01883nas a2200157   4500008004100000022002200041245010800063210006900171260008800240300001400328490000800342520120800350100002201558700001401580856013101594       2003                        eng d  a0016-6731 (Print)00aPopulation genetics of Caenorhabditis elegans: the paradox of low polymorphism in a widespread species.0 aPopulation genetics of Caenorhabditis elegans the paradox of low  aDepartment of Genetics, Rutgers University, Piscataway, New Jersey 08854-8082, USA.  a147–1570 v1633 aCaenorhabditis elegans has become one of the most widely used model research organisms, yet we have little information on evolutionary processes and recent evolutionary history of this widespread species. We examined patterns of variation at 20 microsatellite loci in a sample of 23 natural isolates of C. elegans from various parts of the world. One-half of the loci were monomorphic among all strains, and overall genetic variation at microsatellite loci was low, relative to most other species. Some population structure was detected, but there was no association between the genetic and geographic distances among different natural isolates. Thus, despite the nearly worldwide occurrence of C. elegans, little evidence was found for local adaptation in strains derived from different parts of the world. The low levels of genetic variation within and among populations suggest that recent colonization and population expansion might have occurred. However, the patterns of variation are not consistent with population expansion. A possible explanation for the observed patterns is the action of background selection to reduce polymorphism, coupled with ongoing gene flow among populations worldwide.1 aSivasundar, Arjun1 aHey, Jody  uhttps://nematoda.myspecies.info/content/population-genetics-caenorhabditis-elegans-paradox-low-polymorphism-widespread-species00399nas a2200109   4500008004100000245005300041210005300094260002200147100001800169700001400187856008800201       1998                        eng d00aTesting speciation models with DNA sequence data0 aTesting speciation models with DNA sequence data  bBirkhauser Verlag1 aWakeley, John1 aHey, Jody  uhttps://nematoda.myspecies.info/content/testing-speciation-models-dna-sequence-data