A new glimpse on trophic interactions of 100-million-year old lacewing larvae MARIE K. HÖRNIG, CHRISTINE KIESMÜLLER, PATRICK MÜLLER, CAROLIN HAUG, and JOACHIM T. HAUG Hörnig, M.K., Kiesmüller, C., Müller, P., Haug, C., and Haug, J.T. 2020. A new glimpse on trophic interactions of 100-million-year old lacewing larvae. Acta Palaeontologica Polonica 65 (4): 777–786. Larvae of lacewings (Neuroptera) are known to be fierce predators. According to the morphology of fossil forms this seems to have been the case already in the Early Cretaceous. While being predators, lacewing larvae are also food items for other organisms. Here we report two pieces of amber from Myanmar providing instances of such cases. In one amber piece several isolated stylets of lacewing larvae are preserved closely associated together. The most likely interpretation is that a predator preying on lacewing larvae has regurgitated or defecated these non-digestible pieces, yet the identity of the predator remains unclear. The other amber piece preserves a larva resembling modern day larvae of split-footed lacewings (Nymphidae). The larva has projections on its trunk, allowing it to wear a camouflaging cloak. In the head region, a mite (Acari) is attached to the larva; more precisely, the entire anterior body region of the mite is apparently inserted into the lacewing larva. The mite is smaller than the larva. It is known from the modern fauna that stage 1 larvae of Ascalaphidae can be attacked also by rather small predators, such as ants. The mite can therefore well be interpreted as a true predator instead of a parasite, especially considering the unusual mode of attachment. We briefly review in- teractions of lacewing larvae with other organisms represented in amber from Myanmar and add two new pieces to the puzzle of reconstructing the trophic interactions in the 100-million-year old amber forest. Key words: Neuroptera, Nymphidae, food-web reconstruction, Burmese amber, larvae, syninclusions, Cretaceous, Myanmar. Marie K. Hörnig [[email protected]] and Christine Kiesmüller [[email protected]], Univer- sity of Greifswald, Zoological Institute and Museum, Cytology and Evolutionary Biology, Soldmannstr. 23, D-17489 Greifswald, Germany. Patrick Müller [[email protected]], Friedhofstr. 9, 66894 Käshofen, Germany. Carolin Haug [[email protected]] and Joachim T. Haug [[email protected]], Ludwig-Maximilians-Universität München (LMU), Biocenter, Großhaderner Str. 2, 82152 Planegg-Martinsried, Ger- many and GeoBio-Center, Ludwig-Maximilians-Universität München, Richard-Wagner-Straße 10, 80333 München, Germany. Received 12 September 2019, accepted 27 July 2020, available online 3 December 2020. Copyright © 2020 M.K. Hörnig et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. (i) Predator-prey interactions. Predation, is meant here Introduction in the narrow sense, i.e., an organism, the prey, is killed and at least partly consumed by another organism, the predator, Understanding the structure of food webs has become more during the interaction; the time of interaction is relatively important in recent years as it has direct impact for iden- short (excluding “micropredation”, see point iii) tifying keystone species within the trophic structure of a (ii) Parasitoid-host interactions. Similar to predation, an community (e.g., Bond 1994; de Ruiter et al. 2005; Knight organism, the host, is at least partly consumed and killed et al. 2005; Jordan 2009; Valls et al. 2015). Identifying such during the interaction by the other organism, the parasitoid; keystone species is of prime importance in the protection of yet, unlike in the case of predation, the time of interaction biodiversity and conservation biology. is quite long. There are many different types of trophic interactions in (iii) Temporary parasite-host interactions. Unlike in the biological systems (e.g., Lafferty and Kuris 2002). A simpli- cases mentioned before, the host organism is not killed (on fied list of such interactions among animals includes: purpose), yet similar to predation the time of interaction Acta Palaeontol. Pol. 65 (4): 777–786, 2020 https://doi.org/10.4202/app.00677.2019 778 ACTA PALAEONTOLOGICA POLONICA 65 (4), 2020 between the temporary parasite and the host is rather short. are hence interpreted as interacting with certain other or- Typical examples are mosquitoes and ticks. Note that many ganisms according to the assumed guild. The second frame authors refer to this type of interaction as “micro-predation” is definitely the weaker argumentation scheme, yet espe- because only a small part of the host is consumed (e.g., cially in older communities, for example, early Palaeozoic Lafferty and Kuris 2002). Yet, in many fields of biology ones, this is often the only applicable frame (e.g., Zhu et al. the prefix “micro” refers to a specific fraction of organisms 2004; Vannier 2007). with a small body size. Hence, the term “micro-predator” Direct interaction of two organisms.—This is a type of so- could well refer to small-sized predators that prey on like- called “frozen behaviour”, i.e., two (or more) fossil organisms wise small prey as raptorial waterfleas or raptorial mites. are preserved while interacting (Arillo 2007; Boucot and Therefore, the term “micro-predator” may be easily misin- Poinar 2010). As an example, a predator may be preserved terpreted, while “temporary parasite” appears more specific while directly interacting with its prey. The famous fighting and is used in the following here. dinosaurs may be the most generally known case of such (iv) Permanent parasite-host interactions. In this type of a type of fossilisation (Kielan-Jaworowska and Barsbold interaction the host is not killed by the other organism, the 1972). Yet, as discussed above, predators and temporary par- parasite, and the time of interaction is long. asites interact only for a short amount of time with the prey, Apart from these very direct types of interaction in which hence such occurrences are rare. Permanent parasites that one individual interacts with another one, there are also more attach to their host for longer, or scavengers sitting on a car- indirect types of interactions. For example, some animals de- cass for quite some time seem much more likely to be found pend on remains of other animals, such as e.g., dung beetles (Hanski and Cambefort 2014) or larvae of some representa- as fossils (e.g., Weitschat and Wichard 1998; Arillo 2007; tives of flies (e.g., Sepsidae; Hafez 1948; or some species of Boucot and Poinar 2010: 27–71; Gröhn 2015). Muscidae, Kutty et al. 2014). In this way, the producer of the Remains of the prey or host.—If the prey has been con- faeces will not have direct contact to the other individual, yet sumed by the predator, or parts of the host by the parasite the consumer has a direct interaction with the faeces. Hence, or parasitoid, it will leave vestiges behind. We can therefore this interaction is asymmetric. Also partly indirect is, for have various types of remains of a prey or host organism: example, a scavenger-carcass interaction. (i) Damaged hard shelled organisms, as for examples mol- In modern-day communities, the direct identification of luscan shells that have been attacked by a predator or parasite interactions, as the ones discussed above, can be more or (e.g., Boucot and Poinar 2010: 79; Bicknell and Paterson 2018; less challenging depending on many factors, such as size. Vinn 2018), yet, such traces can be difficult to interpret and In other words, for example in the case of predator-prey differentiate from other factors influencing preservation. interaction, it is much more straightforward to observe a (ii) Stomach and gut content. While it is rarely possible lion preying on a zebra, compared to observing a tiny beetle to find the stomach or gut content sufficiently well pre- preying on a mite. Yet, luckily quite a large variety of meth- served to indeed identify these remains, there are few excep- ods can be used in modern-day communities to reconstruct tional cases (also termed “gastrolites”, fossilized stomach the food web within a community (e.g., Mouchet et al. 2010; contents, “enterospira”, contents preserved in the valvular Morales-Castilla et al. 2015; Casey et al. 2019). intestine, and “cololites”, non-valvular intestinal contents; More challenging is the reconstruction of trophic inter- Hunt 1992; Northwood 2005; Hunt and Lucas 2012). This is actions within fossil communities. Still, also here we can an even better, more reliable type of data than observing the use different approaches for identifying trophic interactions direct interaction between two organisms. In the latter case based on fossils: we still have to assume that the supposed predator would Actuopalaeontology.—If we observe a certain trophic in- later consume the proposed prey, and a supposed parasite teraction within a modern community, or even better in might just use the supposed host for phoresis. In the case of several modern communities, and we find the same two stomach or gut content preservation we can directly observe components in a fossil community, we can suggest a sim- that the prey or parts of the host have been consumed (e.g., ilar trophic interaction also within the fossil community at Wilby and Martill 1992; Kriwet et al. 2007; Vannier 2012). least with a certain (though not absolute) confidence. This (iii) Coprolites. Fossil faeces may also be preserved well approach appears to have been used in two different frames: enough to allow the identification of its components. This (i) a phylogenetic frame, i.e., if all representatives of one is in principle comparable to gut content preservation, yet monophyletic group interact with representatives of another usually we do not know the producer, as coprolites are only monophyletic group, and if we have representatives of both very rarely preserved together with their producer.