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Plant consumption in Australian geckos: sap feeding by the Ocellated Velvet Gecko Oedure monilis

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PPaaggee 88HHeerrppeettooffaauunnaa 3377 ((11)) 22000077
IINNTTRROODDUUCCTTIIOONN
Most lizards are predators of small animals,
and plant consumption in lizards had long
been considered atypical and restricted to a
small proportion of species (Cooper & Vitt,
2002). While completely herbivorous species
make up around 3% of the total lizard fauna
(Iverson, 1982), it is becoming increasingly
apparent that many lizards do eat plant
material, be it only occasionally or in small
quantities (Cooper & Vitt, 2002). For lizards in
which plants form only a small part of the
diet, easily digestible products such as nectar,
pollen, or sap are favoured (Cooper & Vitt,
2002). These products are likely to be valu-
able food resources due to their high concen-
tration of sugars and nutrients (Greer, 1989).
The consumption of a plant material is partic-
ularly infrequent in geckos (Cooper & Vitt,
2002), with exceptions from New Zealand
(Whitaker, 1987), New Caledonia (Bauer &
Sadlier, 1994) and islands in the Indian
Ocean (Nyhagen et al., 2001; Staub, 1988).
While the majority of Australian geckos are
opportunistic arthropod feeders (Greer,
1989), a number have been observed eating
plant sap, particularly species within the pre-
dominantly arboreal genera Gehyra and
Strophurus. To date, sap feeding in Australian
geckos has been reported for Christinus guen-
theri (Cogger et al., 1983), Christinus mar-
moratus (Dell, 1985), Gehyra australis (Letnic
& Madden, 1997), Gehyra cf. baliola
(Couper et al., 1995), Gehyra dubia (Couper
et al., 1995), Gehrya purpurascens
(Gaikhorst & Lambert, 2005), Gehyra varie-
gata (Dell, 1985), Rhacodactylus australis
(Couper et al., 1995), Strophurus assimilis
(Gaikhorst & Lambert, 2005), Strophurus
spinigerus (Couper et al., 1995), and Oedura
reticulata (Dell, 1985). Here we report a
further Australian gecko species feeding on
tree sap, the Ocellated Velvet Gecko (Oedura
monilis).
OOBBSSEERRVVAATTIIOONN
On 25 May 2006, at the James Cook Uni-
versity Kirrama Field Station (18°11’30”S
145°44’25”E, 589 m asl), we observed a
single O. monilis on a lime tree (Tilia sp.). The
lime tree was planted in the vicinity of the field
station building and was surrounded by
open, eucalypt forest. At 2030 hr, the O.
monilis was observed at approximately 1.6 m
in height on the trunk of the tree, licking a
small (approximately 4 cm2) patch of sap
(Figure 1). There were no insects near the sap
patch, and the sap was derived from the tree
rather than from insect exudates (ie. honey-
dew; Markus et al., 2001). We observed the
individual for two hours, and although we
were in very close proximity and took numer-
ous photographs, it did not stop feeding on
the sap during this time. Its tongue move-
ments were slow and deliberate. We moved
away from the animal at approximately 2245
hr, and when we returned at 2300 hr, the
gecko could no longer be located.
DDIISSCCUUSSSSIIOONN
This observation of O. monilis is the first
report of an Australian gecko utilizing food
resources from an introduced tree. All other
reports of Australian geckos feeding on plant
sap have been on native plants including
Acacia (Dell, 1985; Couper et al., 1995),
Grevillea (Gaikhorst & Lambert, 2006) and
Eucalyptus (Shea et al., 1988).
It is perhaps not surprising that O. monilis has
PLANT CONSUMPTION IN AUSTRALIAN GECKOS: SAP FEEDING BY THE
OCELLATED VELVET GECKO OEDURA MONILIS
Jodi J.L. Rowley*, Robert Puschendorf and Scott Cashins
School of Marine and Tropical Biology, James Cook University, Townsville, Qld 4811.
*Email: Jodi.Rowley@gmail.com.
HHeerrppeettooffaauunnaa 3377 ((11)) 22000077PPaaggee 99
never been observed feeding on tree sap,
given the likely highly opportunistic nature of
the act. Other species of gecko have been
found to feed on non-traditional, energy-rich
food resources when presented the opportu-
nity. For example, the Palauan gecko Gehyra
brevipalmata has been observed licking not
only tree sap, but also, open soft drink con-
tainers (Crombie & Pregill, 1999), and a
number of Australian geckos have been
reported feeding on sugar-based substances
in captivity (Greer, 1989).
Utilisation of plant resources such as sap may
be an occasional event for the majority of
lizard species, and as a result has gone
largely undetected. Further incidental obser-
vations such as the present study are likely to
reveal that plant consumption in lizards is
much more widespread than previously
understood. This may be the case particularly
in opportunistic, active foragers such as O.
monilis, which may be more likely to
encounter plant food as they search a wide
area for prey, closely inspect certain plants,
and use their chemical sensors to identify and
locate animal prey (Cooper & Vitt, 2002). It is
likely that further observations will reveal that
the majority of active-foraging geckos in Aus-
tralia and elsewhere opportunistically feed on
‘free’, high-energy plant resources when
accidentally located, and may even use
chemoreception to seek them out, particular-
ly at times of low insect abundance.
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Figure 1. Oedura monilis feeding on tree sap
... However, anecdotal observations of geckos consuming the bark exudates of Acacia spp. suggest that not all Australian geckos are obligate insectivores (Couper et al. 1995;Letnic and Madden 1997;Rowley et al. 2007). ...
... However, the failure of dietary studies to find evidence of plant exudates in geckos' diets could be because exudates are soluble and thus leave little physical evidence of their ingestion (Harley et al. 1989). Without direct experimental observation of gum consumption by geckos, the importance and frequency of gum as a food resource for geckos will remain unknown (Letnic and Madden 1997;Rowley et al. 2007). ...
Full-text available
Article
The diets of many animals are influenced by resource availability, competition, and evolutionary selected traits enabling the utilization of palatable foods. Omnivores are species that maintain their macronutrient balance by supplementing highly abundant but poor nutritional quality food items, with sporadically available but high nutritional quality food items. Although there are anecdotal observations of Australian geckos (Lacertilia: Gekkonidae) consuming plant exudates, the consumption of plant material has long been considered to be anomalous behavior among Australian geckos. Here, we test the idea that sap feeding may not be anomalous behavior but instead a dietary niche of geckos that has gone unappreciated due to constraints on the methods used to quantify geckos’ diets. We tested this idea by investigating the consumption of Acacia victoriae gum by the gecko Gehyra versicolor using timed searches and time-lapse photography. We found that geckos frequently consumed gum, and G. versicolor numbers were five times greater on A. victoriae trees that exhibited significant gum bleeds compared to gecko numbers on non-bleeding trees. Taken together, our observations that G. versicolor spp. frequently feed on gum along with anecdotal reports of geckos consuming gum provide compelling evidence that gum/sap feeding is not anomalous behavior and suggest that many Australian gecko species are omnivores whose diets include plant exudates and animal prey.
... Until recently, the dietary importance of plant-derived resources to lizards had been rarely studied, even though up to 11% of lizard species supplement their diets with plant materials including nectar, sap, fruit and foliage (Whitaker 1987;Eifler 1995;Cooper & Vitt 2002;Rowley et al. 2007). ...
... Flax exudates are largely comprised of xylan, a complex polysaccharide predominantly made of the monosaccharide D-xylose (McIlroy 1951;Sims & Newman 2006;Tauwhare et al. 2006). Although only a few studies have examined the importance of sap in the diets of New Zealand fauna (Beggs 1988;O'Donnell & Dilks 1989;Moorhouse 1997), there is widespread evidence elsewhere that sap can provide an important food resource, particularly when other food resources are scarce (Southwick & Southwick 1980;Blendinger 1999;Schlatter & Vergara 2005;Rowley et al. 2007;Macchi et al. 2011). Flax patches may also have attracted large numbers of geckos because of invertebrate prey inhabiting flax leaf refuges and the shelter flax provides for geckos against predators and harsh environmental conditions. ...
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In many ecosystems food-web dynamics are driven by spatial and temporal variation in the availability of sugar resources, which form the primary or even exclusive dietary constituents for many species. Scale insects (Hemiptera) produce sugar-rich honeydew, which can be a keystone sugar source in honeydew ecosystems worldwide. In New Zealand, most previous research in honeydew ecosystems has been conducted in areas where herpetofauna are heavily suppressed by introduced predators. Consequently, little is known about potential trophic interactions between endemic lizards and scale insects. Korapuki Island is one of the few remaining locations in New Zealand where endemic scale insects and lizards survive in densities likely to be representative of prehuman conditions. We examined the relative importance of different sugar resources on Korapuki Island to Duvaucel’s geckos (Hoplodactylus duvaucelii) and common geckos (Woodworthia maculatus). We recorded the abundance and morphometrics of geckos attending five sugar-producing plant species (two of which host honeydew-producing scale insects) three times daily along a fixed transect. Large numbers of Duvaucel’s and common geckos were recorded nocturnally feeding on honeydew produced by the scale insect Coelostomidia zealandica (Coelostomidiidae). Duvaucel’s geckos of all sizes and genders fed extensively on honeydew throughout the year, favouring ngaio (Myoporum laetum) trees with high scale insect infestations, but were seldom recorded at other sugar resources. In contrast, juvenile common geckos were infrequently recorded on honeydew-producing trees. Common geckos fed on a variety of other sugar resources, with all sizes and sexes abundant on nectar and sap of flax (Phormium tenax) and seasonally exploiting nectar of pohutukawa (Metrosideros excelsa). The strength of interactions between scale insects and geckos, particularly for the Duvaucel’s gecko population on Korapuki Island, indicates the importance of honeydew in addition to more ephemeral sugar resources such as nectar. Accordingly, the re-establishment of honeydew-producing Hemiptera populations should be considered in future conservation and restoration plans.
... Most geckos are carnivorous, mainly feeding on insects, spiders, snails and small vertebrates (Cooper and Vitt, 2002;Bauer, 2013). Nonetheless, the number of examples of occasional observations on the consumption of plant materials, such as fruits, sap, nectar, and pollen, which contain high energy and are easy to digest, is recently increasing (e.g., Olesen and Valido, 2003;Rowley et al., 2007;Murai et al., 2013;Teixeira et al., 2013). In addition, unique feeding behavior, milking, in which geckos directly lick honeydew from the abdomen of a flatid planthopper, has been reported in diurnal geckos, Phelsuma and Lygodactylus, and a nocturnal gecko, Blaesodactylus, in Madagascar (Fölling et al., 2001). ...
Article
Although most geckos are carnivorous, a number of examples of occasional observations on plant consumption have been reported in recent years. Moreover, previous research has reported that several Madagascan geckos lick honeydew excreted from planthoppers. Here, I report feeding on tree sap and honeydew by Geckolepis sp., a fish-scale gecko from northwestern Madagascar. Although, in the previous report, the planthopper showed specific abdomen movement after stimulation by a gecko, the planthopper and the gecko in my observation did not show any specific behavioral interaction. Honeydew milking without a specialized behavioral interaction, which was observed in Geckolepis sp., might be the intermediate stage of the evolutionary transition from simple feeding on plant sap to the highly specialized behavioral interaction that enhances honeydew milking.
... The few records available include Australian arboreal gekkonids: Christinus guentheri (Cogger et al., 1983), Christinus marmoratus (Dell, 1985), Gehyra australis (Letnic & Madden, 1997), Gehyra cf. baliola (Couper et al., 1995), Gehyra dubia (Couper et al., 1995), Gehrya purpurascens (Gaikhorst & Lambert, 2005), Gehyra variegate (Dell, 1985), Rhacodactylus australis (Couper et al., 1995), Strophurus assimilis (Gaikhorst & Lambert, 2005), Strophurus spinigerus (Couper et al., 1995), Oedura reticulata (Dell, 1985), and Oedura monilis (Rowley et al. 2007). Tree exudates (resins, saps, or gums) seem to be part of the diet of Lygodactylus sp. from Madagascar (Föoling et al., 2001). ...
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