Ecological genetics aspects of anthropogenic host-shifts in soapberry bugs (Rhopalidae)
Raveendran Thampy, Prasobh 1987-
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Host range expansion, or adaptation of insects to new hosts, is a worldwide phenomenon that has been observed repeatedly and extensively; still, the genetic mechanisms behind host-shifts are not well known. In this thesis I focus on the morphological and genetic variation associated with two recent anthropogenic host shifts in two species of soapberry bug, Leptocoris tagalicus and Jadera haematoloma.. First, I investigated the host-associated genetic differentiation in Australian Leptocoris soapberry bugs, as determined by genome-wide variation patterns. My results show that specimens feeding on two naturalized Neotropical balloon vines, (Cardiospermum halicacabum and C. grandiflorum) have longer “beaks” that those living on the native trees Atalaya hemiglauca and Alectryon tomentosus. Genetic analyses of mitochondrial haplotypes and amplified fragment length polymorphic (AFLP) markers indicate that the lineage of bugs on the annual vine C. halicacabum, is intermediate between two subspecies of L. tagalicus found on the native hosts. Moreover, where this annual vine and whitewood tree (A. hemiglauca) co-occur, the morphology and genomic composition of the bugs are similar to those occurring in allopatry. These results show that hybridization provided the genetic elements underlying the strongly differentiated ‘halicacabum bugs’. In contrast, the bugs feeding on the recently introduced perennial balloon vine (C. grandiflorum) showed no evidence of admixture, and are genetically indistinguishable from the nearby populations on a native host. Second I used a candidate gene approach to investigate the molecular genetic basis of host-adaptation in Floridian populations of the red-shouldered soapberry bug, J. haematoloma. While in Southern Florida soapberry bugs have long beaks to penetrate the large fruits of the native balloon vine (C. corindum), in northern and central Florida, bugs have evolved to feed on an introduced, flat-podded host, the Taiwanese Golden rain tree (Koelreuteria elegans). Specifically I focused on five genes because of their potential role in host preference (orco), “beak” length (Dll, dac, hth) and the adaptation to the toxic compounds of host-plants (Na+/K+-ATPase). My results suggest these genes are highly conserved in this system, and that genetic variation at these loci is not associated with the different host-plants.
DegreeMaster of Science (M.Sc.)
CommitteeAndres, Jose; Chilton, Neil; Gillott, Cedric; Plante, Yves
Copyright DateApril 2016