Regrowth patterns and rosette attributes contribute to the differential compensatory responses of Arabidopsis thaliana genotypes to apical damage.

A plant's compensatory performance refers to its ability to maintain or increase its reproductive output following damage. The ability of a plant to compensate depends on numerous factors including the type, severity, frequency and timing of damage, the environmental conditions and the plant's genotype. Upon apical damage, a cascade of hormonal and genetic responses often produces dramatic changes in a plant's growth, development, architecture and physiology. All else being equal, this response is largely dependent on a plant's genotype, with different regrowth patterns displayed by different genotypes of a given species. In this study, we compare the architectural and growth patterns of two Arabidopsis thaliana genotypes following apical damage. Specifically, we characterise regrowth patterns of the genotypes Columbia-4 and Landsberg erecta, which typically differ in their compensation to apical meristem removal. We report that Landsberg erecta suffered reductions in the number of stems produced, maximum elongation rate, a delay in reaching this rate, lower average rosette quality throughout the growing period, and ultimately, less aboveground dry biomass and seed production when damaged compared to undamaged control plants. Columbia-4 had no reductions in any of these measures and maintained larger rosette area when clipped relative to when unclipped. Based on the apparent influence of the rosette on these genotypes' compensatory performances, we performed a rosette removal experiment, which confirmed that the rosette contributes to compensatory performance. This study provides a novel characterisation of regrowth patterns following apical damage, with insights into those measures having the largest effect on plant performance.

Differential gene expression in laboratory strains of human head and body lice when challenged with Bartonella quintana, a pathogenic bacterium.

Human head and body lice are obligatory hematophagous ectoparasites that belong to a single species, Pediculus humanus. Only body lice, however, are vectors of the infectious Gram-negative bacterium Bartonella quintana. Because of their near identical genomes, yet differential vector competence, head and body lice provide a unique model system to study the gain or loss of vector competence. Using our in vitro louse-rearing system, we infected head and body lice with blood containing B. quintana in order to detect both differences in the proliferation of B. quintana and transcriptional differences of immune-related genes in the lice. B. quintana proliferated rapidly in body lice at 6 days post-infection, but plateaued in head lice at 4 days post-infection. RNAseq and quantitative real-time PCR validation analyses determined gene expression differences. Eight immunoresponse genes were observed to be significantly different with many associated with the Toll pathway: Fibrinogen-like protein, Spaetzle, Defensin 1, Serpin, Scavenger receptor A and Apolipoporhrin 2. Our findings support the hypothesis that body lice, unlike head lice, fight infection from B. quintana only at the later stages of its proliferation.

Comparison of the transcriptional profiles of head and body lice.

Head and body lice are both blood-feeding parasites of humans although only the body louse is a potent disease vector. In spite of numerous morphological and life history differences, head and body lice have recently been hypothesized to be ecotypes of the same species. We took a comparative genomics approach to measure nucleotide diversity by comparing expressed sequence tag data sets from head and body lice. A total of 10 771 body louse and 10 770 head louse transcripts were predicted from a combined assembly of Roche 454 and Illumina sequenced cDNAs from whole body tissues collected at all life stages and during pesticide exposure and bacterial infection treatments. Illumina reads mapped to the 10 775 draft body louse gene models from the whole genome assembly predicted nine presence/absence differences, but PCR confirmation resulted in a single gene difference. Read per million base pair estimates indicated that 14 genes showed significant differential expression between head and body lice under our treatment conditions. One novel microRNA was predicted in both lice species and 99% of the 544 transcripts from Candidatus riesia indicate that they share the same endosymbiont. Overall, few differences exist, which supports the hypothesis that these two organisms are ecotypes of the same species.

The ghost of genetic diversity past: historical DNA analysis of the greater prairie chicken.

Most, if not all, of the "classic," often-cited examples illustrating the genetic effects of a population bottleneck are open to alternative explanations due to the lack of adequate control populations, that is, low levels of genetic variability are often assumed to be the result of a past population bottleneck without having any prebottleneck measures. Here we provide the first clear case history where both prebottleneck and postbottleneck measures of genetic variability have been collected from a natural system. Analysis of DNA from museum specimens of the greater prairie chicken Tympanuchus cupido from central Illinois revealed the loss of specific alleles (known to have been present earlier in this century) following a demographic contraction. Lost alleles included common ones present in all other populations sampled and others unique to the Illinois population.

The effects of herbivory on paternal fitness in scarlet gilia: better moms also make better pops.

Whether plants can benefit from the direct effects of herbivory has been contentious among ecologists and evolutionary biologists. Although previous studies have provided experimental evidence of enhanced maternal fitness following herbivory in a natural system, an accurate depiction of plant-herbivore interactions must include the effects of herbivory on male as well as female fitness. Here we show that ungulate herbivory on scarlet gilia results in an increase in paternal as well as maternal fitness. This study represents the first evidence of overcompensation in a natural system where both paternal and maternal components of fitness have been assessed.

Field and genetic studies testing optimal outcrossing in Agave schottii, a long-lived clonal plant.

In thisstudy we combine field experiments, designed to test the predictions of optimal outcrossing theory in Agave schottii, with molecular genetic studies, using RAPD (random amplified polymorphic DNA), polymerase chain reaction to assess the underlying genetic hypothesis of optimal outcrossing theory. Initially, 48 "females" of A. schottii were hand-pollinated with pollen collected from 1 m, 10 m, 100 m, and 2500 m distances. Each female received all four distance treatments. Additionally, a subset of the focal females and their pollen donors were used in an analysis of genetic similarity across the four distances. Results of hand-pollinations showed that crosses of 1 m had significantly lower seed set than 10 m and 100 m crosses. Crosses of 2500 m had intermediate seed set. Combined relative fitness was significantly lower for 1 m crosses compared to 10 m crosses, while 100 m and 2500 m crosses were intermediate. Thus, A. schottii experiences inbreeding depression and a trend toward outbreeding depression. Genetic analyses showed a similar pattern: individuals 1 m apart had on average higher genetic similarity (proportion of bands shared) than individuals separated by greater distances, with a trend toward lower genetic similarity for plants located 2500 m distant. The observed spatial genetic patterns are likely maintained by the combined effects of clonal reproduction, clone longevity, limited seed dispersal and the substantial number of inbred progeny produced, counteracting distant allele transfer which tends to reduce population genetic structure. The correspondence between our ecological and genetic results indicates that RAPD markers are useful tools for assessing ecological phenomena.

Genetic analysis of an interspecific hybrid swarm of Populus: occurrence of unidirectional introgression.

Restriction fragment length polymorphisms were used to distinguish genotypes of two species of Populus, P. fremontii ('Fremont') and P. angustifolia ('narrowleaf'). Both inter- and intraspecific polymorphisms were detected in these cottonwood trees. The interspecific variation was much greater than the intraspecific variation. This permitted identification of parental genotypes within individual trees of a hybrid swarm which exists in an overlap zone between the two species. Within this hybrid swarm, individual trees are either F1 hybrids or backcrosses with a pure 'narrowleaf' parent; no progeny were found that could be attributed to crossing between F1 hybrid trees, or to backcrossing between F1 hybrid trees and 'Fremont'.

Individual and population shifts in flower color by scarlet gilia: a mechanism for pollinator tracking.

Individual plants and populations of scarlet gilia (Ipomopsis aggregata) shift from darker to lighter corolla colors during the flowering season. Shifts to lighter color coincide with emigration of hummingbirds from the system. In the absence of hummingbirds, lighter colors attract the remaining pollinator, a hawkmoth. Comparison of plants that shift to lighter colors with those that fail to shift shows that shifting is adaptive in that it enhances reproductive success because of the preference of hawkmoths for lighter colored flowers. Color shifting therefore provides a mechanism for plants to track changing pollinator abundances.