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Nocturnal activity of Antiguan lizards under artificial light


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Widespread human development has led to the proliferation of artificial light at night, an increasingly recognized but poorly understood component of anthropogenic global change. Animals specialized to diurnal activity are presented opportunities to use this night-light niche, but the ecological consequences are largely unknown. While published records make note of nocturnal activity in a diversity of diurnal taxa, few case studies have gone beyond isolated observations to quantify patterns of nocturnal activity, document animal behavior, and describe new species interactions. From 13 June to 15 July 2017, we conducted hourly nocturnal surveys to assess how two species of diurnal Anolis lizards (Leach's Anole, Anolis leachii, and Watt's Anole, A. wattsi) use artificial light on Long Island, Antigua. Our data show that both anole species foraged in artificially illuminated habitats and were more active prior to sunrise compared to the early night. Mark-resight data for a focal species, A. leachii, suggest that patterns of nocturnal activity were not significantly different between individuals. Finally, our behavioral observations for the two anoles and a third lizard species, the nocturnal Thick-tailed Gecko (Thecadactylus rapicauda), reveal a lack of agonistic interactions. Our study reveals an altered temporal niche for two diurnal Antiguan lizards and adds to a growing body of evidence documenting the broad influences of anthropogenic change on biodiversity.
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Herpetological Conservation and Biology 14(1):105–110.
Submitted: 12 September 2018; Accepted: 25 January 2019; Published: 30 April 2019.
NocturNal activity of aNtiguaN lizards
uNder artificial light
Andrew S. MAurer1,2,6, ChriStopher J. thAwley3, AlexAndrA l. FireMAn2,
SeAn t. Giery4, And JAMeS t. Stroud5
1Department of Applied Ecology, North Carolina State University, Campus Box 7617, Raleigh, North Carolina 27695, USA
2Jumby Bay Hawksbill Project, Antigua, West Indies
3Department of Biological Sciences, University of Rhode Island, 120 Flagg Road, Kingston, Rhode Island 02881, USA
4Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06269, USA
5Department of Biology, Washington University in St. Louis, St. Louis, Missouri 63130, USA
6Corresponding author, email:
Abstract.—Widespread human development has led to the proliferation of articial light at night, an increasingly
recognized but poorly understood component of anthropogenic global change. Animals specialized to diurnal
activity are presented opportunities to use this night-light niche, but the ecological consequences are largely
unknown. While published records make note of nocturnal activity in a diversity of diurnal taxa, few case studies
have gone beyond isolated observations to quantify patterns of nocturnal activity, document animal behavior, and
describe new species interactions. From 13 June to 15 July 2017, we conducted hourly nocturnal surveys to assess
how two species of diurnal Anolis lizards (Leach’s Anole, Anolis leachii, and Watt’s Anole, A. wattsi) use articial
light on Long Island, Antigua. Our data show that both anole species foraged in articially illuminated habitats
and were more active prior to sunrise compared to the early night. Mark-resight data for a focal species, A.
leachii, suggest that patterns of nocturnal activity were not signicantly different between individuals. Finally,
our behavioral observations for the two anoles and a third lizard species, the nocturnal Thick-tailed Gecko
(Thecadactylus rapicauda), reveal a lack of agonistic interactions. Our study reveals an altered temporal niche
for two diurnal Antiguan lizards and adds to a growing body of evidence documenting the broad inuences of
anthropogenic change on biodiversity.
Key Words.—Anoles; Anolis leachii; Anolis wattsi; ALAN; articial light at night; light pollution; night light niche
As global anthropogenic change accelerates, the
occurrence of articial light at night is increasing in
extent and density (Hölker et al. 2010; Gaston et al.
2015). Articial lighting during dark hours alters
natural light regimes under which animal behaviors
have evolved. This ecological light pollution has
important biological consequences, including changing
animal activity patterns (Longcore and Rich 2004).
Indeed, as a result of urbanization and articial lighting,
many diurnal species have been recorded extending or
switching typical daytime behaviors into the night (e.g.,
Perry et al. 2008).
Plasticity in activity pattern can allow organisms
to exploit the evolutionarily novel night-light niche
(Garber 1978; Gaston et al. 2014), which may come
with a variety of benets and costs. For example, use
of articially lighted habitats can allow individuals to
acquire additional energy by extending foraging times.
Insectivores may forage on arthropods attracted to
lights (Verheijen 1960), a behavior commonly observed
in lizards (Perry and Fisher 2006; Martín et al. 2018).
Activity at night may also allow for maintenance of
territories, additional opportunities for courtship and
reproduction, and avoidance of competition (Rich and
Longcore 2006). Use of the night-light niche may also
entail costs, including increased energy expenditure,
non-optimal thermal conditions, disruption of
endocrine function, increased competition, or increased
susceptibility to some predators (Petren et al. 1993;
Perry and Lazell 2000; Perry and Fisher 2006; Ouyang
et al. 2018).
Despite a growing interest in the ecological effects
of articial light at night, its effects on animal behavior
remain relatively underexplored. The availability of
articial light is especially relevant for animals whose
dominant sense is sight, such as diurnal lizards of the
genus Anolis (hereafter, anoles). Seventeen species
of anole have been documented using articial lights
(Perry et al. 2008). Most anecdotal observations of
nocturnally active anoles document foraging behaviors
(Perry and Fisher 2006). Reports of displaying males
(Robert Trivers, pers. comm.), courtship (Bowersox et
al. 1994), and reproduction, however, suggest that a
wider range of behaviors regularly occur around articial
Copyright © 2019. Andrew S. Maurer
All Rights Reserved.
Maurer et al.—Nocturnal activity in Antiguan anoles.
lights (Wilson and Porras 1983). Yet, the diversity and
prevalence of such behaviors used at articial lights has
not been systematically studied.
Other relevant questions about the use of the night-
light niche remain unaddressed. For instance, detailed
observations of activity patterns at articial lights across
the entire night have not been made in any anole species.
Moreover, anecdotal reports that typify current literature
do not follow specic individuals. Consequently,
we lack basic information about whether individuals
vary in their use of articially lighted habitats. The
demographics of individuals using lights at night are
also unclear. While anoles of both sexes have been
reported using lights at night, some observations
(e.g., Powell and Henderson 1992) have suggested a
bias towards young males. In sum, moving beyond
an anecdotal listing of species using articial lights is
needed. Determining the behaviors, demographics, and
individual variation associated with use of articial lights
at night is necessary for understanding the ecological
and evolutionary impacts for diurnal organisms.
In summer 2017, we documented the nocturnal
behavior and activity patterns of two species of diurnal
anole, Leach’s Anole (Anolis leachii) and Watts’ Anole
(A. wattsi), at an articial light source in Antigua, West
Indies. During normal diurnal activity, these species
occur alongside various other lizards, most notably
Griswold’s Ameiva, Ameiva griswoldi (Kolbe et al.
2008), and occupy the same habitats used by nocturnal
geckos (e.g., native Thick-tailed Geckos, Thecadactylus
rapicauda, and non-native tropical House Geckos,
Hemidactylus mabouia). We assessed the types and
timing of anole behaviors shown through the night
and monitored marked individuals to assess whether
individuals consistently used the novel niche and how
this behavior varied between individual anoles.
Materials aNd Methods
From 13 June to 15 July 2017, we performed nightly
lizard surveys on Long Island, Antigua (17.156235°N,
61.751053°W) from approximately 2000 to 0600. Over
this period, sunset ranged from 1841 to 1844 and sunrise
from 0533 to 0541. We surveyed an approximately 28
m2 porch featuring a single articial light source that
pointed straight down from the ceiling (height: 3 m). We
conducted visual surveys every hour per night except
during occasional periods in the middle of the night
(e.g., 2200–0100) when we were only able to survey
opportunistically. For every individual lizard observed,
we recorded the time, perch location, and height. At the
start of the study, and when new individuals appeared
thereafter, we captured and marked each A. leachii.
For each individual, we determined its sex, measured
its snout-vent length (SVL), and gave each a unique
alphanumeric dorsolateral mark allowing for future
To assess whether individual A. leachii varied in
their use of the night-light niche, we calculated the
mean proportional similarity (mean PSi; an index of
inter-individual variation, also known as individual
specialization) between individual and cumulative
(population) distributions of activity (following
methods in Kamath and Losos 2017). This procedure
tests whether patterns of nocturnal activity observed
in each individual diverged from those observed for
the entire population. We calculated individual and
population level indices of individual specialization
(PSi) using the PSicalc function in the RInSp R package
(Zaccarelli et al. 2013). The P value was calculated by
comparing observed distributions to randomly sampled
distributions from the population distribution. Values
of PSi range from one (low inter-individual variation)
to zero (high inter-individual variation). We performed
all analyses in R v. 3.2.2 (R Core Team 2015) using
RStudio (version 1.0.136, R Team 2015) with α = 0.05.
We made 99 observations of A. leachii, A. wattsi, and
T. rapicauda. No other lizard species were observed.
We frequently detected all three species during the same
survey, and on several occasions detected multiple A.
leachii individuals on the same survey. We did not
observe any intra- or interspecic agonistic interactions
or visual displays (e.g., headbobbing, push-ups, or
dewlap extensions) during surveys.
The three lizard species exhibited distinct perch
heights: A. leachii typically perched high on walls,
between 2.4 and 3.0 m, A. wattsi was only observed on the
porch oor, and T. rapicauda displayed a variable perch
height, ranging from behind shutters at approximately
1.2 m to using the ceiling at 3.0 m. We observed the
lizards feeding on a variety of nocturnal invertebrates,
particularly small insects and Lepidoptera; foraging
appeared to be the primary behavioral mode. We also
made isolated observations of A. leachii catching and
eating arthropods including a cockroach (Blattodea) and a
tarantula (Cyrtopholis sp., likely C. bartholomaei; Fig. 1).
Our mark-resighting approach resulted in 78 A.
leachii detections with eight conrmed individuals (ve
sightings were attributed to unmarked individuals), 12
A. wattsi sightings of one conrmed individual, and
nine sightings of T. rapicauda (individuals not marked).
We were able to denitively determine the sex of six A.
leachii males based on scales at the base of the tail by the
cloaca, and we expect that the remaining two A. leachii
individuals were also male based on size and behavior.
Anolis wattsi is sexually dimorphic in color (Lynn 1957),
and the single individual we observed was male.
Herpetological Conservation and Biology
Our surveys starting roughly one hour after sunset
revealed activity patterns for A. leachii and A. wattsi
that were both right-shifted (relative to midnight as
the center of the x-axis; Fig. 2). The detections for A.
wattsi, however, were densely distributed around 0500
resulting in a pronounced unimodal peak, whereas A.
leachii detections were more evenly distributed through
the night (Fig. 2). There was no signicant difference
between individual nocturnal activity patterns for A.
leachii (mean PSi = 0.41 ± [SD] 0.30, P = 0.732; Fig.
3). SVL measurements from four A. leachii individuals
indicated a mean body size of 9.5 ± (SE) 0.13 cm; all of
the individuals detected were of similar size.
Our results illuminate several important aspects of
the contemporary natural history of Antiguan lizards.
First, we describe previously undocumented nocturnal
behaviors in A. wattsi alongside the extensive use of
a nocturnal light source by A. leachii. Second, our
observations suggest the primary driver of nocturnal
activity in anoles is foraging opportunity. Third, the
observed nocturnal activity was skewed toward early
morning hours. Fourth, use of the night-light niche was
restricted to male anoles. Fifth, individual variation
in A. leachii nocturnal activity appears to be limited,
suggesting that all individuals are taking advantage of
this novel resource in a similar way.
Our observations suggest that the primary driver of
nocturnal activity in both species of Antiguan anole was
the novel foraging opportunity presented by arthropods
drawn to articial lighting. We did not detect any
behaviors associated with territorial maintenance or
reproduction. Further, we did not observe intra- or
interspecic agonistic interactions during our surveys
(e.g., dewlapping). Because effective communication
via the dewlap is specialized to specic photic conditions
in anoles (Leal and Fleishman 2004), it is possible
figure 1. An adult male Leach’s Anole (Anolis leachii) forages
on a tarantula (Cyrtopholis sp.) under an articial light source
on Long Island, Antigua, in summer 2016. (Photographed by
Alexandra L. Fireman).
figure 2. Overlapping density plots compare the temporal
distributions of nocturnal detections for Leach’s Anole, Anolis
leachii (n = 78 observations), and Watts’ Anole, A. wattsi (n =
12 observations). Sunset (1842) and sunrise (0535) are shown
with dashed gray lines. Hourly surveys typically started at
approximately 2000; the A. leachii curve extends earlier due to
kernel density smoothing.
figure 3. Indices of individual specialization (IS) in nocturnal
activity for eight Leach’s Anole (Anolis leachii) individuals (n =
78 observations). Points represent the mean pairwise similarity of
that individual to all other individuals (PSi); error bars represent
one estimated standard deviation. The mean population level of
individual specialization is represented by a bold blue line and
lighter dotted lines represent one standard deviation (mean PSi =
0.408 ± [SD] 0.30). Nightly surveys were conducted at an articial
light source on Long Island, Antigua, from 13 June to 15 July
2017, resulting in 73 detections of marked individuals.
Maurer et al.—Nocturnal activity in Antiguan anoles.
that the evolutionarily novel photic conditions around
articial lights may disrupt normal communicative
The use of the night-light niche by Antiguan anoles
has interesting implications for interactions with
coexisting nocturnal lizards. At our study location in
Antigua, T. rapicauda were also present around the
focal light source, with typically only a single individual
observed. This species could represent an interspecic
competitor for both A. wattsi and A. leachii or a potential
prey source for large A. leachii; however, we did not
observe any interactions between anoles and geckos, and
nocturnally active A. leachii did not appear to be large
enough to prey on observed T. rapicauda individuals.
We also did not observe any other syntopic lizard
species using articial lights (e.g., Ameiva griswoldi).
Future work should explore if use of the night-light
niche confers physiological or demographic benets (or
costs) to anoles, potentially through competitive release,
protection from predators, or subsidized predation on
aggregated prey.
The observed nocturnal activity patterns for A.
leachii and A. wattsi were right-skewed relative to a
center of midnight, with 48% of observations occurring
within 2 h prior to sunrise. Previous observations
of anole nocturnal activity (including in A. leachii)
were concentrated in the hours following sunset (e.g.,
Schwartz and Henderson 1991; Stroud and Giery 2013),
though A. carolinensis activity has been documented
roughly 2 h prior to sunrise (McCoid and Hensley
1993). With our observed activity concentrated closer to
sunrise, this could provide evidence that the exploitation
of the night-light niche by Antiguan anoles occurred
because of an earlier start to diurnal activity, rather than
an extension of diurnal activity past sunset. Because
our rst survey was typically 45–60 min after sunset,
our inferences here are limited and we do not have data
to rule out a post-sunrise activity period. Our anecdotal
observations, however, support our nding of increased
activity later in the night; we never observed A. wattsi
during the hours around sunset, and several A. leachii
exhibited behavior where they would appear for the rst
time in a survey night after midnight. Irrespective of
specic nocturnal patterns, our daytime observations as
well as those documented in previous studies in Antigua
(e.g., Kolbe et al. 2008) suggest that activity remains
much higher during the day than night for both species.
Kolbe et al. (2008) present diel patterns in abundance
that suggest a crepuscular schedule for A. wattsi and less
pronounced peaks closer to midday for A. leachii. In
sum, it is unclear if we will continue to see a gradual
shift toward more nocturnal use of articial lights, or if
we are observing the rare behavior of a few opportunists
or subset of the population.
Our analysis of inter-individual variation in A.
leachii nocturnal activity showed no difference in the
patterns of the eight marked individuals. This lack
of variation suggests that individuals at our study site
are adapting to the novel night-light niche similarly;
however, three individuals were only detected once
each, and our inferences into inter-individual trends
are limited in general by sample size. We were able
to conclusively determine the sex of six of eight A.
leachii; cloacal scales are pronounced in mature males
and ambiguous in females and subadult males (Lovern
et al. 2004). We made no conrmed sightings of female
anole activity in a set of 90 total observations, and it
seems likely that nocturnal behavior in female A. wattsi
and A. leachii is either nonexistent or very rare at this
site. Therefore, this study suggests a possible sexual
bias in the exploitation of the night-light niche. This
is consistent with previous observations of nocturnal
activity in the Anguilla Bank Anole (A. gingivinus;
Powell and Henderson 1992). Further research would
benet from exploring this sexual bias in activity and
should investigate what factors might drive sex-based
differences in use of the night light niche.
To develop a more comprehensive understanding
of the effects of light pollution, it will be important to
consider how prevalent exploitation of the night-light
niche is across species and contexts, and why individual
species may vary in their use of this evolutionarily novel
opportunity. Though A. wattsi is more abundant than
A. leachii in Antigua (Kolbe et al. 2008), our study
suggests that nocturnal activity is more common in
A. leachii. Moreover, the limited available evidence
suggests that A. leachii has been using articial light
sources for some time (Schwartz and Henderson 1991).
The reasons for this are unclear, but the disparity may
shed light on the traits valuable for taking advantage of
nocturnal opportunities. Anolis leachii is larger than A.
wattsi and thus could be a stronger competitor in any
agonistic interactions with nocturnal species. Further,
A. leachii typically occupies higher perches than does
A. wattsi (Kolbe et al. 2008), a trait that coincides with
a closer proximity to light sources that are most often
located high on walls and ceilings. Perhaps A. leachii
started to use the night-light niche when arthropod
prey aggregated in front of them at light sources at the
beginning of their natural diurnal activity.
Our observations of a single male A. wattsi
exhibiting nocturnal foraging activity may be the result
of idiosyncratic individual behavior. More nocturnal
surveys are needed to better establish how prevalent
this behavioral shift is for the species; however, with
78 A. leachii detections, our inferences are more robust
for this species. Additionally, our observations of A.
leachii using articially lighted habitats are not isolated.
Individuals of the species shifted into the night-light
niche at least as early as 1991 and likely before (Schwartz
and Henderson 1991). We have also incidentally
observed A. leachii nocturnal foraging behavior around
articial lights in other areas of Antigua away from
the focal study area (e.g., Hodge’s Bay and Piccadilly,
Antigua). In each situation A. leachii were foraging on
ying insects by articial light sources, suggesting that
the use of the night light niche by A. leachii could be
widespread on Antigua.
The body of research documenting use of articially
lighted habitats by a variety of taxa continues to grow
(Rich and Longcore 2006). Evidence is mounting
that suggests humans are contributing to increasing
nocturnality in wildlife (e.g., in mammals; Gaynor et
al. 2018). As more ecological impacts become apparent
(Gaston et al. 2014; Dominoni et al. 2016), investigating
the tness consequences of light at night will become
increasingly important. Despite this, light at night
remains understudied as a topic of regional conservation
concern in the Caribbean. We suggest that future
research should examine whether Caribbean species
show an ability to exploit the night-light niche and how
the use of this niche may result in downstream effects on
species persistence and ecosystem function.
Acknowledgments.—This project occurred during
eld work funded by the Jumby Bay Island Company.
We thank them for continual funding for the Jumby Bay
Hawksbill Project. Christopher J. Thawley was sup-
ported by a National Science Foundation Postdoctoral
Research Fellowship in Biology (#1711564).
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aNdrew s. Maurer is a National Science Foundation Graduate Research Fellow at North Carolina State
University, Raleigh, USA, a Fulbright Student Fellow, and a Research Associate with the Jumby Bay
Hawksbill Project in Antigua, West Indies. Andrew received his B.A. (2012) in Environmental Studies
and Spanish from Eckerd College, St. Petersburg, Florida, USA, and went on to pursue a graduate
research program in Hawksbill Sea Turtle (Eretmochelys imbricata) nesting ecology. (Photographed
by Kyle Pagel).
christopher J. thawley is a National Science Foundation Postdoctoral Fellow at the University
of Rhode Island, Kingston, USA, where he studies impacts of urbanization with a focus on articial
light at night (ALAN). Chris received his Ph.D. from Penn State University, University Park, USA,
where he studied adaptation of fence lizards to pressures imposed by invasive re ants. He received
his B.S. (2004) from Davidson College, Davidson, North Carolina, USA, and his M.S. (2011) from the
University of Alabama, Tuscaloosa, USA. Chris is broadly interested in how species adapt to rapid
environmental changes and is a strong proponent of scientic outreach. (Photographed by Fern Graves).
alexaNdra l. fireMaN is an M.S. student at the University of Maryland, Solomons, USA, Chesapeake
Biological Laboratory, and a Field Director for the Jumby Bay Hawksbill Project in Antigua, West
Indies. Alex received her B.A. (2016) in Biology and Earth and Environmental Science from Wesleyan
University, Middletown, Connecticut, USA, and is now pursuing an M.S. degree in Marine Estuarine
Environmental Science. Her research focuses on the foraging ecology and strategy of the Caribbean
Hawksbill Sea Turtle (Eretmochelys imbricata) over time. (Photographed by Alexandra L. Fireman).
seaN t. giery is a Postdoctoral Fellow at the University of Connecticut, Storrs, USA. His research
program examines the evolutionary origins and ecological consequences of phenotypic variation. He
uses natural and human-disturbed ecosystems to identify eco-evolutionary processes and their effects on
population persistence and ecological function. He received his B.S. from the College of Environmental
Science and Forestry of the State University of New York, Syracuse, USA, in 2002, his M.S. from The
University of Hawaii at Manoa, USA (2009), and Ph.D. From North Carolina State University, Raleigh,
USA (2016). (Photographed by Market Zimova).
JaMes t. stroud is a Postdoctoral Research Associate at Washington University in St. Louis, Missouri,
USA. In general, James is interested in understanding how species, particularly Anolis lizards, react
to novel abiotic and biotic conditions, such as behavioral changes with urbanization or patterns of
coexistence with distantly related congenerics. James received his B.Sc. in Zoology with Conservation
from the University of Wales, Bangor, UK (2008), his M.Sc. from the University of Hull, UK (2011),
and his Ph.D. from Florida International University, Miami, USA (2018). (Photographed by James T.
... Presence of illuminated night may be beneficial for diurnal species, that could use the so called "night-time niche" to gain resources (food or reproduction opportunities for instance). It has been demonstrated in some occasions Maurer et al., 2019), but the actual consequences on individual fitness have not been truly tested yet. ...
... However, the absence of effect of light at night may be due to the presence of a nocturnal competitors (the spiny mouse Acomys cahirinus) (Rotics et al., 2011). On the contrary, a study on two diurnal lizard species (Anolis leachii and Anolis wattsi) showed that individuals exposed to artificial light at night were active at night, with an activity peak in early morning hours (Maurer et al., 2019). ...
... V. canescens is inactive at night, but in presence of artificial light the extension of the photophase results in locomotor activity during the night-time. Modifications of diel activity patterns has been found in few diurnal spiders ), birds ) and lizards (Maurer et al., 2019) species. Very often linked to foraging activities, the extension of activity at night is likely to be costly to organisms, due to increased risk of predation, competition for resources with nocturnal species and higher energy expenditure. ...
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Light pollution is a widespread anthropogenic disturbance that affects almost every ecosystem on Earth. It mainly comes from direct illumination due to public street lighting, but can also take the form of skyglow (i.e. the scattering of upwardly-emitted light into the atmosphere) which extends over hundreds of kilometres around urbanised areas. For a long time, light pollution had received less attention than other types of anthropogenic disturbances such as climate change. However, a growing number of studies have highlighted its numerous biological consequences on a large number of organisms, and at all levels of biological organisation (individuals, populations, ecosystems). Light pollution is therefore now considered as an important driver of global change and a major concern for human health and biodiversity. Studies on light pollution have mainly focused on nocturnal organisms, which are more likely to be disturbed by the presence of light at night. This is particularly true for insects, as evidenced by numerous studies that investigated the attractiveness of artificial light sources on moths or the modification of flashing activities in fireflies exposed to light pollution. On the contrary, very little is known about consequences of light pollution on diurnal insects. The aim of my thesis was therefore to investigate experimentally the changes induced by light pollution in a diurnal parasitoid, the wasp Venturia canescens. To do this, I studied behavioural, life-history and physiological traits of female wasps exposed to various intensities of light pollution. First, I addressed changes in behavioural traits related to parasitic efficiency and lifetime reproductive success, in relation to energy reserves, at the intra- and trans-generational levels. I demonstrated that light pollution led diurnal wasps to become active and search for food and hosts at night. In addition, I showed that light at night, depending on its intensity, also modified wasps’ daytime foraging behaviour, but without affecting their energy reserves. Indeed, there was an increased preference for host searching in wasps exposed to low intensity light pollution. However, light at night does not seem to have a strong effect on the lifetime reproductive success of Venturia canescens. Finally, light pollution also acted at the trans-generational level, influencing offspring feeding behaviour and development time. Then, I focused on a physiological trait, the production of melatonin. Melatonin is a key hormone involved in the regulation of circadian rhythm in organisms. It is also known to be strongly impacted by the presence of light at night. This hormone is therefore likely to play a major role in the phenotypic changes observed in organisms exposed to light pollution. Melatonin has been well studied in vertebrates, especially mammals, but knowledge of its synthesis and circadian rhythm in insect is scarce. I therefore developed two methods for quantifying melatonin in Venturia canescens, to describe the variation of melatonin synthesis over a 24-hour cycle in the absence of light pollution. This work could serve as a basis for future studies, to experimentally test the effect of light pollution on melatonin synthesis in Venturia canescens.
... Artificial substrates can serve as preferable perching sites or refuges for urban lizards (French et al., 2018). Increased night light in the city can affect reptiles positively and negatively (Maurer et al., 2019). It can disrupt natural day-night cycles, which can modify hormone secretion affecting metabolism, body mass, and energy expenditure (Ouyang et al., 2018). ...
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Urban environments offer dramatically different habitats for wildlife compared with natural environments. They provide, for example, different levels of resource availability , anthropogenic night light, and microclimates (e.g., urban heat islands). For reptiles, increased temperatures in the city can lead to increased energetic demands and metabolic rates unless they change their morphology and physiology and adapt or acclimatize to the urban conditions. We explored differences in metabolic rate, evaporative water loss, and body size of two lizard species-rock agamas (Lauda-kia vulgaris) and Mediterranean house geckos (Hemidactylus turcicus), from urban habitats and nearby natural open areas. When tested in the lab, we expected to identify physiological adaptations resulting in decreased metabolism in urban individuals. Both species had similar body lengths and masses at both habitat types, suggesting any differences in costs and benefits between urban and natural environments do not affect their overall size or body condition. In the laboratory, metabolic rates were similar in individuals from both habitats for both species, indicating no long-term adaptations in this trait. However, urban geckos (but not agamas) had higher evaporative water loss than conspecifics from more natural habitats. This may suggest different compositions of epidermal lipids affecting the gecko skin's resistance to evaporation between the habitats. Overall, our results highlight different elements of the urban environment that might affect reptiles. However, the differences between species urge caution in interpreting the results to other species and locations. With increasing urbanization worldwide, understanding when and to what degree local adaptations can occur can help us predict reptile species distribution and survival in light of future anthropogenic changes.
... Ainsi, l'habitat nouvellement créé par la présence de lumière artificielle nocturne peut être définit comme étant une « niche lumineuse nocturne » (Garber, 1978;Le Tallec, 2018), dont certaines espèces animales tirent profit. A titre d'exemple, l'Anole à crête, Anolis cristatellus, une espèce diurne, a colonisé la « niche lumineuse nocturne » pour profiter de l'abondance des proies à proximité des sources lumineuses (Garber, 1978;Maurer et al., 2019). Ces modifications sont susceptibles d'affecter les interactions inter-espèces au sein d'une niche écologique (Knop et al., 2017;Hoffmann et al., 2018), notamment dans le cas des relations proie -prédateur (Minnaar et al., 2015;Manfrin et al., 2017;Mcmunn et al., 2019). ...
La lumière artificielle nocturne (ALAN), reconnue comme pollution environnementale, perturbe tous les écosystèmes et affecte la photopériode, synchronisateur externe de nombreux processus biologiques. Par une approche intégrative, cette thèse a pour but d’évaluer expérimentalement l’influence d’ALAN sur le crapaud commun, Bufo bufo, amphibien nocturne couramment retrouvé en zones urbaine et péri-urbaine. Mes travaux montrent qu’en période de reproduction, ALAN réduit l’activité physique nocturne et modifie l’allocation énergétique, sans affecter ni la prise alimentaire, ni la masse corporelle des mâles. De plus, bien qu’aucun effet n’ait été observé sur la testostéronémie salivaire, ALAN affecte le comportement et le succès reproducteurs des mâles en augmentant le temps de latence pour s’accoupler avec la femelle, en diminuant le maintien de l’amplexus et en réduisant le taux de fécondation des œufs. Par ailleurs, une analyse sans a priori de transcriptomes de têtards élevés en présence d’ALAN montre une sous expression nocturne de gènes, notamment ceux impliqués dans l’immunité. Une seconde étude gène-spécifique montre une faible influence d’ALAN sur l’expression des gènes codant deux enzymes impliquées dans la synthèse de la mélatonine ou ses trois récepteurs et ne permet pas de conclure quant au rôle central de la mélatonine dans les perturbations liées à ALAN. Ainsi, cette thèse met en évidence les effets très larges d’ALAN chez le crapaud commun, affectant les processus biologiques de l’expression génique à la fitness. Ces résultats doivent être replacés dans le contexte de biologie de la conservation et pris en compte dans la préservation de l’environnement nocturne.
... The potential benefits associated with opportunistic nocturnal behaviour in lizards include extended activity in the evening in warm climates (Duncan et al., 2003), avoidance of diurnal predators, the availability of nocturnal prey items (Gordon et al., 2010), and night-light niche expansion (Amadi et al., 2021;Maurer et al., 2019). While it is relatively rare that the same species exhibit both diurnal and nocturnal behaviours, human activities and anthropogenic related environmental changes are providing an opportunity for animals to extend what may be crepuscular behaviour into the night time (Gaynor et al., 2018). ...
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On four days in May 2022, I observed a young adult Sceloporus cowlesi active at night in the city of Albuquerque, New Mexico, USA at a location illuminated by artificial light during the night.
... Behavior in this species is well characterized and easily observed [28,37,38], including display behaviors (pushups, head-bobs, and extension of a throat fan called a dewlap) and sleep behavior [10]. There is also a robust body of literature on the impacts of photoperiod on green anole behavior and physiology (e.g., [23,47,58]), and a growing body of research on the impacts of ALAN on anole behavior and physiology (e.g., [42,52,78]). ...
Artificial light at night (ALAN) disrupts biological rhythms across widely diverse organisms. To determine how energy is allocated by animals in different light environments, we investigated the impacts of ALAN on behavior and physiology of diurnal green anole lizards (Anolis carolinensis). Two groups of 24 adult lizards (half males, half females) were maintained in a controlled lab setting for six weeks. One group was exposed to a simulated natural summer light-dark cycle; the other was exposed to ALAN that simulated urban, nocturnal light exposure. After an acclimation period, we conducted four behavioral trials. One trial examined behavioral time allocation over two 24 h periods, and three others were conducted during mid-day and mid-night: open field tests, to examine exploratory behavior; foraging trials, to examine prey consumption; and social interaction trials, to examine same-sex interactions. We then measured each lizard's snout-vent length and mass of its body, abdominal fat pads, liver, and, for males, testes. Lizards exposed to ALAN were more likely to be awake at night, using nocturnal light to explore, forage, and display to conspecifics. However, during the day, ALAN lizards were less likely to be awake, slower to move, and females displayed less frequently. ALAN lizards had heavier fat pads and testes, but ALAN did not impact body mass, liver mass, or snout-vent length. In sum, ALAN appears to cause a broad shift towards increased nocturnal activity and may alter metabolic and reproductive processes. Future work should examine the fitness consequences of these behavioral and physiological changes.
... A growing body of work has documented changes in wildlife behavior due to expanding anthropogenic development (e.g., Lowry, Lill, & Wong, 2013). For example, urbanization is commonly reported to affect habitat use (e.g, Berger, 2007;Elfström, Zedrosser, Støen, & Swenson, 2014;Jones, Cove, Lashley, & Jackson, 2016), activity patterns (Carter, Shrestha, Karki, Pradhan, & Liu, 2012;Gaynor, Hojnowski, Carter, & Brashares, 2018;Maurer, Thawley, Fireman, Giery, & Stroud, 2019;Nix, Howell, Hall, & McMillan, 2018;Ordiz, Saebø, Kindberg, Swenson, & Støen, 2017), and grouping and foraging patterns (Ditchkoff et al., 2006;Tablado & Jenni, 2017). Whereas many large predators avoid urban areas, other species are often attracted to human development. ...
Natural habitats have been converted to urban areas across the globe such that many landscapes now represent matrices of developed and protected lands. As urbanization continues to expand, associated pressures on wildlife will increase, including effects on animals in adjacent protected habitats. For prey species (e.g., ungulates), an understanding of the ecological impacts of urbanization is typically confounded by coincident effects from co-occurring predators. Yet, understanding how urbanization affects prey behaviors in the absence of predators is becoming increasingly relevant as many top predators face extirpation. We placed camera traps at varying distances from urban areas within protected areas in the Florida Keys, USA, to evaluate the influence of urbanization on the behavior of the key deer (Odocoileus virginianus clavium), an endangered species that has been without non-human mammalian predators for ~ 4000 years. We predicted that as distance to urban areas decreased, key deer would use sites at the same rate, exhibit bigger group sizes, and shift activity patterns to be more nocturnal. Our results indicate that intensity of site use decreased with proximity to urban areas, potentially reflecting human avoidance. Group size increased closer to urban areas, consistent with other studies relating this behavior to anthropogenic subsidies and vigilance for humans. Activity patterns changed but did not become more nocturnal near urban areas as predicted by global analyses relating human disturbance to wildlife nocturnality. Our results have important implications for ungulate behavioral ecology and, taken together, suggest that influences on protected species from adjacent land uses are an important consideration when planning land use and designing protected areas.
... Venturia canescens is inactive at night, but in presence of artificial light the extension of the photophase results in locomotor activity during the night-time. Modifications of diel activity patterns have been found in few diurnal spiders (Frank, 2009), birds (Amichai & Kronfeld-Schor, 2019) and lizards (Maurer et al., 2019) species. Very often linked to foraging activities, the extension of activity at night is likely to be costly to organisms, due to increased risk of predation, competition for resources with nocturnal species and higher energy expenditure. ...
Light pollution is a widespread phenomenon with major consequences on nocturnal organisms from individual to community. However, its effects on diurnal organisms are still scarcely studied. We exposed diurnal parasitoid wasps (Venturia canescens) to low (0.7 lux) or high (20 lux) artificial light for two to eight consecutive nights, and quantified its consequences on their physiology and daytime behaviour compared to a control group (0 lux). We next considered potential trans‐generational effects on offspring whose mothers were exposed to light pollution. While in the dark night the wasps showed no activity, exposure to artificial light triggered nocturnal activity and altered diurnal behaviours related to foraging. Wasps exposed to light at night had a greater propensity to choose hosts rather than food compared to controls. They also spent more time feeding when exposed to 0.7 lux of light at night. However, these behavioural modifications were not related to changes in individual energy reserves. Light pollution effects persisted at trans‐generational level: offspring development time and latency before feeding increased when mothers were exposed to 0.7 lux light at night. Even at low intensity, light pollution alters foraging behaviour of a diurnal insect. Searching for hosts or food being essential for fitness, light pollution is likely to have long‐term repercussions on insect populations. Light pollution caused behavioural modifications potentially beneficial for V. canescens in the short term. However, longer term studies (e.g. on lifetime reproductive success) are needed to fully understand its consequences on insects
The natural environment can be negatively impacted by a variety of human activities, including the production of artificial light at night. Recent studies suggest that pollution from anthropogenic light alters animal behavior. Despite being highly nocturnal, little attention has been given to anurans and the effects artificial light at night has on their behavior. This study investigated whether artificial light influenced male call site selection in east Texas anurans. Ambient light levels were quantified at five sites that varied in urbanization and artificial light levels. Calling males were located and ambient light was then measured at the male's call location. Light levels at those call locations were compared to the general light environment as measured at random locations in the area. There was a consistent pattern where males at the brightest sites called from locations darker than the general light environment. However, male call locations at the brightest sites were generally brighter than those at the darker sites suggesting that, while male anurans avoid illuminated areas for calling, males in more urbanized populations may be unable to do so. As such, male anurans at sites with higher light pollution may experience a form of habitat loss where preferred darker habitat is not available.
Animals have evolved with natural patterns of light and darkness, such that light serves as an important zeitgeber, allowing adaptive synchronization of behavior and physiology to external conditions. Exposure to artificial light at night (ALAN) interferes with this process, resulting in dysregulation of endocrine systems. In this review, we evaluate the endocrine effects of ALAN exposure in birds and reptiles, identify major knowledge gaps, and highlight areas for future research. There is strong evidence for ecologically relevant levels of ALAN acting as an environmental endocrine disruptor. However, most studies focus on the pineal hormone melatonin, corticosterone release via the hypothalamus-pituitary-adrenal axis, or regulation of reproductive hormones via the hypothalamus-pituitary-gonadal axis, leaving effects on other endocrine systems largely unknown. We call for more research spanning a diversity of hormonal systems and levels of endocrine regulation (e.g. circulating hormone levels, receptor numbers, strength of negative feedback), and investigating involvement of molecular mechanisms, such as clock genes, in hormonal responses. In addition, longer-term studies are needed to elucidate potentially distinct effects arising from chronic exposure. Other important areas for future research effort include investigating intraspecific and interspecific variability in sensitivity to light exposure, further distinguishing between distinct effects of different types of light sources, and assessing impacts of ALAN exposure early in life, when endocrine systems remain sensitive to developmental programming. The effects of ALAN on endocrine systems are likely to have a plethora of downstream effects, with implications for individual fitness, population persistence, and community dynamics, especially within urban and suburban environments.
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Observations of predation events are rare. These events are important to help understand trophic networks of biological communities in general and of introduced species in particular. Milk frogs (Trachycephalus typhonius) feed on insects and other arthropods, but some cases of vertebrates have been reported in its diet: a Sheep toad (Hypopachus variolosus) in México, a Black Myotis (Myotis nigrescens) in the Pantanal of Brazil, and an adult tree frog of Dendropsophus soaresi also in Brazil. Here we report the predation of an adult Milk frog on a Common house gecko (Hemidactylus frenatus) in Bajamar, Puntarenas, Costa Rica. The observation was made in a house in an area of pastures with trees near a mangrove swamp.
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Alternation between day and night is a predictable environmental fluctuation that organisms use to time their activities. Since the invention of artificial lighting, this predictability has been disrupted and continues to change in a unidirectional fashion with increasing urbanization. As hormones mediate individual responses to changing environments, endocrine systems might be one of the first systems affected, as well as being the first line of defense to ameliorate any negative health impacts. In this Review, we first highlight how light can influence endocrine function in vertebrates. We then focus on four endocrine axes that might be affected by artificial light at night (ALAN): pineal, reproductive, adrenal and thyroid. Throughout, we highlight key findings, rather than performing an exhaustive review, in order to emphasize knowledge gaps that are hindering progress on proposing impactful and concrete plans to ameliorate the negative effects of ALAN. We discuss these findings with respect to impacts on human and animal health, with a focus on the consequences of anthropogenic modification of the night-time environment for non-human organisms. Lastly, we stress the need for the integration of field and lab experiments as well as the need for long-term integrative eco-physiological studies in the rapidly expanding field of light pollution.
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Effects of natural and artificial light on the nocturnal behaviour of the wall gecko. In the present study, we evaluated the effects of nocturnal light level (i.e. lunar phase and artificial lighting) on the activity of wall geckos (Tarentola mauritanica) of different ages in an anthropic environment. Data on individual behaviour were collected by direct observation and later examined by means of generalized linear mixed model (GLMM) analysis. The presence of moonlight increased the number of active wall geckos. Artificial lighting reduced the effect of moonlight on the number of active geckos but not on their individual activity. A greater number of adult geckos was found around artificial light as large individuals monopolized the best foraging sites. The ability to use artificially– lit human habitats, particularly on new moon nights, can benefit the foraging activity of nocturnal lizard species such as the wall gecko.
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Ecological specialization is common across all levels of biological organization, raising the question of whether the evolution of specialization at one scale in a taxon is linked to specialization at other scales. Anolis lizards have diversified repeatedly along axes of habitat use, but it remains unknown if this diversification into habitat use specialists is underlain by individual specialization. From repeated observations of individuals in a population of Anolis sagrei in Florida, we show that the extent of habitat use specialization among individuals is comparable to the extent of specialization in the same traits among ten sympatric Anolis habitat specialist species in Cuba. However, the adaptive correlations between habitat use and morphology commonly seen across species of Anolis were not observed across individuals in the sampled population. Our results therefore suggest that while patterns of ecological specialization can transcend scale, these parallels are the consequence of distinct ecological processes acting at microevolutionary and macroevolutionary scales. This article is protected by copyright. All rights reserved
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The increasing use of electric lights has modified the natural light environment dramatically, posing novel challenges to both humans and wildlife. Indeed, several biomedical studies have linked artificial light at night to the disruption of circadian rhythms, with important consequences for human health, such as the increasing occurrence of metabolic syndromes, cancer and reduced immunity. In wild animals, light pollution is associated with changes in circadian behaviour, reproduction and predator –prey interactions , but we know little about the underlying physiological mechanisms and whether wild species suffer the same health problems as humans. In order to fill this gap, we advocate the need for integrating ecological studies in the field, with chronobiological approaches to identify and characterize pathways that may link temporal disruption caused by light at night and potential health and fitness consequences.
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Anolis equestris is native to Cuba and has been introduced to Florida, USA (Kraus 2009. Alien Reptiles and Amphibians: A Scientific Compendium and Analysis. Springer, Dordrecht, Netherlands. 563 pp.; Krysko et al. 2003. Florida Sci. 66:74–79). This species consumes a wide variety of animals and plants including vertebrates, invertebrates, and fruit (Camposano et al. 2008. Iguana 15:212–219, Giery et al., unpubl.). Documented activity times for populations in southern Florida indicate that A. equestris activity falls between mid-morning and late afternoon, ceasing at sunset (Meshaka et. al. 2004. The Exotic Amphibiansand Reptiles of Florida. Krieger Publ. Co., Malabar, Florida. 166 pp.). Here, we report on nocturnal activity of A. equestris in South Florida. On 18 April 2013 between 2203–2215 h, a single adult Anolis equestris was observed at Fairchild Tropical Botanical Gardens, Miami, Florida, USA (25.677°N, 80.276°W, WGS84; <1 m elev.). This individual was observed consuming Lepidoptera attracted to an artificial light source positioned above a doorway. Nocturnal lizards (Hemidactylus mabouia) were also present around the light source and could represent another potential prey source for nocturnally foraging A. equestris. This is the first documentation of A. equestris using artificial light sources to allow for nocturnal activity.
Nocturnal refuge As the human population grows, there are fewer places for animals to live out their lives independently of our influence. Given our mostly diurnal tendencies, one domain that remains less affected by humans is the night. Gaynor et al. found that across the globe and across mammalian species—from deer to coyotes and from tigers to wild boar—animals are becoming more nocturnal (see the Perspective by Benítez-López). Human activities of all kinds, including nonlethal pastimes such as hiking, seem to drive animals to make use of hours when we are not around. Such changes may provide some relief, but they may also have ecosystem-level consequences. Science , this issue p. 1232 ; see also p. 1185
This is one of the first papers to document ecological consequences of human-altered natural light cycles on other species. Here, the night light niche that is made available in urban and suburban ecosystems around the world, enables certain reptiles and amphibians come out at night and use artificial lights to their benefit. Geckos and toads naturally catch insects that are attracted to lights in cities and suburbs In this paper, the diurnal Puerto Rican lizard, Anolis cristatellus, is now taking advantage of the newly available night-light niche to catch insects during hours when, not very long ago, this was not possible. Anolis lizards, which are spectacular examples of adaptive radiation, have repeatedly evolved morphologically and behaviorally to specific ecological niches. This may be an early indication of how Anolis lizards, and other urban reptiles and amphibians, will quickly adapt to urban and suburban ecosystems.