Experimental Evolution withCaenorhabditisNematodes

Abstract

The hermaphroditic nematode Caenorhabditis elegans has been one of the primary model systems in biology since the 1970s, but only within the last two decades has this nematode also become a useful model for experimental evolution. Here, we outline the goals and major foci of experimental evolution with C. elegans and related species, such as C. briggsae and C. remanei, by discussing the principles of experimental design, and highlighting the strengths and limitations of Caenorhabditis as model systems. We then review three exemplars of Caenorhabditis experimental evolution studies, underlining representative evolution experiments that have addressed the: (1) maintenance of genetic variation; (2) role of natural selection during transitions from outcrossing to selfing, as well as the maintenance of mixed breeding modes during evolution; and (3) evolution of phenotypic plasticity and its role in adaptation to variable environments, including host–pathogen coevolution. We conclude by suggesting some future directions for which experimental evolution with Caenorhabditis would be particularly informative.

Maternal effects and parent–offspring conflict

“…; Teotónio et al. ). Second, given that the impact of parent–offspring conflict depends upon the nature of the disagreement between parent and offspring, we predict that at least partially informative maternal effects are most likely to evolve or persist (even in the face of parent–offspring conflict) when different phenotypes impose similar costs to mothers (e.g., bet‐hedging against different strains of parasites), we would expect partially informative signals to evolve.…”

“…In other words, informative maternal effects should be strongest in contexts of female monogamy or when females reproduce asexually. Such a prediction could, for example be tested among closely related species with different mating systems, as is the case for the nematode genus Caenorhabditis (Fierst et al 2015;Teotónio et al 2017). Second, given that the impact of parent-offspring conflict depends upon the nature of the disagreement between parent and offspring, we predict that at least partially informative maternal effects are most likely to evolve or persist (even in the face of parent-offspring conflict) when different phenotypes impose similar costs to mothers (e.g., bet-hedging against different strains of parasites), we would expect partially informative signals to evolve.…”

How differing modes of non‐genetic inheritance affect population viability in fluctuating environments

“…Full details about the experimental populations and culture protocols can be found in the Supplementary Information (and see Teotonio et al, 2012Teotonio et al, , 2017Noble et al, 2017 for strain derivation). The ancestral population results from long-term laboratory domestication and NaCl (salt) adaptation, and is genetically diverse, with individuals reproducing exclusively by self-fertilisation (Theologidis et al, 2014).…”

Experimental evolution of independent genetic pathways for resistance toPseudomonas aeruginosapathogenicity within the nematodeCaenorhabditis remanei

“…This blunt force approach, however, frequently identifies only the most severe mutations, dominated by those which completely abrogate or grossly impair gene function (Albertson, et al, 2009). This is in stark contrast to the typical trajectory of novel mutations in natural populations where natural selection and genetic drift lead to an accumulation of mutations with small to moderate effects (Rockman, 2012;Noble, et al, 2017;Teotónio, et al, 2017). Models utilizing natural variation in genetic pathways can reveal physiological mechanisms that modify pathogen interactions and disease which would likely be missed using a mutagenesis approach and evolution itself can be used to select for alleles conferring a desired phenotype (Kammenga, et al, 2008;Teotónio et al, 2017;Gao, et al, 2018;Hahnel, et al, 2018).…”

“…Additionally, these worms have interacted with and adapted to bacteria for greater than 600 million years (Irazoqui, et al, 2010). However, the hermaphroditic mating system of C. elegans has resulted in greatly reduced genetic and phenotypic diversity (Andersen, et al, 2012;Phillips, 2012;Teotónio, 2017). This is of particular note because most previous studies examining the genetic basis of pathogen response in nematodes have been conducted using C. elegans, with a common conclusion being that the amount of genetic diversity limits evolutionary diversification and the resultant functional bioactivity (Schulenburg & Ewbank, 2004; Barriére & Félix, 2005;Schulenburg & Boehnisch, 2008).…”