Evolution of the Yellow/Major Royal Jelly Protein family and the emergence of social behavior in honey bees

The genomic architecture underlying the evolution of insect social behavior is largely a mystery. Eusociality, defined by overlapping generations, parental brood care, and reproductive division of labor, has most commonly evolved in the Hymenopteran insects, including the honey bee Apis mellifera. In this species, the Major Royal Jelly Protein (MRJP) family is required for all major aspects of eusocial behavior. Here, using data obtained from the A. mellifera genome sequencing project, we demonstrate that the MRJP family is encoded by nine genes arranged in an approximately 60-kb tandem array. Furthermore, the MRJP protein family appears to have evolved from a single progenitor gene that encodes a member of the ancient Yellow protein family. Five genes encoding Yellow-family proteins flank the genomic region containing the genes encoding MRJPs. We describe the molecular evolution of these protein families. We then characterize developmental-stage-specific, sex-specific, and caste-specific expression patterns of the mrjp and yellow genes in the honey bee. We review empirical evidence concerning the functions of Yellow proteins in fruit flies and social ants, in order to shed light on the roles of both Yellow and MRJP proteins in A. mellifera. In total, the available evidence suggests that Yellows and MRJPs are multifunctional proteins with diverse, context-dependent physiological and developmental roles. However, many members of the Yellow/MRJP family act as facilitators of reproductive maturation. Finally, it appears that MRJP protein subfamily evolution from the Yellow protein family may have coincided with the evolution of honey bee eusociality.

A cis-regulatory sequence within the yellow locus of Drosophila melanogaster required for normal male mating success

Drosophila melanogaster males perform a courtship ritual consisting of a series of dependent fixed-action patterns. The yellow (y) gene is required for normal male courtship behavior and subsequent mating success. To better characterize the requirement for y in the manifestation of innate male sexual behavior, we measured the male mating success (MMS) of 12 hypomorphic y mutants and matched-outbred-background controls using a y+ rescue element on a freely segregating minichromosome. We found that 4 hypomorphs significantly reduced MMS to varying degrees. Reduced MMS was largely independent of adult pigmentation patterns. These mutations defined a 300-bp regulatory region upstream of the transcription start, the mating-success regulatory sequence (MRS), whose function is required for normal MMS. Visualization of gene action via GFP and a Yellow antibody suggests that the MRS directs y transcription in a small number of cells in the third instar CNS, the developmental stage previously implicated in the role of y with regard to male courtship behavior. The presence of Yellow protein in these cells positively correlates with MMS in a subset of mutants. The MRS contains a regulatory sequence controlling larval pigmentation and a 35-bp sequence that is highly conserved within the genus Drosophila and is predicted to bind known transcription factors.

A novel hypothesis on the biochemical role of the Drosophila Yellow protein

In Drosophila melanogaster, the protein product of the yellow gene is necessary for normal pigmentation and male sexual behavior. Although one of the best characterized loci from a genetic standpoint, the function of the Yellow protein in the development of either phenotype is unknown. Here I propose that Yellow acts as a growth factor- or hormone-like molecule in the development of pigmentation and sexual behavior, and discuss the consistency of this theory with experimental observations in flies and humans.

A gene necessary for normal male courtship, yellow, acts downstream of fruitless in the Drosophila melanogaster larval brain

The fruitless (fru) gene is a member of the Drosophila melanogaster somatic sex determination genetic pathway. Although it has been hypothesized that the primary function of fru is to regulate a genetic hierarchy specifying development of adult male courtship behavior, genes acting downstream of fru have not yet been identified. Here we demonstrate that the yellow (y) gene is genetically downstream of fru in the 3(rd)-instar larval brain. Yellow protein is present at elevated levels in neuroblasts, which also show expression of male-specific FRU proteins, compared to control neuroblasts without FRU. A location for y downstream of fru in a genetic pathway was experimentally demonstrated by analysis of fru mutants lacking transcription of zinc-finger DNA binding domains, and of animals with temporal, spatial, or sexual mis-expression of male-specific FRU. A subset of fru and y mutants is known to reduce levels of a specific behavioral component of the male courtship ritual, wing extension, and FRU and Yellow were detected in the general region of the brain whose maleness is necessary for development of that behavior. We therefore hypothesized that ectopic expression of Yellow in the 3(rd)-instar brain, in a y null background, would rescue low levels of wing extension and male competitive mating success, and this was found to be the case. Overall, these data suggest that y is a downstream member of the fru branch of the D. melanogaster sex determination hierarchy, where it plays a currently unknown role in the development of adult male wing extension during courtship.

Immunohistochemical colocalization of Yellow and male-specific Fruitless in Drosophila melanogaster neuroblasts

The Drosophila melanogaster fruitless gene encodes multiple male-specific transcription factors that are hypothesized to regulate a hierarchy of genes responsible for the development of male courtship behavior. Here we show that there are dramatically increased levels of the protein product of the male courtship behavior gene yellow associated with male-specific Fruitless protein in a subset of neuroblasts in third-instar larval male brains. We hypothesize that yellow is downstream of fruitless in a male courtship behavior developmental genetic pathway.

Intraspecific variation in sexual isolation in the jewel wasp Nasonia

Divergence in mate recognition systems can lead to reproductive isolation. In this study, we investigate patterns of intraspecific variation that contribute to premating isolation within and between two haplodiploid species, Nasonia vitripennis and N. longicornis. In a broad-scale survey of 17 North American isofemale lines encompassing the two species, we report strong asymmetric sexual isolation between species and a dramatic level of intraspecific variation for mate discrimination between species. A general lack of incipient speciation was found, with the exception of low levels of interpopulational sexual isolation within N. vitripennis. Regression analysis shows that the degree of intraspecific variation for within-species mating frequency is not associated with the degree for between-species mating frequency. Reinforcement or reproductive character displacement may be involved in some of the variation in interspecies premating isolation.

Testing the heterogeneity theory of late-life mortality plateaus by using cohorts of Drosophila melanogaster

Variation among individuals in robustness has been posed as a general explanation for the lack of increase in late-life mortality rates. Here, we test corollaries of this heterogeneity theory. One is that populations that have undergone strong laboratory selection for differentiated stress resistance should show significant differences in their late-life mortality schedules. To test this corollary, we employed 40 410 flies from three groups of Drosophila melanogaster populations that differ substantially in their resistance to starvation. No significant differences between these groups were found for late-life mortality. Another corollary of the heterogeneity theory is that there should be late-life plateaus in stress resistance that coincide with the plateau stage of the mortality curve. In 20 994 flies from six replicate outbred laboratory populations, we measured mortality rates every other day and starvation and desiccation resistance every 7 days. Both male and female starvation and desiccation resistance clearly decreased with time overall. There was no late-life plateau in male desiccation resistance. A late-life plateau in male starvation resistance may exist, however. Together, these two experiments generally constitute evidence against heterogeneity as a major contributor to the phenomenon of late-life mortality plateaus.