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[
WormBook,
2005]
C. elegans presents a low level of molecular diversity, which may be explained by its selfing mode of reproduction. Recent work on the genetic structure of natural populations of C. elegans indeed suggests a low level of outcrossing, and little geographic differentiation because of migration. The level and pattern of molecular diversity among wild isolates of C. elegans are compared with those found after accumulation of spontaneous mutations in the laboratory. The last part of the chapter reviews phenotypic differences among wild isolates of C. elegans.
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[
WormBook,
2005]
The knowledge about C. elegans provides a paradigm for comparative studies. Nematodes are very attractive in evolutionary developmental biology given the species richness of the phylum and the easiness with which several of these species can be cultured under laboratory conditions. Embryonic, gonad, vulva and male tail development were studied and compared in nematodes of five different families, providing a detailed picture of evolutionary changes in development. In particular, vulva development has been studied in great detail and substantial differences in the cellular, genetic and molecular mechanisms have been observed between C. elegans and other nematodes. For example, vulva induction relies on the single anchor cell in C. elegans, whereas a variety of different cellular mechanisms are used in related species. In recent years, a few species have been developed as satellite systems for detailed genetic and molecular studies, such as Oscheius tipulae and Pristionchus pacificus.
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Genetics,
2022]
Over the last 20 years, studies of Caenorhabditis elegans natural diversity have demonstrated the power of quantitative genetic approaches to reveal the evolutionary, ecological, and genetic factors that shape traits. These studies complement the use of the laboratory-adapted strain N2 and enable additional discoveries not possible using only one genetic background. In this chapter, we describe how to perform quantitative genetic studies in Caenorhabditis, with an emphasis on C. elegans. These approaches use correlations between genotype and phenotype across populations of genetically diverse individuals to discover the genetic causes of phenotypic variation. We present methods that use linkage, near-isogenic lines, association, and bulk-segregant mapping, and we describe the advantages and disadvantages of each approach. The power of C. elegans quantitative genetic mapping is best shown in the ability to connect phenotypic differences to specific genes and variants. We will present methods to narrow genomic regions to candidate genes and then tests to identify the gene or variant involved in a quantitative trait. The same features that make C. elegans a preeminent experimental model animal contribute to its exceptional value as a tool to understand natural phenotypic variation.
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[
WormBook,
2006]
Although several Caenorhabditis species are now studied in laboratories in great detail, the knowledge of the ecology of most Caenorhabditis species is scarce. In this chapter we present data on the habitat, animal associations, and geographical distribution of the eighteen described and five undescribed Caenorhabditis species currently known to science. The habitats of these species are very diverse, ranging from rotting cactus tissue to inflamed auditory canals of zebu cattle. Some species, including C. elegans , have only been isolated from anthropogenic habitats. Consequently, their natural habitat is unknown. All Caenorhabditis species are colonizers of nutrient- and bacteria-rich substrates and none of them is a true soil nematode. Dauer juveniles of many Caenorhabditis species were shown to be associated with terrestrial arthropods or gastropods. An association with invertebrates is also likely for the remaining species. The type of association is either phoresy (for transport to a new habitat) or necromeny (to secure the body of the associated animal as a future food source). There are also some records of Caenorhabditis species associated with vertebrates. The Caenorhabditis stem species was probably a colonizer of nutrient-rich substrates and was phoretic on arthropods. Some evolutionary trends within the taxon are discussed.
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[
WormBook,
2007]
Because of their free-living life cycle alternatives, Strongyloides and related nematode parasites may represent the best models for translating C. elegans science to the study of nematode parasitism. S. stercoralis, a significant pathogen of humans, can be maintained in laboratory dogs and gerbils. Biosafety precautions necessary for work with S. stercoralis, though unfamiliar to many C. elegans researchers, are straightforward and easily accomplished. Although specialized methods are necessary for large-scale culture of the free-living stages of S. stercoralis, small-scale cultures for experimental purposes may be undertaken using minor modifications of standard C. elegans methods. Similarly, the morphological similarities between C. elegans and the free-living stages of S. stercoralis allow investigational methods such as laser cell ablation and DNA transformation by gonadal microinjection to be easily adapted from C. elegans to S. stercoralis. Comparative studies employing these methods have yielded new insights into the neuronal control of the infective process in parasites and its similarity to regulation of dauer development in C. elegans. Furthermore, we have developed a practical method for transient transformation of S. stercoralis with vector constructs having various tissue- and cell-specific expression patterns and have assembled these into a modular vector kit for distribution to the community.
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[
Genetics,
2018]
Since the earliest days of research on nematodes, scientists have noted the developmental and morphological variation that exists within and between species. As various cellular and developmental processes were revealed through intense focus on <i>Caenorhabditis elegans</i>, these comparative studies have expanded. Within the genus <i>Caenorhabditis</i>, they include characterization of intraspecific polymorphisms and comparisons of distinct species, all generally amenable to the same laboratory culture methods and supported by robust genomic and experimental tools. The <i>C. elegans</i> paradigm has also motivated studies with more distantly related nematodes and animals. Combined with improved phylogenies, this work has led to important insights about the evolution of nematode development. First, while many aspects of <i>C. elegans</i> development are representative of <i>Caenorhabditis</i>, and of terrestrial nematodes more generally, others vary in ways both obvious and cryptic. Second, the system has revealed several clear examples of developmental flexibility in achieving a particular trait. This includes developmental system drift, in which the developmental control of homologous traits has diverged in different lineages, and cases of convergent evolution. Overall, the wealth of information and experimental techniques developed in <i>C. elegans</i> is being leveraged to make nematodes a powerful system for evolutionary cellular and developmental biology.
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[
WormBook,
2006]
Transposons are discrete segments of DNA capable of moving through the genome of their host via an RNA intermediate in the case of class I retrotransposon or via a "cut-and-paste" mechanism for class II DNA transposons. Since transposons take advantage of their host''s cellular machinery to proliferate in the genome and enter new hosts, transposable elements can be viewed as parasitic or "selfish DNA". However, transposons may have been beneficial for their hosts as genome evolution drivers, thus providing an example of molecular mutualism. Interactions between transposon and C. elegans research were undoubtedly mutualistic, leading to the advent of needed genomic tools to drive C. elegans research while providing insights into the transposition field. Tc1, the first C. elegans transposon to be identified, turned out to be the founding member of a widespread family of mobile elements: the Tc1/ mariner superfamily. The investigation into transposition regulation in C. elegans has uncovered an unforeseen link between transposition, genome surveillance and RNA interference. Conversely, transposons were utilized soon after their identification to inactivate and clone genes, providing some of the first molecular identities of C. elegans genes. Recent results suggest that transposons might provide a means to engineer site-directed mutations into the C. elegans genome. This article describes the different transposons present in the C. elegans genome with a specific emphasis on the ones that proved to be mobile under laboratory conditions. Mechanisms and control of transposition are discussed briefly. Some tools based on the use of transposons for C. elegans research are presented at the end of this review.
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[
Genetics,
2019]
Males of <i>Caenorhabditis elegans</i> provide a crucial practical tool in the laboratory, but, as the rarer and more finicky sex, have not enjoyed the same depth of research attention as hermaphrodites. Males, however, have attracted the attention of evolutionary biologists who are exploiting the <i>C. elegans</i> system to test longstanding hypotheses about sexual selection, sexual conflict, transitions in reproductive mode, and genome evolution, as well as to make new discoveries about <i>Caenorhabditis</i> organismal biology. Here, we review the evolutionary concepts and data informed by study of males of <i>C. elegans</i> and other <i>Caenorhabditis</i> We give special attention to the important role of sperm cells as a mediator of inter-male competition and male-female conflict that has led to drastic trait divergence across species, despite exceptional phenotypic conservation in many other morphological features. We discuss the evolutionary forces important in the origins of reproductive mode transitions from males being common (gonochorism: females and males) to rare (androdioecy: hermaphrodites and males) and the factors that modulate male frequency in extant androdioecious populations, including the potential influence of selective interference, host-pathogen coevolution, and mutation accumulation. Further, we summarize the consequences of males being common <i>vs</i> rare for adaptation and for trait divergence, trait degradation, and trait dimorphism between the sexes, as well as for molecular evolution of the genome, at both micro-evolutionary and macro-evolutionary timescales. We conclude that <i>C. elegans</i> male biology remains underexploited and that future studies leveraging its extensive experimental resources are poised to discover novel biology and to inform profound questions about animal function and evolution.