An Insect Molecular Clock Dates the Origin of the Insects and Accords with Palaeontological and Biogeographic Landmarks

Abstract

A unified understanding of >390 Myr of insect evolution requires insight into their origin. Molecular clocks are widely applied for evolutionary dating, but clocks for the class Insecta have remained elusive. We now define a robust nucleotide and amino acid mitochondrial molecular clock encompassing five insect orders, including the Blattaria (cockroaches), Orthoptera (crickets and locusts), Hemiptera (true bugs), Diptera, and Lepidoptera (butterflies and moths). Calibration of the clock using one of the earliest, most extensive fossil records for insects (the early ancestors of extant Blattaria) was congruent with all available insect fossils, with biogeographic history, with the Cambrian explosion, and with independent dating estimates from Lepidopteran families. In addition, dates obtained from both nucleotide and amino acid clocks were congruent with each other. Of particular interest to vector biology is the early date of the emergence of triatomine bugs (99.8-93.5 MYA), coincident with the formation of the South American continent during the breakup of Gondwanaland. More generally, we reveal the insects arising from a common ancestor with the Anostraca (fairy shrimps) at around the Silurian-Ordovician boundary (434.2-421.1 MYA) coinciding with the earliest plant megafossil. We explore Tilyard's theory proposing that the terrestrial transition of the aquatic arthropod ancestor to the insects is associated with a particular plant group (early vascular plants). The major output of the study is a comprehensive series of dates for deep-branching points within insect evolution that can act as calibration points for further dating studies within insect families and genera.

Pattern and timing of diversification in Yucca (Agavaceae): specialized pollination does not escalate rates of diversification

“…Whereas the diversification of the Yucca crown group began 6.41-10.19 Myr ago, previous estimates indicate that yucca moths began to diversify ca 40G11.1 Myr (ago; Pellmyr & Leebens-Mack 1999). Although the age estimates for the pollinating moths have recently been revised downwards to 32 Myr (Gaunt & Miles 2002), these are still several million years prior to our very oldest estimates for the common ancestor yuccas and are tens of millions of years older than the maximum-likelihood estimate.…”

The fat-like Gene of Drosophila Is the True Orthologue of Vertebrate Fat Cadherins and Is Involved in the Formation of Tubular Organs

“…3). The C. elegans fat-like-related molecules, Cdh-3 and Cdh-4, are poorly clustered suggesting that the onset of development of modern Fat cadherins may have occurred about 430 million years ago when insects emerged (29).…”

The evolution of novelty in conserved genes; evidence of positive selection in the Drosophila fruitless gene is localised to alternatively spliced exons

“…Such conservation was shown by the ability of the Anopheles gambiae ortholog of fru to function when ectopically expressed in D. melanogaster resulting in the production of the fru-dependent male-specific muscle of Lawrence (Gailey et al, 2006). As A. gambiae and D. melanogaster have been separated for B250 mya (Gaunt and Miles, 2002;Zdobnov et al, 2002), Gailey et al (2006) concluded that fru has been functionally conserved across this time period. This has been further emphasised with the finding that RNAi-mediated knockdown of fru extinguishes male courtship in the cockroach Blattella germanica, suggesting that the large role fru has in the production of male sexual behaviours has been conserved for at least a large portion of insect evolution (Clynen et al, 2011).…”