Rich specialized insect damage on Pliocene leaves from the Mahuadanr Valley (India) growing under a warm climate with weak seasonality.

Plant-insect interactions play a crucial role in shaping terrestrial ecosystems, influencing abundance and distribution of plant species. In the present study, we investigated leaf-mining patterns on fossil leaves from Pliocene strata of the Mahuadanr Valley, Jharkhand, eastern India, deposited under a seasonal tropical climate, and reported complex interactions between plants and insects. We identified 11 distinct mining morphotypes. These morphotypes were mainly found on Dipterocarpaceae, Fabaceae, Lauraceae, and Moraceae; similar mining traces were also observed in the contemporary vegetation surrounding the fossil site. Although mining richness was relatively high, only 2.6% of all leaves in the fossil assemblage were mined. We compared mining richness and abundance values with previously reported values for galling. While richness was slightly lower for galling, almost 50% of all fossil leaves were galled. A literature survey on mining and galling patterns in modern vegetation suggests that there is no global explanation for richness of mining or gall-inducing insects. Thus, low nutrient availability in the ancient forest, dominance of semideciduous leaves with hard texture, and different habitats in the same forest ecosystem, such as well-drained forests and riparian stands, may all have favored different types of specialized plant-insect interactions.

Marginal leaf galls on Pliocene leaves from India indicate mutualistic behavior between Ipomoea plants and Eriophyidae mites.

We report a new type of fossil margin galls arranged in a linear series on dicot leaf impressions from the latest Neogene (Pliocene) sediments of the Chotanagpur Plateau, Jharkhand, eastern India. We collected ca. 1500 impression and compression leaf fossils, of which 1080 samples bear arthropod damage referable to 37 different damage types (DT) in the 'Guide to Insect (and Other) Damage Types in Compressed Plant Fossils'. A few leaf samples identified as Ipomoea L. (Convolvulaceae) have specific margin galls that do not match any galling DT previously described. This type of galling is characterized by small, linearly arranged, irregular, sessile, sub-globose, solitary, indehiscent, solid pouch-galls with irregular ostioles. The probable damage inducers of the present galling of the foliar margin might be members of Eriophyidae (Acari). The new type of gall suggests that marginal gall-inducing mites on leaves of Ipomoea did not change their host preference at the genus level since the Pliocene. The development of marginal leaf galling in Ipomoea is linked to extrafloral nectaries that do not offer protection against arthropod galling but indirectly protect the plant against herbivory from large mammals.

A case of long-term herbivory: specialized feeding trace on Parrotia (Hamamelidaceae) plant species.

Interactions between plants and insects evolved during millions of years of coevolution and maintain the trophic balance of terrestrial ecosystems. Documenting insect damage types (DT) on fossil leaves is essential for understanding the evolution of plant-insect interactions and for understanding the effects of major environmental changes on ecosystem structure. However, research focusing on palaeoherbivory is still sparse and only a tiny fraction of fossil leaf collections have been analysed. This study documents a type of insect damage found exclusively on the leaves of Parrotia species (Hamamelidaceae). This DT was identified on Parrotia leaves from Willershausen (Germany, Pliocene) and from Shanwang (China, Miocene) and on their respective endemic modern relatives: Parrotia perisca in the Hyrcanian forests (Iran) and Parrotia subaequalis in the Yixing forest (China). Our study demonstrates that this insect DT persisted over at least 15 Myr spanning eastern Asia to western Europe. Against expectations, more examples of this type of herbivory were identified on the fossil leaves than on the modern examples. This mismatch may suggest a decline of this specialized plant-insect interaction owing to the contraction of Parrotia populations in Eurasia during the late Cenozoic. However, the continuous presence of this DT demonstrates a robust and long-term plant-herbivore association, and provides new evidence for a shared biogeographic history of the two host plants.

Plant-insect interactions patterns in three European paleoforests of the late-Neogene-early-Quaternary.

Plants and insects are constantly interacting in complex ways through forest communities since hundreds of millions of years. Those interactions are often related to variations in the climate. Climate change, due to human activities, may have disturbed these relationships in modern ecosystems. Fossil leaf assemblages are thus good opportunities to survey responses of plant-insect interactions to climate variations over the time. The goal of this study is to discuss the possible causes of the differences of plant-insect interactions' patterns in European paleoforests from the Neogene-Quaternary transition. This was accomplished through three fossil leaf assemblages: Willershausen, Berga (both from the late Neogene of Germany) and Bernasso (from the early Quaternary of France). In Willershausen it has been measured that half of the leaves presented insect interactions, 35% of the fossil leaves were impacted by insects in Bernasso and only 25% in Berga. The largest proportion of these interactions in Bernasso were categorized as specialist (mainly due to galling) while in Willershausen and Berga those ones were significantly more generalist. Contrary to previous studies, this study did not support the hypothesis that the mean annual precipitation and temperature were the main factors that impacted the different plant-insect interactions' patterns. However, for the first time, our results tend to support that the hydric seasonality and the mean temperature of the coolest months could be potential factors influencing fossil plant-insect interactions.