Possible introgression of B chromosomes between bee species (Genus Partamona )

Abstract

The origin of supernumerary (B) chromosomes is still a de- bated topic, with intra- and interspecific origins being the most plausible options. In the bee Partamona helleri, a se- quence-characterized amplified region (SCAR) marker being specific to B chromosomes suggested the possibility of inter- specific origin. Here, we search for this marker in 3 close rela- tive species and perform DNA sequence comparison be- tween species. The SCAR sequence does not show homolo- gy with other sequences in the databases, but does contain an open reading frame with sequence homology with a re- verse transcriptase. Dot-blot hybridization using the SCAR marker as a probe confirmed that it is present in B-carrying, but not B-lacking larvae of P. helleri, and indicated its pres- ence in adult individuals of P. cupira and P. criptica. Addition- ally, PCR amplification of the SCAR marker was successful on genomic DNA obtained from P. helleri and P. rustica larvae carrying B chromosomes, and on genomic DNA obtained from adult individuals of P. cupira, P. criptica and P. rustica. Finally, a comparison of the DNA sequence of the SCAR markers amplified from these 4 species showed very few nu- cleotide differences between the species. The complete as- sociation between B chromosome and SCAR presence and the scarce divergence observed for this DNA sequence be- tween the 4 species analyzed suggest the possibility that this B chromosome has recently been transferred between spe- cies through several episodes of interspecific hybridization.