Genetic composition of laboratory stocks of the self-fertilizing fish Kryptolebias marmoratus: a valuable resource for experimental research

Abstract

The hermaphroditic Mangrove Killifish, Kryptolebias marmoratus, is the world's only vertebrate that routinely self-fertilizes. As such, highly inbred and presumably isogenic "clonal" lineages of this androdioecious species have long been maintained in several laboratories and used in a wide variety of experiments that require genetically uniform vertebrate specimens. Here we conduct a genetic inventory of essentially all laboratory stocks of the Mangrove Killifish held worldwide. At 32 microsatellite loci, these stocks proved to show extensive interline differentiation as well as some intraline variation, much of which can be attributed to post-origin de novo mutations and/or to the segregation of polymorphisms from wild progenitors. Our genetic findings also document that many of the surveyed laboratory strains are not what they have been labeled, apparently due to the rather frequent mishandling or unintended mixing of various laboratory stocks over the years. Our genetic inventory should help to clarify much of this confusion about the clonal identities and genetic relationships of laboratory lines, and thereby help to rejuvenate interest in K. marmoratus as a reliable vertebrate model for experimental research that requires or can capitalize upon "clonal" replicate specimens.

Figure 1. Summary of intraline and interline genetic variation in laboratory stocks of Kryptolebias marmoratus.

UPGMA phenogram showing relationships among lines is based on D _PS. Names of the laboratory lines are shown along branches of the tree. Each terminal node name consists of two parts: a number indicating the laboratory of origin (as explained in Table 1); and letters that indicate replicate individual fish from that source. Genotypes at 32 microsatellite loci (arranged in columns) are shown for each node with different colors representing different alleles. Homozygous and hererozygous genotypes are indicated by uni-coloured and bi-colored cells, respectively. Major source regions of the laboratory lines are outlined by braces.

Figure 2. Neighbor-joining tree of selected laboratory stocks of Kryptolebias marmoratus based on 2,946-bp mtDNA sequences.

Names of the laboratory lines are preceeded a number indicating the laboratory of origin (as explained in Table 1); letters at the end indicate replicate individual fish from that source. Bootstrap support values are shown along the nodes. Placements of these lines in the larger mtDNA that includes 136 fish from Caribbean and Brazil are shown in Figure S2.