Exposure to artificial light at night during the larval stage has delayed effects on juvenile corticosterone concentration in American toads, Anaxyrus americanus

Longer days, larger grays: carryover effects of photoperiod and temperature in gray treefrogs, Hyla versicolor

Environmental conditions like temperature and photoperiod can strongly shape organisms' growth and development. For many ectotherms with complex life cycles, global change will cause their offspring to experience warmer conditions and earlier-season photoperiods, two variables that can induce conflicting responses. We experimentally manipulated photoperiod and temperature during gray treefrog (Hyla versicolor) larval development to examine effects at metamorphosis and during short (10-day) and long (56-day) periods post-metamorphosis. Both early- and late-season photoperiods (April and August) decreased age and size at metamorphosis relative to the average-season (June) photoperiod, while warmer temperatures decreased age but increased size at metamorphosis. Warmer larval temperatures reduced short-term juvenile growth but had no long-term effect. Conversely, photoperiod had no short-term carryover effect, but juveniles from early- and late-season larval photoperiods had lower long-term growth rates than juveniles from the average-season photoperiod. Similar responses to early- and late-season photoperiods may be due to reduced total daylight compared with average-season photoperiods. However, juveniles from late-season photoperiods selected cooler temperatures than early-season juveniles, suggesting that not all effects of photoperiod were due to total light exposure. Our results indicate that despite both temperature and photoperiod affecting metamorphosis, the long-term effects of photoperiod may be much stronger than those of temperature.

Photoperiod effects in a freshwater community: Amphibian larvae develop faster and zooplankton abundance increases under an early-season photoperiod

Organisms that shift their phenologies in response to global warming will experience novel photic environments, as photoperiod (daylength) continues to follow the same annual cycle. How different organisms respond to novel photoperiods could result in phenological mismatches and altered interspecific interactions. We conducted an outdoor mesocosm experiment exposing green frog (Rana clamitans) larvae, gray treefrog (Hyla versicolor) larvae, phytoplankton, periphyton, and zooplankton to a three-month shift in photoperiod: an early-season photoperiod (simulating April) and a late-season photoperiod (simulating July). We manipulated photoperiod by covering and uncovering tanks with clear or light-blocking lids to mimic realistic changes in daylength. We assessed amphibian life history traits and measured phytoplankton, periphyton, and zooplankton abundances. Green frog larvae and gray treefrog metamorphs were more developed under the early-season photoperiod. Gray treefrog total length was also reduced, but photoperiod did not affect green frog total length. Although phytoplankton and periphyton abundances were not affected by photoperiod, copepod nauplii were in greater abundance under the early-season photoperiod. Overall, this simplified aquatic community did not exhibit significant changes to structure when exposed to a three-month shift in photoperiod. Temperate amphibians that breed earlier in the year may develop faster, which may have long-term costs to post-metamorphic growth and performance. Asynchronous shifts in zooplankton abundances in response to altered photoperiods could subsequently affect freshwater community structure. While photoperiod has been shown to individually affect freshwater organisms, our study using replicated outdoor wetland communities shows that the comprehensive effects of photoperiod may be less important than other cues such as temperature and precipitation.

The country toad and the city toad: comparing morphology of invasive cane toads (Rhinella marina) from rural and urban environments

Urbanization is a principal driver of global biodiversity loss. Although many studies have examined the impacts of urbanization on biodiversity, we are only beginning to study urbanization as an evolutionary force. Urban environments are hotspots for invasive species, but most previous studies have focused on phenotypic changes in native species responding to urbanization. Quantifying the phenotypic responses of invasive species to urbanization may help reveal mechanisms promoting invasion. There are, however, few studies investigating the phenotypic response of invasive species to urbanization. We compared morphological traits of invasive cane toads (Rhinella marina) between urban and rural areas in three cities in north-eastern Australia using generalized linear mixed models. We found that the parotoid glands, which are the major anti-predator defence of toads were smaller in urban than in rural populations. The tibiofibula length of males in urban populations was longer than those in rural populations, but females showed opposite trends, suggesting potential effects of urbanization on sexual dimorphism. These results demonstrate that urbanization drives morphological changes in invasive toads, suggesting they may adapt to urban environments rapidly.

The morphological effects of artificial light at night on amphibian predators and prey are masked at the community level

Artificial light at night (ALAN) is a pervasive pollutant that influences wildlife at both the individual and community level. In this study, we tested the individual-level effects of ALAN on three species of tadpole prey and their newt predators by measuring prey pigmentation and predator and prey mass. Then we evaluated whether the individual-level effects of ALAN on pigmentation and mass had cascading community-level effects by assessing the outcome of predator-prey interactions. We found that spring peepers exposed to ALAN were significantly darker than those reared under control conditions. Additionally, wood frogs reared in ALAN conditions were significantly smaller than those reared in control conditions. In contrast, Eastern newts collected earlier in the spring that were exposed to ALAN were significantly larger than controls while those collected later in the spring were not affected by ALAN, suggesting phenological differences in the effect of ALAN. To understand how changes in pigmentation and size due to ALAN influence predation rates, we ran predation assays in both ALAN-polluted and ALAN-free outdoor environments. After the predation assay, the size disparity in wood frogs reared in ALAN was eliminated such that there was no longer a treatment difference in wood frog size, likely due to size-selective predation. This demonstrates the beneficial nature of predators' selective pressure on prey populations. Lastly, despite individual-level effects of ALAN on pigmentation and mass, we did not detect cascading community-level effects on predation rates. Overall, this study highlights important species-level distinctions in the effects of ALAN. It also emphasizes the need to incorporate ecological complexity to understand the net impact of ALAN.

Artificial night light alters ecosystem services provided by biotic components

The global catastrophe of natural biodiversity and ecosystem services are expedited with the growing human population. Repercussions of artificial light at night ALAN are much wider, as it varies from unicellular to higher organism. Subsequently, hastened pollution and over exploitation of natural resources accelerate the expeditious transformation of climatic phenomenon and further cause global biodiversity losses. Moreover, it has a crucial role in global biodiversity and ecosystem services losses via influencing the ecosystem biodiversity by modulating abundance, number and aggregation at every levels as from individual to biome levels. Along with these affects, it disturbs the population, genetics and landscape structures by interfering inter- and intra-species interactions and landscape formation processes. Furthermore, alterations in normal light/dark (diurnal) signalling disrupt the stable physiological, biochemical, and molecular processes and modulate the regulating, cultural and provisioning ecosystem services and ultimately disorganize the stable ecosystem structure and functions. Moreover, ALAN reshapes the abiotic component of the ecosystem, and as a key component of global warming via producing greenhouse gases via emitting light. By taking together the above facts, this review highlights the impact of ALAN on the ecosystem and its living and non-living components, emphasizing to the terrestrial and aquatic ecosystem. Further, we summarize the means of minimizing strategies of ALAN in the environment, which are very crucial to reduce the further spread of night light contamination in the environment and can be useful to minimize the drastic impacts on the ecosystem.

Effects of artificial light at night and predator cues on foraging and predator avoidance in the keystone inshore mollusc Concholepas concholepas

The growth of Artificial Light At Night (ALAN) is potentially having widespread effects on terrestrial and coastal habitats. In this study we addressed both the individual effects of ALAN, as well as its combined effect with predation risk on the behaviour of Concholepas concholepas, a fishery resource and a keystone species in the southeastern Pacific coast. We measured the influence of ALAN and predation risk on this mollusc's feeding rate, use of refuge for light and crawling out of water behaviour. These behavioural responses were studied using light intensities that mimicked levels that had been recorded in coastal habitat exposed to ALAN. Cues were from two species known to prey on C. concholepas during its early ontogeny: the crab Acanthocyclus hassleri and the seastar Heliaster helianthus. The feeding rates of C. concholepas were 3-4 times higher in darkness and in the absence of predator cues. In contrast, ALAN-exposed C. concholepas showed lower feeding activity and were more likely to be in a refuge than those exposed to control conditions. In the presence of olfactory predator cues, and regardless of light treatment, C. concholepas tended to crawl-out of the waterline. We provide evidence to support the hypothesis that exposure to either ALAN or predation risk can alter the feeding behaviour of C. concholepas. However, predator cue recognition in C. concholepas was not affected by ALAN in situations where ALAN and predator cues were both present: C. concholepas continued to forage when predation risk was low, i.e., in darkness and away from predator cues. Whilst this response means that ALAN may not lead to increased predation mortality in C. concholepas, it will reduce feeding activity in this naturally nocturnal species in the absence of dark refugia. Such results may have implications for the long-term health, productivity and sustainability of this keystone species.

Light at Night and Disrupted Circadian Rhythms Alter Physiology and Behavior

Life on earth has evolved during the past several billion years under relatively bright days and dark nights. Virtually, all organisms on the planet display an internal representation of the solar days in the form of circadian rhythms driven by biological clocks. Nearly every aspect of physiology and behavior is mediated by these internal clocks. The widespread adoption of electric lights during the past century has exposed animals, including humans, to significant light at night for the first time in our evolutionary history. Importantly, endogenous circadian clocks depend on light for synchronization with the external daily environment. Thus, light at night can derange temporal adaptations. Indeed, disruption of natural light-dark cycles results in several physiological and behavioral changes. In this review, we highlight recent evidence demonstrating how light at night exposure can have serious implications for adaptive physiology and behavior, including immune, endocrine, and metabolic function, as well as reproductive, foraging, and migratory behavior. Lastly, strategies to mitigate the consequences of light at night on behavior and physiology will be considered.