Fossil evidence for key innovations in the evolution of insect diversity

Abstract

Explaining the taxonomic richness of the insects, comprising over half of all described species, is a major challenge in evolutionary biology. Previously, several evolutionary novelties (key innovations) have been posited to contribute to that richness, including the insect bauplan, wings, wing folding and complete metamorphosis, but evidence over their relative importance and modes of action is sparse and equivocal. Here, a new dataset on the first and last occurrences of fossil hexapod (insects and close relatives) families is used to show that basal families of winged insects (Palaeoptera, e.g. dragonflies) show higher origination and extinction rates in the fossil record than basal wingless groups (Apterygota, e.g. silverfish). Origination and extinction rates were maintained at levels similar to Palaeoptera in the more derived Polyneoptera (e.g. cockroaches) and Paraneoptera (e.g. true bugs), but extinction rates subsequently reduced in the very rich group of insects with complete metamorphosis (Holometabola, e.g. beetles). Holometabola show evidence of a recent slow-down in their high net diversification rate, whereas other winged taxa continue to diversify at constant but low rates. These data suggest that wings and complete metamorphosis have had the most effect on family-level insect macroevolution, and point to specific mechanisms by which they have influenced insect diversity through time.

Mechanics of the thorax in flies

“…There are numerous examples of similar mechanical structures that ensure precise coordination in insects or other arthropods (Patek et al, 2011). Because such structures are typically involved in fast and repetitive movements, they are compelling systems in which to explore adaptations for energy efficiency, such as elastic storage or amplification.…”

“…complete metamorphosis; e.g. Nicholson et al, 2014) in the first four of these orders, the evolutionary success of hyper-diverse orders is thought to predicate on the combination of two major factors: one, the evolution of small body size, which greatly facilitated adaptability by increasing their ecological range; and two, the evolution of flight, which enabled dispersal, migration, predation or rapid escape from predator attacks.…”

The fossil record and macroevolutionary history of the beetles

“…By contrast, very few polyphagan families have gone extinct, so the extinction rate of Polyphaga is always effectively zero (figure 4d). When compared with family-level extinction rates for other fossil animals [11,26,54], the Polyphaga have some of the lowest levels of extinction.…”

“…Other than the work of Labandeira & Sepkoski [10] and Nicholson et al [11], which focused on the fossil record of insects overall, there have been no quantitative analyses of the beetle fossil record. Furthermore, the pattern of beetle diversification documented in the fossil record and its correspondence to molecular-phylogenetic estimates remains unclear (but see [12] for a more ecological approach).…”

Ancient origin of high taxonomic richness among insects

“…Evolutionary innovations such as the evolution of flight and the origin of complete metamorphosis may be among the key drivers [2][3][4]. Ecological characteristics of insect clades probably also played an important role in their rapid diversification.…”