Global patterns of insect diversification: towards a reconciliation of fossil and molecular evidence?

Fabien L Condamine,Matthew E Clapham,Gael J Kergoat

doi:10.1038/srep19208

Abstract

Macroevolutionary studies of insects at diverse taxonomic scales often reveal dynamic evolutionary patterns, with multiple inferred diversification rate shifts. Responses to major past environmental changes, such as the Cretaceous Terrestrial Revolution, or the development of major key innovations, such as wings or complete metamorphosis are usually invoked as potential evolutionary triggers. However this view is partially contradicted by studies on the family-level fossil record showing that insect diversification was relatively constant through time. In an attempt to reconcile both views, we investigate large-scale insect diversification dynamics at family level using two distinct types of diversification analyses on a molecular timetree representing ca. 82% of the extant families, and reassess the insect fossil diversity using up-to-date records. Analyses focusing on the fossil record recovered an early burst of diversification, declining to low and steady rates through time, interrupted by extinction events. Phylogenetic analyses showed that major shifts of diversification rates only occurred in the four richest holometabolous orders. Both suggest that neither the development of flight or complete metamorphosis nor the Cretaceous Terrestrial Revolution environmental changes induced immediate changes in diversification regimes; instead clade-specific innovations likely promoted the diversification of major insect orders.

Highlights

Most molecular studies generally focus on specific groups or on particular timeframes[6,7,8,9,10,11,12,13,14], which precludes investigating and understanding what is behind the tremendous insects’ biodiversity? only mixed support has been provided for the effect of mass extinctions; for instance most fossil-based studies recovered an effect for the Permian-Triassic (P-T) mass extinction[1,4], while phylogenetic studies suggested that it had no impact[14]
The most common explanations propose that intrinsic features of insects such as their small size, the presence of an exoskeleton, or the development of new key-innovations best explain the long-lasting evolutionary success of insects
Our study attempts to bring new insights to progress in our understanding of insect diversification with an assessment of the fossil record and phylogenetic tree at the family level

Summary

Introduction

In the first study[26], the authors relied on a family-level time-calibrated phylogeny including 82% of the insect families and used a maximum likelihood method (MEDUSA) that is explicitly designed to identify upshifts and downshifts of diversification rates on a dated phylogeny[27] They identified 45 shifts in diversification rates across the insect tree of life, two shifts of which were characterized as major and associated to the origins of flight and of complete metamorphosis[26]. We re-analyse a recently published molecular phylogenetic dataset using two distinct state-of-the-art diversification analysis methods, which either complement (TreePar31) or outperform (BAMM32) the earlier MEDUSA approach Both the analyses of fossil and molecular data are expected to provide additional insights into the pattern of insect diversification over time, especially in relation to the role of (i) mass extinctions, (ii) environmental changes associated with the KTR and (iii) key innovations such as wings and complete metamorphosis

Methods

Results

Conclusion