First-generation linkage map for the common frog Rana temporaria reveals sex-linkage group

Abstract

The common frog (Rana temporaria) has become a model species in the fields of ecology and evolutionary biology. However, lack of genomic resources has been limiting utility of this species for detailed evolutionary genetic studies. Using a set of 107 informative microsatellite markers genotyped in a large full-sib family (800 F1 offspring), we created the first linkage map for this species. This partial map-distributed over 15 linkage groups-has a total length of 1698.8 cM. In line with the fact that males are the heterogametic sex in this species and a reduction of recombination is expected, we observed a lower recombination rate in the males (map length: 1371.5 cM) as compared with females (2089.8 cM). Furthermore, three loci previously documented to be sex-linked (that is, carrying male-specific alleles) in adults from the wild mapped to the same linkage group. The linkage map described in this study is one of the densest ones available for amphibians. The discovery of a sex linkage group in Rana temporaria, as well as other regions with strongly reduced male recombination rates, should help to uncover the genetic underpinnings of the sexdetermination system in this species. As the number of linkage groups found (n ¼ 15) is quite close to the actual number of chromosomes (n ¼ 13), the map should provide a useful resource for further evolutionary, ecological and conservation genetic work in this and other closely related species.

Within‐population polymorphism of sex‐determination systems in the common frog (Rana temporaria)

“…All adults analysed turned out to possess the Western‐clade haplotype, which differs markedly from the Eastern‐clade haplotype found in the Swedish populations on which Cano et al . () based their recombination map. Amplified fragments had the expected size (approximately 600 bp) and were all digested by StyI enzyme (Palo et al ., ).…”

“…A total of 55 markers, from all linkage groups identified by Cano et al . (), were optimized and tested for amplification. These included 14 markers on LG2, among which three ( RtSB03 , Bfg201 and Bfg266 ) had shown sex linkage in Finnish populations (Matsuba et al ., ; Alho et al ., ).…”

High-density sex-specific linkage maps of a European tree frog (Hyla arborea) identify the sex chromosome without information on offspring sex

“…Although Haldane (1922) and Huxley (1928) noted that recombination tends to be lower in the heterogametic sex, many exceptions have been observed and comprehensive explanations for this phenomenon are still lacking (Mank, 2009). In frogs, previous low-density linkage maps documented a strong asymmetry in recombination between males and females, with males having greatly reduced recombination (see, for example, Nishioka and Sumida, 1994;Sumida and Nishioka, 1994;BersetBrändli et al, 2008;Cano et al, 2011;Rodrigues et al, 2013). Our high-density linkage map allows us to localize the recombination events along each linkage group.…”

The genetic contribution to sex determination and number of sex chromosomes vary among populations of common frogs (Rana temporaria)

“…In common frogs (Rana temporaria), sex associates with linkage group 2 (LG 2 ), as first discovered by sex differences in allele frequencies at microsatellite markers (Matsuba et al, 2008;Alho et al, 2010;Cano et al, 2011;Rodrigues et al, 2013). However, the strength of association varies within and among populations (Matsuba et al, 2008;Rodrigues et al, 2013), seemingly with a cline in sexchromosome differentiation along a latitudinal transect in Sweden (Rodrigues et al, 2014).…”