The Dark Side of Light: Investigating the Effects of Low-Level Artificial Light at Night on Testes Size and Melatonin Production in Male Acomys russatus and Acomys cahirinus

Abstract

Many cities produce artificial light at night (ALAN) that illuminates the sky far beyond their borders. For animals that use the changing photoperiod to determine their mating season, ALAN can interfere with their ability to recognize the natural light cues that signal the changing seasons. Both diurnal spiny mice (Acomys russatus) and nocturnal spiny mice (Acomys cahirinus) are seasonal reproducers that rely on the photoperiod, and both species produce significantly fewer offspring when exposed to environmentally relevant levels of ALAN (Vardi-Naim et al. 2022). In this study, we measured two reproductive metrics, melatonin levels and testes size, in male spiny mice. Our findings suggest that there is no significant effect of ALAN on these parameters in Acomys russatus and Acomys cahirinus, which is a positive indication for the potential effects of ALAN on the reproductive health of male spiny mice. This suggests that the decrease in fecundity found in Vardi-Naim et al. is due to other factors such as behavior, female reproductive health, or the viability of offspring. It is important to remain vigilant and continue investigating this issue as urbanization and its associated ALAN continue to grow.