# Dietary melatonin supplementation mitigates the negative effects of artificial light at night in the Pacific field cricket, Teleogryllus oceanicus

## TL;DR

Dietary melatonin can reduce the harmful effects of artificial night light on the reproduction of Pacific field crickets.

## Contribution

This study demonstrates that melatonin supplementation can rescue reproductive outcomes in crickets exposed to artificial light at night.

## Key findings

- Lifelong artificial light exposure accelerated juvenile development but did not affect adult body mass.
- Melatonin supplementation improved male sperm viability and female daily egg production.
- The rescue effect of melatonin was sex- and potentially age-specific.

## Abstract

Artificial light at night (ALAN) is linked to negative behavioural and physiological consequences in animals. A potential mechanism for these adverse effects is artificial light at night’s inhibition of melatonin synthesis, a zeitgeber for cellular processes and a powerful antioxidant. Accordingly, melatonin supplementation can ameliorate artificial light at night-linked pathologies. Most studies expose animals to artificial light at night across their whole lifespan or a single life stage, but many nocturnal species experience variable exposure across heterogeneously lit landscapes. We investigated the effects of artificial light at night during both early- and late-juvenile development on adult reproduction in the Pacific field cricket Teleogryllus oceanicus, and whether dietary melatonin supplementation could mitigate these effects. We found life-stage-specific developmental effects of artificial light at night. Lifelong artificial light at night exposure accelerated juvenile development, yet did not affect late-juvenile development, total development time or adult body mass. Moreover, we confirm the potential for melatonin supplementation to rescue male sperm viability and daily egg production by females. The degree of ‘rescue’ was sex, and potentially age specific, which may be explained by the differential effect of artificial light at night on early-juvenile development. Critically, this effect would have been masked had we not partitioned this early life stage, underscoring the importance of considering life-stage-specific artificial light at night exposure when evaluating ecological and physiological consequences.