Identification of Multiple Loci Associated with Social Parasitism in Honeybees.
In colonies of the honeybee Apis mellifera, the queen is usually the only reproductive female, which produces new females (queens and workers) by laying fertilized eggs. However, in one subspecies of A. mellifera, known as the Cape bee (A. m. capensis), worker bees reproduce asexually by thelytoky, an abnormal form of meiosis where two daughter nucleii fuse to form single diploid eggs, which develop into females without being fertilized. The Cape bee also exhibits a suite of phenotypes that facilitate social parasitism whereby workers lay such eggs in foreign colonies so their offspring can exploit their resources. The genetic basis of this switch to social parasitism in the Cape bee is unknown. To address this, we compared genome variation in a sample of Cape bees with other African populations. We find genetic divergence between these populations to be very low on average but identify several regions of the genome with extreme differentiation. The regions are strongly enriched for signals of selection in Cape bees, indicating that increased levels of positive selection have produced the unique set of derived phenotypic traits in this subspecies. Genetic variation within these regions allows unambiguous genetic identification of Cape bees and likely underlies the genetic basis of social parasitism. The candidate loci include genes involved in ecdysteroid signaling and juvenile hormone and dopamine biosynthesis, which may regulate worker ovary activation and others whose products localize at the centrosome and are implicated in chromosomal segregation during meiosis. Functional analysis of these loci will yield insights into the processes of reproduction and chemical signaling in both parasitic and non-parasitic populations and advance understanding of the process of normal and atypical meiosis.
Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
Andreas
0000-0002-9081-9663
A
Wallberg
Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
Christian W
CW
Pirk
Plant Protection Research Institute, Agricultural Research Council, Stellenbosch, South Africa.
Mike H
MH
Allsopp
Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
Matthew T
0000-0003-1141-2863
MT
Webster
D000349:Africa; D000818:Animals; D001516:Bees / Q000235:genetics*; D002874:Chromosome Mapping; D005260:Female; D005828:Genetics, Population; D016678:Genome; D005838:Genotype; D005843:Geography; D006720:Homozygote; D008297:Male; D018895:Microsatellite Repeats; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D012098:Reproduction / Q000235:genetics; D012641:Selection, Genetic; D012726:Sexual Behavior, Animal; D012919:Social Behavior