Heat waves: Chronic heat stress reduces sperm quality in males of Scaptotrigona aff. depilis (Apidae, Meliponini)?

• Grant number: 23/16486-1
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: April 01, 2024
• End date: March 31, 2025
• Field of knowledge: Biological Sciences - Physiology - Compared Physiology
• Principal Investigator: Michael Hrncir
• Grantee: Cristiane Saturnino Mendes Lemes
• Host Institution: Instituto de Biociências (IB). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

In Brazil, an increase in both intensity and frequency of extreme weather events, such as heat waves, is expected for the coming decades. Such alterations of the climate are one of the main current threats to the reproductive success of organisms. Due to the high sensitivity of sperm cells to increases in temperature, even small variations in temperature can have a strong negative impact on the fertility of individuals. Therefore, factors such as sperm quality can be good indicators of vulnerability to climate change. The present project aims at evaluating the effects of heat waves on the reproduction of stingless bees (Apidae Meliponini), one of the most important groups of pollinators in the tropics. Using thermography techniques, we will evaluate the thermal stress (maximum temperatures) that males of Scaptotrigona aff. depilis in aggregations face during these extreme weather events. Furthermore, drones (N = 20) will be exposed to simulated heat waves in BOD incubators (temperature increase from 29 ± 1 °C to 38 ± 1 °C for one hour/day periodically for 3 subsequent days). After the experiment, the seminal vesicles will be extracted, and sperm viability will be evaluated under a fluorescence microscope. The sperm viability of experimental individuals will be compared to that of males from a control group (N = 20; 29 ± 1 °C constant). We expect a significant reduction in sperm viability in the experimental group compared to the control group. The results of this study will provide important information about the impact of climate change on stingless bees, which may be useful for planning conservation and management strategies for these bees.