Quantitative analysis of lacewing larvae over more than 100 million years reveals a complex pattern of loss of morphological diversity

Abstract

Loss of biodiversity and especially insect decline are widely recognised in modern ecosystems. This decline has an enormous impact due to the crucial ecological roles of insects as well as their economic relevance. For comparison, the fossil record can provide important insights on past biodiversity losses. One group of insects, for which a significant decline over the last 100 million years has often been postulated, but not demonstrated quantitatively, is Neuroptera (lacewings). Many adult lacewings are pollinators, while the larvae are mostly predators, which becomes very obvious from their prominent stylet-like mouthparts. We investigated the fossil record of larvae of all neuropteran lineages as well as a large share of extant neuropteran larvae. Based on these, we performed an outline analysis of the head with stylets. This analysis provides a quantitative frame for recognising the decline of lacewings since the Cretaceous, indicating also a severe loss of ecological roles.

The Diversity of Larvae with Multi-Toothed Stylets from About 100 Million Years Ago Illuminates the Early Diversification of Antlion-like Lacewings

“…Different structures of the larvae were considered and analysed with the aid of an elliptic Fourier transformation. The data set was based on the directly studied specimens and larvae from the literature, partly assembled from earlier datasets [44,83,84,[87][88][89], including all lacewing larvae that possess teeth. In total, 424 larvae were considered (for a specimen list, see table in Supplementary Materials), including:…”

“…(2) stylets (424 specimens); and (3) head capsule (132 specimens). To quantitatively compare these outlines, we employed elliptic Fourier analysis (EFA) following earlier studies [44,81,99]. Hereby, the two-dimensional shield outline is decomposed into a mathematical object.…”

“…In contrast to the modern-day fauna, Neuroptera has been assumed to have been more diverse in the past [36,43]. Despite this common assumption, demonstrating this loss quantitatively remained challenging [44] and could best be recognised by investigating the larval forms.…”

“…These stylets are piercingsucking mouthparts that are used to inject venom into their prey, then inject saliva, and finally suck out the dissolved tissues of the prey [50]. Studying losses of lacewing larval diversity over geological time spans is facilitated by a rich fossil record of these larvae in different types of ambers: Baltic amber [51][52][53][54][55][56][57][58][59][60][61], Dominican and Mexican amber [62][63][64], New Jersey amber [65], Myanmar amber [44,, French amber [100], Spanish amber [101][102][103], Lebanese amber [104,105], and Chinese amber [106].…”

“…A major share of the diversity in Neuroptera is formed by the group of antlion-like lacewings, Myrmeleontiformia [41]. Traditionally, five major extant lineages ("families") have been distinguished [36], yet newer analyses have either reduced that number to four [107] or increased it to nine [108][109][110], demonstrating again that ranked taxonomy cannot be used for reliable quantitative comparisons [44]. Unchallenged extant lineages include Psychopsidae (silky lacewings), Nymphidae (split-footed lacewings), and Nemopteridae (although its two major ingroups, Nemopterinae and Crocinae, are sometimes treated not as "subfamilies" but as "families"; e.g., [108]).…”