Fire ant social chromosomes: Differences in number, sequence and expression of odorant binding proteins

Has gene expression neofunctionalization in the fire ant antennae contributed to queen discrimination behavior?

“…In the former case, the SiOBP12b′ flanking region should be adjoined, while in the latter case, we may be able to find SiOBP12b′ (or its remnants) in the genome of Solenopsis geminata , an outgroup species to the South American socially polymorphic clade of fire ants that includes S. invicta (Gotzek, Clarke, & Shoemaker, ; Martins, Fernando de Souza, & Bueno, ). In contrast to a previous study, which suggested that OBP12 in S. geminata ( SgOBP12 ) was partially degenerated (Pracana et al, ), we found that the 17 kb OBP gene cluster containing Gp‐9 ( Gp‐9 , OBP4 , OBP13 , and OBP12 ) is conserved in the two species (identity >95%, blast results in Dryad). However, the SiOBP12b ′ region is a complex duplication of ~30 kb that is absent in the S. geminata genome while its 5′ and 3′ adjacent regions are conserved and separated by only a ~2 kb unconserved fragment (Figure ).…”

“…The OBP Gp‐9 is a classic, although disputed, candidate that may have this function with regard to regulating social form differences (Gotzek & Ross, ; Gotzek, Shoemaker, & Ross, ; Keller & Ross, ; Krieger & Ross, ; Leal & Ishida, ). Our study showed that Gp‐9 is not differentially expressed in the antennae or in different body parts between the three worker classes (Figure ; see also Pracana et al, ). Previous studies showed that Gp‐9 was highly expressed in polygyne queens compared to monogyne queens (Morandin et al, ; Pracana et al, ).…”

“…Our study showed that Gp‐9 is not differentially expressed in the antennae or in different body parts between the three worker classes (Figure ; see also Pracana et al, ). Previous studies showed that Gp‐9 was highly expressed in polygyne queens compared to monogyne queens (Morandin et al, ; Pracana et al, ). Thus, differential expression of Gp‐9 could possibly be important in queens but is unlikely in workers; functional differences in workers, if any, would have to be mediated by protein sequence differences.…”

“…The fate of a gene duplicate is typically loss of one of the copies but sometimes neofunctionalization. While the SiOBP12b ′ sequence has an intact open reading frame, SiOBP12B and SiOBP12b appeared to have become nonfunctional independently because of an early stop codon caused by a C‐to‐T substitution at the 46 th nucleotide relative to the start codon in SiOBP12B or a 17‐base frame‐shifting insertion in SiOBP12b (Pracana et al, ). The nonfunctional SiOBP12b allele is consistent with no (this study) or very low expression of this allele (1 of 32 OBP12 reads; Gotzek et al, ; Table ).…”

“…Genes may also neofunctionalize in terms of gene expression. Prior studies have shown that many OBPs, including Gp‐9 and SiOBP12 , are expressed in nonantennal tissues (Morandin et al, ; Pracana et al, ; Zhang, Wanchoo, Ortiz‐Urquiza, Xia, & Keyhani, ). We tested whether SiOBP12 (in an assay that cannot distinguish between paralogs) was also differentially expressed in the worker heads (without antennae), thoraces, and abdomens using qRT‐PCR assays.…”