ramiflora.…”