What does convergent evolution mean? The interpretation of convergence and its implications in the search for limits to evolution

Quantifying the extent of morphological homoplasy: A phylogenetic analysis of 490 characters in Drosophila

Homoplasy is a fundamental phenomenon in evolutionary biology but an appraisal of its extent at the morphological level is still lacking. Here, we analyzed the evolution of 490 morphological characters conceptualized among 56 drosophilid species. We found that two thirds of morphological changes were homoplastic and that the level of homoplasy depended on the stage of development and the type of the organ, with the adult terminalia being the least homoplastic. In spite of its predominance at the character change level, homoplasy accounts for only ∼13% of between species similarities in pairwise comparisons. These results provide empirical insights on the limits of morphological changes and the frequency of recurrent evolution.

Traitpedia: a collaborative effort to gather species traits

Summary

Traitpedia is a collaborative database aimed to collect binary traits in a tabular form for a growing number of species.

Availability and implementation

Traitpedia can be accessed from http://cbdm-01.zdv.uni-mainz.de/~munoz/traitpedia.

Supplementary information

Supplementary data are available at Bioinformatics online.

Tail Weaponry in Ankylosaurs and Glyptodonts: An Example of a Rare but Strongly Convergent Phenotype

The unusual clubbed tails of glyptodonts among mammals and ankylosaurines among dinosaurs most likely functioned as weapons of intraspecific combat or interspecific defense and are characterized by stiffening of the distal tail and, in some taxa, expansion of the distal tail tip. Although similarities in tail weaponry have been noted as a potential example of convergent evolution, this hypothesis has not been tested quantitatively, particularly with metrics that can distinguish convergence from long-term stasis, assess the relative strength of convergence, and identify potential constraints in the appearance of traits during the stepwise, independent evolution of these structures. Using recently developed metrics of convergence within a phylomorphospace framework, we document that convergence accounts for over 80% of the morphological evolution in traits associated with tail weaponry in ankylosaurs and glyptodonts. In addition, we find that ankylosaurs and glyptodonts shared an independently derived, yet constrained progression of traits correlated with the presence of a tail club, including stiffening of the distal tail as a precedent to expansion of the tail tip in both clades. Despite differences in the anatomical construction of the tail club linked to lineage-specific historical contingency, these lineages experienced pronounced, quantifiable convergent evolution, supporting hypotheses of functional constraints and shared selective pressures on the evolution of these distinctive weapons. Anat Rec, 303:988-998, 2020. © 2019 Wiley Periodicals, Inc.

The shadow of the past: Convergence of young and old South American desert lizards as measured by head shape traits

Convergence is a pervasive phenomenon in the Tree of Life, and evolution of similar phenotypes sharing the same environmental conditions is expected in phylogenetically closely related species. In contrast, contingent factors are probably more influential in shaping phenotypic diversity for distantly related taxa. Here, we test putative convergent evolution of lizard head morphologies among relatively closely related desert dwelling Liolaemus species, and the very distantly related Ctenoblepharys adspersa. We estimated a multilocus time-calibrated phylogeny of 57 species of South American liolaemus lizards, based on seven molecular markers. We collected head shape data for 468 specimens, and used three phylogenetic comparative methods (SURFACE, CONVEVOL, and WHEATSHEAF index) to test for and estimate the strength of convergence. We found strong evidence for convergence among Pacific desert lizard C. adspersa, Liolaemus audivetulatus, Liolaemus insolitus, Liolaemus poconchilensis, Liolaemus stolzmanni, and a candidate species (Liolaemus "Moquegua"). Our results suggest that, despite the long divergence and phylogenetic distance of C. adspersa with respect to convergent Liolaemus species, natural selection was probably more important than historical contingency in shaping phenotypic evolution in these desert lizards.

Delayed trait development and the convergent evolution of shell kinesis in turtles

Understanding developmental processes is foundational to clarifying the mechanisms by which convergent evolution occurs. Here, we show how a key convergently evolving trait is slowly 'acquired' in growing turtles. Many functionally relevant traits emerge late in turtle ontogeny, owing to design constraints imposed by the shell. We investigated this trend by examining derived patterns of shell formation associated with the multiple (at least 8) origins of shell kinesis in small-bodied turtles. Using box turtles as a model, we demonstrate that the flexible hinge joint required for shell kinesis differentiates gradually and via extensive repatterning of shell tissue. Disproportionate changes in shell shape and size substantiate that this transformation is a delayed ontogenetic response (3-5 years post-hatching) to structural alterations that arise in embryogenesis. These findings exemplify that the translation of genotype to phenotype may reach far beyond embryonic life stages. Thus, the temporal scope for developmental origins of adaptive morphological change might be broader than generally understood. We propose that delayed trait differentiation via tissue repatterning might facilitate phenotypic diversification and innovation that otherwise would not arise due to developmental constraints.

Environmental determinism, and not interspecific competition, drives morphological variability in Australasian warblers (Acanthizidae)

Interspecific competition is thought to play a key role in determining the coexistence of closely related species within adaptive radiations. Competition for ecological resources can lead to different outcomes from character displacement to, ultimately, competitive exclusion. Accordingly, divergent natural selection should disfavor those species that are the most similar to their competitor in resource use, thereby increasing morphological disparity. Here, we examined ecomorphological variability within an Australo‐Papuan bird radiation, the Acanthizidae, which include both allopatric and sympatric complexes. In addition, we investigated whether morphological similarities between species are related to environmental factors at fine scale (foraging niche) and/or large scale (climate). Contrary to that predicted by the competition hypothesis, we did not find a significant correlation between the morphological similarities found between species and their degree of range overlap. Comparative modeling based on both a priori and data‐driven identification of selective regimes suggested that foraging niche is a poor predictor of morphological variability in acanthizids. By contrast, our results indicate that climatic conditions were an important factor in the formation of morphological variation. We found a significant negative correlation between species scores for PC1 (positively associated to tarsus length and tail length) and both temperature and precipitation, whereas PC2 (positively associated to bill length and wing length) correlated positively with precipitation. In addition, we found that species inhabiting the same region are closer to each other in morphospace than to species outside that region regardless of genus to which they belong or its foraging strategy. Our results indicate that the conservative body form of acanthizids is one that can work under a wide variety of environments (an all‐purpose morphology), and the observed interspecific similarity is probably driven by the common response to environment.

A rich diversity of opercle bone shape among teleost fishes

The opercle is a prominent craniofacial bone supporting the gill cover in all bony fish and has been the subject of morphological, developmental, and genetic investigation. We surveyed the shapes of this bone among 110 families spanning the teleost tree and examined its pattern of occupancy in a principal component-based morphospace. Contrasting with expectations from the literature that suggest the local morphospace would be only sparsely occupied, we find primarily dense, broad filling of the morphological landscape, indicating rich diversity. Phylomorphospace plots suggest that dynamic evolution underlies the observed spatial patterning. Evolutionary transits through the morphospaces are sometimes long, and occur in a variety of directions. The trajectories seem to represent both evolutionary divergences and convergences, the latter supported by convevol analysis. We suggest that that this pattern of occupancy reflects the various adaptations of different groups of fishes, seemingly paralleling their diverse marine and freshwater ecologies and life histories. Opercle shape evolution within the acanthomorphs, spiny ray-finned fishes, appears to have been especially dynamic.

Inconsistent reproductive isolation revealed by interactions between Catostomus fish species

Interactions between species are central to evolution and ecology, but we do not know enough about how outcomes of interactions between species vary across geographic locations, in heterogeneous environments, or over time. Ecological dimensions of interactions between species are known to vary, but evolutionary interactions such as the establishment and maintenance of reproductive isolation are often assumed to be consistent across instances of an interaction between species. Hybridization among Catostomus fish species occurs over a large and heterogeneous geographic area and across taxa with distinct evolutionary histories, which allows us to assess consistency in species interactions. We analyzed hybridization among six Catostomus species across the Upper Colorado River basin (US mountain west) and found extreme variation in hybridization across locations. Different hybrid crosses were present in different locations, despite similar species assemblages. Within hybrid crosses, hybridization varied from only first generation hybrids to extensive hybridization with backcrossing. Variation in hybridization outcomes might result from uneven fitness of hybrids across locations, polymorphism in genetic incompatibilities, chance, unidentified historical contingencies, or some combination thereof. Our results suggest caution in assuming that one or a few instances of hybridization represent all interactions between the focal species, as species interactions vary substantially across locations.

Approaches to Macroevolution: 1. General Concepts and Origin of Variation

Approaches to macroevolution require integration of its two fundamental components, i.e. the origin and the sorting of variation, in a hierarchical framework. Macroevolution occurs in multiple currencies that are only loosely correlated, notably taxonomic diversity, morphological disparity, and functional variety. The origin of variation within this conceptual framework is increasingly understood in developmental terms, with the semi-hierarchical structure of gene regulatory networks (GRNs, used here in a broad sense incorporating not just the genetic circuitry per se but the factors controlling the timing and location of gene expression and repression), the non-linear relation between magnitude of genetic change and the phenotypic results, the evolutionary potential of co-opting existing GRNs, and developmental responsiveness to nongenetic signals (i.e. epigenetics and plasticity), all requiring modification of standard microevolutionary models, and rendering difficult any simple definition of evolutionary novelty. The developmental factors underlying macroevolution create anisotropic probabilities-i.e., an uneven density distribution-of evolutionary change around any given phenotypic starting point, and the potential for coordinated changes among traits that can accommodate change via epigenetic mechanisms. From this standpoint, "punctuated equilibrium" and "phyletic gradualism" simply represent two cells in a matrix of evolutionary models of phenotypic change, and the origin of trends and evolutionary novelty are not simply functions of ecological opportunity. Over long timescales, contingency becomes especially important, and can be viewed in terms of macroevolutionary lags (the temporal separation between the origin of a trait or clade and subsequent diversification); such lags can arise by several mechanisms: as geological or phylogenetic artifacts, or when diversifications require synergistic interactions among traits, or between traits and external events. The temporal and spatial patterns of the origins of evolutionary novelties are a challenge to macroevolutionary theory; individual events can be described retrospectively, but a general model relating development, genetics, and ecology is needed. An accompanying paper (Jablonski in Evol Biol 2017) reviews diversity dynamics and the sorting of variation, with some general conclusions.

Toward a Predictive Framework for Convergent Evolution: Integrating Natural History, Genetic Mechanisms, and Consequences for the Diversity of Life

A charm of biology as a scientific discipline is the diversity of life. Although this diversity can make laws of biology challenging to discover, several repeated patterns and general principles govern evolutionary diversification. Convergent evolution, the independent evolution of similar phenotypes, has been at the heart of one approach to understand generality in the evolutionary process. Yet understanding when and why organismal traits and strategies repeatedly evolve has been a central challenge. These issues were the focus of the American Society of Naturalists Vice Presidential Symposium in 2016 and are the subject of this collection of articles. Although naturalists have long made inferences about convergent evolution and its importance, there has been confusion in the interpretation of the pattern of convergence. Does convergence primarily indicate adaptation or constraint? How often should convergence be expected? Are there general principles that would allow us to predict where and when and by what mechanisms convergent evolution should occur? What role does natural history play in advancing our understanding of general evolutionary principles? In this introductory article, I address these questions, review several generalizations about convergent evolution that have emerged over the past 15 years, and present a framework for advancing the study and interpretation of convergence. Perhaps the most important emerging conclusion is that the genetic mechanisms of convergent evolution are phylogenetically conserved; that is, more closely related species tend to share the same genetic basis of traits, even when independently evolved. Finally, I highlight how the articles in this special issue further develop concepts, methodologies, and case studies at the frontier of our understanding of the causes and consequences of convergent evolution.

Hunting Darwin's Snark: which maps shall we use?

The 11 contributions to this thematic volume touch on a large range of issues concerning the landscape of biological possibilities and the manner by which it may be traversed by evolving life forms. The contributors also consider how this landscape might be mapped by evolutionary biologists, with an emphasis on how one might identify the limits of such maps. While some agreements emerge on the question of limits on evolution, not surprisingly few contributors look towards the same horizons. Rather than providing a potted summary of the 11 papers, our aim in this introduction is to identify eight principal themes that might serve as common ground and, as importantly, to listen out for the sound of rushing subterranean waters that hint at caverns of concealed knowledge. By no means all of these themes are addressed by all authors, but in gathering the many strands of enquiry we hope that this will allow us to ask: What, if any, are the limits to evolution?