Support for the reproductive ground plan hypothesis in a solitary bee: links between sucrose response and reproductive status

Abstract

In social bees, foraging behaviour is correlated with reproductive status and sucrose sensitivity via endocrine pathways. This association led to the hypothesis that division of labour in social insect societies is derived from an ancestral ground plan that functions to synchronize dietary preferences with reproductive needs in solitary insects. However, the relationship between these traits is unknown for solitary bees, which represent the ancestral state of social bees. We used the proboscis extension response assay to measure sucrose response among reproductive females of the solitary alkali bee ( Nomia melanderi ) as a function of acute juvenile hormone (JH) treatments and reproductive physiology. We also tested long-term effects of JH on reproductive development in newly emerged females. JH did not have short-term effects on reproductive physiology or sucrose response, but did have significant long-term effects on ovary and Dufour's gland development. Dufour's gland size, not ovary development, was a significant predictor of sucrose response. This provides support for the reproductive ground plan hypothesis, because the Dufour's gland has conserved reproductive functions in bees. Differing results from this study and honeybees suggest independent origins of division of labour may have evolved via co-option of different components of a conserved ground plan.

Juvenile hormone, but not nutrition or social cues, affects reproductive maturation in solitary alkali bees (Nomia melanderi)

“…Seminal fluid is known to trigger oogenesis in several 252 insect species (Avila et al, 2011), and mating limitation is known to influence reproductive activity in other halictid bees (Yanega, 1989;Yanega, 1992). However, lab-reared females of another halictid bee, (Kapheim et al, 2012). If mating is a reproductive limitation in alkali bees, it can apparently be 256 overridden by JH treatments, as some JH-treated females in our study reached reproductive maturity, 257 even in the absence of mating or ecological cues.…”

“…Little is known about the factors that influence alkali bee reproductive development. However, a recent 68 study demonstrated that JH accelerates reproductive maturation (Kapheim and Johnson, 2017). It was 69 also recently documented that adult female alkali bees consume pollen on a daily basis (Cane et al, 70 2016).…”

“…Pollen-sugar mixture was shaken vigorously 98 before each feeding to achieve homogeneity, and then pipetted into feeding troughs made from 1.5 ml 99 microcentrifuge tubes with the tapered tip removed. The cages were kept at 22-28ºC, 40-85% RH and 100 full spectrum lighting 13 L: 11 D, as has been previously described (Kapheim and Johnson, 2017). At the 101 end of the 10 d rearing period, bees were chilled for 3 min at 4ºC, placed in individually-labeled tubes, 102 and flash-frozen in liquid nitrogen.…”

A novel protocol for studying bee cognition in the wild

“…Besides basic work on comparative cognition, FMPER's potential for assessing gustatory responsiveness (similar to Ma, Kessler, Simpson, & Wright, ) is relevant to many aspects of bee biology (Scheiner et al., ), including tests of hypotheses relating to the evolution of sociality (e.g. the reproductive ground plan hypothesis: Kapheim & Johnson, ).…”

“…The second main protocol used to study cognition in insects is the “Proboscis Extension Response (PER) protocol” (honeybees: Bitterman, Menzel, Fietz, & Schäfer, ; Takeda, ; bumblebees: Laloi et al., ; Riveros & Gronenberg, ; fruitflies: Tully & Quinn, ; mosquitoes: Tomberlin, Rains, Allan, Sanford, & Lewis, ; moths: Daly & Smith, ; stingless bees: Mc Cabe et al., ; solitary bees: Kapheim & Johnson, ; hymenopterous parasitoids: Kaiser, Pérez‐Maluf, Sandoz, & Pham‐Delègue, ). In the PER protocol, a bee is harnessed (only its antennae and proboscis free to move [Figure b]), before being trained to an association between a CS and US.…”