evolution

Giraffe Weevils

In January this year the Museum helped run a night-spotting Whanganui Summer Programme field trip to Bushy Park. The participants were lucky enough to see, up-close, two long skinny insects that had been found by DOC’s Scotty Moore under a rotten log. They were giraffe weevils, New Zealand’s longest beetle.

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A male giraffe weevil (Lasiorhynchus barbicornis) found by Scotty Moore at Bushy Park
Photo: Whanganui Regional Museum

The giraffe weevil’s Latin name, Lasiorhynchus barbicornis, means “hairy-nose with a bearded horn”. Its Māori name is pepeke nguturoa, or long-beaked beetle. (By the way, nguturoa is another Māori name for kiwi). They’re also called tūwhaipapa, after the god of newly-made waka, because their nose resembles a canoe prow. All these names refer to the male, who has a snout as long as the rest of his body with a fringe of hairs underneath.

Male and female giraffe weevils look very different, and were named as two different species when the specimens collected by Sir Joseph Banks on Captain James Cook’s first voyage were studied back in Europe. Female giraffe weevils are tiny compared to males, and have a shorter snout which they use to drill an egg-laying hole into dead trees. Their eggs hatch into grubs which eat fungus inside rotting wood for two years, finally pupating and digging their way out of the tree as adult weevils in summer. Peak emergence time is February, so right now is your best opportunity to see adult giraffe weevils in the wild, as they only live for a few weeks before mating and dying.

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 Male giraffe weevil guarding a small female, who is busy digging a hole for her egg
Photo: Christina Painting / CC-BY-SA

An adult male giraffe weevil’s primary concern is finding a female, and they use their enormously long noses to fight other males by biting and wrestling, trying to dislodge their opponents from the tree trunk. When they find a mate they literally stand over her while she lays an egg, driving off all challengers. Some much smaller males employ a different reproductive strategy: while the big macho males are distracted by fighting and posturing, these little males will sneak in and mate with the female under their rival’s enormous nose. Research by biologist Chrissie Painting at Auckland University revealed that both these tactics were roughly equally successful at fathering offspring, which is why we see such a range of body sizes in male giraffe weevils. It’s like a field experiment in evolution: if one strategy were more successful, natural selection would favour it, and eventually male giraffe weevils would have all evolved a similar body size.

Chrissie was able to find several dying karaka trees in Matuku Reserve near Auckland where she could watch males battle and sneak, and observe their life cycle. She used tiny dots of coloured nail polish to mark the different males so she could tell them apart, and filmed them tossing each other off trees. Giraffe weevils are a useful study animal for observing evolution in action, because they’re active in the daytime (unlike many beetles) and easy to observe. After having to work long nights studying native harvestmen, she describes the weevils as “little angels”.

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Female giraffe weevil, showing her much smaller snout, with antennae halfway along it, allowing her to chew nest holes; male antennae are near the tip of the snout
Photo: Christina Painting / CC-BY-SA

If you want to see real-life giraffe weevils for yourself, you could venture into lowland native bush between October and March, look on the trunks of rotten trees, and, if you’re lucky, see two long-nosed insects jousting.

 

Dr Mike Dickison is Curator of Natural History at Whanganui Regional Museum.

Boning up on specialist matter

Boning up on specialist matter

Dr Eric Dorfman, director of the Whanganui Regional Museum, has a predilection for skeletons – and makes no bones about it. The museum is mausoleum, I mean home, to a remarkable number of bony structures, including a complete skeleton of a long extinct great auk. As well as a fascination for extinct species, among Eric’s many accomplishments was a time spent teaching zoology at the University of Sydney, so the anatomy of animals is of particular interest.

The object of this article is to make morphological comparisons between skeletons of different species, showing, mostly, the similarities.  We looked at the skeleton of a penguin, then that of a lizard, a lace monitor or goanna, seeing the bones of a ‘hand’ – similar components, scaled differently – in each and every bony framework, and not a lot different from a human hand. And look! A flamingo skeleton!

Using the skeletons of a hawk, the lizard, the flamingo and the penguin, as well as a large animal skull, probably from a cow, Eric made comparisons of particular bony parts. “What’s interesting about this is that it is a real lesson in evolution when you start looking at how these things are the same basic morphology [structure],” says Eric. “If you look at the hawk, as on most birds, the upper bill is thicker and bigger than the lower bill. But if you look at the flamingo, the reverse is true. It’s because to feed, they hold their heads upside down. They lower their head into the water and filter out brine shrimp.”

So how did that beak structure happen? “Undoubtedly the behaviour precedes the morphology,” says Eric, “in that over time the birds that had a subtle difference in their beaks had more offspring because they fed at a more efficient rate, they were healthier and they had more eggs survive.”

Interesting fact: the colour of the flamingo is determined by its diet. “The pink comes from sequestering the pigment from the shrimp in their feathers. If you stop feeding flamingos their native food they turn white or very light pink.” You are what you eat.

“The beak of the hawk is for tearing, the penguin bill is for grabbing … but they are modified from the exact same origin.”  We carefully arranged the skeletons of the hawk, lizard and penguin on a table, together with the cow skull – kind of a mini-representation of House of Bones, a museum exhibition currently showing.

“Aside from the fact it’ll be a lot of fun, the most exciting thing for me is to show a rich skeletal collection and, what I’m hoping people will get from the exhibition will be an intimate look at skeletal structure and what different bones are used for. I hope also for an understanding about the connection between different biological groups that are actually similar and closely related.”

The hawk and penguin are obviously closely related, Eric pointed out, but those similarities extend to other species. “If you compare the goanna to the hawk, the spine is extremely similar and so much more is the same. To me, evolution is obvious when you look at these things together.”

The good doctor’s knowledge of ancient species is encyclopaedic but the evolution of birds and lizards comprised much of Eric’s discussion as we looked at the skeletons. “If you were to investigate an emu you can see a little ‘thumb’ in its wing,” says Eric, “and this is one of things to remember – not everything has a purpose. One of the mistakes we make is to think that everything we see on an animal has to have meaning and we look for that meaning.”

He compared the skull of the goanna with that of the hawk and the similarities were unmistakable. Cover them with flesh and life and you would never know how much the same they are.

 

Original article appeared in the Wanganui Midweek in September 2013.  Reproduced with permission from the Publishers.