Implications of season and management protocol on the landscape of gene regulation during diapause development in the Alfalfa Leaf Cutting Bee

Authors: Yocum, George; Childers, Anna; Rinehart, Joe; Kemp, William - Bill; Pitts Singer, Theresa; BOWSHER, JULIA - North Dakota State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/10/2014
Publication Date: 6/12/2014
Citation: Yocum, G.D., Bennett, A.K., Rinehart, J.P., Kemp, W.P., Pitts Singer, T., Bowsher, J.H. 2014. Implications of season and management protocol on the landscape of gene regulation during diapause development in the Alfalfa Leaf Cutting Bee [abstract]. 8th Annual Arthropod Genomics Sympsium. 06/12-14/2014. University of Illinois at Urbana-Champaign. Paper No. 43.

Interpretive Summary: The alfalfa leaf cutting bee, Megachile rotundata, is the world’s most intensively managed solitary bee for commercial pollination. It is the primary pollinator of seed alfalfa, a valuable crop for dairy cow feed. Overwintering bees emerge in the spring during alfalfa bloom to mate and lay eggs. Larvae develop in brood cells provisioned by the mother. In nature, larval development is typically completed by the fall when bees undergo diapause and overwinter as prepupa. However, with elevated late summer temperatures, including scenarios associated with global climate change, an increasing proportion of the population will avert diapause and produce a second generation, the progeny of which will predominately diapause. Management practices during the prepupal stage affect the physiology of the adult bee and likewise have implications for overwintering survival, so it is important to understand how diapause is regulated. Diapausing bees laid early and late in the season were collected on September 1st and divided between two management groups, those managed in the laboratory and those kept in an unheated barn. Each of the four treatment groups was sampled monthly from October to July. Gene expression was assayed at four time points (November, January, March and May) that were chosen to span the diapause maintenance, termination and post-diapause quiescence stages of development. Distinctly different gene expression landscapes underlie each treatment group with uniquely expressed genes found in each group. This unprecedented characterization of diapause will provide a foundation for understanding the sequence of gene expression during diapause and will aid in commercial management decisions for this important pollinator.

Technical Abstract: : The alfalfa leaf cutting bee, Megachile rotundata, is the world’s most intensively managed solitary bee for commercial pollination. It is the primary pollinator of seed alfalfa, a valuable crop for dairy cow feed. Overwintering bees emerge in the spring during alfalfa bloom to mate and lay eggs. Larvae develop in brood cells provisioned by the mother. In nature, larval development is typically completed by the fall when bees undergo diapause and overwinter as prepupa. However, with elevated late summer temperatures, including scenarios associated with global climate change, an increasing proportion of the population will avert diapause and produce a second generation, the progeny of which will predominately diapause. Management practices during the prepupal stage affect the physiology of the adult bee and likewise have implications for overwintering survival, so it is important to understand how diapause is regulated. Diapausing bees laid early and late in the season were collected on September 1st and divided between two management groups, 6°C constant temperature and those kept in an unheated barn. Each of the four treatment groups was sampled monthly from October to July. Four time points (November, January, March and May) were chosen to span the diapause maintenance, termination and post-diapause quiescence stages of development. Two lanes of paired-end Illumina sequencing was performed on RNA from three bees from each of the four months (48 samples). The Tuxedo Suite was used for transcript assembly and differential gene expression analyses. Distinctly different gene expression landscapes underlie each treatment group with uniquely expressed genes found in each group. This unprecedented characterization of diapause will provide a foundation for understanding the sequence of gene expression during diapause and will aid in commercial management decisions for M. rotundata.