Multi-level analysis of reproduction in an Antarctic midge identifies female and male accessory gland products that are altered by larval stress and impact progeny viability

Abstract

The Antarctic midge, Belgica antarctica, is a wingless, non-biting midge endemic to Antarctica. Larval development requires at least 2 years, but adults live only 2 weeks. The nonfeeding adults mate in swarms and females die shortly after oviposition. Eggs are suspended in a gel of unknown composition that is expressed from the female accessory gland. This project characterizes molecular mechanisms underlying reproduction in this midge by examining differential gene expression in whole males, females, and larvae, as well as in male and female accessory glands. Functional studies were used to assess the role of the gel encasing the eggs, as well as the impact of stress on reproductive biology. RNA-seq analyses revealed sex- and development-specific gene sets along with those associated with the accessory glands. Proteomic analyses were used to define the composition of the egg-containing gel, which is generated during multiple developmental stages and derived from both the accessory gland and other female organs. Functional studies indicate the gel provides a larval food source as well as a buffer for thermal and dehydration stress. All of these function are critical to juvenile survival. Larval dehydration stress directly reduces production of storage proteins and key accessory gland components, a feature that impacts adult reproductive success. Modeling reveals that bouts of dehydration may have a significant impact on population growth. This work lays a foundation for further examination of reproduction in midges and provides new information related to general reproduction in dipterans. A key aspect of this work is that reproduction and stress dynamics, currently understudied in polar organisms, are likely to prove critical in determining how climate change will alter their survivability.

Rapid stress hardening in the Antarctic midge improves male fertility by increasing courtship success and preventing the decline of accessory gland proteins following cold exposure

“…Larval development extends over two years; developmental progression occurs during the austral summer, and larvae overwinter frozen or immobile within the ice (Usher and Edwards, 1984). Females produce a single batch of eggs or sometimes two smaller clutches (Finch et al, 2020;Harada et al, 2014). The eggs are deposited within a gel matrix produced by the female accessory gland (Finch et al, 2020), and numerous proteins from the accessory gland are critical for nourishing developing larvae, preventing egg/larval dehydration, and thermally buffering the developing larvae.…”

“…Females produce a single batch of eggs or sometimes two smaller clutches (Finch et al, 2020;Harada et al, 2014). The eggs are deposited within a gel matrix produced by the female accessory gland (Finch et al, 2020), and numerous proteins from the accessory gland are critical for nourishing developing larvae, preventing egg/larval dehydration, and thermally buffering the developing larvae. These proteins are produced during both the larval and adult stages and are synthesized by multiple organs.…”

“…These proteins are produced during both the larval and adult stages and are synthesized by multiple organs. Consequently, stress exposure during larval stages can reduce reproductive output of the females (Finch et al, 2020).…”

“…During the austral summer, mating occurs in swarms where numerous males court and attempt to mate (Convey et al, 1996;Finch et al, 2020;Sugg et al, 1983). Males produce a suite of accessory proteins that are transferred to the females during mating, and based on sequence similarity to accessory gland proteins from other insects, these proteins are likely to impact female fertility and male sperm viability along with competition (Avila et al, 2011;Chapman et al, 2000;Simmons, 2019;Sitnik et al, 2016;Wolfner, 1997).…”

“…Males produce a suite of accessory proteins that are transferred to the females during mating, and based on sequence similarity to accessory gland proteins from other insects, these proteins are likely to impact female fertility and male sperm viability along with competition (Avila et al, 2011;Chapman et al, 2000;Simmons, 2019;Sitnik et al, 2016;Wolfner, 1997). As with females, stress exposure of male larvae impacts subsequent male fertility (Finch et al, 2020). It is not known how cold exposure impacts fertility when males are exposed to cold as adults.…”