Biology subjects

Wenk, M. R.

Publications and source records attributed to Wenk, M. R..

3 recordsLinked to original sources

bioRxiv2018

Step-wise evolution of temperature-mediated phenotypic plasticity in eyespot size across nymphalid butterflies

There are two disparate views regarding phenotypic plasticity. One regards plasticity as a derived adaptation to help organisms survive in variable environments1, 2 while the other views plasticity as the outcome of flexible, non-canalized, developmental processes, ancestrally present in most organisms, that helps them colonize or adapt to novel environments3-5 e.g., a pre-adaptation. Both views of plasticity currently lack a rigorous, mechanistic examination of ancestral and derived states and direction of change2. Here we show that the origin of phenotypic plasticity in eyespot size in response to environmental temperature observed in Bicyclus anynana butterflies is a derived adaptation of this lineage. Eyespot size is regulated by temperature-mediated changes in levels of a steroid hormone, 20E, that affects proliferation of eyespot central cells expressing the 20E receptor (EcR)6, 7. By estimating the origin of the known physiological and molecular components of eyespot size plasticity in a comparative framework, we showed that 20E titer plasticity in response to temperature is a pre-adaptation shared by all butterfly species examined, whereas the origin of expression of EcR in eyespot centers, and the origin of eyespot sensitivity to the hormone-receptor complex are both derived traits found only in a subset of species with eyespots. The presence of all three molecular components required to produce a plastic response is only observed in B. anynana. This gradual, step-wise, physiological/molecular response to temperature is a likely adaptation to temperature variation experienced across wet and dry seasons in the habitat of this species. This work supports, thus, the first view of plasticity as a derived adaptation.

evolutionary biology↗

bioRxiv2017

Slowing ageing using drug synergy in C. elegans

Pharmacological interventions that target human ageing would extend individual healthspan and result in dramatic economic benefits to rapidly ageing societies worldwide. For such interventions to be contemplated they need to comprise drugs that are efficacious when given to adults and for which extensive human safety data are available. Here we show that dramatic lifespan extension can be achieved in C.elegans by targeting multiple, evolutionarily conserved ageing pathways using drugs that are already in human use. By targeting multiple synergistic ageing pathways, we are able to slow ageing rate, double lifespan and improves healthspan while minimize developmental and fitness trade-offs. Moreover, we established that there is no synergistic benefit in a daf-2 or daf-7 background, implying the involvement of the TGF{beta} and IGF pathways in this synergy. Employing lipidomics and transcriptomics analysis we found lipid metabolism to be affected resulting in increased monounsaturated fatty acids (MUFA) and decrease membrane peroxidation index. Our best drug combination showed a conserved lifespan extension in fruit flies. To the best of our knowledge, this is the largest lifespan effect ever reported for any adult-onset drug treatment in C. elegans. This drug-repurposing approach, using drugs already approved for humans to target multiple conserved aging pathways simultaneously, could lead to interventions that prevent age-related diseases and overall frailty in a rapidly ageing population.

biochemistry↗

bioRxiv2017

Sex Differences In 20-Hydroxyecdysone Hormone Levels Control Sexual Dimorphism In Bicyclus anynana Butterfly Wing Patterns

In contrast to the important role of hormones in the development of sexual dimorphic traits in vertebrates [1], the differentiation of these traits in insects is attributed exclusively to variation in cell-autonomous mechanisms controlled by members of the sex determination pathway [2], such as doublesex (dsx). Although hormones can shape the development of sexual traits in insects, and interact with dsx to create dimorphisms, variation in hormone levels are not known to cause dimorphism in these traits [3]. Here we show that butterflies use sex-specific differences in 20-hydroxyecdysone (20E) hormone titers to create sexually dimorphic wing ornaments, without the local involvement of dsx. Females of the dry season (DS) form of Bicyclus anynana display a larger sexual ornament on their wings than males, whereas in the wet season (WS) form both sexes have similarly sized ornaments [4]. High levels of circulating 20E during larval development in DS females and WS forms cause proliferation of the cells fated to give rise to this wing ornament, and results in sexual dimorphism in the DS forms. This study advances our understanding of how the environment regulates sex-specific patterns of plasticity of sexual ornaments and conclusively shows that sex-specific variation in hormone titers can play a role in the development of secondary sexual traits in insects, just like they do in vertebrates.\n\nHighlights O_LISex-specific levels of 20E, an insect molting hormone, regulate secondary sexual trait dimorphism and plasticity in butterflies.\nC_LIO_LI20E levels above a threshold promote local patterns of cell division in one sex, but not in the other sex, to create sexually dimorphic eyespots.\nC_LI\n\neTOCSexual selection drives the evolution of ornaments for individuals to display to the opposite sex. Yet, the mechanisms by which sexual selection operates are still not well understood. Here Bhardwaj et al. provide conclusive evidence, for the first time, that male and female insects use variation in levels of hormones to create dimorphism in their sexual ornaments. Authors show that 20-hydroxyecdyone, the insect molting hormone, also functions as a sex hormone in a butterfly. They also show how the environment shapes the development of sexual ornaments at a proximate level.

developmental biology↗