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Effects of ultraviolet radiation on 25-hydroxyvitamin D3 synthesis in red-eared slider turtles (Trachemys scripta elegans)



To determine whether there are increased concentrations of 25-hydroxyvitaminn D(3) in red-eared slider turtles (Trachemys scripta elegans) after exposure to UV radiation. 12 yearling turtles recently removed from aestivation. Turtles were randomly allocated to 2 groups (6 turtles/group). An initial blood sample was collected from all turtles for measurement of 25-hydroxyvitamin D(3) concentrations. Turtles of 1 group were then provided no supplemental lighting, whereas turtles of the other group were exposed to full-spectrum coil bulbs at a distance of 22.86 cm. The UV-A and UV-B radiation generated by the supplemental lighting was measured by use of a radiometer-photometer at weekly intervals. Measurements were collected 2.54 and 22.86 cm from the bulb surface. The study was continued for a 4-week period. At the end of the study, a second blood sample was collected from all turtles for measurement of 25-hydroxyvitamin D(3). Mean +/- SD 25-hydroxyvitamin D(3) concentrations differed significantly between turtles provided supplemental UV radiation (71.7 +/- 46.9 nmol/L) and those not provided UV radiation (31.4 +/- 13.2 nmol/L). Appropriate husbandry recommendations for raising and maintaining red-eared slider turtles should include use of sunlight that is unobstructed by UV-B filtering material or provision of an artificial source of UV-B radiation.
2046 AJVR, Vol 67, No. 12, December 2006
itamin D
is an important hormone that is involved
in numerous physiologic processes.
Although the
most widely recognized function of this hormone is the
regulation of calcium metabolism, which is needed for
the development and maintenance of healthy bones,
the reproductive success of some reptilian species has
also been associated with optimized amounts of vita-
min D
Vitamin D
can be obtained through the diet
or synthesized through exposure of the skin to UV-B
(290 to 320 nm) radiation.
There is wide variation
among vertebrate species between the need for dietary
vitamin D
and the ability to synthesize the hormone.
The source and function of vitamin D
have been
examined in mammals and birds.
have been performed in reptiles have focused on
dietary requirements and synthesis during basking in
various lizards. The authors are not aware of any stud-
ies to determine whether chelonians synthesize vita-
min D
during basking or obtain vitamin D
from the
diet. This is unfortunate because many of these species
are raised in captivity as pets. Because these animals
potentially have long lives, it is important that specific
husbandry requirements be elucidated for them.
In addition to maintaining these animals as pets,
there is an increased interest in the conservation of
these reptiles. Currently, programs are underway to
prepare juvenile chelonians in captivity for release
to the wild. These programs typically release larger
animals that are less likely to be preyed on. If expo-
sure to UV-B radiation is required for chelonians to
maximize serum 25-hydroxyvitamin D
tions, then full-spectrum lights capable of inducing
production of this hormone should be used.
The purpose of the study reported here was to
determine whether red-eared slider turtles (Trachemys
scripta elegans) exposed to UV-B radiation under
controlled conditions would have increased concentra-
tions of 25-hydroxyvitamin D
concentrations, com-
pared with concentrations for control turtles. We pro-
posed to test 3 specific hypotheses. First, turtles
exposed to UV-B radiation would have higher concen-
trations of 25-hydroxyvitamin D
, compared with con-
centrations for control turtles. Second, turtles fed a diet
that included amounts of vitamin D
would have an
increase in 25-hydroxyvitamin D
concentrations over
time. Finally, the amount of UV-B radiation generated
by commercially available coil fluorescent bulbs would
decrease over time.
Materials and Methods
Animals—Twelve yearling red-eared slider turtles were
used in the study. The turtles were being housed outdoors for
the winter of 2005 to 2006 and were removed from aestiva-
tion for the study. Turtles were allowed to acclimate in the
laboratory environment for 7 days prior to the start of the
study. This project was performed in accordance with the
regulations established by the Institutional Animal Care and
Use Committee at Louisiana State University (protocol No.
Turtles were housed in 78 X 53 X 41.9-cm plastic con-
Each container was filled with 35 L of chlorinated
tap water. Two concrete stones were placed in each contain-
er to provide a basking area. The laboratory environment was
maintained at a temperature of 30.0
to 31.1
C. Water tem-
perature in each container was maintained at 25.5
to 26.6
Water in the containers was replaced every 48 hours with
fresh chlorinated tap water; a water filtration system was not
used. Each day, commercially available chow formulated for
was provided in each container.
Received June 30, 2006.
Accepted August 2, 2006.
From the Department of Veterinary Clinical Sciences, School of
Veterinary Medicine, Louisiana State University, Baton Rouge, LA
Supported by Fluker Farms.
Address correspondence to Dr. Acierno.
Effects of ultraviolet radiation
on 25-hydroxyvitamin D
synthesis in red-eared
slider turtles (
Trachemys scripta elegans
Mark J. Acierno, DVM; Mark A. Mitchell, DVM, PhD; Marlana K. Roundtree; Trevor T. Zachariah, DVM
Objective—To determine whether there are
increased concentrations of 25-hydroxyvitaminn D
red-eared slider turtles (
Trachemys scripta elegans
after exposure to UV radiation.
Animals—12 yearling turtles recently removed from
Procedures—Turtles were randomly allocated to 2
groups (6 turtles/group). An initial blood sample was
collected from all turtles for measurement of 25-
hydroxyvitamin D
concentrations. Turtles of 1 group
were then provided no supplemental lighting, whereas
turtles of the other group were exposed to full-spec-
trum coil bulbs at a distance of 22.86 cm. The UV-A and
UV-B radiation generated by the supplemental lighting
was measured by use of a radiometer-photometer at
weekly intervals. Measurements were collected 2.54
and 22.86 cm from the bulb surface. The study was
continued for a 4-week period. At the end of the study,
a second blood sample was collected from all turtles
for measurement of 25-hydroxyvitamin D
Results—Mean ± SD 25-hydroxyvitamin D
trations differed significantly between turtles provided
supplemental UV radiation (71.7 ± 46.9 nmol/L) and
those not provided UV radiation (31.4 ± 13.2 nmol/L).
Conclusions and Clinical Relevance—Appropriate
husbandry recommendations for raising and main-
taining red-eared slider turtles should include use of
sunlight that is unobstructed by UV-B filtering materi-
al or provision of an artificial source of UV-B radiation.
Am J Vet Res
06-06-0192r.qxp 11/15/2006 10:18 AM Page 2046
AJVR, Vol 67, No. 12, December 2006 2047
Experimental procedures—After the initial 7-day accli-
mation period, a blood sample (0.5 mL) was collected from
the subcarapacial sinus of each turtle (day 0). Blood samples
were stored in lithium heparin microtainers.
Blood samples
were centrifuged within 60 minutes after collection. Plasma
was harvested and frozen. Plasma samples were submitted on
frozen gel packs to a university laboratory
for measurement
of 25-hydroxyvitamin D
After collection of the initial blood sample, turtles were
allocated into 2 groups (6 turtles/group) by use of a random
number generator. Turtles of 1 group were not provided
supplemental lighting, whereas turtles of the other group
were provided with supplemental lighting. Lights
used to
provide supplemental lighting were positioned at a height
of 22.86 cm directly over the basking stones. Lighting was
provided for 12 continuous hours each day.
Radiation (UV-A and UV-B) generated by the coil bulbs
was measured by use of a radiometer-photometer.
Measurements were collected at a distance of 2.54 and
22.86 cm from the bulb surface. Amounts of UV-A and UV-
B radiation were measured in triplicate at each distance, and
the arithmetic mean value was calculated and used for sta-
tistical analysis. Measurements of UV-A and UV-B were also
collected at the surface of the basking stone for the turtles
that did not receive supplemental lighting. Amounts of UV-
A and UV-B were measured on a weekly basis at the same
time of day during each successive week, with the excep-
tion of the first measurement, which was recorded immedi-
ately after the lights were turned on.
The turtles were weighed weekly. Weight measurements
were rounded to the nearest 0.1 g. Weight measurements
were collected after the bulbs had been on for 4 hours.
The study was continued for 4 weeks. At the end of that
period, a second blood sample was collected (day 30) from
each turtle for use in measuring 25-hydroxyvitamin D
centrations. Collection of blood samples, processing, and
shipment to a university laboratory for testing were similar to
the techniques described for the blood samples obtained on
day 0.
Statistical analysis—Distribution of the data was evalu-
ated by use of the Shapiro-Wilk test. Mean, SD, minimum,
and maximum values were reported for data that had a nor-
mal distribution, whereas the median, 10th to 90th per-
centiles, minimum, and maximum values were reported for
data that did not have a normal distribution. Data that were
not normally distributed were logarithmically transformed
for parametric analysis.
A paired-sample t test was used to determine within-
subject differences throughout the study for 25-hydroxyvita-
min D
concentrations and body weight. An unpaired t test
was used to assess differences in 25-hydroxyvitamin D
centrations and body weight between turtles provided UV
radiation and those that did not receive UV radiation. A
repeated-measures ANOVA was used to assess the quantity of
UV-A and UV-B radiation generated at the bulb surface and
the surface of the basking stone during the 4-week study.
When differences were found, post hoc comparisons were
made by estimating the marginal means. A value of P 0.05
was used to determine significance. A commercially available
statistical program
was used to analyze the data.
Concentrations of 25-hydroxyvitamin D
significantly (P = 0.001) between days 0 and 30 for
both groups (Table 1). Mean ± SD concentrations of
25-hydroxyvitamin D
differed significantly between
turtles provided supplemental UV radiation (71.7 ±
46.9 nmol/L) and turtles that were not provided sup-
plemental UV radiation (31.4 ± 13.2 nmol/L).
Body weight did not differ significantly (P = 0.50)
between the 2 groups of turtles. Therefore, body
weights for both groups were pooled and evaluated
over time. Body weight increased significantly (P =
0.001) during the course of the study. At the beginning
of the study, mean ± SD body weight for the turtles was
115.9 ± 23.4 g (minimum, 88 g; maximum, 170 g). At
the end of the study, body weight of the turtles had
increased by 10% (mean, 128.6 ± 21.8 g; minimum,
102 g; and maximum, 174 g).
We detected significant differences in the amount
of UV-B radiation at the bulb surface (F = 20.9; P =
0.006) and surface of the basking stone (F = 11.9; P =
0.002) during the course of the study (Table 2). There
was also a significant (F = 89.8; P < 0.001) difference
in the amount of UV-A radiation at the bulb surface
during the course of the study (Table 3). However,
Table 1—Plasma concentrations of 25-hydroxyvitamin D
for 2 groups of red-eared slider turtles (6 tur-
tles/group) at the beginning (day 0) and end (day 30) of the study in which 1 group of turtles received
supplemental UV radiation and the other group was exposed to only ambient light.
SD Minimum Maximum
Sample Group (nmol/L) (nmol/L) (nmol/L)
Day 0 No UV radiation 11.2 4.3 6.0 16.0
Supplemental UV radiation 10.7 3.4 5.0 14.0
Day 30 No UV radiation 31.4 13.2* 15.0 44.0
Supplemental UV radiation 71.7 46.9*† 34.0 155.0
*Value differs significantly (
= 0.001) from value for the same group on day 0. †Value differs significantly
0.05) from the value for the other group on day 30.
Table 2—Amount of UV-B radiation measured at the bulb sur-
face and surface of the basking stone during the course of the
SD Minimum Maximum
Location Day (
Bulb* 0 686 109.4
495 803
7 488 67.5
400 564
14 414 67.3
309 489
21 426 58.4
348 489
Basking stone† 0 14.1 1.7
12.1 16.1
7 18.6 3.3
14.0 24.3
14 17.3 2.3
13.4 19.9
21 18.2 3.6
15.0 24.9
*Radiation was measured 2.54 cm from the bulb surface.
†Radiation was measured 22.86 cm from the bulb surface.
Day 0 = First day of the study.
Values with different superscript letters differ significantly
06-06-0192r.qxp 11/15/2006 10:18 AM Page 2047
there was not a significant (F = 0.4; P = 0.70) differ-
ence in UV-A radiation at the surface of the basking
stone during the study. The amount of UV-B (< 0.01
) and UV-A (< 10 W/cm
) radiation measured
at the surface of the basking stone for turtles provided
only ambient light (ie, no supplemental radiation) was
All vitamin D is ultimately the result of the photo-
synthetic conversion of 7-dehydrocholesterol to previt-
amin D
in the skin of vertebrates exposed to UV-B.
Previtamin D
is an unstable molecule that undergoes
temperature-dependent isomerization to become vita-
min D
Newly formed vitamin is transported to the
liver, where it is hydroxylated to form 25-hydroxyvita-
min D
This represents the storage form of the
hormone, which is bound to protein for systemic circu-
The kidneys are responsible for the final con-
version of 25-hydroxyvitamin D
to 1,25-dihydroxyvit-
amin D
, which is the active form of the hormone.
Vitamin D
can be obtained directly through expo-
sure of the skin to UV-B radiation (290 to 320 nm) or
through consumption of prey that has already per-
formed the biosynthesis. The need for appropriate
plasma concentrations of vitamin D
is so important
that the skin of some nocturnal species of lizards, such
as the Mediterranean house gecko (Hemidactylus turci-
cus), has developed the ability to synthesize the hor-
mone in minimal light conditions, whereas other
species can modify their basking to compensate for
variations in dietary amounts of vitamin D
Interestingly, animals vary in their capacity to photo-
synthesize or extract this important hormone from
their diet. Some carnivorous mammals, such as cats,
are unable to photosynthesize vitamin D and must rely
totally on dietary sources, whereas some lizards rely
primarily on photosynthesis to produce vitamin D.
In the study reported here, 25-hydroxyvitamin D
concentrations increased significantly in all turtles
from the time they were removed from aestivation until
the end of the study. Although we cannot eliminate
ambient UV-B radiation as a possible cause for this
increase, half of the turtles had exposure to only insub-
stantial amounts of UV-B radiation (< 0.01 W/cm
Therefore, absorption of vitamin D
from the diet is the
most likely explanation for the observed increase.
Turtles that were exposed to supplemental UV-B radia-
tion had significantly higher 25-hydroxyvitamin D
concentrations than the turtles that did not receive
supplemental lighting.
The information reported here reinforces results of
a study
of another species of freshwater turtle
(Emydura signata) in which it was reported that those
turtles were commonly observed basking, but their
body temperature was in thermoconformity with the
water. Considering the thermal conductivity of water,
compared with that of air, it seems logical that an
aquatic species would gain little thermal benefit from
basking for relatively short periods. Thus, it would
appear that in at least some freshwater turtles, sun-
seeking behavior is a strategy for vitamin D synthesis
rather than a thermoregulatory adaptation.
Body weight of all turtles increased significantly
from the time they were removed from aestivation until
the end of the study. There was no difference in body
weight between turtles exposed to supplemental UV-B
and turtles that did not receive supplemental lighting.
Vitamin D
is important in the development and main-
tenance of healthy bones. Because these turtles were all
from the same colony and had been housed outdoors,
it seems unlikely that measurable differences in body
weight from bone demineralization or changes in gen-
eral health would be detectable in such a short study
(ie, 4 weeks). Even had the study period been longer,
we would have needed to conduct a more sensitive
measure of bone density to detect weight attributable
to demineralization of bone.
The coil fluorescent bulbs used in the study were
the most current addition to the selection of full-spec-
trum lights available for reptiles. Historically, fluores-
cent tubes have been the most commonly used
Those bulbs provide adequate UV-B radiation
in the range of 290 to 320 nm.
In the experience of
one of the authors, the coil bulbs used in the study
reported here generated greater quantities of UV-B
radiation at the bulb surface and distances of 15 and
30 cm, compared with the amount generated by the
more common full-spectrum fluorescent tubes. It was
for this reason that the coil fluorescent bulbs were
selected for use in the study.
The bulbs produced 40% and 27% less UV-B and
UV-A radiation, respectively, at the bulb surface during
the course of the study. Investigators in another study
also found that the quantities of UV-B radiation pro-
duced by fluorescent tubes significantly decreased over
time. Interestingly, the amount of UV-A radiation at the
surface of the basking stone did not decrease during the
course of the study. One possibility is that the initial
measurements for the bulbs were obtained as soon as
they were energized, and they may not have had suffi-
cient time to generate maximum output. In our experi-
ence, these bulbs do not necessarily produce a maximal
quantity of radiation immediately after being turned on.
It is also possible that initial measurements at the sur-
face of the basking stone were conducted incorrectly.
However, the same 2 investigators (MJA and MKR)
measured the UV-A and UV-B radiation throughout the
study in an effort to minimize the chance of error. If
either scenario was true, then the difference at the bulb
surface would have been even greater.
2048 AJVR, Vol 67, No. 12, December 2006
Table 3—Amount of UV-A radiation measured at the bulb sur-
face and surface of the basking stone during the course of the
SD Minimum Maximum
Location Day (
Bulb* 0 3,463 248.3
3,160 3,800
7 2,595 160.6
2,340 2,750
14 2,438 258.0
2,160 2,910
21 2,318 104.2
2,180 2,470
Basking stone† 0 73.7 9.5 61.9 82.9
7 73.5 8.6 65.6 84.5
14 76.4 6.1 69.7 85.5
21 78.1 9.7 65.0 91.0
Table 2 for key.
06-06-0192r.qxp 11/15/2006 10:18 AM Page 2048
AJVR, Vol 67, No. 12, December 2006 2049
Currently, we are evaluating the long-term pro-
duction of UV-B and UV-A radiation by these bulbs to
determine their spectral characteristics and longevity.
Interestingly, UV-B radiation at the surface of the bask-
ing rock generated by the coil florescent tube was con-
sistent with UV-B radiation measured during overcast
conditions in early May in Louisiana. Red-eared slider
turtles have the potential for living long periods in cap-
tivity and are popular as pets. Therefore, it is important
to consider the effect of UV radiation on the human
caregivers. As newer, more powerful bulbs are devel-
oped, they may begin to pose health risks to humans.
To the authors’ knowledge, this risk has not yet been
The study reported here provides important new
information regarding the husbandry of red-eared slid-
er turtles. It would appear that the appropriate hus-
bandry recommendations for raising and maintaining
these aquatic turtles should include sunlight that is
unobstructed by UV-B filtering material or an artificial
source of UV-B radiation (290 to 320 nm) that is locat-
ed no more than 23 cm from the basking area.
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... Vit D is generally obtained through food that is rich in vit D or through UV radiation, such as sun exposure [25]. Many vertebrate species rely on sun exposure for health, as not all diets are rich in vit D, and studies have shown that supplemental UV radiation can help boost vit D levels in reptiles [35], including corn snakes (Elaphe guttata) [35] and red-eared sliders (Trachemys scripta elegans) [36]. Agamid and iguanid lizards exposed to natural sunlight also had significantly higher levels of vit D than those exposed only to artificial UV light and/or dietary vit D [37]. ...
... PCV values at intake/capture were highest in IRG turtles (range 24.5-42.5%) and lowest in VT+ turtles (range 5-27%), with VT− turtles intermediate (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39).5%) ( Figure 1). Even though VT− turtles had intermediate values, there was a significant difference between VT+ and both IRG and VT− turtles (p < 0.005). ...
... Studies of both mammals and reptiles show greater vitamin D levels when animals are exposed to sunlight. Dairy cows exposed to natural sunlight or artificial UVB light for 73 days had increased plasma vitamin D levels [54], for example, while red eared slider turtles provided UV supplementation had significantly higher plasma vitamin D levels after 30 days compared to individuals kept only in ambient light [36]. Corn snakes also showed higher plasma vitamin D levels when exposed to supplemental UV light [35], as did agamid and iguanid lizards exposed to natural sunlight vs. those exposed only to artificial lights indoors [37]. ...
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Green sea turtles (Chelonia mydas) are an endangered species, which as juveniles are prone to the debilitating disease green turtle fibropapillomatosis (FP). Previous work has shown an association between reduced immune function and FP. As vitamin D has been linked to immune function in numerous animals, the aim of this study was to compare vitamin D levels in green sea turtles with and without evident FP and determine if exposure to sunlight would influence vitamin D levels and other health parameters. Various health markers, including vitamin D, in turtles with and without evident tumors being treated at a rehabilitation facility in southeast Florida were compared to apparently healthy wild-caught juvenile green turtles. Turtles receiving treatment were housed in tanks exposed to higher or lower levels of sunlight for up to 6 months. Upon intake, tumored individuals had lower plasma vitamin D and ionized calcium levels and higher parathyroid hormone levels when compared to both wild-caught and rehabilitation turtles without evident tumors. Individuals exposed to greater sunlight showed greater increases in plasma vitamin D and a more successful recovery. The results suggest that increasing sun exposure in rehabilitation facilities may enhance health and recovery in green turtles with FP.
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Desert tortoise populations continue to decline throughout their range. Head-starting (the captive rearing of offspring to a size where they are presumably more likely to survive post-release) is being explored as a recovery tool for the species. Previous head-starting programs for the Mojave Desert Tortoise (Gopherus agassizii) have reared neonates exclusively outdoors. Here, we explore using a combination of indoor and outdoor rearing to maximize post-release success and rearing efficiency. We assigned 68 neonates (2016 cohort) to one of two treatments: Outdoor head-starting (HS; n = 38), where neonates were reared exclusively in outdoor predator proof enclosures, and Combination (Combo) HS (n = 30), where neonates were reared indoors for 1 y followed by outdoor rearing for 1 y. After 2 y of captive rearing, we released 24 Outdoor HS and 24 Combo HS juveniles in the Mojave National Preserve, California, USA, on 25 September 2018. We compared pre-release size, body condition, and shell hardness as well as first year post-release movement and survival between the treatment groups. Body condition was not significantly different between groups. Outdoor HS tortoises, however, were significantly smaller and had significantly softer shells than Combo HS tortoises. Released head-starts experienced 78.2% survival through their first year after release. Combo HS tortoises dispersed significantly shorter distances than Outdoor HS animals. Our findings that Combo HS animals were larger and had harder shells at release, and exhibited high survival but low dispersal following release, support the use of combination head-starting as a recovery tool for the Mojave Desert Tortoise.
Freshwater turtles are physiologically unique in their adaptations to life on both land and freshwater habitats. Appropriate interpretation of laboratory values specific to these species is important for both conservation efforts in free-ranging populations and in captive populations, especially because these animals become increasingly popular as pets. Although normal physiology has been well characterized, understanding of clinicopathologic changes in response to disease processes in freshwater chelonian species is relatively limited. This article reviews the current knowledge of hematology, plasma biochemistry, and urinalysis specific to freshwater turtles, with correlates to other chelonian species when specific data are unavailable.
Vitamin D is an essential hormone that can be acquired via the diet, exposure to ultraviolet B (UVB) radiation, or a combination of both. Studies in reptiles suggest that the acquisition of vitamin D can vary between species; thus, species-specific evidence-based research should be pursued to develop appropriate husbandry recommendations. The objective of this study was to determine whether artificial UVB could be used to increase circulating 25-hydroxyvitamin D3 (25-OHD3) concentrations in juvenile Blanding’s turtles (Emydoidea blandingii). Sixteen juvenile turtles from an on-going headstart program at the DuPage County Forest Preservation District (Wheaton, IL, USA) were used for this study. The turtles were randomly divided into two groups of eight using a random number generator. The treatment group was exposed to three compact UVB fluorescent bulbs (23 watts) 12 hours/day for 6 months, while the control group was not provided supplemental UVB lighting. Bulbs were placed 15.2 cm (6 inches) from the water surface. A radiometer was used to measure UVB radiation 15.2 cm from the bulb surface on days 0 and 180. Blood samples were collected at a single time point (day 180) to measure 25-OHD3 concentrations. There was a significant difference (P < 0.001) in plasma 25-OHD3 concentrations between groups, with 25-OHD3 concentrations being 5.5 times higher in the UVB group compared with the controls. Based on the results of this study, the authors recommend exposing juvenile Blanding’s turtles to artificial UVB as part of their standard care.
Over a century of ecophysiological studies on lizards have perpetuated the assumption that basking and shuttling movements between sun and shade function solely for temperature regulation. However, these behaviors also modulate exposure to ultraviolet (UV) wavelengths that are essential for maintaining physiological homeostasis as well as ensuring proper growth and development and enhancing long‐term fitness. An alternative hypothesis is that lizards also actively regulate their UV exposure. In this scenario, UV needs may even override temperature needs (or vice versa), generating asymmetries in the ability of a lizard to regulate both conditions equally. We test this hypothesis using field and laboratory data collected on adult Sceloporus undulatus. We found that S. undulatus actively regulate UV exposure and prioritize UV over temperature, favoring body temperatures much higher than preferred values to sustain preferred UV exposure. In stark contrast, temperature had no reciprocal impact on UV regulation behavior. Our field data support these patterns, suggesting that lizards may even seek out hotter environments despite thermal costs to enhance UV exposure. We conclude that S. undulatus actively regulate for UV as well as temperature. Unfortunately, outside of zoos and private hobbyists, appreciation of the importance of UV for ectotherm survival and reproductive success has been minimal. Addressing this deficit will therefore be vital to improve our understanding of the factors shaping the evolution of ectotherm photoregulation behavior in nature.
Lymph contamination of peripheral blood samples is common in reptile species due to a close association of the lymphatic and vascular systems. Grossly lymph-diluted samples are generally discarded due to potential effects on hematologic and biochemical parameters. Differences in biochemistry values from different sample sites in chelonians are often attributed to lymph contamination. Previous studies have evaluated blood-lymph mixtures but provide limited information since the proportion of lymph is unknown. Differences in biochemistry values of pure lymph compared to plasma are unknown in chelonian species. Paired plasma samples collected from the jugular vein and lymph samples collected from the dorsal lymphatic ring adjacent to the subcarapacial plexus were collected from 11 (6 females, 5 males) Krefft’s river turtles ( Emydura macquarii krefftii ) for comparison of biochemical analytes. No statistically significant differences were found between lymph and plasma samples for chloride, glucose, alanine aminotransferase, aspartate aminotransferase, creatinine kinase, urea nitrogen, and total bilirubin. Statistically significant (P ≤ 0.05) differences were found between lymph and plasma samples for gamma-glutamyltransferase (GGT), total protein, globulin, and uric acid. Sex and sample differences were statistically significant for sodium, potassium, calcium, phosphorous, magnesium, lactate dehydrogenase (LDH), albumin, and triglycerides, while significant sex differences only were found for alkaline phosphatase, cholesterol, and iron. Severe lymph dilution (1:1 with plasma) may cause clinically significant decreases of potassium, total protein, globulin, and LDH, and increases of GGT and uric acid in both sexes, as well as clinically significant decreases of calcium and triglycerides in female Krefft’s river turtles.
Basking is an essential behavior for thermoregulation in turtles. Although basking is widely studied, this behavior varies among populations, habitats, and microclimates. In this study, we evaluated the effectiveness of game cameras for studying basking activity of Rio Grande Cooter (Pseudemys gorzugi), a New Mexico state-threatened species. From August 2018 to July 2019, images were taken hourly from 07:00 to 19:00 at 3 locations along or near the Black River, New Mexico. We used a generalized linear mixed-effect model to find associations between basking patterns and environmental variables. The species was active year-round, with the greatest number of basking turtles in spring. Basking activity was significantly correlated with water temperature, season, light intensity, difference between water and air temperatures, and time of day. Game cameras were effective for long-term monitoring of turtles in this study. This method was noninvasive and created low disturbances while providing high-resolution data. Overall, this study provides a deeper understanding of the basking habits of P. gorzugi as well as its activity periods across seasons, which can also aid in determining an appropriate time for conducting visual surveys of the species in southeastern New Mexico.
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Vitamin D is an important regulator of calcium and phosphorus homeostasis in animals. It can be acquired from the diet or synthesised de novo when skin is exposed to UVb. Vitamin D deficiency can lead to a complex of diseases collectively called metabolic bone disease (MBD). Diurnal lizards without access to UVb are prone to develop vitamin D deficiency, even when dietary vitamin D3 is provided. A trial was conducted to determine whether juvenile nocturnal lizards require access to UVb to prevent vitamin D deficiency. All leopard geckos (Eublepharis macularius) were supplemented with dietary vitamin D3. One group was exposed to low level UVb radiation (33-51 μW/cm2) from hatching until 6 months of age and a second group remained unexposed. Animals were fed ad libitum and their growth and weight gain compared with non-exposed controls. At the end of the trial, blood samples were analysed for vitamin D3 metabolites. The concentration of the vitamin D3 metabolite, 25(OH)D3, was higher in UVb exposed animals (61 ± 20 vs. 38 ± 8 nmol/L), confirming cutaneous synthesis with UVb exposure. Growth and weight gain were similar in both groups, and this, together with the absence of clinical symptoms, suggests that dietary vitamin D3 alone can meet the vitamin D requirements for growth of this nocturnal gecko, during the first six months of life. It remains to be investigated whether the higher vitamin D metabolite levels holds other health benefits for this species, such as improved bone density or immune response.
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The abilities of freshwater turtles to control their body temperatures by behavioural means have implications for activity, food ingestion and digestion, growth, reproduction and potential responses to climate change. I compared various forms of basking in nature, and responses to aquatic and aerial photothermal gradients in the laboratory, among three species of Australian chelid turtles: Chelodina expansa, C. longicollis and Emydura macquarii. Proclivity for behavioural thermoregulation varied substantially among these species, being highest in C. longicollis and lowest in C. expansa. However, C. expansa had a thermophilic response to feeding. For C. longicollis and E. macquarii, behavioural thermoregulation may enhance colonisation of more southerly latitudes or higher elevations as climatic warming proceeds. However, increasing air temperatures may pose a hazard to turtles dispersing or sheltering terrestrially (for example, when water bodies dry during drought). C. longicollis appears the best placed of the three species to avoid this hazard through its abilities to thermoregulate behaviourally and to aestivate in terrestrial microenvironments that are buffered against temperature extremes.
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The opportunity and ability to photobiosynthesize vitamin D3 by exposing skin to ultraviolet-B (UVB) irradiation from the sun was compared using the nocturnal/crepuscular Mediterranean House Gecko Hemidactylus turcicus and the diurnal Texas Spiny Lizard Sceloporus olivaceous. Texas spiny lizards had a greater opportunity for photobiosynthetic production of vitamin D3 than geckos. This was revealed by vitamin D3 photoproduct production in models (ampoules containing an alcohol solution of vitamin D3 precursor) placed at locations inhabited by free-living lizards at similar times of occupancy. Alternatively, geckos seemed able to maximize their limited photobiosynthetic opportunity with a higher rate of conversion of provitamin D3 to photoproducts. This was revealed by photoproduct conversion in patches of lizard skin exposed to ultraviolet lamps in the laboratory. Stomach-content analysis showed the spiny lizards to have dietary sources of vitamin D3, the geckos may or may not. This is the first documentation that mostly nocturnal geckos may rely on photobiosynthesis of vitamin D3 and that they might have a more sensitive mechanism than diurnal lizards to compensate for their limited exposure to natural UVB radiation. Future studies should investigate sexual, seasonal, age, and species differences in photobiosynthetic opportunity and ability.
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The apparent plasma concentration of vitamin D binding protein (DBP) in an iguanian lizard, Pogona barbata, and the affinity of this protein for 25-hydroxyvitamin D3 (25(OH)D3), 25-hydroxyvitamin D2 (25(OH)D2), and 1,25-dihydroxyvitamin D3 (1,25(OH)D3) was found to resemble more closely that of the domestic hen than that of the human. The characteristics of Pogona DBP, the pattern of vitamin D metabolites derived from injected radioactive vitamin D3 and the plasma concentrations of endogenous 25-hydroxyvitamin D (25(OH)D) in a range of iguanian lizards have been examined. The findings suggest that 25-hydroxyvitamin D (25(OH)D) is the major metabolite of vitamin D, and that it may represent the storage form of vitamin D in these species in the same way as in mammals. High concentrations of vitamin D within iguanian embryos and egg yolks suggest a role for this compound in embryogenesis in these species, and perhaps indicates that there is a mechanism for vitamin D delivery to eggs comparable to that found in the domestic chicken.
Vitamin D is scarce in most foods, and technically is not a nutrient, but a hormone. Our ancestors obtained sufficient exposure of their skin to solar ultraviolet radiation B, 390-320 nm, (UV-B), the wavelengths that permit conversion of pre-vitamin D to vitamin D, to satisfy their requirements for vitamin D. In the United States, milk is fortified with vitamin D to assure adequate intakes, particularly since many believe that avoidance of the sun is an important safeguard against skin cancer. While estimates of dietary requirements for humans appear rational, we know very little about effective and safe levels of vitamin D for reptiles (1). This is a critical issue since both deficiency and toxicity can produce abnormal calcium and phosphorus metabolic responses. Long term feeding of vitamin D at 4,000 IU per kg of diet will produce signs of toxicity in some domestic animals (2).
We measured body temperatures of free-ranging Brisbane River Turtles, Emydura signata with radiotelemetry. These and other species of freshwater turtle are commonly observed "basking" on logs or other elevated sites, a behavior which is usually interpreted as thermoregulatory. However, body temperatures of eight E. signata monitored for more than 112 turtle days in winter, spring, and summer showed a striking thermoconformity with the water and provided no data showing that this species routinely elevates its body temperature above water temperature. The biological significance of basking is obscure in this population of E. signata, and the study highlights the need for direct measurements of body temperature in freeranging individuals of other freshwater turtle species.
A variety of lamps are used in animal husbandry, but data with respect to ultraviolet irradiances from these lamps, which may be important for alleviating or preventing metabolic bone disease, are generally unavailable. This paper reports irradiances from representative lamps as well as transmission and reflective properties of various materials.
To assess the importance of diet and light for indoor maintenance, hatchling panther chameleons were reared for 1 year on crickets fed diets that differed in vitamin concentrations and in different light environments. Dietary transfer of vitamins from the cricket diet to the lizards via the crickets was quantified, as was UV irradiance. There was a statistically significant dietary enhancement of growth by both vitamins on males. UV-A irradiation significantly suppressed growth of females. Low vitamin A shortened life span and resulted in a number of gross and histological pathologies. Hepatocellular lipidosis, indicating a possible toxicosis, occurred with all diets and light treatments. Higher vitamin A resulted in mild soft-tissue mineralization, and high vitamin D shortened the life span of females. Low vitamin A drastically reduced reproduction in both sexes. The intermediate levels of dietary vitamins resulted in the best production of viable eggs by females. However, without high UV-B irradiation, all viable eggs died at term and contained different vitamin levels than hatching eggs from wild-caught females. Baseline levels of egg calcium are given for hatching eggs from wild-caught females. Modifications in current husbandry procedures are recommended. © 1996 Wiley-Liss, Inc.
Having previously documented experimentally the need for ultraviolet B (UVB) irradiation (290–315 nm) in the light environment of captive female panther chameleons (Furcifer pardalis) to ensure hatching success of their eggs, we investigated optimal UVB irradiation levels. From 1996–1998 28 hatchling female panther chameleons were raised to maturity and bred (using vitamin and mineral-fortified insect diets low in vitamin D) in nine different artificial UVB light environments. Seven of the environments included long (12 hr/day) low irradia-tion exposures ranging from 1.7 to 22 μW/cm2 UVB, with a corresponding conversion of provitamin D3 to photoproducts in in vitro models of 0.18 to 1.52% in 2 hr. Two environments included short (0.5 and 1.0 hr/day), high irradiation exposures of 55 and 49 μW/cm2 UVB, respectively, with a corres-ponding conversion of provitamin D3 to photoproducts in in vitro models of 8.3% to 14.6% in the respective 0.5- and 1.0-hr time periods. Females raised with the mid-level long/low exposures (5–15 μW/cm2 UVB; 0.52–1.32% conversion to photoproducts in in vitro models) produced viable eggs with a significantly higher percentage of hatching compared to those with the extreme (highest or lowest) long/low exposures. Those raised with the short-/high-exposure environments produced viable eggs with a generally high percentage of hatching, but success was variable. The results and techniques for light quality assessment are interpreted, with recommendations for practical application by the herpetoculturist desiring to successfully breed panther chameleons in captivity. Zoo Biol 21:525–537, 2002. © 2002 Wiley-Liss, Inc.
Sunlight has long been recognized as a major provider of vitamin D for humans; radiation in the UVB (290-315 nm) portion of the solar spectrum photolyzes 7-dehydrocholesterol in the skin to previtamin D3, which, in turn, is converted by a thermal process to vitamin D3. Latitude and season affect both the quantity and quality of solar radiation reaching the earth's surface, especially in the UVB region of the spectrum, but little is known about how these influence the ability of sunlight to synthesize vitamin D3 in skin. A model has been developed to evaluate the effect of seasonal and latitudinal changes on the potential of sunlight to initiate cutaneous production of vitamin D3. Human skin or [3 alpha-3H]7-dehydrocholesterol exposed to sunlight on cloudless days in Boston (42.2 degrees N) from November through February produced no previtamin D3. In Edmonton (52 degrees N) this ineffective winter period extended from October through March. Further south (34 degrees N and 18 degrees N), sunlight effectively photoconverted 7-dehydrocholesterol to previtamin D3 in the middle of winter. These results quantify the dramatic influence of changes in solar UVB radiation on cutaneous vitamin D3 synthesis and indicate the latitudinal increase in the length of the "vitamin D winter" during which dietary supplementation of the vitamin may be advisable.