Dr. Wen-Juan Ma

I am broadly interested in evolutionary biology, in particular topics such as sex determination, sex chromosome, reproductive system etc. During the PhD, I investigated evolutionary genetics of sex determination and parthenogenesis in haplodiploid wasps. Currently, I investigate the evolutionary genomics of sex determination and young sex chromosomes in two highly divergent lineages: the frog system Rana and the plant system Mercurialis. Particularly I am addressing the following questions:

Patterns of sex chromosome turnover in the frog family Ranidae
(in collaboration with Dr. Alan Brelsford)
Unlike the systems of mammals, birds, and flies, sex chromosomes in ~96% of frog species are undifferentiated, partly because of frequent turnovers in sex chromosomes and therefore also the sex determination systems. A recent review of data for Ranidae (Miura 2007) has shown not only that turnovers are frequent in this family, but that a limited set of chromosomes (out of the 13 pairs) are regularly co-opted as sex chromosomes. In this project, by gathering data from additional Ranidae species with restriction site associated DNA sequencing (RADseq) approach, we will quantify the rate of turnover within the family, ask whether some chromosomes are indeed more likely than others to take over the role of sex-determiner, and test whether evolutionary transitions in sex-chromosome identity are more likely to retain the same heterogametic sex.

The evolutionary genomics of sex determination in R. temporaria
(in collaboration with Nicolas Rodrigues)
Contrasting with the view of distinguished category between genetic and environmental sex determinations, recent studies show that it is a continuum gradient to determine the sex (Beukeboom & Perrin, 2014). Consistent with this, sex chromosome should evolve to have different differentiation levels along the gradient under natural selection. Sex chromosomes in amphibians are generally undifferentiated due to high sex chromosome turnover rate and/or occasional X-Y recombination, and thus provide ideal materials to investigate. It is currently unknown that: what gene(s) or genomic regions determine sex? Is there a strong negative correlation between heterochromosome degeneration level and environmental effects? How does environmental factors interact with genetics? The common frog Rana temporaria is suitable to investigate the evolution of sex determination mechanisms. It has been documented to have both latitudinal and altitudinal clines for sex determination systems, e.g. from genetic to epigenetic mechanism (Rodrigues et al., 2013, 2014). In this project, we aim to investigate the genetic and genomic basis of sex determination, understand the evolution of the different mechanisms in R. temporaria, by combining approaches of candidate gene and development-series of genome-wide gene expression (RNAseq).

Signature of sexual antagonistic selection on the X/Y chromosome
(in collaboration with Dr. Paris Veltsos)
It is reported that sexual antagonistic (SA) genes and sex determination regions (SDR) have a distinguished signature in the molecular variation on recombining sex chromosomes. In addition, coalescent models point out that the neutral variation between X and Y (measured as Fst) increases dramatically in the neighborhood of SA loci and sex determination loci (Guerrero et al., 2012). It is exciting to test this signature in the young sex chromosomes. In this project, using genomic scan of sequence variation on sex chromosomes, we aim to detect the SA signature in R. temporaria.

The origin and evolutionary genomics of inflorescence architecture in Mercurialis annua
(In collaboration with Dr. Luis Santos del Blanco)
Most flowering plants are hermaphrodites. However, evolutionary transitions between hermaphrodites and separate sexes have been quite frequent. Compared to the hermaphrodite individuals, males or females tend to have more distinct sexual characteristics, which could be under strong sexually antagonistic selection. Sexually antagonistic (SA) selection occurs when an allele increases fitness in one sex and decreses it in the other. However, we know very little about the genetic basis of sexual dimorphism. In the Mercurialis annua species complex, hexaploid hermaphrodites are typically similar to the females in their inflorescence architecture, bearing their subsessile inflorescence on the leaf axils. Males produce a large numbers of flowers allocated along long peduncles. Excitingly, several populations of hermaphrodites bearing male-like peduncles have been recently discovered in eastern Spain. Since the long-peduncle trait for male flower is strictly associated with male function and never found in females (or hermaphrodites), we hypothesize that genes controlling peduncle inflorescence are on Y chromosome, possibly are close to sex determination regions, and that the genes are probably under SA selection. Thus, the genetic architecture of this trait would shed light on the sex determination mechanism and SA selection in Mecurialis. In particular, we are addressing the following questions:

1. What is the origin of the pedunculate hermaphrodites? how do they evolve, and do they evolve from hermaphrodites or males?
2. What is the genetic architecture underlying the peduculate inflorescence in hermaphrodite individuals?
3. What is the genomic basis of pedunculate inflorecence variation among natural populations?