Biology subjects

Budd, G. E.

Publications and source records attributed to Budd, G. E..

7 recordsLinked to original sources

bioRxiv2026

Modelling a rapid radiation of crown-group placentals

The timing of the origins of the crown-group placental mammals has provided one of the classic battlefields in the long-running debate over when clades arise. Undoubted fossil crown-group placentals appear only in the Paleogene, but even so most molecular analyses, and many palaeontologists, have suggested their true origin is somewhere between 70-100 Ma. However, apart from the fact of the fossil record itself, there are several reasons to believe that the true origin is indeed post-Cretaceous, including consideration of the dynamics of stem and crown groups, which strongly favour crown-group origins to lie just after, and not just before, mass extinctions. Here we consider this "hard explosive" model in the light of the newly-developed "Covariant Evolutionary Tempo (CET)" model which allows diversification and molecular evolution rates to covary. It predicts "early bursts" in both lineage creation and molecular evolution at the base of major radiations which lead to highly unequally-sized clades; and an inheritance of rapid rates from this initial event by extant rapidly-evolving clades. We show that when the placentals are constrained to emerge after the K-Pg boundary, they indeed show elevated rates of both diversification and molecular evolution, which rapidly decline. Nevertheless, although elevated, these rates are comparable to the fastest rates seen in extant clades such as the rodents. In addition, the contiguous lineages leading from the origin to the rodents and other fast evolving clades also show elevated rates. These patterns suggest that not only is a Paleogene origin for the placental crown-group plausible, as fossil evidence suggests, but they also provide support for the CET model, which should be considered in other cases of pronounced fossil record/molecular clock mismatch.

evolutionary biology↗

bioRxiv2024

A covariant model of molecular and diversification patterns through time and the history of large clades

AO_SCPLOWBSTRACTC_SCPLOWRate shifts in speciation and extinction have been recognised as important contributors to the creation of evolutionary patterns. In particular, the distribution of modern clade sizes is difficult to reconcile with models that do not include them. Although recent advances have allowed rate shifts to be integrated into evolutionary models, these have largely been for the purpose of inferring historical rate shifts across phylogenetic trees. In addition, these models have typically assumed an independence between patterns of diversification and rates of molecular and morphological evolution, despite there being mounting evidence of a connection between them. Here, we develop a new model with two principal goals: first, to explore the general patterns of diversification implied by constantly changing rates, and secondly to integrate diversification, molecular and morphological evolution into a single coherent framework. We thus develop and analyse a covariant birth-death process in which rates of all evolutionary processes (i.e. speciation, extinction and molecular and morphological change) covary continuously, both for each species and through time. We use this model to show that modern diversity is likely to be dominated by a small number of extremely large clades at any historical epoch; that these large clades are expected to be characterised by explosive early radiations accompanied by elevated rates of molecular evolution; and that extant organisms are likely to have evolved from species with unusually fast evolutionary rates. In addition, we show that under such a model, the amount of molecular change along a particular lineage is essentially independent of its height, which further weakens the molecular clock hypothesis. Finally, our model predicts the existence of "living fossil" sister groups to large clades that are both species poor and have exhibited slow rates of morphological and molecular change. Although our model is highly stochastic, it includes no special evolutionary moments or epochs. Our results thus demonstrate that the observed historical patterns of evolution can be modelled without invoking special evolutionary mechanisms or innovations that are unique to specific times or taxa, even when they are highly non-uniform: instead they could emerge from a process that is fundamentally homogeneous throughout time.

evolutionary biology↗

bioRxiv2022

Two notorious nodes: a critical examination of MCMCTree relaxed molecular clock estimates of the bilaterian animals and placental mammals

The popularity of MCMCTree for Bayesian inference of clade origin timings has generated several recent publications with focal results considerably older than the fossils of the clades in question. Here we critically examine two such clades; the animals (with focus on the bilaterians) and the mammals (with focus on the placentals). Each example displays a set of characteristic pathologies which, although much commented on, are rarely corrected for. We conclude that in neither case does the molecular clock analysis provide any evidence for an origin of the clade deeper than what the fossil record might suggest. In addition, both these clades have other features (including, in the case of the placental mammals, proximity to a large mass extinction) that allow us to generate precise expectations of the timings of their origins. Thus, in these instances the fossil record can provide a powerful test of molecular clock methodology, and why it goes astray.

paleontology↗

bioRxiv2021

Fossil data do not support a long Pre-Cretaceous history of flowering plants

The origin of angiosperms is a classic macroevolutionary problem, because of their rapid rise in the Early Cretaceous fossil record, beginning about 139 Ma ago, and the conflict this creates with older crown-group ages based on molecular clock dating1. Silvestro et al.2 use a novel methodology to model past angiosperm diversity based on a Bayesian Brownian Bridge model of fossil finds assigned to extant families, concluding that a Cretaceous origin is vanishingly unlikely. However, their results strongly conflict with the known temporal distribution of angiosperm fossils, and, while we agree that statistical analysis aids interpretation of the fossil record, here we show the conclusions of Silvestro et al.2 are unsound.

paleontology↗

bioRxiv2020

A single origin of animal excretory organs

Excretion is an essential physiological process, carried out by all living organisms regardless of their size or complexity(1-3). Most animals, which include both protostomes (e.g. flies, flatworms) and deuterostomes (e.g. humans, sea urchins) (together Nephrozoa(4, 5)), possess specialized excretory organs. Those organs exhibit an astonishing diversity, ranging from units composed of just three distinct cells (e.g. protonephridia) to complex structures, built by millions of cells of multiple types with divergent morphology and function (e.g. vertebrate kidneys)(6, 7). Although some molecular similarities between the development of kidneys of vertebrates and the regeneration of the protonephridia of flatworms have been reported(8, 9), the molecular development of nephrozoan excretory organs has never been systematically studied in a comparative context(6). Here we show that a set of highly conserved transcription factors and structural proteins is expressed during the development of excretory organs of six species that represent major protostome lineages and non-vertebrate deuterostomes. We demonstrate that the molecular similarity witnessed in the vertebrate kidney and flatworm protonephridia(8) is also seen in the developing excretory organs of other Nephrozoa. In addition, orthologous structural proteins forming the ultrafiltration apparatus are expressed in all these organs in the filter-forming cells. Our results strongly suggest that excretory organs are homologous and are patterned by the conserved set of developmental genes. We propose that the last common nephrozoan ancestor possessed an ultrafiltration-based, ciliated excretory organ, a structure that later gave rise to the vast diversity of extant excretory organs, including the human kidney. Significance statementMost of the bilaterally symmetrical animals excrete through specialized excretory organs, such as kidneys and nephridia. However, due to the morphological diversity of these organs, it remains unknown whether those structures evolved from a common ancestral organ or appeared several times independently during evolution. In order to answer the question about the origin of excretory organs we investigated the molecular pathways and structural genes involved in the development of nephridia in 6 animal species representing major evolutionary lineages. We show that diverse excretory organs share an ancient molecular patterning and structural molecules. Our results provide strong evidence that all excretory organs originated from a single, simple organ that performed urine production by ultrafiltration in deep geological past.

evolutionary biology↗

bioRxiv2019

The dynamics of stem and crown groups

ABSTRACTThe fossil record of the origins of major groups is of great interests to many biologists, especially when the fossil record apparently conflicts with timings based on molecular clock estimates. Here we model the diversity of “stem” (basal) and “crown” (modern) members of groups as seen in the fossil record, using a “birth-death model”. Under background conditions, the stem group members must diversify rapidly until the modern crown group emerges, at which point their diversity rapidly collapses, followed shortly by their extinction. Mass extinctions can disturb this pattern to create very diverse stem groups such as the dinosaurs and trilobites. Understanding these null-hypothesis patterns is essential for framing ecological and evolutionary explanations for how major groups originate and subsequently evolve.View Full Text

paleontology↗

bioRxiv2017

History is written by the victors: the effect of the push of the past on the fossil record

Phylogenies may be modelled using \"birth-death\" models for speciation and extinction, but even when a homogeneous rate of diversification is used, survivorship biases can generate remarkable rate heterogeneities through time. One such bias has been termed the \"push of the past\", by which the length of time a clade has survived is conditioned on the rate of diversification that happened to pertain at its origin. This creates the illusion of a secular rate slow-down through time that is, rather, a reversion to the mean. Here we model the controls on the push of the past, and the effect it has on clade origination times, and show that it largely depends on underlying extinction rates. An extra effect increasing early rates of lineage generation is also seen in large clades. These biases are important but relatively neglected influences on many aspects of diversification patterns, such as diversification spikes after mass extinctions and at the origins of clades; they also influence rates of fossilisation, changes in rates of phenotypic evolution and even molecular clocks. These inevitable features of surviving and/or large clades should thus not be generalised to the diversification process as a whole without additional study of small and extinct clades.

paleontology↗