Amphibians are well known as osmotically sensitive organisms due to their highly permeable skin and eggs and, as such, biologists have mostly discounted their presence in saline environments. Yet, ...from the 1800s to the present day, scientists have repeatedly found amphibians living and breeding in a variety of saline coastal and inland habitats. Despite this plethora of observations, their presence in these habitats is still mostly ignored, and the last (and only) complete literature review documenting amphibians in brackish and saline habitats was completed over 50 yr ago. Here we provide a review of the literature of amphibians in saline waters and present data on 144 species, in 28 families, on every continent except Antarctica. In doing so, we make the case that salt tolerance in amphibians may not be as rare as generally assumed. Through classifying habitats and studies, we conclude that the abilities of dozens of species to locally adapt to coastal and inland saline habitats have been extensively studied, although more work on most observed species is still needed. Our understanding of the evolutionary processes leading to this adaptation is also in its infancy. We summarize the existing knowledge on this subject and present a possible framework toward the development of an evolutionary model of amphibian adaptation to salt, based on genetic variation for salt tolerance in populations and the nature of selection events in osmotically stressful environments. Finally, we discuss some possible limitations on the ability of amphibians to tolerate salt water. Understanding the abilities and constraints of amphibian populations to adapt to salt will become more critical as humans continue to impact the world’s freshwater resources through climate change, landscape modification, and pollution, and these habitats thus become increasingly stressful for amphibians.
Light is fundamental to biological systems, affecting the daily rhythms of bacteria, plants, and animals. Artificial light at night (ALAN), a ubiquitous feature of urbanization, interferes with these ...rhythms and has the potential to exert strong selection pressures on organisms living in urban environments. ALAN also fragments landscapes, altering the movement of animals into and out of artificially lit habitats. Although research has documented phenotypic and genetic differentiation between urban and rural organisms, ALAN has rarely been considered as a driver of evolution. We argue that the fundamental importance of light to biological systems, and the capacity for ALAN to influence multiple processes contributing to evolution, makes this an important driver of evolutionary change, one with the potential to explain broad patterns of population differentiation across urban–rural landscapes. Integrating ALAN's evolutionary potential into urban ecology is a targeted and powerful approach to understanding the capacity for life to adapt to an increasingly urbanized world.
Artificial light at night (ALAN) is a recognised disruptor of biological function and ecological communities. Despite increasing research effort, we know little regarding the effect of ALAN on woody ...plants, including trees, or its indirect effects on their colonising invertebrates. These effects have the potential to disrupt woodland food webs by decreasing the productivity of invertebrates and their secretions, including honeydew and lerps, with cascading effects on other fauna. Here, we cultivated juvenile river red gums (Eucalyptus camaldulensis) for 40 weeks under experimentally manipulated light (ALAN) or naturally dark (control) conditions. To assess direct impacts on tree growth, we took multiple measures of growth at four time periods, and also measured physiological function, biomass and investment in semi-mature trees. To assess experimentally the direct and indirect (tree-mediated) impacts of ALAN on invertebrates, from 19 weeks onwards, we matched and mismatched trees with their original ALAN environments. We colonised trees with a common herbivore of E. camaldulensis, the red gum lerp psyllid (Glycaspis nr. brimblecombei) and then measured the effects of current and historic tree lighting treatment on the psyllid life cycle. Our data revealed direct effects of ALAN on tree morphology: E. camaldulensis trees exposed to ALAN shifted biomass allocation away from roots and into leaves and increased specific leaf area. However, while the intensity of ALAN was sufficient to promote photosynthesis (net carbon gain) at night, this did not translate into variation in tree water status or photosystem adaptation to dim night-time light for ALAN-exposed trees. We found some evidence that ALAN had broad-scale community effects—psyllid nymphs colonising ALAN trees produced more lerps—but we found no other direct or indirect impacts of ALAN on the psyllid life cycle. Our results suggest that trees exposed to ALAN may share morphological responses with trees under dim daylight conditions. Further, ALAN may have significant ‘bottom-up’ effects on Eucalyptus woodland food webs through both trees and herbivores, which may impact higher trophic levels including woodland birds, mammals and invertebrates.
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•Artificial light at night (ALAN) affects tree morphology and herbivore productivity.•Eucalyptus trees cultivated under ALAN shift biomass from roots to leaves.•ALAN also increases specific leaf area, but does not alter leaf photosystem.•Lerp psyllid nymphs raised under ALAN produced 8% more lerps.•ALAN did not affect psyllid fitness or tree water relations.
Freshwater organisms are increasingly exposed to elevated salinity in their habitats, presenting physiological challenges to homeostasis. Amphibians are particularly vulnerable to osmotic stress and ...yet are often subject to high salinity in a variety of inland and coastal environments around the world. Here, we examine the physiological responses to elevated salinity of rough-skinned newts (Taricha granulosa) inhabiting a coastal stream on the Pacific coast of North America and compare the physiological responses to salinity stress of newts living in close proximity to the ocean with those of newts living farther upstream. Although elevated salinity significantly affected the osmotic (body weight, plasma osmolality), stress (corticosterone), and immune (bactericidal ability) responses of newts, animals found closer to the ocean were generally less reactive to salt stress than those found farther upstream. Our results provide possible evidence for some physiological tolerance in this species to elevated salinity in coastal environments. As freshwater environments become increasingly saline and more stressful, understanding the physiological tolerances of vulnerable groups such as amphibians will become increasingly important to our understanding of their abilities to respond, to adapt, and, ultimately, to survive.
The world is increasingly impacted by a variety of stressors that have the potential to differentially influence life history stages of organisms. Organisms have evolved to cope with some stressors, ...while with others they have little capacity. It is thus important to understand the effects of both developmental and evolutionary history on survival in stressful environments. We present evidence of the effects of both developmental and evolutionary history on survival of a freshwater vertebrate, the rough-skinned newt (Taricha granulosa) in an osmotically stressful environment. We compared the survival of larvae in either NaCl or MgCl2 that were exposed to salinity either as larvae only or as embryos as well. Embryonic exposure to salinity led to greater mortality of newt larvae than larval exposure alone, and this reduced survival probability was strongly linked to the carry-over effect of stunted embryonic growth in salts. Larval survival was also dependent on the type of salt (NaCl or MgCl2) the larvae were exposed to, and was lowest in MgCl2, a widely-used chemical deicer that, unlike NaCl, amphibian larvae do not have an evolutionary history of regulating at high levels. Both developmental and evolutionary history are critical factors in determining survival in this stressful environment, a pattern that may have widespread implications for the survival of animals increasingly impacted by substances with which they have little evolutionary history.
The introduction of artificial light at night (ALAN) into natural and urbanised landscapes is a known and highly pervasive disruptor of invertebrate communities. However, the effect of variation in ...intensity and spectra of ALAN on invertebrate communities inhabiting different spatial niches is little understood. Further, the remarkable ability of ALAN to continue to disrupt biodiversity even in chronically illuminated urban landscapes is not often acknowledged.
Here, we simultaneously sampled airborne and ground‐dwelling invertebrate assemblages under and between urban street lights to explore the effects on community composition and abundance of (a) proximity to decadal (i.e. long‐illuminated) nocturnal street lighting and (b) variation in the spectral output of light.
The two assemblages responded differently. For airborne invertebrates, night‐time abundance doubled, and night‐time assemblage composition was significantly different for traps under, compared with between, street lights. These differences in abundance were not affected by street light intensity, and were absent in day samples, suggesting that even weak ALAN may be causing short‐term redistribution of nocturnal invertebrates. Further, the abundance (but not composition) effects of ALAN on airborne invertebrates increased when the street lights emitted a higher proportion of short‐wavelength light.
In contrast, for ground‐dwelling invertebrates, we found only marginal effects of proximity and spectrum of lighting on abundance and no effect on assemblage composition. However, more intense street lighting reduced abundance and altered composition at traps both under and between lights.
Synthesis and Applications. Public lighting managers must consider ALAN impacts on invertebrate communities not only when introducing ALAN to naïve environments, but also when changing lighting in areas that are highly urbanised and exposed to decades of ALAN. Further, lighting proposals and environmental monitoring of invertebrate communities must take into account the effects on both ground‐dwelling and airborne assemblages, as these may respond very differently to the presence, intensity and spectrum of ALAN.
Public lighting managers must consider artificial light at night (ALAN) impacts on invertebrate communities not only when introducing ALAN to naïve environments, but also when changing lighting in areas that are highly urbanised and exposed to decades of ALAN. Further, lighting proposals and environmental monitoring of invertebrate communities must take into account the effects on both ground‐dwelling and airborne assemblages, as these may respond very differently to the presence, intensity and spectrum of ALAN.
Toxin-resistant predators may suffer costs from eating chemically defended prey and do not feed exclusively on toxic prey. Common Gartersnakes (Thamnophis sirtalis (Linnaeus, 1758)) have been ...considered the drivers of an evolutionary arms race with highly toxic newts (genus Taricha Gray, 1850), which they consume with few or no deleterious effects. However, how frequently newts are consumed in nature is less clear. To address this question, we investigated the diets of Th. sirtalis at a site in central Oregon where snakes have high levels of resistance and newts have high levels of tetrodotoxin in the skin. Because snake diets are difficult to quantify using traditional means, we used stable isotopes to estimate the proportion of Th. sirtalis diets made up of newts. Our estimate for the proportion of Th. sirtalis diet made up of Rough-skinned Newts (Taricha granulosa (Skilton, 1849)) at this site is 3.2%. Mole Salamanders (genus Ambystoma Tschudi, 1838) were predicted to be the most important prey, followed by slugs, chorus frogs, and mice, with a very minor role for earthworms. Our results demonstrate that even though Th. sirtalis are physiologically capable of consuming toxic prey, they do not often do so. Generalist predators can be exposed to very strong selection from, and exert reciprocal selection on even rarely eaten, chemically defended prey.
Anthropogenic factors, such as artificial light at night (ALAN), are increasingly linked to significant modifications in animal behaviours, such as foraging or migration. However, few studies have ...investigated directly whether the presence of ALAN affects the ability to find a mate (mate location). One direct effect of the presence of ALAN is that it can create a light barrier in an otherwise dark environment. This may have significant behavioural implications for nocturnally active species if it affects their ability to respond to potential mates. Our study, using the acoustically orienting Australian black field cricket, Teleogryllus commodus, determined experimentally whether the presence of a fragmented light environment influenced movement patterns of virgin females and males. Moreover, given the importance of male song for reproductive outcomes in this species, we assessed simultaneously whether such behaviours were modified by the presence of a male attraction call. We found that while initiation of movement was slower in the presence of ALAN, the behavioural shifts associated with its presence were relatively small compared to the influence of a broadcast male attraction call. The response to the male attraction call was typically stronger for females than for males, but both males and females modified aspects of behaviour when it was present regardless of whether their immediate environment was fragmented by artificial light at night or not. Artificial light at night may alter subtle aspects of movement and mating behaviour in this species, but ultimately does not provide a barrier to movement or mate location.
•Artificial light at night (ALAN) is a potent pollutant that affects animal movement.•Animals may avoid lit areas, altering mate-finding behaviour in urban habitats.•We tested ALAN's effects on cricket movement and response to male calling.•Initial movement was slower in presence of ALAN; response to calls was not altered.•ALAN does not provide a barrier to movement or mate location in this species.
Ecosystem disturbance through urbanization and agriculture, coupled with anthropogenic climate change, poses a pervasive threat to ecosystem health. Such landscape disturbance can manifest as ...salinization, particularly in Australia. Increasing salinization of both soils and waterways has the potential to render habitats unsuitable for amphibians. However, some species exist naturally in brackish and saline habitats, which suggests the capacity to adapt to salinization. To assess this adaptability in amphibians, we examined current brackish habitat utilization by a common Australian Froglet, Crinia signifera, and determined the tolerance of eggs and tadpoles of this species to acute and chronic exposure to brackish water. Crinia signifera lay eggs in brackish water and, through laboratory experiments, we determined that short-term survival in water up to 7.5 parts per thousand (ppt) salinity is possible but may vary among populations. Chronic exposure experiments demonstrated that C. signifera can successfully complete larval development to metamorphosis in brackish water (up to 5.0 ppt). Data presented here, together with previously published reports of salinity tolerance in other Australian frog species, collectively demonstrate a capacity for adaptation to landscape salinization. This has probably been mediated by an evolutionary history in the saline landscapes so common in Australia.
Filarial helminths infect approximately 120 million people worldwide initiating a type 2 immune response in the host. Influenza A viruses stimulate a virulent type 1 pro-inflammatory immune response ...that in some individuals can cause uncontrolled immunopathology and fatality. Although coinfection with filariasis and influenza is a common occurrence, the impact of filarial infection on respiratory viral infection is unknown. The aim of this study was to determine the impact of pre-existing filarial infection on concurrent infection with influenza A virus. A murine model of co-infection was established using the filarial helminth
and the H1N1 (A/WSN/33) influenza A virus (IAV). Co-infection was performed at 3 different stages of
infection (larval, juvenile adult, and patency), and the impact of co-infection was determined by IAV induced weight loss and clinical signs, quantification of viral titres, and helminth counts. Significant alterations of IAV pathogenesis, dependent upon stage of infection, was observed on co-infection with
. Larval stage
infection alleviated clinical signs of IAV co-infection, whilst more established juvenile adult infection also significantly delayed weight loss. Viral titres remained unaltered at either infection stage. In contrast, patent
infection led to a reversal of age-related resistance to IAV infection, significantly increasing weight loss and clinical signs of infection as well as increasing IAV titre. These data demonstrate that the progression of influenza infection can be ameliorated or worsened by pre-existing filarial infection, with the outcome dependent upon the stage of filarial infection.
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