The impacts of artificial light at night on gammarid crustaceans

Abstract

Artificial light at night (ALAN) is proliferating at an alarming rate across the globe, particularly around aquatic habitats. Natural and predictable light cycles can dictate much of an individual organism’s life by acting as a major signal for their circadian clock, driving rhythmic behaviours and physiological changes throughout the body. Light cycles also help populations coordinate group behaviour and can greatly impact the interspecies dynamics of a community. Research into the ecological impacts of ALAN has highlighted numerous effects on these biological processes, including higher predation rates, impaired growth and development, and diminished reproductive efforts. Making up the vast majority of species, invertebrates play an undeniable role in ecosystem functioning. Many species have been shown to have robust daily rhythms, as such, it is vital to understand how ALAN may disrupt not only their behavioural patterns but their circadian clocks. The aims of this thesis were, first, to monitor the impacts of increasing levels of light at night (1 lux – 80 lux), as well as constant light and constant darkness on the behavioural rhythms of the intertidal amphipod, Echinogammarus marinus and the freshwater species, Gammarus pulex. Second, to compare the expression of genes under a natural light/dark cycle against a light/ALAN cycle and to determine how light at night alters the rhythmicity and differential expression of both clock-controlled and arrhythmic genes in male E. marinus. Finally, to identify circadian clock genes in the gammarids E. marinus and G. pulex through transcriptome and genome mining, in order to characterise the clock design of gammarid crustaceans.
G. pulex activity was not strongly synchronised to any of the light at night treatments. E. marinus, however, exhibited strong behavioural rhythmicity in diurnal cycles with dark night periods. All the ALAN treatments resulted in a significant decrease in E. marinus rhythmicity and overall activity. Moreover, ALAN between 1-50 lux disrupted nocturnality in this species. Over 1,200 daily cycling genes were found in E. marinus. 87.0% of genes that were rhythmic under LD became arrhythmic under ALAN. ALAN also led to the upregulation of genes associated with ribosomal biogenesis, glycolysis, heat shock proteins, and chitin production compared to the control treatment. There was evidence of 12-hour cycling in genes related to oxidative phosphorylation regardless of the light treatment. The persistence of these 12-hour rhythms under both LD and ALAN conditions suggests the involvement of internal circadian, metabolic or circatidal oscillators in their regulation. We identified sequences for Clock, Cycle/Bmal1, period, and cryptochrome 2 and 16 clock-associated genes in E. marinus. While in G. pulex, we identified sequences for Cycle/Bmal1 and period, as well as 16 clock-associated genes. Neither cry1 nor tim could be found in either gammarid, which suggests the molecular makeup of their clock more closely resembles the mammalian design over the Drosophila model. That is consistent across the Amphipoda clade.
These results indicate that while some gammarids show some adaptive plasticity when it comes to light pollution, others may experience strong direct impacts on their activity. Furthermore, ALAN can disrupt key physiological processes that could have deleterious impacts on an organism’s health. This may be relevant to individual and population level fitness of vulnerable species in more heavily urbanised areas.

More information

Identifiers

ORCID for Charlotte Underwood: orcid.org/0000-0003-0012-0099

ORCID for Herman Wijnen: orcid.org/0000-0002-8710-5176

Catalogue record

Export record