PDK1 and HR46 Gene Homologs Tie Social Behavior to Ovary Signals

Abstract

The genetic basis of division of labor in social insects is a central question in evolutionary and behavioral biology. The honey bee is a model for studying evolutionary behavioral genetics because of its well characterized age-correlated division of labor. After an initial period of within-nest tasks, 2–3 week-old worker bees begin foraging outside the nest. Individuals often specialize by biasing their foraging efforts toward collecting pollen or nectar. Efforts to explain the origins of foraging specialization suggest that division of labor between nectar and pollen foraging specialists is influenced by genes with effects on reproductive physiology. Quantitative trait loci (QTL) mapping of foraging behavior also reveals candidate genes for reproductive traits. Here, we address the linkage of reproductive anatomy to behavior, using backcross QTL analysis, behavioral and anatomical phenotyping, candidate gene expression studies, and backcross confirmation of gene-to-anatomical trait associations. Our data show for the first time that the activity of two positional candidate genes for behavior, PDK1 and HR46, have direct genetic relationships to ovary size, a central reproductive trait that correlates with the nectar and pollen foraging bias of workers. These findings implicate two genes that were not known previously to influence complex social behavior. Also, they outline how selection may have acted on gene networks that affect reproductive resource allocation and behavior to facilitate the evolution of social foraging in honey bees.

Insulin-like peptides (AmILP1 and AmILP2) differentially affect female caste development in the honey bee (Apis mellifera)

“…DNase (RNase-free, DNase kit, Applied Biosystems, Bedford. MA, USA) was added to the total RNA extract to remove trace DNA contaminants, and 1 μg of treated RNA was used for reverse transcription following an established method (Wang et al, 2009) using TaqMan reverse transcription reagents (Applied Biosystems).…”

“…Ovary size defines the reproductive status of queens and workers (Winston, 1987), and regulates worker social behaviors (Wang et al, 2009;Wang et al, 2010). The adult honey bee queen has up to 150 ovarioles in each of her ovaries and is only responsible for laying eggs.…”

“…However, the ovariole numbers may vary, and in vitro rearing experiments showed that there is a morphospace gradient in which ovary phenotypes of the queen and worker are the extremes (Leimar et al, 2012;Linksvayer et al, 2011). In addition, ovary size is also correlated with foraging behavior in workers: workers with more ovarioles perform less retinue behavior (D. Galbraith, Y.W., G.V.A., R. E. Page and C. G. Grozinger, unpublished data), initiate foraging tasks earlier in life (Wang et al, 2009;Wang et al, 2010), prefer to collect pollen over nectar, and are more sensitive to sucrose than workers with fewer ovarioles (Amdam et al, 2006;Wang et al, 2009).…”

Worker division of labor and endocrine physiology are associated in the harvester ant,Pogonomyrmex californicus

“…JH has been associated with division of labor among workers of the honey bee (reviewed by Robinson and Vargo, 1997), the bumble bee (Bloch et al, 2000a), the queenless ant Streblognathus peetersi (Brent et al, 2006) and Polistes wasps (Giray et al, 2005). Although no causal route from ecdysteroid content to division of labor has been demonstrated (Hartfelder et al, 2002), this group of hormones is suspected of having priming effects on honey bee worker behavior (Velarde et al, 2009;Wang et al, 2009;Amdam and Page, 2010), and has links to adult reproductive activity (Robinson et al, 1991). Ecdysteroids act via effects on the axis of brain/fat body/ovaries (Wang et al, 2010;Yamazaki et al, 2011), and ecdysteroid production is often linked to insect ovarian activation (Raikhel et al, 2005;Dong et al, 2009).…”

Regulation of behaviorally associated gene networks in worker honey bee ovaries

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Fat body expression of hormone receptor-like in 46 (HR46) and phosphoinositide-dependent kinase-1 (PDK1) correlates with ovary size as well as worker division of labor (Wang et al, 2009). HR46 is a possible nuclear hormone receptor for ecdysteroid hormones Accepted 28 September 2011 SUMMARY Several lines of evidence support genetic links between ovary size and division of labor in worker honey bees.

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