The evolutionary history of wood-associated beetle larvae and the contribution of amber fossils

Zippel, Ana (2023): The evolutionary history of wood-associated beetle larvae and the contribution of amber fossils. Dissertation, LMU München: Fakultät für Biologie

Abstract

Beetles (Coleoptera) comprise more than 380,000 described species and are not only highly taxonomically diverse today but also ecologically and morphologically. The fossil record of beetles is not scarce, however, it is mostly represented by adult specimens. Beetle larvae, especially preserved in amber, have a reputation to be rare, and wood-associated beetle larvae have been claimed to be 'anecdotal'. It has been suggested that small and soft-bodied larvae do not get fossilized easily, especially the larvae leading a hidden way of life within the wood. I wanted to research whether they really are as rare in amber as it seems from the literature. In my thesis, I studied specimens preserved mostly in ~100-million-year-old Kachin, ~40-million-year-old Baltic, and ~25-million-year-old Mexican ambers. Through my contributions, in the form of 9 publications, I demonstrate that wood-associated beetle larvae can actually be considered relatively abundant in ambers. In fact, such finds should not surprise since the fossil larvae probably inhabited areas close to the origin of the plant resin. The resin dripped on the animal, or the animal stumbled or fell in. Once the animal became stuck and engulfed within the resin it became a biological inclusion within hardened and fossilized resin, now considered amber. However, the fossil record of diverse groups of beetles within ambers seems biased towards adults, especially males. The reports of beetle larvae stay scarce, even though they are of great importance for understanding the evolutionary history of beetles and their biodiversity. In Holometabola, a group including beetles as well, modern representatives have life cycles including an adult, a pupa, and larval stages. Interestingly, most of the lifespan of many extant beetles is spent in the larval stages. Therefore, larvae of beetles not only increase the morphological and often ecological diversity of the group but are a big, if not the biggest, part of the beetle biomass. In addition, the modern wood-associated beetle larvae have another important role, they help in breaking and decomposing of wood, therefore, enhancing carbon cycling. It seems that wood as a substrate offers many different microenvironments depending on the state it is in. In this study I differentiate several functional groups of modern representatives of beetle larvae that feed on wood in different states: hardwood borers, softwood borers, fungus-infected wood borers, submerged wood borers, and in-wood predators. Even though predators are not directly feeding on wood, they are often encountered within the wood, especially within the galleries and tunnels of wood-feeding larvae that they prey upon. I was wondering whether such differentiation of wood-associated larvae already existed within the extinct representatives of past faunas. In the scope of this thesis I present two publications with possible hardwood borers, three publications considering possible softwood borers (even though, one specimen is likely a larva of Holometabola, but possibly not of Coleoptera), one manuscript with fungus feeders, one publication and one manuscript with submerged-wood borers and two publications with in-wood predaceous beetle larvae. Therefore, the wood habitats were crawling with life also in ecosystems of the past. Within the incorporated manuscripts and publications, my co-authors and I presented the fossil beetle larvae and their morphological characters on images created with a digital microscope, x-ray microcomputed tomography, and synchrotron radiation micro-computed tomography. The (rendered) images were further processed with programs such as Adobe Photoshop or Inkscape for easier interpretation by readers. Additionally, many of the new fossil larvae showed morphologies unknown from modern beetle larvae. Hence implying that the morphologies of extinct beetle larvae differed and occupied a different range of morphospace than the morphologies known from the modern beetle larvae. In order to compare the range of morphologies through time within the morphospace we used the pipeline of programs SHAPE that uses an Elliptic Fourier Analysis and a Principal Component Analysis.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Fakultät für Biologie
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 25. Oktober 2023
• 1. Bericht­erstatter:in: Haug, Joachim