Abstract
Tilapia species exhibit a large ecological diversity and an important propensity to interspecific hybridisation. This has been shown in the wild and used in aquaculture. However, despite its important evolutionary implications, few studies have focused on the analysis of hybrid genomes and their meiotic segregation. Intergeneric hybrids between Oreochromis niloticus and Sarotherodon melanotheron, two species highly differentiated genetically, ecologically, and behaviourally, were produced experimentally. The meiotic segregation of these hybrids was analysed in reciprocal second generation hybrid (F2) and backcross families and compared to the meiosis of both parental species, using a panel of 30 microsatellite markers. Hybrid meioses showed segregation in accordance to Mendelian expectations, independent from sex and the direction of crosses. In addition, we observed a conservation of linkage associations between markers, which suggests a relatively similar genome structure between the two parental species and the apparent lack of postzygotic incompatibility, despite their important divergence. These results provide genomics insights into the relative ease of hybridisation within cichlid species when prezygotic barriers are disrupted. Overall our results support the hypothesis that hybridisation may have played an important role in the evolution and diversification of cichlids.
Highlights
Interspecific hybridisation has been suggested to be an important evolutionary force that generates biological diversity by the recombination of genetic material among divergent lineages [1,2,3]
A high percentage of the markers were polymorphic in both species (Table 2), with a slightly lower diversity in S. melanotheron (77%) than in O. niloticus (97%)
Our analysis permitted to track the origin and transmission of alleles across 17 independently mapped anchors distributed over the tilapia genome, including 8 genomic segments represented by 2 to 4 linked loci to survey variation of recombination between hybrids, parental species, and/or sexes
Summary
Interspecific hybridisation has been suggested to be an important evolutionary force that generates biological diversity by the recombination of genetic material among divergent lineages [1,2,3]. The role of introgressive hybridisation has been shown in case of humanmediated evolution and especially domestication [8]. Convincing evidence suggests that inter-specific hybridisation has played an important role during evolution and diversification of cichlid fish [10]. Some cichlid adaptive radiations may have been initiated through hybridisation between distantly related lineages, forming a “hybrid swarm,” such as the radiations of Lakes Victoria [11], Malawi [12], and Makgadikgadi [13]. Hybridisation can occur later during the process of radiation between divergent or already diverged species, forming “syngameon”, as suggested for some Lake Tanganyika lineages [14,15,16]. Several cases of introgressive hybridisation have been recorded in the wild, under natural conditions, either during the process of adaptive
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