Notes on the ecology and natural history of the rarely recorded gekkonid lizard Heteronotia binoei in the Great Victoria Desert of Western Australia

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by  Eric R Pianka

NOTES ON THE ECOLOGY AND NATURAL HISTORY OF
THE RARELY RECORDED GEKKONID LIZARD
HETERONOTIA BINOEI IN THE GREAT VICTORIA
DESERT OF WESTERN AUSTRALIA
By ERIC R. PIANKA
Integrative Biology,
University of Texas at Austin
Austin, Texas 78712 USA
Email: [email protected]
ABSTRACT
Ecological data on the uncommonly encountered terrestrial
gecko Heteronotia binoei are presented and discussed.
Although Heteronotia is widespread in Australia occurring
in many different habitats, it is rarely found in semi-
pristine desert habitats. Heteronotia is composed of a
complex of both sexual and asexual populations which
may help explain its rarity. Sex ratio is biased towards
females. Heteronotia exploit burrows of other animals for
shelter and daytime retreats. Compared to other species of
desert lizards, Heteronotia is a dietary generalist with a
relatively broad dietary niche. These geckos reproduce in
the Austral spring and have fixed clutch sizes of two eggs.
Relative clutch mass averaged 9.9%.
INTRODUCTION Heideman 1993). Asexuality
appears to have arisen multiple
Heteronotia binoei is widespread
times: both bisexual and uni¬
in Australia (Cogger 1992) and
sexual forms can occur in
like most geckos, Heteronotia is
sympatry (Fujita et al. 2007),
nocturnal, but it can often be
where they hybridize (Strasburg
found in diurnal retreats such as
and Kearney 2005). A population
under objects in rubbish tips (the
of this gecko in the Pilliga scrub
first stop for many herpe¬
in New South Wales was studied
tologists). However, it is seldom
by mark and recapture by
found in semi-pristine outback
Bustard (1968) who found the
desert habitats (Pianka 2014).
geckos below bark at the base of
This gecko is a species complex dead trees or stumps. He reported
consisting of both sexual and data on movements, growth, tail
parthenogenetic populations loss and regeneration as well as
(Fujita and Moritz 2009, Moritz on diet.
1983, 1991a, 1991b, Moritz and
120
METHODS whether eggs were ovarian or
oviductal was noted [some of
During 11 separate expeditions to
these data were summarized in
the Great Victoria Desert (GVD)
appendices in Pianka (1986)].
of Western Australia from 1966
Niche breadths were calculated
through 2008, my assistants and 1
using the inverse of Simpson’s
spent 41 months (1256 days) in
(1949) index of diversity [D = 1/ Ej?.2]
the field primarily during
where p. is the proportion of
Austral springs collecting and
resource state i.
studying lizards (Pianka 1969a,b,
1982,1986,1994, 1996; Pianka and
Goodyear 2012). Extensive data
RESULTS
were gathered at ten major study
areas in the GVD (for exact Sex Ratios and Presence of Males.
locations, see Pianka 1986 and Among the 25 adult individuals
Pianka and Goodyear 2012) as collected on the 8 study areas
well as at other non-study sites with Heteronotia, six males were
nearby. Lizards were collected by present at four of the eight areas
any means possible using a wide (B 3 , E 1, N 1, and R 1) but only
variety of different techniques females were found at the other
including turning over rubbish four study areas (A 6, G 2, L 3, and
and fallen logs, exhuming, grab¬ Y 3) (numbers represent number
bing, shooting, eyeshine, body of individuals of a given sex).
shine and pit trapping. Out of a Four other females were found
total of more than 20,000 lizards, on sites with males. Thus overall
only 66 individual Heteronotia sex ratio on the eight study areas
binoei were encountered, 13 of is 6/25 or 0.24. Samples are too
which were juveniles. This small to argue that no sexual
species was found at 8 of the 10 forms were present on the four
study areas and might well be sites without males. Among 28
present on the two other areas other adult specimens collected
but was not encountered due to incidentally on 15 non-study
small sample sizes. sites, six other males were also
found, a sex ratio of 6/28 or
We recorded air and body
0.214. Combining samples yields a
temperatures, times of activity,
significantly female-biased sex
microhabitat, fresh snout-vent
ratio of 12/ 53 = 0.226.
length (SVL), tail length, and
weight for as many lizards as Habitat and Microhabitats.
possible. Stomach contents were Heteronotia exploit burrows of
identified and prey volumes other animals for shelter and
estimated for all lizards collected. daytime retreats. They are some¬
Reproductive condition was also times found while exhuming
recorded: for males, lengths of burrows of Liopholis (formerly
testes were measured; for females, Egernia) striata. They also dig
egg sizes were measured and their own small burrows off to
numbers were counted, and the sides of larger burrows such
121
as those dug by monitor lizards four were in litter beneath
or rabbit warrens. Of 66 geckos, Marble Gum trees.
all but two were found on desert
Thermal Relations. Like all
flats and sandplains, one was
nocturnal geckos, Heteronotia are
caught at the base/slope of a
thermoconformers, with body
sandridge and another was
temperatures positively corre¬
captured on a sandridge crest. Six
lated with ambient air tempera¬
individuals were dug up in
tures (Figure 1). No statistical
various burrows mostly those
thermal difference exists be¬
dug by Liopholis. Of 24 indi¬
tween active geckos versus those
viduals found active at night,
found in diurnal retreats. Body
one was at the mouth of such a
temperatures of these geckos
burrow, two were found emerg¬
tend to be slightly above ambi¬
ing at dusk from the mouth of a
ent temperature especially when
rabbit warren, two were in hol¬
they are cold.
low termite mounds, one was
about 7 cm above ground at the Diet. Heteronotia are dietary
base of a termite mound, one was generalists, consuming a wide
60 cm above ground in a rock variety of arthropods, especially
crevice, nine were out in the spiders, grasshoppers and crickets
open, two were close to spinifex (Table 1). Based on these data,
tussocks, two near bushes, and dietary niche breadth is 7.72.
Figure 1. Body temperatures plotted against ambient air temperature for 24
Heteronotia. Circles are active geckos at night whereas squares are those in diurnal
retreats. The line represents body temperature equal to ambient air temperature.
122
Table 1. Summary of stomach contents of 66 Heteronotia.
Number Volume Proportion
Centipedes 1 0.05 0.020
Spiders 21 0.69 0.282
Scorpions 1 0.01 0.001
Ants 5 0.09 0.037
Wasps 1 0.01 0.004
Locustids 6 0.36 0.147
Thysanurans 2 0.02 0.008
Roaches 1 0.17 0.069
Mantids/ Phasmids 2 0.05 0.020
Beetles 6 0.11 0.045
Termites 42 0.13 0.053
Hemipterans 9 0.13 0.053
Lepidopterans 2 0.14 0.057
Larvae 5 0.09 0.037
Other Insects 8 0.14 0.057
Vertebrates 4 0.18 0.074
Vegetation 1 0.04 0.016
Other Unidentified 1 0.05 0.02
Totals 119 2.46 1.00
Reproduction. Ten females had at 5 sites and only in very small
either enlarged yolked ovarian numbers at other sites where this
eggs or shelled eggs in their gecko was present. Only 19
oviducts from September to geckos were collected at ten
January. All had clutches of two study areas over the course of
eggs. Relative clutch mass (egg two years of field work. I won¬
volume over female fresh body dered how it could be a dietary
weight) averaged 9.9% for three generalist and occur at most sites
females with shelled eggs in their but still be so uncommon. Craig
oviducts. Average snout vent Moritz’s discovery of partheno-
length (SVL) of gravid females is genetic forms offered an answer
44.1 mm. Average SVL of 12 adult to this dilemma: an all female
males is 46 mm. unisexual does not require males
and females could persist at near
vanishingly low densities. 1
DISCUSSION remain baffled about how this
rare gecko manages to disperse so
When I assembled data for my
effectively across the vast desert
1986 book, 1 was puzzled by the
landscape.
rarity of Heteronotia — this
species was present on 8 of my 10 Extensive pit trapping from 1989
study areas but only as singletons to 2008 (over 62,000 pit trap
123
days) at 3 study sites yielded only Texas at Austin, the Denton A.
22 additional specimens, con¬ Cooley Centennial Professorship
firming the rarity of Heteronotia. in Zoology at The University of
Texas at Austin, the US National
Science Foundation, and the US
ACKNOWLEDGEMENTS National Aeronautics and Space
Administration. 1 also thank
For companionship and assist¬
staffs of the Department of
ance in the field, I thank R.
Zoology at the University of
Allen, D. Beaton, K. Beaton, D.
Western Australia, the Western
Bennett, H. L. Dunlap, R.
Australian Museum, the De¬
Dybdahl, A. Frank, W. F. Giles, S.
partment of Conservation and
E. Goodyear, W. B. Jennings, D. R.
Land Management (CALM) in
King, F. Odendaal, D. J. Pearson,
Kalgoorlie, and the Western
M. Peterson, G. A. Pianka, C.
Australian Department of En¬
Roscoe, W. Saunders, K. Smith, L.
vironment and Conservation
A. Smith, and G. G. Thompson.
(DEC). Lizards were collected
Others who contributed in
under permits issued by CALM
various ways to this research
and DEC with the approval of
include J. Anderson, K. Aplin, S.
appropriate animal ethics com¬
Argus, J. Banning, A. A. Burbidge,
mittees in Australia and the
M. A. Cowan, H. Gordon, M.
University of Texas. Specimens
Grenadier, R. A. How, V. Johnson
are housed in the Los Angeles
Dennison, G. A. Kaufman, I.
County Museum of Natural
Kealley, A. R. Main, B. Maryan, N.
History and the Western Aus¬
Scade, and G. M. Storr. Stomach
tralian Museum.
contents were identified by M. E.
Egan, S. E. Goodyear, C. Harp, S.
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