By Jesús Gómez-Zurita
New Caledonia, an island archipelago east of Australia, has long been recognized as a hotspot for biodiversity, maintaining a rich and mostly endemic flora and fauna, including some emblematic examples of island oddities and living fossils.
As is typically the case in the tropics, despite the obvious appeal of New Caledonia for biodiversity studies, there is a very incomplete knowledge of the actual diversity of life forms in the archipelago, and this is especially true for the insects, where it is estimated that we only know 20-50 percent of the island species.
Nonetheless, a detailed knowledge of the species inventory is the key to a meaningful understanding of island communities and their evolution.
Location map of New Caledonia courtesy of CIA World Factbook
We have been interested in Chrysomelidae, the leaf beetles, a highly diverse group of herbivorous insects worldwide, and also in New Caledonia. To date, some 200 species have been described, but 2-3 times as many may be awaiting discovery.
This group of beetles includes supposedly ancient species, with links that may be traced back to Gondwanan times, but most likely they come from comparatively modern colonizations from current or disappeared lands, as well as recent radiations and invasions.
Our goal, sponsored by the National Geographic Committee for Research and Exploration, is to characterize the diversity of this beetle family and, by using DNA sequence data, investigate its evolutionary history: source and number of origins and time scale of events.
Sampling leaf beetles (Chrysomelidae) in the delta of the Néra River (Baie de Bourail) in one small patch of New Caledonia’s highly diverse, yet unfortunately highly threatened tropical dry forest.
Photo credit: Anabela Cardoso
One small New Caledonian radiation of leaf beetles corresponds to the flea beetle genus Arsipoda. The genus, diverse in Australia and New Guinea, was known from five very closely related species in New Caledonia.
Our entomological exploration of the island, including remote and insufficiently surveyed areas, such as the Kouakoué peak in the Humboldt massif, revealed the existence of two new species belonging to this genus, which were later confirmed in the laboratory using DNA sequences.
One of the species, precisely collected near to the summit (1315 m.) of Mont Kouakoué, was named Arsipoda geographica in recognition for the sponsorship of the National Geographic Society of our work.
Arsipoda geographica, the new leaf beetle named after National Geographic. Analysis of the contents of its gut found plant groups scientists have not yet found in New Caledonia.
Photo courtesy of Jesús Gómez-Zurita.
Thanks to the study of DNA sequence divergence, we could establish an origin for this group in the Middle Miocene, some 15 million years ago, and DNA sequences from gut contents also provided us with the clue about the diet of these insects using innovative methods. Interestingly, their food could be appointed to plant groups not yet discovered in the island!
Our immediate plans involve studying in detail the diversity of this group of beetles, the Chrysomelidae, exploiting the information and detail offered by DNA sequence data and phylogenetic methods.
Our first campaign, thanks to CRE support, furnished hundreds of specimens which will be the basis for a sound assessment of biodiversity for this group and enhance species discovery, as in the case of Arsipoda.
Preliminary work on sequence data for over 800 specimens of a single New Caledonian chrysomelid subfamily, the Eumolpinae, hint at doubling the number of species known to science, and direct our efforts to specific areas where we need to sample more intensively.
The intriguing results obtained for the diet of Arsipoda are a powerful stimulus to plan a large-scale study of the ecology of Chrysomelidae using DNA-based diet diagnosis. The combined and detailed knowledge of leaf beetle species inventory and their ecological interactions should be the basis for conservation initiatives on an island museum of so many and unique natural wonders.
“At eight o’clock, as we were steering to the south, land was discovered bearing S.S.W., and at noon it extended from S.S.E. to W. by S., distant about six leagues.” So is the account of Captain James Cook upon setting eyes for the first time on New Caledonia in his second voyage round the world on board of HMS Resolution.
Cook and his crew had arrived at present day Balade, near the islet Pudioué (which he called Observatory Island, because the expedition arranged to be there to observe a solar eclipse). These lay at the northeastern-most tip of a large island in the Pacific (16,372 square miles), the Grande Terre, which runs for some 400 km in the NW-SE direction, some 1500 km east from Queensland in Australia.
Unlike most other islands in the Pacific, New Caledonia is not entirely of volcanic origin. It is an old piece of emerged land that separated off the northeast margin of the supercontinent Gondwana some 70-80 million years ago with the opening of the Tasman Sea, the same geological process that isolated New Zealand and the smaller Lord Howe and Norfolk islands, in the western Pacific.
The history of New Caledonia makes it of capital importance to biogeographers and evolutionary biologists alike to understand the processes that shape the diversity of life in isolation.
Thus the flora and fauna of New Caledonia incorporate some of the emblematic examples that propelled the
hypothesis of vicariant evolution by continental drift, the patterns of diversification of organisms consistent with the breakage pattern of emerged land.
These include, among plants, the living fossil Amborella, a neocaledonian endemism representing the most ancient split of flowering plants, but also the southern beeches of the genus Nothofagus, once distributed in most of Gondwana.
Among animals, it is worth mentioning the troglosironids, ancient and endemic blind harvestmen, extremely unlikely to disperse across sea barriers, or the flightless and enigmatic bird known as Kagu (Rhynochetos), traditionally considered related to extinct birds in New Zealand and more distantly to extant sunbittern (Eurypiga), in South America.
However, this is not the end of the story. The scientific debate moved a step forward after realization
that the biota in New Caledonia could be of recent origin, as recent as the Oligocene, some 20-30 million years ago, after a geological episode that may have submerged entirely the island miles below the ocean surface.
As an evolutionary biologist interested in the causes that promote the origin of new species, particularly among beetles, which are extremely diverse and perplexing in New Caledonia, this scenario offers excellent research opportunities.
Meet the Beetle
The rich beetle fauna of New Caledonia has incredibly high levels of endemicity, with nine in every ten species exclusively found in the island, and likely the result of isolation and local adaptation.
But this group of animals is also singular in the island for seemingly including some survivors of ancient times, members of evolutionary lineages which were once possibly very diverse and widespread in the world and which nowadays count with a handful of species scattered in corners of their vast original range.
Bohumiljania is one of these relicts. This genus, named by Pierre Jolivet after the Czech entomologist Bohumila Špringlová, currently counts with only two species, both in New Caledonia (B. caledonica, in the picture, and B. humboldti).
Bohumiljania caledonica (foreground) resting on the author’s finger (background) after being knocked down from its myrtle host plant, Syzygium, near Sarramea (Prov. Sud, Grande Terre).
Photo credit: José A. Jurado-Rivera
The animal was discovered by the French entomologist Fauvel at the turn of the 14th Century, and although he did not formally describe it, he ranked it with the Chilean genus Stenomela.
Only recently both genera have been recognised to belong to a very peculiar and ancient group of leaf beetles, the Spilopyrinae, which in all currently harbours 26 species in seven genera: Bohumiljania (New Caledonia), Stenomela and Hornius (Chile), Spilopyra, Macrolema (Australia and New Guinea), and Richmondia and Cheiloxena (Australia). Their fragmented distribution is suggestive of a Gondwanian origin, in the Southern Hemisphere supercontinent which broke up into smaller parts, including the neocaledonian Grande Terre, by the end of the Cretaceous and now in great part under Antarctic ice.
The spilopyrines are exceptional evolutionary witnesses which may well bear clues about that turbulent geological past, as important in their humble and inconspicuous bug self as other perhaps flashier groups investigated on the same grounds, such as the ratite birds (ostriches, emus, moas) or the southern beeches.
From the Instituto de Biología Evolutiva (Barcelona, Spain) and the Institute Agronomique néo-calédonien (La Foa, New Caledonia), we are investigating the evolutionary history of these animals and their highly diverse relatives, the
Eumolpinae (another group of leaf beetles), using DNA as the ultimate source of information to understand the tempo and mode of their diversification.
More information: Gómez-Zurita, J., Cardoso, A., Jurado-Rivera, J.A., Jolivet, P., Cazères, S. Mille, C. 2010. “Discovery of new species of New Caledonian Arsipoda Erichson, 1842 (Coleoptera: Chrysomelidae) and insights on their ecology and evolution using DNA markers” Journal of Natural History 44(41-42): 2557-2579, 2010.
Born in Palma de Mallorca, Spain, in 1972, Jesús Gómez-Zurita obtained the equivalent to MSc (1995) and his PhD (2000) in Biology from the University of the Balearic Islands. He worked for nearly 20 years on faunistics, cytogenetics, systematics, phylogeography, phylogenetics and evolutionary biology of leaf beetles (Chrysomelidae) with support from the Spanish government, EU Marie Curie Actions or the German Alexander von Humboldt Foundation. Author of more than 35 articles in these fields, he holds a permanent position as researcher for the Spanish High Research Council (CSIC) at the Institute of Evolutionary Biology in Barcelona.
The photo of Jesús was taken in New Caledonia, close to Cascade de Tao, by Jose A. Jurado-Rivera.