Approaches to Macroevolution: 2. Sorting of Variation, Some Overarching Issues, and General Conclusions

Abstract

Approaches to macroevolution require integration of its two fundamental components, within a hierarchical framework. Following a companion paper on the origin of variation, I here discuss sorting within an evolutionary hierarchy. Species sorting—sometimes termed species selection in the broad sense, meaning differential origination and extinction owing to intrinsic biological properties—can be split into strict-sense species selection, in which rate differentials are governed by emergent, species-level traits such as geographic range size, and effect macroevolution, in which rates are governed by organism-level traits such as body size; both processes can create hitchhiking effects, indirectly causing the proliferation or decline of other traits. Several methods can operationalize the concept of emergence, so that rigorous separation of these processes is increasingly feasible. A macroevolutionary tradeoff, underlain by the intrinsic traits that influence evolutionary dynamics, causes speciation and extinction rates to covary in many clades, resulting in evolutionary volatility of some clades and more subdued behavior of others; the few clades that break the tradeoff can achieve especially prolific diversification. In addition to intrinsic biological traits at multiple levels, extrinsic events can drive the waxing and waning of clades, and the interaction of traits and events are difficult but important to disentangle. Evolutionary trends can arise in many ways, and at any hierarchical level; descriptive models can be fitted to clade trajectories in phenotypic or functional spaces, but they may not be diagnostic regarding processes, and close attention must be paid to both leading and trailing edges of apparent trends. Biotic interactions can have negative or positive effects on taxonomic diversity within a clade, but cannot be readily extrapolated from the nature of such interactions at the organismic level. The relationships among macroevolutionary currencies through time (taxonomic richness, morphologic disparity, functional variety) are crucial for understanding the nature of evolutionary diversification. A novel approach to diversity-disparity analysis shows that taxonomic diversifications can lag behind, occur in concert with, or precede, increases in disparity. Some overarching issues relating to both the origin and sorting of clades and phenotypes include the macroevolutionary role of mass extinctions, the potential differences between plant and animal macroevolution, whether macroevolutionary processes have changed through geologic time, and the growing human impact on present-day macroevolution. Many challenges remain, but progress is being made on two of the key ones: (a) the integration of variation-generating mechanisms and the multilevel sorting processes that act on that variation, and (b) the integration of paleontological and neontological approaches to historical biology.

Developmental bias, macroevolution, and the fossil record

“…Wagner, 2018). This release was followed by subsequent ecological crowding, as in the Valentine-Walker model discussed by Jablonski (2017b), with the early Cenozoic diversification perhaps enhanced by, but not initiated by, the simple set of regulatory interactions underlying beak formation in at least some modern passerine birds, noted above. This view posits an interaction between development and function that recalls Van Valen's (1973) dictum that evolution is the control of development by ecology, and thus provides a broader perspective on developmental bias.…”

“…(a) Likely ancestor Pachyrisma, resembling many modern bivalves (from Morris & Lycett, 1853;see Schneider, 2017). Short-lived lineages, or lineages that fail to branch, are likely to generate less disparity through time, or to capitalize on an advantageous novelty, than lineages having longer durations and high rates of cladogenesis (e.g., Futuyma, 2015;Jablonski, 2017b;Rabosky et al, 2013; note that this observation is divorced from the relation between present-day species richness and disparity, which can be decoupled for many reasons). (c) Range of morphologies, from conical forms partly embedded in sediment (1-6), to coiled and flattened forms (7-9), to arcuate and stellate forms that reclined at the sediment surface (10-12); lengths range from 15 cm (1) to 2 m (11; after Ross and Skelton 1993); (b,c) by kind permission of Peter W. Skelton phenotypes it can most readily expose to selection and other forces-but on its inherent origination and extinction rates, and how those rates vary across a given phylogeny.…”

“…From Jablonski (2017b), inspired by Gould (1982) and Stanley (1979) (Jablonski, 2005a(Jablonski, , 2009(Jablonski, , 2017b. For example, a phenotypic trait within a tropical clade, where taxonomic diversification can be prolific, will have a different future in terms of further exploration of morphospace-including the potential for macroevolutionary expression of developmental bias-than the same trait captured by a boreal clade, where diversification tends to be more modest.…”

Cope's Rule in a modular organism: Directional evolution without an overarching macroevolutionary trend

“…Second, species can also increase in size over time due to selection at the level of the individual (Kingsolver and Pfenning ). Last, species that have small sizes can have higher extinction rates and/or those with larger sizes can have higher speciation rates (Jablonski ).…”

Unravelling the history of biodiversity in mountain ranges through integrating geology and biogeography

“…As argued in many studies on body size evolution, it remains unclear whether body size was indeed the trait under selection or simply an effective proxy for key traits that played fundamental roles in lineage persistence through time (e.g. Finarelli, ; Jablonski, ). To understand the selectivity in faunal turnover, we thus suggest future investigations not only need to expand the current data coverage to allow finer‐scale analyses but also include traits that more directly reflect the interactions between animals and their environment, such as the dietary preference and locomotion mechanism.…”