Punctuated evolution in the learned songs of African sunbirds

Learned traits are thought to be subject to different evolutionary dynamics than other phenotypes, but their evolutionary tempo and mode has received little attention. Learned bird song has been thought to be subject to rapid and constant evolution. However, we know little about the evolutionary modes of learned song divergence over long timescales. Here, we provide evidence that aspects of the territorial songs of Eastern Afromontane sky island sunbirds Cinnyris evolve in a punctuated fashion, with periods of stasis of the order of hundreds of thousands of years or more, broken up by evolutionary pulses. Stasis in learned songs is inconsistent with learned traits being subject to constant or frequent change, as would be expected if selection does not constrain song phenotypes over evolutionary timescales. Learned song may instead follow a process resembling peak shifts on adaptive landscapes. While much research has focused on the potential for rapid evolution in bird song, our results suggest that selection can tightly constrain the evolution of learned songs over long timescales. More broadly, these results demonstrate that some aspects of highly variable, plastic traits can exhibit punctuated evolution, with stasis over long time periods.

Influence of phylogeny on the estimation of diet from dental morphology in the Carnivora

Because teeth are the most easily preserved part of the vertebrate skeleton and are particularly morphologically variable in mammals, studies of fossil mammals rely heavily on dental morphology. Dental morphology is used both for systematics and phylogeny as well as for inferences about paleoecology, diet in particular. We analyze the influence of evolutionary history on our ability to reconstruct diet from dental morphology in the mammalian order Carnivora, and we find that much of our understanding of diet in carnivorans is dependent on the phylogenetic constraints on diet in this clade. Substantial error in estimating diet from dental morphology is present regardless of the morphological data used to make the inference, although more extensive morphological datasets are more accurate in predicting diet than more limited character sets. Unfortunately, including phylogeny in making dietary inferences actually decreases the accuracy of these predictions, showing that dietary predictions from morphology are substantially dependent on the evolutionary constraints on carnivore diet and tooth shape. The “evolutionary ratchet” that drives lineages of carnivorans to evolve greater degrees of hypercarnivory through time actually plays a role in allowing dietary inference from tooth shape, but consequently requires caution in interpreting dietary inference from the teeth fossil carnivores. These difficulties are another reminder of the differences in evolutionary tempo and mode between morphology and ecology.

Rapid increase in snake dietary diversity and complexity following the end-Cretaceous mass extinction

The Cenozoic marked a period of dramatic ecological opportunity in Earth history due to the extinction of non-avian dinosaurs as well as to long-term physiographic changes that created new biogeographic theaters and new habitats. Snakes underwent massive ecological diversification during this period, repeatedly evolving novel dietary adaptations and prey preferences. The evolutionary tempo and mode of these trophic ecological changes remain virtually unknown, especially compared with co-radiating lineages of birds and mammals that are simultaneously predators and prey of snakes. Here, we assemble a dataset on snake diets (34,060 observations on the diets of 882 species) to investigate the history and dynamics of the multidimensional trophic niche during the global radiation of snakes. Our results show that per-lineage dietary niche breadths remained remarkably constant even as snakes diversified to occupy disparate outposts of dietary ecospace. Rapid increases in dietary diversity and complexity occurred in the early Cenozoic, and the overall rate of ecospace expansion has slowed through time, suggesting a potential response to ecological opportunity in the wake of the end-Cretaceous mass extinction. Explosive bursts of trophic innovation followed colonization of the Nearctic and Neotropical realms by a group of snakes that today comprises a majority of living snake diversity. Our results indicate that repeated transformational shifts in dietary ecology are important drivers of adaptive radiation in snakes and provide a framework for analyzing and visualizing the evolution of complex ecological phenotypes on phylogenetic trees.

Strong trait correlation and phylogenetic signal in North American ground beetle (Carabidae) morphology

Functional traits mediate species’ responses to and roles within their environment, and are constrained by evolutionary history. While we have a strong understanding of trait evolution for macro-taxa such as birds and mammals, our understanding of invertebrates is comparatively limited. Here we address this gap in North American beetles with a sample of ground beetles (Carabidae), leveraging a large-scale collection and digitization effort by the National Ecological Observatory Network (NEON). For 154 ground beetle species, we measured seven morphological traits, which we placed into a recently-developed effect-response framework that characterizes traits by how they predict species’ effects on their ecosystems or responses to environmental stressors. We then used cytochrome oxidase one sequences from the same specimens to generate a phylogeny and tested evolutionary tempo and mode of the traits. We found strong phylogenetic signal in, and correlations among, morphological ground beetle traits. These results indicate that, for these species, beetle body shape trait evolution is constrained, and phylogenetic inertia is a stronger driver of beetle traits than (recent) environmental responses. Strong correlations among effect and response traits suggest that future environmental drivers are likely to affect both ecological composition and functioning in these beetles.

Phylogenetic Comparative Methods: A User’s Guide for Paleontologists

Recent advances in statistical approaches called Phylogenetic Comparative Methods (PCMs) have provided paleontologists with a powerful set of analytical tools for investigating evolutionary tempo and mode in fossil lineages. However, attempts to integrate PCMs with fossil data often present workers with practical challenges or unfamiliar literature. In this paper, we present guides to the theory behind, and application of, PCMs with fossil taxa. Based on an empirical dataset of Paleozoic crinoids, we present example analyses to illustrate common applications of PCMs to fossil data, including investigating patterns of correlated trait evolution, and macroevolutionary models of morphological change. We emphasize the importance of accounting for sources of uncertainty, and discuss how to evaluate model fit and adequacy. Finally, we discuss several promising methods for modelling heterogenous evolutionary dynamics with fossil phylogenies. Integrating phylogeny-based approaches with the fossil record provides a rigorous, quantitative perspective to understanding key patterns in the history of life.

Patterns of evolutionary tempo and mode in the radiation of Melanopsis (Gastropoda; Melanopsidae)

The Paratethyan basins of eastern Europe and western Asia became isolated from marine influence in the Late Miocene, and were the sites of several remarkable endemic radiations of brackish and freshwater organisms. Here I describe the patterns of tempo and mode before and during the radiation of the gastropod Melanopsis in the Pannonian basin of eastern and central Europe, and I explore the underlying mechanisms of evolutionary change.The most ancient melanopsid species in this area, M. impressa, was present in freshwater areas marginal to the basin well before the radiation. Widely spaced samples of M. impressa indicate that this species underwent a period of stasis lasting at least 7 m.y. The end of stasis corresponded with the extinction of the last of the normal marine fauna in the basin, suggesting that the lack of other fauna and/or reduced salinity in the basin permitted expansion of the melanopsids from the basin margins into the basin proper. Stasis ended with the onset of changes in size, shouldering, and ontogeny, which led eventually to M. fossilis. Change occurred over a 2-m.y. interval; a series of intermediates is present for all three characters. Within-sample correlations provide no evidence that the three characters are constructionally linked; instead they appear to be changing independently. The mode of change in the M. impressa–M. fossilis lineage appears to have been anagenetic. Alterations in the rate and direction of selection (and/or genetic links between characters) are probably required to explain the overall slowness of the change.Most Pannonian basin melanopsid species arose by rapid cladogenesis in the Middle Pannonian Stage. Physical factors in the basin probably influenced the timing of this diversification; contrasting patterns of variation and diversity between two melanopsid clades suggest that intrinsic factors influenced the extent of diversification.

Evolutionary tempo and mode in a sequence of the Upper Cretaceous bivalve Pleuriocardia

This study addresses the question of evolutionary tempo and mode in a sequence of Upper Cretaceous bivalves in the genus Pleuriocardia from the Western Interior Basin of North America. Change between species was probably phyletic (without persistence of ancestors). There is some evidence for weak gradual change within the lineage, but most important change is concentrated in short intervals of time. Detailed examination of the differences among samples reveals pronounced geographic variation, whereas temporal variation within localities is generally minor. The relatively rapid episodes of change fit the model of punctuated equilibrium, but the phyletic nature of species-level change does not.The value of the debate about the punctuated and gradualistic models has been to force a more criticial examination of fossil sequences, but these sequences should not be forced into narrowly defined categories. A variety of evolutionary patterns may exist in the fossil record, and it is this variation in pattern that will inform us of the underlying processes.

Resolution analysis: A new approach to the gaps in the fossil record

Fine-scale sampling and analysis of fossiliferous sequences have been used in the debate over gradual vs. punctuated evolutionary transitions between species. The time scale and completeness of these studied sequences can be evaluated using criteria based on compilations of sedimentation rates over different time spans. A set of procedures, herein termed “resolution analysis,” provides the means for estimating the time scale and quality of sequences from which evolutionary patterns are distilled. Seven such published studies are evaluated with these procedures. In general, most fossil sequences are too incomplete on fine time scales to show changes operating within a standing population. Short segments of some sequences have the potential to document nearly complete morphological histories on time scales approaching generation-to-generation processes. Resolution analysis is a necessary step in inferences regarding fossil evidence of evolutionary tempo and mode.Stratigraphic incompleteness necessarily results from the episodic nature of sedimentation. Many stratigraphic gaps result from minor, temporary shifts in sediment distribution, though other, more profound gaps result from changes in habitat conditions that must have had an effect on local biotic distribution. Analyzing paleontological patterns involves not only the positive evidence provided by fossiliferous strata, but also the negative evidence left as gaps by shifting habitat conditions. Thus, incomplete sequences may not be “flawed” records of continuous populations. Incomplete sequences may be a faithful, literal record of separate populations separated in time by local extinctions and re-invasions.