Publications

intraspecific differences in olfactory sensilla in relation to diet breadth in uroleucon ambrosiae (homoptera: aphididae).	the olfactory plate organs found on the proximal segments of aphid antennae, the secondary rhinaria, were studied in apterae of the aphid uroleucon ambrosiae. the numbers and shapes of these structures are important taxonomic characters in aphididae, but they also show intraspecific variation within a morph. in this study, numbers were found to vary with aphid size but, independent of size, were greater in aphids collected in the eastern than in the southwestern united states. in addition, the s ...	2000	10906745
intraspecific variation in symbiont genomes: bottlenecks and the aphid-buchnera association.	buchnera are maternally transmitted bacterial endosymbionts that synthesize amino acids that are limiting in the diet of their aphid hosts. previous studies demonstrated accelerated sequence evolution in buchnera compared to free-living bacteria, especially for nonsynonymous substitutions. two mechanisms may explain this acceleration: relaxed purifying selection and increased fixation of slightly deleterious alleles under drift. here, we test the divergent predictions of these hypotheses for int ...	2001	11156972
intraspecific phylogenetic congruence among multiple symbiont genomes.	eukaryotes often form intimate endosymbioses with prokaryotic organisms. cases in which these symbionts are transmitted cytoplasmically to host progeny create the potential for co-speciation or congruent evolution among the distinct genomes of these partners. if symbionts do not move horizontally between different eukaryotic hosts, strict phylogenetic congruence of their genomes is predicted and should extend to relationships within a single host species. conversely, even rare 'host shifts' amon ...	2000	11197128
independent origins and horizontal transfer of bacterial symbionts of aphids.	many insect groups have obligate associations with primary endosymbionts: mutualistic bacteria that are maternally transmitted and derived from an ancient infection. often, the same insects are hosts to 'secondary' bacterial symbionts which are maternally transmitted but relatively labile within host lineages. to explore the dynamics of secondary symbiont associations in aphids, we characterized bacteria infecting 15 species of macrosiphine aphids using dna sequencing, diagnostic polymerase chai ...	2001	11251800
estimating population size and transmission bottlenecks in maternally transmitted endosymbiotic bacteria.	many species of bacterial endosymbionts are acquired by animal hosts before birth, through direct transmission from mothers to eggs or embryos. this vertical transmission imposes a reduction in numbers or "bottleneck," and the size of this bottleneck affects the population structure and evolution of symbiotic lineages. we have estimated the size of the transmission bottleneck in buchnera, the bacterial symbiont of aphids, using basic light and electron microscopy techniques. by serial-sectioning ...	2002	12087426
extremely low levels of genetic polymorphism in endosymbionts (buchnera) of aphids (pemphigus).	molecular evolutionary studies have suggested that vertically transmitted endosymbionts are subject to accumulation of deleterious mutations through genetic drift. predictions of this hypothesis for patterns of intraspecific polymorphism were borne out in the single relevant study available, on the symbiont buchnera aphidicola of uroleucon ambrosiae. in order to examine the generality of this result, we surveyed dna sequence variation in buchnera of the distantly related aphid, pemphigus obesiny ...	2002	12453247
low and homogeneous copy number of plasmid-borne symbiont genes affecting host nutrition in buchnera aphidicola of the aphid uroleucon ambrosiae.	the bacterial endosymbiont of aphids, buchnera aphidicola, often provides amino acids to its hosts. plasmid amplification of leucine (leuabcd) and tryptophan (trpeg) biosynthesis genes may be a mechanism by which some buchnera over-produce these nutrients. we used quantitative polymerase chain reaction to assess the leuabcd/trpeg copy variability within uroleucon ambrosiae, an aphid with a wide diet breadth and range. both leuabcd and trpeg abundances are: (i) similar for aphids across 15 popula ...	2003	12753227
Sequence conservation and functional constraint on intergenic spacers in reduced genomes of the obligate symbiont Buchnera.	Analyses of genome reduction in obligate bacterial symbionts typically focus on the removal and retention of protein-coding regions, which are subject to ongoing inactivation and deletion. However, these same forces operate on intergenic spacers (IGSs) and affect their contents, maintenance, and rates of evolution. IGSs comprise both non-coding, non-functional regions, including decaying pseudogenes at varying stages of recognizability, as well as functional elements, such as genes for sRNAs and ...	2011	21912528