A Genome-wide hybrid incompatibility landscape between Caenorhabditis briggsae and C. nigoni.
PLoS Genet 2015;
11:e1004993. [PMID:
25692300 PMCID:
PMC4334894 DOI:
10.1371/journal.pgen.1004993]
[Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 01/08/2015] [Indexed: 11/19/2022] Open
Abstract
Systematic characterization of ẖybrid incompatibility (HI) between related species remains the key to understanding speciation. The genetic basis of HI has been intensively studied in Drosophila species, but remains largely unknown in other species, including nematodes, which is mainly due to the lack of a sister species with which C. elegans can mate and produce viable progeny. The recent discovery of a C. briggsae sister species, C. nigoni, has opened up the possibility of dissecting the genetic basis of HI in nematode species. However, the paucity of dominant and visible marker prevents the efficient mapping of HI loci between the two species. To elucidate the genetic basis of speciation in nematode species, we first generated 96 chromosomally integrated GFP markers in the C. briggsae genome and mapped them into the defined locations by PCR and Next-Generation Sequencing (NGS). Aided by the marker, we backcrossed the GFP-associated C. briggsae genomic fragments into C. nigoni for at least 15 generations and produced 111 independent introgressions. The introgression fragments cover most of the C. briggsae genome. We finally dissected the patterns of HI by scoring the embryonic lethality, larval arrest, sex ratio and male sterility for each introgression line, through which we identified pervasive HI loci and produced a genome-wide landscape of HI between the two nematode species, the first of its type for any non-Drosophila species. The HI data not only provided insights into the genetic basis of speciation, but also established a framework for the possible cloning of HI loci between the two nematode species. Furthermore, the data on hybrids confirmed Haldane’s rule and suggested the presence of a large X effect in terms of fertility between the two species. Importantly, this work opens a new avenue for studying speciation genetics between nematode species and allows parallel comparison of the HI with that in Drosophila and other species.
Hybrid incompatibility (HI) has been intensively studied among Drosophila species, but remains largely unknown in other species. Model organism is a species of choice for the HI study because these species provide sophisticated molecular and genetic tools for illustrating mechanism underlying a given HI. C. elegans as a model organism contributed little to the field due to the lack of a sister species with which it can mate and produce viable progeny. The recent discovery of a C. briggsae sister species, C. nigoni, has made it possible to study the HI between nematode species. However, the paucity of molecular and genetic tools in both species inhibits their use in such studies. To empower the use of this species pair in HI studies, we first created a collection of fluorescent markers over the C. briggsae genome to facilitate the directional introduction of the marker-associated C. briggsae genomic fragments into the C. nigoni background. We next mapped the marker insertion sites and introduced the markers into C. nigoni by repeated crossings. Finally, we generated a genome-wide HI landscape between the two species by scoring the HI phenotypes of their hybrid progeny. The study not only provides an invaluable resource for the molecular cloning of HI loci between C. briggsae and C. nigoni, but also permits comparative analysis of speciation genetics between nematode and other species.
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