02. Tree Lobsters Reborn

02. Tree Lobsters Reborn

Deep Time, as it relates to ecology, evolution, and climate change, is reflected significantly in human endeavor by the field of conservation. So, for a moment, let us dwell in the shallows for my absolutely favorite tale of modern conservation success, bringing a species back from the brink of extinction against all odds.

The Lord Howe Island group is comprised of the main island proper and a number of smaller islets, the most notable being Blackburn, Roach, and Mutton Bird Islands, each within a kilometer or two of the Lord Howe, and Balls Pyramid, which is 23 km away, a volcanic spire that juts up half a kilometer out of the ocean, adorned with a handful of small plants. The main island is heavily forested, with two small (under one km tall) but prominent mountains, Gower and Lidgbird.

Lord Howe island Group in relation to Australia (Inset) (Taken from Priddel et al. 2003)

Lord Howe island Group in relation to Australia (Inset) (Taken from Priddel et al. 2003)

Islands are frequently the source of a large number of endemic species (species unique to them), and Lord Howe Island is, or perhaps more appropriately, was, no exception. Having a number of unique birds, plants, and insects, the introduction of mice, and later black rats to the island had a devastating effect on the native ecosystem. This story focuses in one of the most interesting ones.

Stick insects, of the order Phasmatodea, are called such because, unsurprisingly they typically look like sticks. Very narrow brown bodies, delicate, long limbs. Some Phasmatodea have other body morphs, however, including leaf shaped, and something affectionately termed "tree/land lobster". Lord Howe Island was historically home to the Lord Howe Island Stick Insect (LHISI), Dryococelus australis, which fell into this latter ecomorph. Tree lobsters are defined by being much larger in mass than standard stick insects, and have robust bodies, which is thought to aid in deterring the few predators on their island communities (Whitman and Vincent, 2008). On Lord Howe, the insects were notably abundant and docile (Etheridge 1889), and locals would often pluck them up to use as fishing bait. They were noted to feed on tree foliage, and during the day retreat into the moist hollows of trees to protect themselves from dessication.

Until the rats came. In 1918 aboard the trading vessel Makambo (Wilkinson and Willson 1981 in Hutton 1991)). Lacking an ecological equivalent, the population of Lord Howe Stick Insects was wiped from the face of the Earth by the 1920's, 1935 at the latest (Paramonov 1963). And so along with some birds, plants, and other forms of unique biodiversity, the world became a little less colorful.

Until 1964, when a rock climber produced photos taken on Balls Pyramid of deceased tree lobsters (McAlpine 1966), suggesting the premise on this small volcanic spire. Soon more remains were found near the few bushes on Balls Pyramid, and despite later attempts to find live specimens over the next thirty years, none were found. In 2001 (Priddel et al., 2003) and later in 2002, Priddel and his colleagues undertook a set of surveys of the island, both during the day and during the night (when the steep rock faces make access particularly difficult), and sighted live Dryococelus australis seen in over seventy years. The shrub they were living on was an endemic tea-tree, Melaleuca howeana, ~50 of which were present on the island, some of which being threatened by an invasive vine. On these visits, only 24 individuals were sighted. It was found that in place of the woody hollows of the mainland, this population were using damp rocky crevasses that had accumulated dirt and plant matter which could retain the needed moisture.

Balls Pyramid (Wikipedia)

Balls Pyramid (Wikipedia)

I'll take a brief pause from this narrative to say that there are a few features of the LHISI that make them, in my opinion, rather adorable. Firstly, they form monogamous pairs (which will be relevant later). This is partly notable due to the fact that when they are inactive, the male places several of its limbs over that of the female, which we could anthropomorphizingly refer to as a hug, or snuggling, but regardless of its actual function, the behavior is heartwarming to see.

Look, they're "Hugging"!. The colored dots on their bodies are temporary labels for tracking individuals. (taken from Honan, 2008)

As a result, and because of the already devastatingly small population, exactly two mating pairs were taken off of Balls Pyramid to begin attempts at breeding programs. Of these pairs, after a lengthy struggle, one pair survived, and bred successfully. The details of how this breeding program then developed is elaborated in detail elsewhere both in pop science articles and the literature (Honan, 2008), but the end result is wonderful: there are now thousands of LHISI alive in captive breeding programs, and there is even a new population of them within an enclosed preservation on their original home of Lord Howe Island.

The next major step in this conservation Cinderella story is developing a program to eradicate the still-present rat population (as well as several other invasives that will be trouble) to allow for a restoration of the population on the island proper. Of course, there is some amount of feelings on the subject from the locals, and so many of the obstacles to closing this loop involves ensuring the human factor is welcome to these fantastic creatures (Wilkinson and Priddel, 2011). One of the most notable, and I would hope successful means of doing this is a wonderful video of one of these elongate LHISI emerging from its egg, underscored with soothing music.

Considering the extensive conservation efforts taken in the past decade, an investigation was undertaken to examine the significance of the species in the context of Phasmotodean diversity. Historically, D. australis, several other “tree lobster” stick insect ecomorphs, and a few other stick insects from the same regions (New Guinea and New Caledonia, Northeast of Australia) have been grouped together in the subfamily Eurycanthinae. The key takeaway from the previous sentence is the idea that our (scientists) impression was that the various tree lobsters were closely related, as they were all located in the Oceania region on various islands. 

In a recent study, various groups of Phasmatodea were analyzed using mitochondrial and nuclear DNA in conjunction with fossil evidence. It was found that a vast number of the Euphasmatodean (a broader group that contains all Phasmatodea and their closest relative) subfamilies maintained their monophyletic status, but their interrelations were drastically different than previous phylogenetic analyses had described. Most significantly, the Eurycanthinae, our group of interest, was found to form five distinct lineages. Two of these lineages each contained one of the nontree lobster species, while the remaining three contained the New Guinean tree lobster species, D. australis, and the New Caledonian/New Zealand species, respectively. D. australis and the New Caledonian/New Zealand clade are both contained with the clade Lanceocercata, which contains a large number of Australasian groups formerly though to not be related, while the New Guinean species is located far more basally.

What this means is that the existing morphological data, which had previously grouped the tree lobster ecomorphs together needed to be reevaluated, as the molecular evidence showed that each of the some of the tree lobsters had through convergent adaptation acquired their ecomorph, serving as an effective way to thrive in a nonarboreal lifestyle. Notably, other ecomorphs, such as giant winged stick insects, and those with leaf shapes, also had arisen multiple times in the various lineages.

Lord Howe Island as it exists today is the remnants of a shield volcano dating only seven million years old, which makes this story's place here in The Deep questionable at first, but of course, LHISI has only been there within that span. Just as the island did not emerge fully formed from the sea, neither did the LHISI. The island is one part of a long stretch of terrain, now almost entirely underwater, that once composed the microcontinent geologists call Zealandia. The process by which land, and more importantly for this story and others, islands, form and fall helps to bridge the long gaps of time when LHISI ancestors dwelled elsewhere, and is detailed in further nuance in another post, Island Hopping.

So, while the recovery of the Lord Howe Island Stick Insect is a story of the shallows, the movement, the distribution, the origin and evolution of these types of stick insect, especially our Lord Howe Island native, is soundly one of The Deep.

 

References

Buckley, TR, Attanayake, D and S Bradler. 2009 Extreme convergence in stick insect evolution: phylogenetic placement of the Lord Howe Island tree lobster. Proc. R. B 276: 1055-1062

Etheridge, R. (1889). The general zoology of Lord Howe Island. Australian Museum Memoirs2, 3-42.

Honan, P. (2008). Notes on the biology, captive management and conservation status of the Lord Howe Island Stick Insect (Dryococelus australis)(Phasmatodea). Journal of Insect Conservation12(3-4), 399-413.

Hutton I. 1991. Birds of Lord Howe Island: Past and Present. Ian Hutton, Coffs Harbour, Australia.

McAlpine D.K. 1966. Rediscovery of Lord Howe Island phasmid. Australian Entomological Society News Bulletin 2: 71.

Paramonov S.J. 1963. Lord Howe Island, a riddle of the Pacific, Part III. Pacific Science 17: 361–373.

Priddel, D., Carlile, N., Humphrey, M., Fellenberg, S., & Hiscox, D. (2003). Rediscovery of the ‘extinct’Lord Howe Island stick-insect (Dryococelus australis (Montrouzier))(Phasmatodea) and recommendations for its conservation. Biodiversity and Conservation12(7), 1391-1403.

Wilkinson, I. S., & Priddel, D. (2011). Rodent eradication on Lord Howe Island: challenges posed by people, livestock, and threatened endemics. Island Invasives: Eradication and Management’.(Eds CR Veitch, MN Clout and DR Towns.) pp, 508-514.

Whitman, D. W., & Vincent, S. (2008). Large size as an antipredator defense in an insect. Journal of Orthoptera Research17(2), 353-371.

Wilkinson B.A. and Willson R.K. 1981. The Main Line Fleet of Burns Philip. The Nautical Association of Australia, Canberra, Australia.

03. Sunlit Slugs

01. What is The Deep?

01. What is The Deep?