Maintenance of quiescent oocytes by noradrenergic signals

All females adopt an evolutionary conserved reproduction strategy; under unfavorable conditions such as scarcity of food or mates, oocytes remain quiescent. However, the signals to maintain oocyte quiescence are largely unknown. Here, we report that in four different species – Caenorhabditis elegans, Caenorhabditis remanei, Drosophila melanogaster, and Danio rerio – octopamine and norepinephrine play an essential role in maintaining oocyte quiescence. In the absence of mates, the oocytes of Caenorhabditis mutants lacking octopamine signaling fail to remain quiescent, but continue to divide and become polyploid. Upon starvation, the egg chambers of D. melanogaster mutants lacking octopamine signaling fail to remain at the previtellogenic stage, but grow to full-grown egg chambers. Upon starvation, D. rerio lacking norepinephrine fails to maintain a quiescent primordial follicle and activates an excessive number of primordial follicles. Our study reveals an evolutionarily conserved function of the noradrenergic signal in maintaining quiescent oocytes.

Dietary Restriction Improves Fitness of Aging Parents But Reduces Fitness of Their Offspring in Nematodes

Dietary restriction (DR) is a well-established intervention to extend lifespan across taxa. Recent studies suggest that DR-driven lifespan extension can be cost-free, calling into question a central tenant of the evolutionary theory of aging. Nevertheless, boosting parental longevity can reduce offspring fitness. Such intergenerational trade-offs are often ignored but can account for the “missing costs” of longevity. Here, we use the nematode Caenorhabditis remanei to test for effects of DR by fasting on fitness of females and their offspring. Females deprived of food for 6 days indeed had increased fecundity, survival, and stress resistance after re-exposure to food compared with their counterparts with constant food access. However, offspring of DR mothers had reduced early and lifetime fecundity, slower growth rate, and smaller body size at sexual maturity. These findings support the direct trade-off between investment in soma and gametes challenging the hypothesis that increased somatic maintenance and impaired reproduction can be decoupled.

Dietary restriction improves fitness of ageing parents but reduces fitness of their offspring

Dietary restriction (DR) is a well-established intervention to extend lifespan across taxa. Recent studies suggest that DR-driven lifespan extension can be cost-free, calling into question a central tenant of the evolutionary theory of ageing. Nevertheless, boosting parental longevity can reduce offspring fitness. Such intergenerational trade-offs are often ignored but can account for the ‘missing costs’ of longevity. Here, we use the nematode Caenorhabditis remanei to test for effects of DR by fasting on fitness of females and their offspring. Females deprived of food for six days indeed had increased fecundity, survival and stress resistance after re-exposure to food compared to their counterparts with constant food access. However, offspring of DR mothers had reduced early and lifetime fecundity, slower growth rate, and smaller body size at sexual maturity. These findings support the direct trade-off between investment in soma and gametes challenging the hypothesis that increased somatic maintenance and impaired reproduction can be decoupled.

Environmental variation mediates the evolution of anticipatory parental effects

Theory maintains that when future environment is predictable, parents should adjust the phenotype of their offspring to match the anticipated environment. The plausibility of positive anticipatory parental effects is hotly debated and the experimental evidence for the evolution of such effects is currently lacking. We experimentally investigated the evolution of anticipatory maternal effects in a range of environments that differ drastically in how predictable they are. Populations of the nematode Caenorhabditis remanei, adapted to 20°C, were exposed to a novel temperature (25°C) for 30 generations with either positive or zero correlation between parent and offspring environment. We found that populations evolving in novel environments that were predictable across generations evolved a positive anticipatory maternal effect, since they required maternal exposure to 25°C to achieve maximum reproduction in that temperature. In contrast, populations evolving under zero environmental correlation had lost this anticipatory maternal effect. Similar but weaker patterns were found if instead rate-sensitive population growth was used as a fitness measure. These findings demonstrate that anticipatory parental effects evolve in response to environmental change so that ill-fitting parental effects can be rapidly lost. Evolution of positive anticipatory parental effects can aid population viability in rapidly changing but predictable environments.Impact summaryParents can help their offspring by adjusting offspring’s phenotype to match their environment. Such anticipatory parental effects would be beneficial, but only if parents can accurately predict the environment in which their offspring will develop and live. The plausibility of such anticipatory parental effects is hotly debated. The theory is clear that the predictability of the environment should play a defining role. We used an “experimental evolution” approach in a fast reproducing nematode worm Caenorhabditis remanei to tackle this question and follow the evolution of parental effects in different environments in real-time. We found that populations evolving in a novel but predictable environment indeed had anticipatory parental effects that increased fitness of their offspring in that environment. In contrast, when evolving in an unpredictable environment where such parental effects would be disadvantageous, the parental effect was rapidly lost in evolution. Our novel experimental environments were constructed by exposing worms to increased temperature. Anticipatory parental effects play an important role in adaptation to novel environments and will affect the viability of populations under climate heating.

Experimental evolution of independent genetic pathways for resistance to Pseudomonas aeruginosa pathogenicity within the nematode Caenorhabditis remanei

ABSTRACTPathogenic host-microbe interactions can result from continuous evolution of a host’s ability to resist infection and a pathogen’s ability to survive and replicate. Pseudomonas aeruginosa is a versatile and opportunistic pathogen, ubiquitous in the environment, and capable of damaging plants, vertebrates, and invertebrates. Previous studies in nematodes suggest that the pathogenic effects of P. aeruginosa can result from multiple distinct pathways: a toxin-based effect that kills within a few hours and a generalized virulence that kills over the course of multiple days. Using experimental evolution in the highly polymorphic nematode Caenorhabditis remanei, we show that nematode resistance to the two modes of pathogenesis in P. aeruginosa evolves through genetically independent pathways. These results demonstrate that multiple virulence patterns in a pathogen can result in multiple responses in the host, and the genetic lines established here create resources for further exploration of the genetic basis for resistance to P. aeruginosa.

Environmental and evolutionary drivers of the modular gene regulatory network underlying phenotypic plasticity for stress resistance in the nematode Caenorhabditis remanei

ABSTRACTIn response to changing environmental conditions, organisms can acclimate through phenotypic plasticity or adapt by evolving mechanisms to cope with novel stressors. Changes in gene expression, whether dynamic or evolved, are an important way in which environmental responses are mediated; however, much is still unknown about how the molecular networks underlying plastic phenotypes evolve. Here, we compare transcriptional responses to acute heat stress among four populations of the nematode Caenorhabditis remanei—one selected to withstand heat stress, one selected under oxidative stress, an unselected control, and the ancestral population. We used a weighted gene coexpression network analysis within these lines to identify transcriptional modules, which are sets of genes that respond similarly to stress via plastic responses, evolutionary responses, or both. The transcriptional response to acute heat stress is dominated by a plastic response that is shared in the ancestor and all evolved populations. However, we also identified several modules that respond to artificial selection by (1) changing the baseline level of expression, (2) altering the magnitude of the plastic response, or (3) a combination of the two. Our findings reveal that while it is possible to perturb the nature of the transcriptional response network with short bouts of intense selection, the overall structure of transcriptional plasticity is dominated by inherent, ancestral regulatory systems.

Metagenome-Assembled Draft Genome Sequence of a Novel Microbial Stenotrophomonas maltophilia Strain Isolated from Caenorhabditisremanei Tissue

ABSTRACT Stenotrophomonas maltophilia is a Gram-negative aerobic bacterium and emerging nosocomial pathogen. Here, we present a draft genome sequence for an S. maltophilia strain assembled from a metagenomic DNA extract isolated from a laboratory stock of the nematode worm Caenorhabditis remanei.