Fossil oak galls preserve ancient multitrophic interactions

Area of Science:

• Paleontology
• Evolutionary Biology
• Entomology

Background:

• Insect feeding trace fossils enhance understanding of insect-plant interactions.
• Galls, complex herbivory structures, often identify the gall inducer.
• Most fossil galls lack detail for identifying causers or associated communities.

Purpose of the Study:

• To report the first evidence of multitrophic associations in Pleistocene fossil galls.
• To identify gall inducers and associated organisms in Eemian interglacial galls.
• To reconstruct past insect-plant interactions and host plant distributions.

Main Methods:

• Analysis of exceptionally well-preserved fossil galls from the Eemian interglacial (130,000–115,000 years ago) in The Netherlands.
• Morphological identification of gallwasps (Hymenoptera: Cynipidae) and their host oaks (Quercus).
• Phylogenetic analysis to infer host plant alternation and past species distributions.

Main Results:

• Fossil galls attributed to extant Andricus gallwasps (Hymenoptera: Cynipidae) on oaks (Quercus).
• First fossil evidence of herbivorous inquiline gallwasps attacking plant galls.
• Phylogenetic placement suggests a second oak species, Quercus cerris, was present, previously unknown in Eemian fossils from northwestern Europe.

Conclusions:

• The study provides the earliest fossil evidence of complex gallwasp-associated communities.
• The presence of Quercus cerris suggests a return to preglacial distribution limits for this oak species.
• These findings offer insights into ancient gallwasp ecology and biogeography, potentially linked to human influence in later periods.