Hybrids – Chances and challenges of novel genomic combinations

Project 8: Genetic conflicts over sex determination and sexual reproduction in hybridogenetic beetles

PI: Susanne Dobler; co-PIs: Bernhard Hausdorf, Jutta Schneider

 

Sex-determining systems are inherently prone to generate conflict between cytoplasmic and nuclear genes (Werren & Beukeboom 1998). In insects parasitic cytoplasmic elements, e.g. Wolbachia bacteria, have been recognized as a frequent cause of female biased sex-ratios with the additional potential to create selective sweeps in infected populations (Werren et al. 2008).

These predictions fit with the situation observed in Altica flea beetles: This species harbors three highly divergent mitochondrial haplotypes, each of which is widely associated with a particular strain of Wolbachia bacteria (Jäckel et al. 2013). One of these haplotypes (HT1) exclusively occurs in females which invariably produce all female offspring. The presence of parasitic bacteria alone is not sufficient to explain these reproductive anomalities. This project will test whether genomic conflicts between introgressed mtDNA genes and nuclear genes lead to the lack of heterogametic males. Paternity analses hint to a gynogenetic mode of reproduction in HT1 females excluding the paternal genome. This project should also elucidate how zygotes are formed in this case. 

Using RAD sequencing offspring of crosses between the three haplotypes will be analysed to determine whether specific RAD markers onyl occur in males. This strategy can identify genomic regions where specific alleles are incompatible with HT1 mtDNA leading to the death of male offspring. Constructing genomewide RAD linkage maps will help establishing whether HT1 females exclusively reproduce gynogenetically (without traces of paternal alleles in the offspring) and what their exact mode of reproduction is. Linkage maps of RAD allele and an analysis of patterns of heterozgosity around the centromeres can help decide between various types of automixis (Svendsen et al. 2015).

 

Jäckel R, Mora D, Dobler S. 2013. Evidence for selective sweeps by Wolbachia infections: Phylogeny of Altica leaf beetles and their reproductive parasites. Mol. Ecol. 22: 4241-4255

Werren JH, Beukeboom LW. 1998. Sex determination, sex ratios, and genetic conflict. Annu. Rev. Ecol. Syst. 29:233–61

Werren JH, Baldo L, Clark ME. 2008. Wolbachia: master manipulators of invertebrate biology. Nature Rev. Microbiol. 6: 741-751.

Svendsen, N, Reisser, CMO, Dukic, M, Thuillier, V, Segard, A, Liautard-Haag, C, Fasel, D, Hurlimann, E, Lenormand, T, Galimov, Y, Haag, CR. 2015. Uncovering cryptic asexuality in Daphnia magna by RAD sequencing. Genetics 201, 1143-1155.