Host-Associated Differentiation (HAD) is the formation of genetically divergent hostassociated
lineages maintained by ecological isolation. HAD is potentially an important
route to ecological speciation in parasites including many insects. While HAD case
studies are accumulating, there is a dearth of negative results in the literature making it
difficult to know how common the phenomenon really is or whether there are specific
traits of parasites which promote HAD. To address these two problems, studies are
needed which both publish negative results (i.e., parasites not showing HAD) and test
for HAD in multiple parasite species on the same pair of host species (i.e., control for
host plant effects).
In this study, HAD was tested in three species of herbivorous insects and one parasitoid
species on the same two host tree species: pecan and water hickory. The insects were
selected based on the presence or absence of two traits, parthenogenesis and endophagy.
A test for HAD was considered “positive” when population substructure was explained
by host-association. To test for the presence of HAD, insects were sampled sympatrically to eliminate geographical isolation as a confounding factor, sampling was
replicated spatially to assure that HAD persisted, and multiple loci were sampled from
each individual. Genetic data was analyzed using cluster analyses. HAD was found in
both pecan leaf phylloxera and yellow pecan aphid but not in pecan bud moth or in the
parasitoid of the yellow pecan aphid, Aphelinus perpallidus. Interestingly, both taxa
showing HAD are parthenogenetic and both taxa not showing HAD reproduce sexually.
Species showing HAD were tested for the presence of a pre-mating reproductive
isolating mechanism (RIM) which could be maintaining HAD despite the potential for
gene flow. Selection against migrants to the alternative host was tested in yellow pecan
aphid using a no-choice fitness experiment. The overall contribution of this RIM to total
isolation was positive and ranged from 0.614 to 0.850. The RIM of “habitat preference”
was tested in pecan leaf phylloxera using a dual-choice preference experiment. In this
species, preference was only detected for phylloxera originating from water hickory
suggesting that host discrimination ability may be a less important factor promoting
differentiation in phylloxera.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-12-8695 |
| Date | 2010 December 1900 |
| Creators | Dickey, Aaron |
| Contributors | Medina, Raul F. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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