I welcome comments on my blog posts and normally approve them even if I disagree with them (I can always comment right back, can’t I?) but occasionally I receive one which raises questions which deserve more consideration. Continue reading “House geckos – pests or not?”
I spotted this little lizard on the trunk of our poplar gum a fortnight ago and took photos because I had never seen one quite like it before. Its size (3.5 – 4 cm) and proportions told me it was only a baby, and its feet and smooth skin told me it was a gecko, but its markings are not at all like the two geckos we usually see here, the Dtella and its nearly identical Asian rival.
A little research allowed me to identify it as a Mourning Gecko, Lepidodactylus lugubris. Like our other geckos, the species is nocturnal, not very big (10 – 11 cm), and feeds on small insects. It also feeds on flower nectar; I’m not sure whether our others do that but it’s not unlikely.
Beyond that, the Mourning Gecko is an interesting little beast: it’s a hybrid, and it’s parthenogenic.
In other words, the ultimate ancestor of my little lizard was a female produced by the mating of two geckos of different species, and the family consists of an endless mother-daughter sequence. Adults are known to engage in female-female pseudo-copulation which apparently stimulates egg production, but even that is not necessary: one female on her own can and will lay viable eggs, usually two every few weeks.
As if that wasn’t strange enough, “The species consists of a number of clonal genetic lineages thought to arise from different hybridization events,” i.e. the ancestral species successfully hybridised on several different occasions, so there are variant ‘families’ of Mourning Geckos, each as closely related to the others as members of normal species are, but each producing a succession of genetically identical daughters.
But there’s more! “Surprisingly, parthenogenetic females of this species occasionally produce male offspring, which are thought to be the result of non-genetic hormonal inversions. While these males are anatomically normal, they produce abnormal sperm and are sterile.”
As Steve Wilson notes in A Field Guide to Reptiles of Queensland, the fact that it doesn’t need to mate to produce viable offspring has no doubt contributed to the Mourning Gecko’s success as an island coloniser, since a single stowaway can produce a whole new population. Wherever and whenever the species arose, it is now widespread across the islands and coastal areas of the Western Pacific and Indian Ocean.
It seems to be a very recent arrival in Australia. The distribution map at The Australian Reptile Online Database shows a coastal distribution in Queensland but Fitzsimons, in ‘Southward range expansion of the Mourning Gecko Lepidodactylus lugubris on mainland Australia and nearshore islands’ (2011, available here), goes into more detail. He analyses Australian records of the species to come to the conclusion that its range is extending southwards quite rapidly, from Port Douglas and Mission Beach to Townsville in the late 1990s and now Bowen, Gladstone and Heron Island. As he notes, this, “may be important for conservation, as the Mourning Gecko has the potential to compete with native Australian geckos.”
We know that snakes shed their skin and we know that lizards, like snakes, are reptiles. It follows logically enough that lizards, even including little soft geckos, shed their skins but I must admit that the thought had never crossed my mind until I found this shed skin under a piece of loose bark on a fallen tree trunk.
It is the skin of a gecko about the size of our house geckos. Given that I found it in a rural area, well away from any house, it probably came from the native house gecko or Dtella. The fact that I can see no sign of tail-spines supports that guess, but it’s hard to be sure – the whole skin is so soft, light and delicate that it floats to ground like a feather when dropped, and any spines wouldn’t stand out as they do on the animal. My first photo, of course, is an extreme close-up: the whole skin is only about 10cm long.
We always have lots of geckos around the house so I wondered why I had never seen a shed skin before. It turns out that most lizards, including geckos, normally shed their skin in patches rather than in one piece so my near-complete skin is a bit unusual. And it wouldn’t normally last long, either: a friendly herpetologist told me that the lizard often eats its skin as it lifts off. If not, I guess something else soon will – why waste good protein?
More: Shedding in other groups of reptiles at MadSci Network
Soon after I arrived in Townsville I learned that two species of gecko lived in the houses here, one native and the other a recent arrival from Asia. They looked almost exactly the same and had the same lifestyle, and no-one I knew could reliably tell the difference between them except that the Asian geckos chirped.
That’s where my knowledge stopped until I decided recently that it was time I sorted them out. Here goes:
Both of them are generally known simply as ‘gecko’ and I have also heard ‘jelly lizard’ as a common name from an older resident.
They are both about the same size, growing to approximately 15cm overall. Both of them change colour according to their surroundings and are usually dark with a distinct pattern by day but pale and almost patternless at night.
Both of them are primarily nocturnal and their hunting strategies are very similar: both are “ambush” hunters in that they sit and wait for prey rather than actively roam in search of it.
The most reliable way of distinguishing them is that the Asian gecko has a series of small spines along the top and edges of the tail (in its original state); the top row extends onto the lower back as small bumps. If you catch one, you can check its toes: all toes of the Asian gecko have claws, but the inner toes of the Dtella are clawless. Also, the native gecko generally has paired white spots along the spine, as in my second photo on this page, though they may not be at all obvious in darker colour modes.
The two species can also be distinguished, more easily though not so reliably, by their calls. The Asian gecko calls more often and more loudly than the native species; its loud “chuck-chuck-chuck” is obviously the origin of its Indonesian common name, Chichak or Cheechak. The native gecko’s call is a softer chattering.
There are slight behavioral differences between the species. It appears* that the Asian geckos are willing to tolerate brighter lights while hunting than the native species, which means that native geckos are more likely to lurk in the shade of curtains or picture frames and dart out at nearby prey whereas Asian geckos often rest in brightly lit open spaces, relying on immobility to remain unnoticed by their prey. It probably gives Asian geckos a competitive advantage in our houses, too.
The Department of Agriculture, Fisheries and Forestry information sheet on Asian geckos (pdf here) doesn’t give quite the same reasons but comes to similar conclusions:
H. frenatus is an aggressive and territorial species, features that allow it to successfully compete with native species. … Male and female H. frenatus are known to eat juveniles of other gecko species as well as their own progeny (Bolger and Case, 1992).
The ability of H. frenatus to replace locally native gecko species seems most pronounced in urban areas. Artificial lighting on buildings attracts large numbers of insects and H. frenatus is well adapted to utilise this food resource, perhaps more so than native gecko species, which may be better adapted to hunting more dispersed insect populations.
I walked around my house with a camera one evening to see whether I could identify the species we had here and the results lined up very neatly with that light tolerance. (For the record, I saw three or four geckos in each room and there are probably just as many in each bedroom. We don’t bother them, since they eat lots of insects and they don’t bother us at all except by leaving neat little black and white droppings.) I found only Asian geckos in the kitchen (most brightly lit and fewest shady hiding spots), only native geckos in the lounge/TV room (dimmest lighting) and both species in the study-cum-reading-room (mid-level lighting and plenty of hiding places).
- Dtella: Queensland Museum
- Asian house gecko: Queensland Museum
- More species of gecko, with photos: ozanimals
*Information from Professor Lin Schwarzkopf of James Cook University’s School of Marine and Tropical Biology, which confirmed and explained a vague memory I had of being told, years ago, about a difference in hunting styles.