Escape from floral herbivory by early flowering in Arabidopsis halleri subsp. gemmifera

Natural selection on flowering phenology has been studied primarily in terms of plant-pollinator interactions and effects of abiotic conditions. Little is known, however, about geographic variation in other biotic factors such as herbivores and its consequence for differential selection on flowering phenology among populations. Here, we examine selection by floral herbivores on the flowering phenology of Arabidopsis halleri subsp. gemmifera using two adjacent populations with contrasting herbivory regimes. Intensive floral herbivory by the leaf beetle Phaedon brassicae occurs in one population, while the beetle is absent in another population. We tested the hypothesis that the two populations experience differential selection on flowering time that is attributable to the presence or absence of floral herbivory. A two-year field study showed that early flowering was favoured in the population under intensive floral herbivory, whereas selection for early flowering was not found in oneyear in the population where floral herbivory was absent. Selection for early flowering disappeared when the abundance of floral herbivores was artificially decreased in a field experiment. Thus, the heterogeneous distribution of P. brassicae was a major agent for differential selection on flowering time. However, flowering time did not differ between the two populations when plants were grown in the laboratory. The lack of genetic differentiation in flowering time may be explained by ongoing gene flow or recent invasion of P. brassicae. This study illustrates that the role of floral herbivory in shaping geographic variation in selection on flowering phenology may be more important than previously though

Left-right asymmetric expression of dpp in the mantle of gastropods correlates with asymmetric shell coiling

Background: Various shapes of gastropod shells have evolved ever since the Cambrian. Although theoretical analyses of morphogenesis exist, the molecular basis of shell development remains unclear. We compared expression patterns of the decapentaplegic (dpp) gene in the shell gland and mantle tissues at various developmental stages between coiled-shell and non-coiled-shell gastropods. Results: We analyzed the expression patterns of dpp for the two limpets Patella vulgata and Nipponacmea fuscoviridis, and for the dextral wild-type and sinistral mutant lineage of the pond snail Lymnaea stagnalis. The limpets had symmetric expression patterns of dpp throughout ontogeny, whereas in the pond snail, the results indicated asymmetric and mirror image patterns between the dextral and sinistral lineages. Conclusion: We hypothesize that Dpp induces mantle expansion, and the presence of a left/right asymmetric gradient of the Dpp protein causes the formation of a coiled shell. Our results provide a molecular explanation for shell, coiling including new insights into expression patterns in post-embryonic development, which should aid in understanding how various shell shapes are formed and have evolved in the gastropods.ArticleEVODEVO. 4:15 (2013)journal articl

Coexistence of Trichome Variation in a Natural Plant Population: A Combined Study Using Ecological and Candidate Gene Approaches

The coexistence of distinct phenotypes within populations has long been investigated in evolutionary ecology. Recent studies have identified the genetic basis of distinct phenotypes, but it is poorly understood how the variation in candidate loci is maintained in natural environments. In this study, we examined fitness consequences and genetic basis of variation in trichome production in a natural population of Arabidopsis halleri subsp. gemmifera. Half of the individuals in the study population produced trichomes while the other half were glabrous, and the leaf beetle Phaedon brassicae imposed intensive damage to both phenotypes. The fitness of hairy and glabrous plants showed no significant differences in the field during two years. A similar result was obtained when sibling hairy and glabrous plants were transplanted at the same field site, whereas a fitness cost of trichome production was detected under a weak herbivory condition. Thus, equivalent fitness of hairy and glabrous plants under natural herbivory allows their coexistence in the contemporary population. The pattern of polymorphism of the candidate trichome gene GLABROUS1 (GL1) showed no evidence of long-term maintenance of trichome variation within the population. Although balancing selection under fluctuating biotic environments is often proposed to explain the maintenance of defense variation, the lack of clear evidence of balancing selection in the study population suggests that other factors such as gene flow and neutral process may have played relatively large roles in shaping trichome variation at least for the single population level

Escape from floral herbivory by early flowering in Arabidopsis halleri subsp. gemmifera

Natural selection on flowering phenology has been studied primarily in terms of plant-pollinator interactions and effects of abiotic conditions. Little is known, however, about geographic variation in other biotic factors such as herbivores and its consequence for differential selection on flowering phenology among populations. Here, we examine selection by floral herbivores on the flowering phenology of Arabidopsis halleri subsp. gemmifera using two adjacent populations with contrasting herbivory regimes. Intensive floral herbivory by the leaf beetle Phaedon brassicae occurs in one population, while the beetle is absent in another population. We tested the hypothesis that the two populations experience differential selection on flowering time that is attributable to the presence or absence of floral herbivory. A two-year field study showed that early flowering was favoured in the population under intensive floral herbivory, whereas selection for early flowering was not found in oneyear in the population where floral herbivory was absent. Selection for early flowering disappeared when the abundance of floral herbivores was artificially decreased in a field experiment. Thus, the heterogeneous distribution of P. brassicae was a major agent for differential selection on flowering time. However, flowering time did not differ between the two populations when plants were grown in the laboratory. The lack of genetic differentiation in flowering time may be explained by ongoing gene flow or recent invasion of P. brassicae. This study illustrates that the role of floral herbivory in shaping geographic variation in selection on flowering phenology may be more important than previously though

Frequency-dependent herbivory by a leaf beetle, Phaedon brassicae, on hairy and glabrous plants of Arabidopsis halleri subsp. gemmifera

Frequency-dependent prey choice by natural enemies may influence the coexistence of multiple prey types, but little is known about whether frequency-dependent foraging choice occurs in herbivory on plants showing resistance polymorphism within a single population. Here we examined frequency-dependent foraging by a crucifer-feeding leaf beetle, Phaedon brassicae, on trichome-producing (hairy) and trichomeless (glabrous) plants coexisting within a natural population of the perennial herb Arabidopsis halleri subsp. gemmifera. Larvae of P. brassicae fed on hairy leaves showed slower growth than those fed on glabrous leaves. Although adult beetles consumed similar amounts of leaves when they were fed either hairy or glabrous leaves in no-choice conditions, our choice experiment showed that adult beetles fed at less than the proportionally expected level on hairy leaves compared to glabrous leaves when the hairy leaves were less or equally abundant. Both types of leaves were consumed at the proportionally expected levels when the hairy leaves were more abundant than the glabrous leaves. In a natural population, the leaf damage on the hairy plants was negatively correlated with the local proportion of the glabrous plants in a 1-m diameter patch across 2 years, while correlations between the leaf damage on the glabrous plants and their proportion differed between the 2 years. Additionally, we found five glucosinolates in leaves of A. halleri, but their accumulation did not differ between hairy and glabrous plants. Our experimental results indicate that hairy plants incur less herbivory by P. brassicae when glabrous plants are abundant. The field pattern provides evidence suggestive of frequency-dependent herbivory acting on hairy plants. The present study highlights one of the putative mechanisms of maintaining plant resistance polymorphism

Molecular mechanisms of neural induction and patterning in the zebrafish embryo

The brain is our most complex organ, with an estimated 1011 neurons. With the spinal cord, it forms the central nervous system which controls our movements and our senses, holds our memories and creates our thoughts. Because of this, neurodegenerative disorders can be extremely distressing and a thorough understanding of how the nervous system develops is essential if progress is to be made in finding ways to treat them. Critically, this includes understanding how the nervous system forms, i.e., the nature of the signals that promote neural identity (neural induction) and determine correct positional information (patterning). The zebrafish (Danio rerio) has become established as a model for embryological studies due to ease of experimental manipulation. Taking advantage of this, the aims of this PhD were to contribute to unravelling the molecular mechanisms of neural induction and patterning, using a variety of embryological and molecular methods. In the first project, functional analyses of the eve1 gene identified a key factor for posterior neural development. Eve1 was found to be a critical posteriorising factor, with an additional role in posterior neural induction. An outstanding question in neural induction is the relative contribution to this process of two key developmentally important signalling pathways, Bmp and Fgf. In the second project, differential analyses of maternal versus zygotic Bmp and Fgf signalling revealed crucial maternal roles for these two pathways in neural development as neural and epidermal capacitators. The results further suggested that Fgf signalling may be the critical neural inducer. Finally, as a third project, a zebrafish ectodermal explant assay was developed using the organiser-deficient ichabod mutant. The aim was to develop a system to analyse how key molecules directly affect ectoderm and neural development, free of mesoderm and endoderm influences, as signalling from these layers can directly or indirectly influence neural development.EThOS - Electronic Theses Online ServiceBBSRCGBUnited Kingdo

Seasonal variation in oestrogenic potency and biological effects of wastewater treatment works effluents assessed using ERE-GFP transgenic zebrafish embryo-larvae

International audienceEffluents from wastewater treatment works (WwTW) exhibit both temporal and spatial variation in oestrogenicity, however few studies have attempted to quantify how this variation affects biological responses in fish. Here we used an oestrogen-responsive green fluorescent protein (ERE-GFP) transgenic zebrafish (Danio rerio) to quantify oestrogenic activity and health effects for exposure to three different WwTW effluents. Endpoints measured included survival/hatching rate, GFP induction (measured in target tissues or gfp mRNA induction in whole embryos) and vtg mRNA induction in whole embryos. Exposure to one of the study effluents (at 100%), resulted in some mortality, and exposure to all three effluents (at 50% and 100%) caused decreases in hatching rates. Higher levels of vtg mRNA corresponded with higher levels of steroidal oestrogens in the different effluents, with lowest-observed-effect concentrations (LOECs) between 31 ng/L and 39 ng/L oestradiol equivalents (EEQs). Tissue patterns of GFP expression for all three WwTWs effluents reflected the known targets for steroidal oestrogens and for some other oestrogenic chemicals likely present in those effluents (i.e. nonylphenol or bisphenolic compounds). GFP induction was similarly responsive to vtg mRNA induction (a well-established biomarker for oestrogen exposure). We thus demonstrate the ERE-GFP transgenic zebrafish as an effective model for monitoring the oestrogenic potency and health effects for exposure to complex mixtures of chemicals contained within WwTW effluents

Seasonality of interactions between a plant virus and its host during persistent infection in a natural environment

継続感染における植物ウイルスと宿主植物との相互作用の季節性を解明 --ウイルスの生態学 : 自然生態系における植物とウイルスの関係を長期に研究--. 京都大学プレスリリース. 2019-11-01.Persistent infection, wherein a pathogen is continually present in a host individual, is widespread in virus–host systems. However, little is known regarding how seasonal environments alter virus–host interaction during such metastability. We observed a lineage-to-lineage infection of the host plant Arabidopsis halleri with Turnip mosaic virus for 3 years without severe damage. Virus dynamics and virus–host interactions within hosts were highly season dependent. Virus accumulation in the newly formed leaves was temperature dependent and was suppressed during winter. Transcriptome analyses suggested that distinct defence mechanisms, i.e. salicylic acid (SA)-dependent resistance and RNA silencing, were predominant during spring and autumn, respectively. Transcriptomic difference between infected and uninfected plants other than defence genes appeared transiently only during autumn in upper leaves. However, the virus preserved in the lower leaves is transferred to the clonal offspring of the host plants during spring. In the linage-to-linage infection of the A. halleri–TuMV system, both host clonal reproduction and virus transmission into new clonal rosettes are secured during the winter–spring transition. How virus and host overwinter turned out to be critical for understanding a long-term virus–host interaction within hosts under temperate climates, and more generally, understanding seasonality provides new insight into ecology of plant viruses

Acute Toxicity, Teratogenic, and Estrogenic Effects of Bisphenol A and Its Alternative Replacements Bisphenol S, Bisphenol F, and Bisphenol AF in Zebrafish Embryo-Larvae

International audienceBisphenol A (BPA), a chemical incorporated into plastics and resins, has estrogenic activity and is associated with adverse health effects in humans and wildlife. Similarly structured BPA analogues are widely used but far less is known about their potential toxicity or estrogenic activity in vivo. We undertook the first comprehensive analysis on the toxicity and teratogenic effects of the bisphenols BPA, BPS, BPF, and BPAF in zebrafish embryo-larvae and an assessment on their estrogenic mechanisms in an estrogen-responsive transgenic fish Tg(EREGal4ff)(UASGFP). The rank order for toxicity was BPAF > BPA > BPF > BPS. Developmental deformities for larval exposures included cardiac edema, spinal malformation, and craniofacial deformities and there were distinct differences in the effects and potencies between the different bisphenol chemicals. These effects, however, occurred only at concentrations between 1.0 and 200 mg/L which exceed those in most environments. All bisphenol compounds induced estrogenic responses in Tg(EREGal4ff)(UASGFP) zebrafish that were inhibited by coexposure with ICI 182 780, demonstrating an estrogen receptor dependent mechanism. Target tissues included the heart, liver, somite muscle, fins, and corpuscles of Stannius. The rank order for estrogenicity was BPAF > BPA = BPF > BPS. Bioconcentration factors were 4.5, 17.8, 5.3, and 0.067 for exposure concentrations of 1.0, 1.0, 0.10, and 50 mg/L for BPA, BPF, BPAF, and BPS, respectively. We thus show that these BPA alternatives induce similar toxic and estrogenic effects to BPA and that BPAF is more potent than BPA, further highlighting health concerns regarding the use of BPA alternatives