#	Pagina
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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - MALEPREG (Male pregnancy â€“ Unravelling the coevolution of parental investment and immune defence)

Teaser

Summary

In this project we the unique evolution of male pregnancy in sex-role reversed syngnathids (pipefishes and seahorses) that show a gradient from external fertilisation to full viviparity and are, thus, ideal to study the evolution of viviparity. Only this genus allows the role of egg production and viviparity to be disentangled, as both traits co-occur in the female in most other species. As immunological tolerance is fundamentally associated with the evolution of pregnancy, I investigate how male pregnancy has coevolved with adaptive immune system rearrangements and the broodpouch specific microbiota.
Investigating the evolution of parental investment and male pregnancy, in particular, will give insight into patterns of convergent evolution. This will permit comparing the mechanisms and functions behind sex roles, which ultimately allows identifying the molecular basis and driving forces for the multiple evolution of parental investment and viviparity.

Humans are fascinated by sex and sex roles. Our society is intrigued by the never-ending discussion of similarities and disparities between men and women. The cultural evolution of human societies can only be understood by considering the deep biological function and route of sex roles. As our knowledge about sex roles and parental investment mostly stems from mammalian biology, we need to examine how species of other classes have evolved towards to successful raise of offspring.

Male pregnancy coevolved with immunological tolerance â€“ the syngnathid phylogeny exhibits a paternal investment gradient. At the base of the clade, we find extant species with external fertilisation and little brood care, gluing the eggs to the outside of the maleâ€™s belly, while the most advanced genera have a placenta-like structure within a brood pouch. Syngnathids, thus, represent an ideal model system to examine the coevolution of immunological tolerance against non-self with male pregnancy. I expect an induced tolerance against foreign tissue in species with full pregnancy correlated with either a loss or a reduction in the diversity of genes of the MHC II pathway and fully functional MHC class II in related species without placentation. This will be evaluated with tissue transplant experiments, followed by transcriptomics and comparative genomics.

The limited data available suggest an overlap of genes involved in independent evolutionary events leading to female viviparity. Also, genes with a potential function both in female and male pregnancy evolution were identified. It is time for an extensive search for key candidate genes that mediated the parallel evolution of pregnancy. This will enlighten the origins of parental investment and provide a comprehensive insight into mating system evolution. Comparing systems with female and male pregnancy is highly promising, as the overlap of genes in those two extremes will likely consist over the full continuum of pregnancy evolution. I suggest an in-depth RNAseq approach in syngnathids to identify genes involved in pouch development and male pregnancy.

To elucidate if male pregnancy coevolved with a pouch-specific microbiota, I will examine the microbial composition in the brood pouches of syngnathids. The bacteria in female gonads, male brood pouches and embryos will be genotyped to assess sex-specific microbial contribution to offspring. Microbial re-inoculation experiments will determine the sex-specific parental transfer of microbes and their impact on offspring performance. The interaction of parental transfer of immunity and microbiota will be examined over microbial genotyping from parents that were either permitted to transfer immunity or prohibited to do so.

Work performed

In the first project period we expanded the breeding of several pipefish and seahorse species (Hippocampus erectus, Syngnathus typhle, Nerophis ophidion, Aeoliscus strigatus, Dunckerocampus pessuliferus). Most of them do now reproduce under laboratory conditions. We established in situ hybridisation for localisation and visualization of gene expression during male pregnancy. We are currently analysing the gene data of a comparative transcriptome approach (RNAseq) of male pregnancy in four different syngnathid species to identify the core candidate genes that will be used for in situ hybridisation and later for knock-out via CRISPR/cas9. We have successfully done the transplant experiments and are currently assessing the genes involved in self-non-self-recognition. We further cultivated the brood pouch microbiota of Syngnathus typhle and genotyped the bacteria over Sanger sequencing of the 16s gene. In addition, we are currently analysing the data of a comparative 16s rRNA sequencing study assessing brood pouch and gut microbiota of three different syngnathid species.

Final results

We made good progress during the first project phase. Scientifically no major issues have been encountered so far. However, due to the belated move of GEOMAR (was suggested to happen in 2019 and is now scheduled for 2023) to a new building with access to genetic safety level 1 (S1) climate chambers and genetic safety level 2 (S2) laboratories, we had to overcome some challenges by refurbishing out climate chamber to get S1 status. This should now be resolved such that we can start working with genetically modified organisms (knock-out of genes over CRISPR/cas9). The start of the Bioinformatician postdoc had to be delayed as we could not find a suitable candidate.