Our paper is online at Scientific Reports!
This was a collaboration led by Tali Reiner Brodetzki and Abraham Hefetz (TAU) to resolve species delimitation in the Cataglyphis niger complex. Previous studies identified three clades within this species complex: C. niger, C. savignyi, and C. drusus. The three were distinct monophyletic clades according to their mitochondrial haplotypes, and they also display distinct social colony structures: C. niger is polygyne, whereas C. savignyi and C. drusus are monogyne. In this new paper we show using RAD sequencing and population structure analysis of thousands of SNP loci that these three mitochondrial clades are not monophyletic in terms of their nuclear DNA. In fact, there is no detectable genetic divergence among them, and they form one un-differentiated population cluster in the STRUCTURE results:
We also conducted a maximum likelihood test for gene flow (using 3s) and rejected the null model of no gene flow between these clades. That is, there is significant evidence for gene flow between all these populations and between colonies of different social structure. Finally, we show that the spermatheca of polygyne queens with the C. niger mitotype contains mostly sperm with the C. savignyi mitotype. That is, polygyne queens mate mostly with males from monogyne colonies. Therefore, C. niger is one species that harbors a social polymorphism similar to other ants such as Solenopsis invicta and Formica selysi.
We do not know yet if the social polymorphism in C. niger is controlled by a supergene ("social chromosome") as found in the other two systems. C. niger is also distinct in that the social form is completely linked to the mitochondrial lineage. That is, daughter queens always inherit the social form of their mothers. This raises the intriguing possibility of maternal imprinting. It remains to be seen if this system will turn out to be genetically controlled as in the social chromosome systems, or rather epigenetically controlled.