Polyphenism of a Novel Trait Integrated Rapidly Evolving Genes into Ancestrally Plastic Networks.

Developmental polyphenism, the ability to switch between phenotypes in response to environmental variation, involves the alternating activation of environmentally sensitive genes. Consequently, to understand how a polyphenic response evolves requires a comparative analysis of the components that make up environmentally sensitive networks. Here, we inferred coexpression networks for a morphological polyphenism, the feeding-structure dimorphism of the nematode Pristionchus pacificus. In this species, individuals produce alternative forms of a novel trait-moveable teeth, which in one morph enable predatory feeding-in response to environmental cues. To identify the origins of polyphenism network components, we independently inferred coexpression modules for more conserved transcriptional responses, including in an ancestrally nonpolyphenic nematode species. Further, through genome-wide analyses of these components across the nematode family (Diplogastridae) in which the polyphenism arose, we reconstructed how network components have changed. To achieve this, we assembled and resolved the phylogenetic context for five genomes of species representing the breadth of Diplogastridae and a hypothesized outgroup. We found that gene networks instructing alternative forms arose from ancestral plastic responses to environment, specifically starvation-induced metabolism and the formation of a conserved diapause (dauer) stage. Moreover, loci from rapidly evolving gene families were integrated into these networks with higher connectivity than throughout the rest of the P. pacificus transcriptome. In summary, we show that the modular regulatory outputs of a polyphenic response evolved through the integration of conserved plastic responses into networks with genes of high evolutionary turnover.

Regulators of an ancient polyphenism evolved through episodic protein divergence and parallel gene radiations.

Polyphenism is a form of developmental plasticity that transduces environmental cues into discontinuous, often disparate phenotypes. In some cases, polyphenism has been attributed to facilitating morphological diversification and even the evolution of novel traits. However, this process is predicated on the origins and evolutionary maintenance of genetic mechanisms that specify alternate developmental networks. When and how regulatory loci arise and change, specifically before and throughout the history of a polyphenism, is little understood. Here, we establish a phylogenetic and comparative molecular context for two dynamically evolving genes, eud-1 and seud-1, which regulate polyphenism in the nematode Pristionchus pacificus. This species is dimorphic in its adult feeding-structures, allowing individuals to become microbivores or facultative predators depending on the environment. Although polyphenism regulation is increasingly well understood in P. pacificus, the polyphenism is far older than this species and has diversified morphologically to enable an array of ecological functions across polyphenic lineages. To bring this taxonomic diversity into a comparative context, we reconstructed the histories of eud-1 and seud-1 relative to the origin and diversification of polyphenism, finding that homologues of both genes have undergone lineage-specific radiations across polyphenic taxa. Further, we detected signatures of episodic diversifying selection on eud-1, particularly in early diplogastrid lineages. Lastly, transgenic rescue experiments suggest that the gene's product has functionally diverged from its orthologue's in a non-polyphenic outgroup. In summary, we provide a comparative framework for the molecular components of a plasticity switch, enabling studies of how polyphenism, its regulation, and ultimately its targets evolve.

A draft genome for a species of Halicephalobus (Panagrolaimidae).

Halicephalobus is a clade of small, exclusively parthenogenic nematodes that have sometimes colonized remarkable habitats. Given their phylogenetic closeness to other parthenogenic panagrolaimid species with which they likely share a sexually reproducing ancestor, Halicephalobus species provide a point of comparison for parallelisms in the evolution of asexuality. Here, we present a draft genome of a putatively new species of Halicephalobus isolated from termites in Japan.Halicephalobus is a clade of small, exclusively parthenogenic nematodes that have sometimes colonized remarkable habitats. Given their phylogenetic closeness to other parthenogenic panagrolaimid species with which they likely share a sexually reproducing ancestor, Halicephalobus species provide a point of comparison for parallelisms in the evolution of asexuality. Here, we present a draft genome of a putatively new species of Halicephalobus isolated from termites in Japan.

OBGYN providers' lack of knowledge and management of genetic risks due to advanced paternal age underscore the need for updated practice guidance.

The objective of this pilot study was to characterize healthcare professionals' knowledge of advanced paternal age (APA), the associated risks, as well as current clinical practices regarding APA. Our study utilized an online survey that questioned providers who see children with genetic conditions and patients who are or may become pregnant regarding demographic information, APA knowledge, APA guideline familiarity, and their clinical practices. A total of 67 providers responded to the survey. We had responses from 54 physician participants in the specialties of medical genetics (GEN), maternal fetal medicine (MFM), and obstetrics and gynecology (OBGYN). OBGYN, but not MFM, reported significantly lower agreement that current data supports an association between APA and certain genetic diseases compared to GEN. Furthermore, OBGYN were less likely to identify established risks associated with APA and more likely to incorrectly identify unestablished risks compared to GEN and MFM. Regardless of specialty, the majority of physicians were unfamiliar with the most recently published APA guidelines. This study revealed a desire for more information regarding APA risks and management among our participants. Our data suggest that GEN, MFM, and OBGYN would benefit from updated and more visible guidelines regarding APA. Additionally, OBGYN consistently showed knowledge gaps and misconceptions regarding the risks of APA. Targeted educational or guidance materials regarding APA may also be beneficial for OBGYNs.

Decoding the architecture and origins of mechanisms for developmental polyphenism.

Developmental polyphenism affords a single genotype multiple solutions to match an organism to its environment. Because polyphenism is the extreme example of how development deviates from a linear genetic blueprint, it demands a genetic explanation for how environmental cues shunt development to hypothetically alternative modules. We highlight several recent advances that have begun to illuminate genetic mechanisms for polyphenism and how this recurring developmental novelty may arise. An emerging genetic knowledge of polyphenism is providing precise targets for testing hypotheses of how switch mechanisms are built-out of olfactory, nutrient-sensing, hormone-reception, and developmental and genetic buffering systems-to accommodate plasticity. Moreover, classic and new model systems are testing the genetic basis of polyphenism's proposed causal roles in evolutionary change.