Plant-insect Interactions From The Lopingian Kayitou Formation Of Zhaotong,Yunnan,Southwest China

Plants and insects are the two most diverse groups among today's terrestrial macro-organisms.They interact with each other and form the most important components of the terrestrial ecosystems,Lopingian(late Permian)is a critical time period in the developrment and evolution of terrestrial plants,and it is also a major turning point in the evolutionary history of insects.Investigation on plants and insects during this period provides comprehensive understanding of the biodiversity,the relationships and co-evolution of plants and insects,and the terrestrial ecosystems through the geological deep times.The Lopingian Kayitou Formation in Zhaotong City of Yunnan Province,Southwest China,yields abundant fossil plants that containing diverse herbivorous insect damages.On the basis of a thorough study of 1712 specimens,23 genera and 36 species of fossil plants have been recognised in the current flora.Systematically,the flora comprises lycopsids(2 species of 2 genera,5.56%),sphenopsids(3 species of 2 genera,8.33%),ferns and seed ferns(21 species of 14 genera,58.33%),cycado-phytes(1 species of 1 genus,2.78%),ginkgophytes(2 species of 2 genera,5.56%),gymnosperm seeds(3 species of 1 genus,8.33%),incertae sedis(1 species of 1 genus,2.78%)and 3 problematic types(8.33%),representing a typical Cathaysian Flora.Combined light microscopy and scanning electron microscopy reveal 171 insect damages on the plant fossils,which can be asgined to 24 Damage Types(DTs)of four major Functional Feeding Groups(FFGs).The external feeding FFG(77.78%of total damage occurences)includes 15 DTs,margin feedings(6 DTs,35.09%of the total damage occurrences),hole feedings(5 DTs,33.32%of the total damage occurences)and surface feedings(4 DTs,9.36%of the total damage occurences);there are 3 DTs of galls,making up 5.26%of the total damage occurrences(12.5%of total DTs);there are 2 DTs of oviposition,accounting for 7.02%of the total damage occurences(8.33%of total DTs);there are 4 DTs of pieceing-and-sucking,constiting 9.94%of the total damage occurrences(16.67%of total DTs).Statistical analysis of the occurrence,richness,diversity and frequency of DTs indicate that the Gigantopterids are the main host plants for the insect herbivores in the current flora.Comparing with other mid-to late Permian floras,significant distinction of in-sect damage can be recognised in different palaeo-latitudinal phytogeographic regions.Despite the different major target plant hosts in different floras,the richness and di-versity of insect DTs in the mid-to high latitudinal floras are remarkably lower than those in the lower latitudinal to(sub)tropical floras.This notable phenomenon is con-cerned that the terrestrial ecosystems with higher biodiversity in the lower latitudes have higher levels of ecological complexity,and obvious latitudinal gradients have been probably well-established in the terrestrial ecosystems during the late Paleozoic Era.This is the first systematic study of plant-insect interactions based on detailed analysis of insect damages in the Lopingian flora of China.This paper sheds new lights on the plant evolution,the ecological relationships between plants and insects,as well as the terrestrial ecosystems of the late Paleozoic Cathaysian Flora.