Wen-Juan Ma Research

Unlike mammals, birds, and flies, sex chromosomes in >96% of frog species are not degenerated and homomorphic, partly because of frequent turnovers in sex chromosomes and sex reversals. In addition, sex-chromosome evolution is expected to lead to major changes in gene expression due to sex-specific patterns of selection and inheritance, resulting in X chromosomes often enriched in female-biased genes (feminization), and Z chromosomes in male-biased genes (masculinization). Such patterns have been documented in many species with highly degenerated sex chromosomes. However, we do not know how quickly sexualisation of gene expression and transcriptional degeneration evolve after sex-chromosome formation, and little is known about how sex-biased gene expression varies throughout development.

The common frog, Rana temporaria, provides an ideal model to investigate these questions, as it possesses homomorphic sex chromosomes and thus represents an early stage of sex-chromosome evolution, distributed widely throughout Europe and has a variable sex-determination system ranging from genetic to non-genetic. In the projects, in combination of fieldwork, molecular, genetic, NGS sequencing and bioinformatic approaches, we use the common brown frogs to investigate various questions below:

Evolution and dynamics of sex-biased gene expression in three populations with various Y-chromosome differentiation levels

The sex determination mechanism of the common frog

Differentiation and signature of sexual antagonistic selection along X/Y chromosomes

Phytogeography and evolutionary origin of Y chromosomes in the common frog

Patterns of sex chromosome turnover in the true frog Ranidae

Polyploidy has played a major role in the diversification of land plants, likely because of the expansion in the ecological niche of polyploid populations, and because reproductive isolation is immediately established between a new polyploid population and its diploid progenitor species. It is now well established that most polyploid species are polyphyletic, with multiple independent origins, and that polyploid genomes may undergo rapid change after their duplication and hybridization associated with their origin.

In the M. annua species complex, diploid populations are dioecious, but hexaploid populations are either monoecious or androdioecious. Diploid and polyploid males hold their flowers in erect ‘pedunculate’ inflorescences above the plant, whereas diploid females and hexaploid monoecious individuals (which are effectively modified pollen-producing females) typically hold both their male and female flowers in sub-sessile inflorescence in the leaf axils. However, we recently documented the existence in some populations of hexaploid monoecious individuals of M. annua that, like males, hold their male flowers on erect peduncles rather than in the sub-sessile axillary inflorescences that are more typical for hexaploid M. annua. One might expect such a superior strategy for pollen dispersal to quickly spread throughout the species range, particularly as it does not appear very costly in terms of other fitness components. Using the two broadly sympatric hexaploid lineages of the wind-pollinated annual plant Mercurialis annua, in combination with common garden experiments, ploidy assessment, reciprocal crosses and phylogenetic construction, and RADseq approaches, we aim to answer the following questions:

1. Reproductive isolation between divergent hexaploid populations of Mercurialis annua with contrasting inflorescence architecture: the role of multiple origins of polyploidy for functional diversification
2. Sex-linked markers across the annual plant Mercurialis annua species complex
3. The evolutionary origin and population genetic differentiation of male-like inflorescence in M. annua

During my PhD, I was interested in evolution and genetics of sex determination mechanisms in haplodiploid wasps.

1) Using experimental crosses and simulation-modelling approaches, I tested for the so called Complementary Sex Determination (CSD) mechanisms in the four parasitoid Asobara wasp (PLoS ONE). We could excluded up to ten CSD loci and argued that it is unlikely they would evolve CSD system.

2) For the asexual Asobara japonica, using introgression experiment and qPCR to detect Wolbachia density, I discovered a novel role of Wolbachia (bacteria) titre, involving in two separate steps of diploidisation and feminisation following fertilisation (BMC Evolutionary Biology).

3) In order to understand the genetic architecture of the decayed sexual traits, we performed four generations of introgression experiments between sexual and asexual strains and tested various sexual traits. We revealed the genetic architecture of decayed female sexual traits are likely a few loci with major effects (Heredity).

4) Furthermore, I developed genome-wide SNP markers to construct a linkage map for a QTL study on decayed sexual traits.

5) I also wrote invited review articles regarding endosymbiont manipulation of host reproduction and sex determinations (Sexual Development, 2014; Journal of Evolutionary Biology, 2017).