The walking track through the hills between Nelly Bay and Arcadia, with its extensions to the Sphinx Lookout and the Forts walk carpark, is longer than most and I hadn’t found an opportunity to explore it until last weekend. The weather was gorgeous and the landscape was at its best.
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.”
Those snippets are from wikipedia’s article on parthenogenesis in reptiles. The Reptile Database provides more information on the ancestral species if you’re curious.
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.”
Australia has just over twenty species of goanna (aka monitor lizard) but if anyone talks about seeing ‘a goanna’ they usually mean the largest local species. In our case, that’s the Lace Monitor, Varanus varius, which happens to be the second-largest in the country. (The Perentie of the central deserts is a little larger, growing to 2.4m as against the Lace Monitor’s 2.1m.)
The normal colour scheme of our Lace Monitors (I’m simply going to call them ‘goannas’ from here on) is dull grey-black with a generous spattering of creamy spots, as in my photographs of goannas at Wallaman Falls, on Whitehaven Beach and in the hills above Mission Beach (scroll down each page for the pics).
When we saw this reptile crossing the back yard of a weekender on Hervey’s Range we were surprised enough to check the reference books. It was close to two metres from nose to tail, so there weren’t many possibilities.
This strongly-banded sand-and-charcoal goanna is, in fact, still Varanus varius, although the ‘Lace’ name doesn’t suit it very well at all. It is known as ‘Bell’s form’ or ‘Bell’s phase’ and is more common in the drier inland than on the coast.
The Hervey’s Range property is just on the inland side of the crest of the range, although with a higher rainfall than regions further West, so a Bell’s form goanna is not too far out of its normal territory. That said, Wikipedia has one from the Fraser Coast (Hervey Bay – Maryborough) in its Lace Monitor gallery, so the geographical separation can’t be too strict.
A couple of days ago my system informed me that, “A new comment on the post Green Tree Frogs – not always green is waiting for your approval.” Readers come up with some fascinating observations so I clicked through straight away. Here’s the email conversation which followed, complete except for the usual greetings, etc.
Yvette: Hi Malcolm,
I live in Darwin NT and have many green tree frogs in the garden. I hunt and catch cane toads every night and came across a black tree frog. I’ve seen many dark green but never black. Have you heard of black tree frogs before? I have a photo of it next to a green one which I’m happy to email to you if you wish.
Malcolm: Black? New to me! I would love to see a photo.
Yvette: Yeah new to me too. We have dozens of green tree frogs of various shades in our garden but this is the first black one we’ve seen. I had to get my hubby Mark to confirm that, yes it really was black!
I googled black frogs also which is how I found your site. Have attached a couple of pics. Let me know what you think.
Malcolm: Thanks for the photos [cropped for publication].
I think you’re right – a very, very dark Green Tree Frog seems to be the only possibility. I played with the photos in my image editor, over-exposing them, and it is clear that the underlying colour is greenish rather than brownish. The red eyes, I guess, are just the red-eye effect of the flash.
I would like to post all this on my blog, if that’s okay.
Yvette: Yeah go for it. … I went out again later to see if he was still around and found him playing leap frog (minus the leap) with the green one. While still very very dark, he had a slightly greener tinge. Maybe it was a mood thing. :-)
Yvette (later): Apparently black tree frogs are quite common here according to NT Parks and Wildlife, however no one is clear on why they appear so black. My son found two in his yard this week and was also surprised at how black they seemed. We’ve been here for 20 years and this are the first we’ve seen. We’ve seen many dark olive green frogs though.
Thought I’d pass this on and will continue to update you with further info if we receive any (if you wish).
Malcolm: Yes, please do – and thanks again for your photos and for getting in touch in the first place.
A bit more searching on the net found me this page which says,
While extreme changes in color, for example a frog who is always mostly green turning and staying a dark brown, can indicate stress or illness, changing shades of colors is a normal and natural process for these frogs. Part of these variations in color are an indicator of mood changes, and part of them are a means of camouflage.
Several tree frogs have a super ability to melt from one color to the next. Frogs have three layers of pigments that they can change. Color morphing can be subtle or dramatic. The changes are not based on environmental color as much as they are on the temperature and light background. A frog is likely to change color during the seasons. Many times the change takes weeks to complete, but a noticeable difference in color can be observed within hours. The frog slowly blends into the lighter or darker trees of summer or fall. Not only does this provide some camouflage for the frog, but is an energy and heat conservation tactic. When the weather is warmer, the frog will be lighter so as to reflect heat and stay cooler and vice versa with cooler temperatures. The frog will become darker to soak up heat and create more energy. Whites tree frog changes from green to brown.
Neither of these are high-powered science sites so treat their information with due caution although it does match your observations. Yours is by far the darkest I’ve seen, whatever its reasons for going black.