Pliocene Insect Herbivory Dynamics in Central Europe as Key to the Future
Final Report Abstract
Insects are the most diverse animals on Earth, and neatly associated with plants they represent two of the major groups of organisms both in species diversity and biomass quantity. The majority of their interactions involve insect feeding and insect parasitism (such as galls forming) mostly on leaves. Plant and insect compose one of the main trophic levels in ecosystems over the 325 million years. Today, the continuous and fast rising of temperature mostly due to human activities since the last century is disturbing the balance of ecosystems on Earth. This is named "global change". Consequently, to understand the role of plant and insect interactions, through time but also trophic networks, becomes crucial. It is in this general context that the aim of the thesis pursued. The fossil record is an exceptional opportunity to survey responses of plant-insect interaction to climate variations over long time interval through traces of plants reactions caused by interaction with insects, as Earth has already experienced many climate changes. For the last 3 million years (Ma), oscillations between long cold periods, marked by the rifting of ice cap in Northern Hemisphere, and short warm periods have occurred. European ecosystems have been particularly impacted by these climatic variations. This project emphasized a particular interest to the famous Lagerstätte of Willershausen in Germany, which contained more than 8000 leaves from angiosperm with potentially abundant insect feeding traces. This analysis was completed by a focus of Berga in Germany, a quite similar fossil leaf assemblage and Bernasso in France, a more recent fossil leaf assemblage but with same taxa. Furthermore, in order to obtain accurate results without specific problem due to fossil preservation, a part of this project focused also on the modern Hyrcanian forest in Iran. This actual forest is considered as the best analogue one of the European paleoforest from the Plio-Pleistocene boundary, represented by Willershausen, Berga and Bernasso. The different comparison in these different contexts provided three major results, which must to be considerate for the next study in the topic of plant-insect interactions. 1. Climate seasonality. Both hydric and temperature seasonality seems to have a major impact on the variations of plant-insect interactions. It appeared that ecosystems subject to intense hydric seasonality (i.e. important variations of precipitation during the year) could led to higher specialization of plant-insect interaction inferred by higher rate of observed damages du to ‘specialists insects’. This hypothesis was firstly suggested for Willershausen in comparison with Berga and Bernasso location. Bernasso which could be suggested to higher climate seasonality due especially to its Mediterranean climate, presented drastically more specialized damage type than both Willershausen and Berga. In addition, this hypothesis was also supported by the study on the modern Hyrcanian forest. Indeed, along the longitudinal gradient of the Hyrcanian forest, marked by strong difference of annual precipitation especially, the location with the highest seasonality of the precipitation during the year, presented also the highest proportion of specialized interaction, mainly due to galling damage. 2. Coolest annual temperature. The coolest temperature during the year seems to be a major factor in the low diversity of damage in paleoforests. This is presumably due to lower insect metabolism, as the insects are mostly in diapause during the cold period of the year. This hypothesis, while is plausible according to the fossil leaf assemblage and the known climatic condition of the three paleoforests, could not be supported by the modern analogue as the period of the study was too short, not during, at least, the whole year. Deeper investigations in the fossil record but also nowadays must to be done in this way. 3. Abiotic factor more important than local biotic factors. This is certain that understand potential impact of biotic parameters, such as inter competition between plant species and/or insect species is quite complicated especially in the fossil record. However, absence of convergent correlations between plant richness and damage richness could suggest that influence of climatic factors override impact of these local biotic factors. In contrast, influence of those climatic factors for example, can drive close phylogenetic plant species in the same way that was observed in Willershausen about the whole species belonging to Betulaceae.
Publications
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2016. Bernasso, a paleoforest from the early Pleistocene: New input from plant–insect interactions (Hérault, France). Palaeogeogr. Palaeoclimatol. Palaeoecol. 446, 78-84
Adroit, B., Wappler, T., Terral, J-F., Ali, AA., Girard, V.
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2016. First Record of the Family Trogossitidae (Insecta, Coleoptera) in the Late Pliocene Deposits of Willershausen (Germany). PalZ 90, 681-689
Kolibáč, J., Adroit, B., Gröning, E., Brauckmann, C., Wappler,T.
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Herbivore density and leaf damage on Persian ironwood, Parrotia persica, in the Caspian Hyrcanian mixed forest. 87th Annual Conference of the Paläontologische Gesellschaft, 11-15 September 2016, Dresden, Germany. Abstracts, p. 5
Malekhosseini, M., Adroit, B., Wappler, T.
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Plant-insect interaction at Willershausen (-3 Ma, Germany): insights into the structuration of an important late European Palaeoecosystem. 7th International Conference on Fossil Insects, Arthropods & Amber, 26 April-1 May 2016, Edinburgh, Scotland. Abstracts, p. 4
Adroit, B., Girard, V., Terral., J-F., Wappler, T.
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Structure of the European palaeoecosystems from the Plio-Pleistocene transition: inputs of the plant-insect interactions. 88th Annual Conference of the Paläontologische Gesellschaft, 26-30 March 2017, Münster, Germany. Abstracts, p. 23
Adroit., B., Girard, V., Terral., J-F., Wappler, T.
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Structure of the European palaeoecosystems from the Plio-Pleistocene transition: inputs of the plant-insect interactions. 88th Annual Conference of the Paläontologische Gesellschaft, 26-30 March 2017, Münster, Germany. Abstracts, p. 23
Adroit., B., Girard, V., Terral., J-F., Wappler, T.
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2018, Changes on herbivory pattern on the Persian ironwood (Parrotia persica) over the last 3 million years. Rev. Palaeobot. Palynol 258, 22-35
Adroit, B., Malekhosseini, M., Girard, V., Abedi, M., Rajaei, H., Terral, J-F., Wappler, T.
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2018. Plant-insect interactions patterns in three European paleoforests of the late-Neogene – early-Quaternary. PeerJ 6, e5075
Adroit, B., Girard, V., Kunzmann, Lutz., Terral, J-F., Wappler, T.
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The Plio-Pleistocene biogeographic history of Parrotia persica highlighted by a new plant-insect interaction. 5th International Paleontological Congress – Paris, 9th -13th July 2018. Abstracts, p. 342
Adroit, B., Girard, V., Terral., J-F., Wappler, T.
