Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

FP7

DamaNMP Report Summary

Project reference: 618961
Funded under: FP7-PEOPLE

Periodic Report Summary 1 - DAMANMP (Evolution of partly genetic sex determination in Daphnia)

In the animal kingdom, sex determination occurs along a continuum between genetic sex determination (GSD) and environmental sex determination (ESD). Under GSD, sex is determined genetically, meaning that males and females have different alleles or genotypes at one or several loci (“sex-determining loci”). Under ESD, any genotype can develop into a male or a female, depending on environmental cues. ESD is thought to be the ancestral state in animals and the evolutionary transition from ESD to GSD is believed to be closely linked with the initial steps of sex chromosome evolution. However, due to a lack of suitable empirical systems, the early stages of this transition remain poorly understood.
In Daphnia, parthenogenetic reproduction alternates with sexual reproduction. Individuals of both sexes that belong to the same parthenogenetic line are genetically identical and their sex is determined by the environment. However, some lines never produce males, and these non male producing ("NMP") genotypes can only persist through phases of sexual reproduction if they co-occur with normal ("MP") genotypes that produce both males and females. The distinction between MP and NMP is genetically determined. Hence, Daphnia have a partially genetic and partially environmental sex determination. Here I exploit this unique polymorphism to study the early stages of the evolutionary transition between ESD and GSD and to investigate its genetic basis and genetic/genomic consequences, including the evolution of novel sex chromosomes.
Objective 1: Investigate the genetic basis and evolutionary origin of NMP
a. Does the region containing the NMP locus show features of a young W chromosome?
b. Does the NMP region contain any genes known to be involved in sex determination?
c. What is the age and sequence divergence between NMP and MP chromosomes and when did recombination suppression evolve?
d. Did NMP evolve several times independently or just once in D. magna?
e. How can its occurrence in lineages with strongly divergent mitochondrial haplotypes be explained?
Progress and results (objective 1):
This part of the project has largely been completed (Svendsen et al. 2015, Reisser et al. In preparation). The first study confirmed that NMP strains indeed do not produce male, not even at a low rate. Hence its occurrence in lineages with strongly divergent mitochondrial haplotypes is explained by common ancestry or parallel evolution, but not by paternal transmission. The study also shows that NMP are not unable colonize an empty pond on their own: they are capable of rare parthenogenetic reproduction via automixis. The second study showed that the NMP phenotype indeed is determined by a whole genomic region, showing characteristics of a young W chromosome and containing several genes known to be involved in sex determination in arthropods. Three independent mapping crosses all found NMP do be determined by the same region, suggesting that common ancestry is the most likely explanation. However, this will be further tested using comparative mapping with another Daphnia species also showing NMP and with a functional analysis of the most promising candidate genes within the region.


Objective 2: Investigate the evolutionary advantage of NMP
a. Test the hypothesis that the advantage of NMP is conferred by obligate outcrossing
b. Investigate why NMP occurs in some populations and not in others
c. Test / expand existing theoretical predictions on the expected equilibrium frequency of NMP
Progress and results (objective 2):
The experiments have been initiated and are at different stages of data collection. No results are available yet.

Objective 3: Investigate the evolutionary consequences of NMP
Here we will test the predicted (partial) specialization of MP clones on male function in populations in which they co-occur with NMP. Two predictions can be made, which will be tested:
a. MP genotypes in populations containing NMP genotypes should show a higher propensity and / or efficiency of sexual reproduction via the male function than MP genotypes in populations without NMP.
b. MP genotypes in populations containing NMP genotypes should show a lower propensity and /or efficiency of sexual reproduction via the female function than MP genotypes in populations without NMP.

In addition, if male specialization does occur in MP genotypes co-occurring with NMP, then it is predicted that the genes contributing to this specialization might be found on the Z chromosome in the region homologous to the NMP region on the W chromosome (Charlesworth and Mank 2010). Therefore, if evidence for (incomplete) male specialization is found, we will
c. Investigate the genetic basis of male specialization in MP genotypes co-occurring with NMP.
Progress and results (objective 3):
The experiments have been initiated and are at different stages of data collection. No results are available yet.

Contact

Mere, Jocelyn (Head of Technology Tansfer and Partnership)
Tel.: +33 4 67 61 35 35
Fax: +33 4 67 04 32 36
E-mail

Subjects

Life Sciences
Record Number: 183823 / Last updated on: 2016-06-13
Information source: SESAM