THE ORIGIN AND EARLY EVOLUTION OF LEAF-MINING INSECTS IN THE WAKE OF THE END-PERMIAN ECOLOGICAL CRISIS

A major consequence of the end-Permian (P-Tr) ecological crisis was extensive reorganization of terrestrial ecosystems and accompanying taxonoic turnover that resulted in extinction of many plant and insect lineages. The feeding relationships between insects and plants was a major victim of this profound transition, and included several types of feeding interactions that regionally were extirpated but subsequently re-evolved during the ensuing Triassic. For the Karoo Basin P-Tr sequence in South Africa, the abundance and diversity of Permian plant-insect interactions dramatically declined, and included extirpation of many external foliage feeding, piercing and sucking, oviposition and galling damage types (DTs). Until recently, leaf mining was not thought to occur during the Permian. Current evidence indicates that leaf mining was present in one latest Permian site in Kwa Zulu-Natal (Kwa Yaya), represented by a distinctive blotch mine on a particular glossopterid leaf morphotype. Although this mine type, and its plant host, did not survive the P-Tr event, leaf mining re-evolved, probably twice, during the Middle Triassic in Gondwana. For the Karoo Basin, two groups of Late Triassic leaf mines, collectively assignable to eight DTs, have been recorded on a broad spectrum of vascular plants. the first group represents robust, long, linear mines with sinusoidal frass trails that excavate most of the mesophyll layer and are very similar to modern polyphagan beetle mines. These mines occur in the foliage of woody seed-plant hosts of conifers (Heidiphyllum), cycads (Pseudoctenis), three major lineages of ginkgophytes (Paraginkgo, Sphenobaiera, Dejerseya), corystosperms or umkomsialeans (Dicroidium), and an unaffiliated taxon (Linguifolium). The second group is gracile, short, abbreviated mines with mostly linear frass trails typically lodged in the epidermis of nonwoody hosts, and resemble the mines of basal moth lineages. This latter group of mines occurs in the nodal zones of horesetails (Equisetites), pinnules and rachises of ferns (Cladophlebis), and leaves of the herbaceous ginkgophyte Kannaskoppifolia. There probably were two, parallel diversification events of leaf-mining insect lineages, each targeting a different plant physiognomy within the Molteno Biota.