The hymenopteran Partamona helleri is found in southwestern Brazil in the Mata Atlântica from the north of the state of Santa Catarina until the south of Bahia. This work shows that P. helleri can carry up to four B chromosomes per individual. In order to obtain more information about P. helleri B chromosomes, the RAPD technique was used to detect DNA fragments associated with these chromosomes. The results showed that the RAPD technique is useful to detect specific sequences associated with B chromosomes. One RAPD marker was identified, cloned and used as probe in a DNA blot analysis. This RAPD marker hybridized with sequences present only in individuals containing B chromosomes.

The origin of supernumerary (B) chromosomes is still a debated topic, with intra- and interspecific origins being the most plausible options. In the bee Partamona helleri, a sequence-characterized amplified region (SCAR) marker being specific to B chromosomes suggested the possibility of interspecific origin. Here, we search for this marker in 3 close relative species and perform DNA sequence comparison between species. The SCAR sequence does not show homology with other sequences in the databases, but does contain an open reading frame with sequence homology with a reverse 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 presence in adult individuals of P. cupira and P. criptica. Additionally, 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 nucleotide differences between the species. The complete association between B chromosome and SCAR presence and the scarce divergence observed for this DNA sequence between the 4 species analyzed suggest the possibility that this B chromosome has recently been transferred between species through several episodes of interspecific hybridization.

Genetic diversity, population structure and demographic history of Chaetodipterus faber in SW Atlantic were investigated using mitochondrial DNA cytochrome c oxidase subunit I (620 bp) and D-loop (817 bp) sequences. Individuals were collected in five sampling units (SUs) located in latitudes between 2°S and 27°S, southernmost limit of species distribution. The COI sequences from Brazilian sampling units were compared with eight sequences from the Gulf of Mexico and Caribbean, resulting in no significant genetic differences (K2P b 0.32%). On the contrary, pairwise F ST analysis based on D-loop datasets from the five SUs indicated divergence between Tropical and Subtropical clades of SW Atlantic C. faber. The SAMOVA approach was consistent with this divergence and revealed maximal variance among groups (63.59%) when two clades are simulated (k = 2), setting apart Tropical and Subtropical SUs. Demographic analyses support the hypothesis of population expansion, both for Tropical and Subtropical clades. Moreover, Subtropical population size increase was dated after the Tropical clade reached the demographic stability, around 10 kyr ago, during the beginning of interglacial Pleistocene-Holocene transition. The historical demographic results, along with the lower genetic diversity and the starshaped haplotype network of the Subtropical clade corroborate an ancient scenario of the species' adaptive radiation southward.

Chromosomes in hymenopteran insects cannot currently be analysed in adult individuals. The only available cytogenetic techniques need to be performed in larvae. Here we develop and implement a SCAR (Sequence Characterized Amplified Region) marker, associated with B chromosomes in the bee Partamona helleri, which has proven to be very useful to reveal B chromosome presence in adults from natural populations. The marker was tested in ten different colonies simultaneously analysed by both molecular (ten adults per colony) and cytogenetic (20 larvae per colony) techniques. The presence of the SCAR marker always showed the same pattern as B chromosome presence: both were present or absent in all individuals from a same colony, or both were present in only part of the individuals from a same colony. This molecular marker is thus a useful tool for analysing new aspects of this B chromosome system such as B frequency and geographical distribution, B transmission, or B effects in adult individuals.

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