The Behavioral Ecology and Evolution of Kleptoparasitism in Australian Gall Thrips

Abstract

We used a combination of behavioral-ecological and molecular-phylogenetic data to analyze the origin and diversification of kleptoparasitic (gall-stealing) thrips in the genus Koptothrips, which comprises four described species that invade and breed in galls induced by species of Oncothrips and Kladothrips on Australian Acacia. The genus Koptothrips is apparently monophyletic and not closely related to its hosts. Two of the species, K. dyskritus and K. flavicornis, each appears to represent a suite of closely-related sibling species or host races. Three of the four Koptothrips species are facultatively kleptoparasitic, in that females can breed within damaged, open galls by enclosing themselves within cellophane-like partitions. Facultative kleptoparasitism may have served as an evolutionary bridge to the obligately kleptoparasitic habit found in K. flavicornis. Evidence from phylogenetics, and Acacia host-plant relationships of the kleptoparasites and the gall-inducers, suggests that this parasite-host system has undergone some degree of cospeciation, such that speciations of Koptothrips have tracked the speciations of the gall-inducers. Quantification of kleptoparasitism rates indicates that Koptothrips and other enemies represent extremely strong selective pressures on most species of gall-inducers. Although the defensive soldier morphs found in some gall-inducing species can successfully defend against Koptothrips invasion, species with soldiers are still subject to high rates of successful kleptoparasite attack. Gall-inducing thrips exhibit three main types of life-history adaptation that have apparently evolved in response to kleptoparasite pressure: (1) "fighters", which exhibit long-lived galls and soldier morphs, (2) "runners", which have quite short-lived galls, from which offspring disperse as second instar larvae, and (3) "hiders", whose galls are long-lived, especially tight-sealing, and induced on a taxonomically-distinct group of Acacia host plants that is seldom attacked.