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A novel technique for capturing arboreal geckos

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358 Herpetological Review 35(4), 2004
Herpetological Review, 2004, 35(4), 358–359.
© 2004 by Society for the Study of Amphibians and Reptiles
A Novel Technique for Capturing Arboreal
Geckos
NICHOLAS C. COLE
School of Biological Sciences, University of Bristol
Woodland Road, Bristol BS8 1UG, United Kingdom
email: nik.cole@bristol.ac.uk
When conducting research on lizards it is often necessary to
capture individuals unharmed. Popular methods for the capture of
arboreal lizards include hand capture, noosing, or using rubber
bands as projectiles (Simmons 1987), chasing lizards into mesh
barriers (Patterson 1998), attracting individuals to baited traps
(Durden et al. 1995; Zani and Vitt 1995), or fishing for them with
baited lines (Krysko 2000; Strong et al. 1993). Other methods in-
clude using wire hooks to pull lizards from refugia (Bedford et al.
1995), glue boards for passive capture (Bauer and Sadlier 1992),
or sticky poles for active capture (Durtsche 1996).
Any capture technique has inherent problems (Krysko 2000),
but for the capture of small, skittish, and fast-moving lizard spe-
cies, such as geckos that perch high on building walls, the tech-
niques listed above make capture without harm extremely diffi-
cult and, in many cases, inappropriate. The most suitable of these
techniques is noosing, but often the lizard flees at the sight of the
approaching pole, evades the noose, or bites the noose pulling it
closed (pers. obs.). Furthermore, the thread of the noose has to be
thin, making it difficult to see more than 3-m away and difficult to
keep steady. Using a baited line poses similar problems to using a
noose.
To overcome the problems of safely catching arboreal geckos
from buildings, I describe a novel technique I developed to cap-
ture native and introduced geckos in Mauritius using a laser pointer.
All geckos rely on their vision to capture predominantly insec-
tivorous prey and are, in general, opportunistic feeders, attacking
any small moving object within range. A small dot projected onto
a wall from a laser pointer within view of a gecko will entice the
lizard to give chase and repeatedly lunge and bite at the dot. The
dot can then be moved down the wall to a point permitting cap-
ture, generally at chest height, close to an awaiting hand. To keep
the gecko moving it is necessary to keep the laser dot within 5–10
cm of the gecko’s head.
Lasers are grouped into five
classes (1, 2, 3A, 3B, and 4), the
higher the class the greater risk of
laser radiation hazard. Most
commercially available laser point-
ers belong to Class 1 or 2. The output
power of a Class 1 laser is such that
exposure of the eye to the beam will
not cause damage and is, therefore,
considered eye safe. The output
power of a Class 2 laser is higher and
prolonged eye exposure is potentially
harmful, although a person’s natural
involuntary response, such as the
blink reflex and/or head aversion is
quicker than the maximum permissible exposure time, therefore
avoiding damage to the eye. The International Electrotechnical
Commission (IEC 60825–1 1993) and British Standards (BS EN
60825–1 1994) state that only Class 1 or 2 devices should be used
in unsupervised areas. Of course, when using any type of laser
pointer, do not shine the laser beam into the eyes of any person or
animal. The risk of shining the beam of the laser into the eyes of a
gecko is easily avoided by continually moving the laser away from
the target animal. Catching geckos from reflective surfaces, such
as glass windows, should be avoided. Researchers, should consult
regional laws and regulations before undertaking fieldwork using
laser pointers because some countries have laws associated with
possession and use of laser pointers.
The efficiency of the technique is illustrated for four species of
nocturnal gecko and the daytime capture of two diurnal species
(Table 1). The laser pointer was only used for geckos that could
not be caught by noose or by hand. Individual geckos were not
captured more than once for this trial. The utility of this method,
therefore, is untested for experimental designs requiring multiple
captures of the same individual. More than 90% of all geckos pur-
sued the laser dot and almost 80% of these were brought to a point
of capture. Five geckos were so intent on eating the laser dot that
they chased the dot down onto the ground (up to 11 m) and two
were coaxed onto the palm of my hand. Of the 19 geckos that
were not brought to a point of capture, seven showed no response
to the laser dot, one ran off, six terminated their pursuit after chas-
ing the laser dot (one after pursuing it for 8 m), and five either
encountered and ate an insect or were chased off by another gecko
whilst following the laser dot.
Nocturnal geckos responded similarly in chasing the laser dot
over unlit (51%) and lit (49%) walls and over smooth (cemented/
bricked [58%)]) and rough (old stone [42%]) walls. All diurnal
geckos were found on shaded walls. It is doubtful whether geckos
would be able to see the laser dot in full sunlight. Eighty six per-
cent of diurnal geckos were found on smooth surfaces, so it is
difficult to determine whether wall texture had an effect on effi-
ciency of laser use.
This technique is quick to use, inexpensive, requires minimal
equipment, and aids in the capture of individuals from high, un-
reachable places without harm. The use of the laser pointer has
also been successful in enticing adult Phelsuma ornata down the
trunks of coconut trees (data not included here), indicating that its
use may not be restricted to relatively flat surfaces, such as walls.
TABLE 1. Number of each lizard species indicating the percentage of adults (rounded to nearest whole
digit), the efficiencies of the laser technique, and distances they moved.
Species N Geckos Brought to Mean distance (m)
chasing laser hand capture moved by responsive
dot (%) (%) geckos (SD, maximum)
Gehyra mutilata 97878 4.3 (1.1, 6)
Hemidactylus brookii 7 100 86 6.1 (2.3, 9)
Hemidactylus frenatus 58 97 85 4.4 (2.2, 11)
Hemiphyllodactylus typus 36733 3.5 (0.7, 4)
Phelsuma cepediana 36767 3.5 (0.7, 4)
Phelsuma ornata 14 86 71 3.3 (1.7, 6)
Total or Mean (%) 94 92 80 4.3 (2.1, 11)
Herpetological Review 35(4), 2004 359
This method is also likely useful in facilitating the capture of other
small insectivorous lizards. Another potential use could be in so-
cial experiments wherein an individual is enticed into the territory
of another to test behavioral interactions.
Acknowledgments.—This technique was developed under a NERC grant
NER/S/A/2001/05996 and a grant from the Zoological Society of Wales.
I thank S. Harris and C. Austin for their comments and improvements of
the manuscript.
LITERATURE CITED
BAUER, A. M., AND R. A. SADLIER. 1992. The use of mouse glue traps to
capture lizards. Herpetol. Rev. 23:112–113.
BEDFORD, G. S., K. CHRISTIAN, AND B. BARRETTE. 1995. A method for catch-
ing lizards in trees and rock crevices. Herpetol. Rev. 26:21–22.
BS EN 60825–1. 1994. Safety of laser products Part 1. Equipment classi-
fication, requirements and users guide. British Standards Instit. Lon-
don.
DURDEN, L. A., E. M. DOTSON, AND G. N. VOGEL. 1995. Two efficient tech-
niques for catching skinks. Herpetol. Rev. 26:137.
DURTSCHE, R. D. 1996. A capture technique for small, smooth–scaled liz-
ards. Herpetol. Rev. 27:12–13.
IEC 60825–1. 1993 Safety of laser products Part 1. Equipment classifica-
tion, requirements and users guide. International Electrotechnical
Commission, Geneva.
KRYSKO, K. L. 2000. A fishing technique for collecting the introduced
knight anole (Anolis equestris) in southern Florida. Carib. J. Sci. 36:162.
PATTERSON, A. 1998. A new capture technique for arboreal lizards. Herpetol.
Rev. 29:159.
SIMMONS, J. E. 1987. Herpetological collecting and collections manage-
ment. SSAR Herpetol. Circ. 16.
STRONG, D., B. LEATHERMAN, AND B. H. BRATTSTROM. 1993. Two new simple
methods for catching small fast lizards. Herpetol. Rev. 24:22–23.
ZANI, P. A., AND L. J. VITT. 1995. Techniques for capturing arboreal liz-
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Herpetological Review, 2004, 35(4), 359–361.
© 2004 by Society for the Study of Amphibians and Reptiles
A New Method for Preparing Preserved
Hemipenes of Lizards for Scanning Electron
Microscopy
AMANDA C. TODD
and
JAN C. MCKENZIE
School of Biological Sciences, University of Canterbury
PB 4800, Christchurch, New Zealand
e-mail (ACT): amanda_todd@hotmail.com
e-mail (JCM): jan.mckenzie@canterbury.ac.nz
Lizard hemipenis morphology has a long history of use in tax-
onomy (e.g., Arnold 1986a, b; Branch 1982; Cope 1895, 1896). In
other taxa the morphology of intromittent organs has also pro-
vided valuable insight into the mating strategies of a species
(Arnqvist 1997; Arnqvist et al. 1997; Dixson 1987; Eberhard 1985;
Patterson and Thaeler 1982). Thus, detailed studies of hemipenis
morphology can be useful in a number of research fields.
Investigations of hemipenis morphology are best made on freshly
prepared material, as this minimizes the potential for artifacts and
allows the natural shape of the organ to be studied. Unfortunately,
fresh material is not always readily available and researchers of-
ten must rely on material from museum specimens.
Squamate hemipenes are particularly difficult to study once pre-
served, as they lie in an inverted state within the base of the tail
when not erect. Consequently, to observe their structure and sur-
face features, it is necessary to evert these organs. This is best
done at the time of preservation because fixation tends to harden
tissue, making it difficult to evert fixed hemipenes without caus-
ing damage to their structure. As a result, it is common for re-
searchers to dissect inverted organs of preserved specimens in situ
to investigate their surface features (e.g., Arnold 1973; 1986a;
Böhme 1988; Dowling and Savage 1960). The disadvantage of
this method is that it provides little insight into the overall struc-
ture of the everted organ.
More recently, Pesantes (1994) described a method for soften-
ing fixed snake hemipenes by soaking the material in a 2% solu-
tion of potassium hydroxide (KOH) for 3 d. We tested this tech-
nique on eight species of New Zealand geckos but found that it
led to tissue damage. In this paper we report these results and
describe a new technique for softening fixed hemipenes that is
easy to use and causes little tissue damage.
As part of a comparative study on interspecific variation in
hemipenis morphology of New Zealand geckos (Gekkonidae), we
initially followed Pesantes (1994) method to soften the inverted
hemipenes of 16 museum specimens belonging to eight gecko
species that had been fixed in formalin. The condition of the fixed
specimens was compared with the hemipenes of six Hoplodactylus
maculatus that had been preserved in ethanol and did not require
any treatment prior to eversion because the hemipenial tissue had
remained soft and pliable.
The preparation history of the 16 museum specimens used in
our study was uncertain, but all had been fixed in formalin (con-
centration and duration unknown) and stored in 70% ethanol. The
specimens had been stored for 19–35 yr. Hemipenes were first
dissected in their entirety from the base of the tail (following Arnold
1986a). Samples were rehydrated from 70% ethanol to distilled
water in decreasing concentrations of ethanol (50 and 30%), by
soaking the tissues for a minimum of 1 h at each concentration.
The hemipenes were then softened using KOH (Pesantes 1994).
We found that samples (N = 6) that had been soaked in a 2% solu-
tion of KOH for 3 d either partially or totally disintegrated. There-
fore, we modified this method and obtained best results when the
hemipenes were soaked in a 1% solution of KOH for 5–11 h. Fol-
lowing softening, hemipenes were rinsed in 0.05N HCl for 10 min
and soaked overnight in distilled water. Specimens were then
everted in distilled water using round-tipped forceps and a blunt
probe to push the lobes inside out. It is usual for researchers to
inflate everted hemipenes to obtain maximal turgidity (e.g., Böhme
1988; Glaw et al. 1999; Myers and Cadle 2003; Zaher and Prudente
2003). However, the degree of inflation that naturally occurs is
unknown and it is thought that organs are often over-inflated
(Arnold 1986a). In addition, it is difficult to standardize the amount
that an organ is inflated. Consequently, for interspecific compari-
sons in which the surface features rather than the size of the organ
are of primary interest, it is preferable to avoid this procedure if
possible. Because the hemipenes of the species studied were very
small, the organs could be fully everted with relative ease, allow-
ing the surface features to be observed without inflation.
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