Sperm can't take the heat: Short-term temperature exposures compromise fertility of male bumble bees (Bombus impatiens). (April 2023)

• Record Type: Journal Article
• Authors: Campion, Claire; Rajamohan, Arun; Dillon, Michael E.
• Is Part Of: Journal of insect physiology. Volume 146(2023)
• Publication Date: 2023-04
• Subjects: Bumble bee -- Bombus -- Climate change -- Thermal stress -- Fertility -- Spermatozoa -- Reproductive physiology; Insects -- Physiology -- Periodicals; Insectes -- Physiologie -- Périodiques; Insects -- Physiology; Periodicals; 571.157
• DOI: 10.1016/j.jinsphys.2023.104491
• Languages: English
• ISSNs: 0022-1910

Abstract

Graphical abstract: Highlights: Short-term heat exposure reduced sperm viability in male bumble bees. Heat is more damaging than cold. Thermal tolerance of bumble bee sperm is similar in vitro and in vivo. Abstract: Bumble bee (genus Bombus ) populations are increasingly under threat from habitat fragmentation, pesticides, pathogens, and climate change. Climate change is likely a prime driver of bumble bee declines but the mechanisms by which changing climates alter local abundance, leading to shifts in geographic range are unclear. Heat tolerance is quite high in worker bumble bees (CTmax ∼ 48–55 °C), making it unlikely for them to experience these high temperatures, even with climate warming. However, the thermal tolerance of whole organisms often exceeds that of their gametes; many insects can be sterilized by exposure to temperatures well below their upper thermal tolerance. Male bumble bees are independent from the colony and may encounter more frequent temperature extremes, but whether these exposures compromise spermatozoa is still unclear. Using commercially-reared Bombus impatiens colonies, males were reared in the lab and spermatozoa were exposed ( in vivo and isolated in vitro ) to sublethal temperatures near lower and upper thermal tolerance (CTmin and CTmax, respectively). Heat exposure (45 °C for up to 85 min) reduced spermatozoa viability both for whole males ( in vivo ; control = 79.5 %, heat exposed = 58 %, heat stupor = 57.7 %) and isolated seminal vesicles ( in vitro ; control = 85.5 %, heat exposed = 62.9 %). Whole males exposed to 4 °C for 85 min ( in vivo ; control = 79.2 %, cold = 72.4 %), isolated seminal vesicles exposed to 4 °C for 85 min ( in vitro ; control = 85.5 %, cold = 85.1 %), and whole males exposed to for 4 °C for 48 h ( in vivo ; control = 88.7 %, cold = 84.3 %) did not differ significantly in spermatozoa viability. After<85 min at 45 °C, males had significantly reduced spermatozoa viability, suggesting that short-term heat waves below CTmax could strongly reduce the fertility of male bumble bees with potential population-level impacts.