The New Nature Read online

  About 250 pure black-ears remain, nearly all in one tract of mallee in South Australia. The last true New South Wales bird was seen in 1985. Saving black-eared miners means filling in dams, evicting goats and roos, and killing yellow-throated miners. Even when it works, something special has already been lost. ‘We haven’t found a colony that doesn’t have hybrids in it,’ Rohan said. ‘The hybrids are now very important. If you take them all out of a colony it just collapses. So while we can afford to take out the occasional yellow-throated miners, we can’t afford to take out all the hybrids. I expect that we’re always going to have some yellow-throated genes in the black-eared miner population.’

  Here’s another variety of change we’ve brought on Australia: genetic mixing. DNA is trading places as never before. Exchanges are going on between species and within, in response to all that biotic movement mentioned before. Sometimes the repercussions are dire. Genetic issues lie at the heart of many conservation calamities.

  Maclear’s rat (Rattus macleari) evolved in the isolated splendour of Christmas Island. English naturalist Charles Andrews encountered them in ‘swarms’ when he went ashore in 1897, but by 1904 none remained. Their ticket in paradise was taken by the exotic black rats that arrived in 1899 in a cargo of hay. Black rats are greyish-brown (not black) with greyish bellies and big ears. Maclear’s rats were larger, chestnut-brown, with cream bellies and small ears. The last few were seen in 1901 when the London School of Tropical Medicine collected specimens for beri-beri research. But some of the rats they caught proved puzzling. Labelled at the time as ‘half-breeds’, they were big and brown, big-eared, with grey or white bellies. Maclear’s rat presumably survives as strands of DNA inside the black rats skulking in Christmas Island pantries.

  A similar fate befell the grey-headed blackbird (Turdus poliocephalus poliocephalus) of Norfolk Island, a unique form of the widespread island thrush. It vanished in the 1970s. The English blackbirds that skip about on lawns there today don’t look quite right. They are sometimes pale where English blackbirds should not be pale. The young have pale heads. Hybrids? Experts think so. The native blackbirds were dying out (blame black rats again) and the last of their line must have paired up with English invaders. Grey-headed blackbirds aren’t entirely extinct, they are just hiding inside English blackbirds.

  An endangered rainforest palm could go the same way. Ptychosperma bleeseri (numbering 11440) grows astride a few springs near Darwin, and all is not well. When these rare palms are cultivated, they trade pollen with Queensland palms (P. macarthurii) growing in nearby gardens, spawning hybrid young. Queensland palms are so popular that Darwin’s urban creep has brought them within 3 kilometres of the largest stand of endangered palms. Hybridisation appears inevitable. Botanist David Liddle wants bans imposed on growing other palms nearby, but doubts they would be enforced. ‘If it’s a lost cause, which is a possibility, then we’ve probably got to look at the possibility of establishing Ptychosperma in more remote locations.’ Aborigines, by eating the crowns of these palms, probably curbed their numbers; the problem today is more subtle.

  Lamentable outcomes like these arise when populations are small. That’s not an issue for our best-known duck, the black duck, which all too often accepts unseemly advances from English mallards, which were brought here to brighten up parks. Mallard drakes are dramatic, with green heads and purple breasts. Females are sombre, like black ducks (of both sexes). The hybrids appear often enough to win a place in field guides. Mallards wander down to subantarctic Macquarie Island and hybridisation is suspected even there. New Zealand boasts millions of mallards, and the black ducks there have been swamped. Our black ducks won’t turn into mallards, which they vastly outnumber, but mallard genes will seep through the entire black duck population. Domestic ducks were bred from mallards, and some of our mallards have domestic duck ancestors, which means we’ve injected something of the English farmyard into our billabongs and bores. At best we could end up with black ducks better suited to park ponds and farm dams. Mallardisation of other ducks goes on in North America and South Africa.

  Hybrids arise most often among birds, fish and plants. They occur between species, and between different populations of the same species. I’ve mentioned miners, blackbirds, ducks and New Zealand stilts, and other bird examples include the long-billed and Western corellas hybridising around Perth, and the fairy terns and little terns mating on southen beaches.

  Near Melbourne a new plant was discovered and named Nicotiana flindersiensis, then never seen again. It was the hybrid spawn of a weed – South American tree tobacco (N. glauca) – and a native tobacco (N. suaveolens). When the weed crosses with any of our native tobaccos (which it scarcely resembles) the offspring are rare and probably infertile. That’s usually the best outcome hybridisation can produce. Other prospects are extinction, merging of populations, and transfer of genes.

  Plants are embroiled in the largest number of imbroglios because native gardening is so popular. Grevilleas are notoriously promiscuous, often spawning hybrids when species are brought together, as plant breeders well know. Garden hybrids often cross with wild plants. Near Melbourne a complex hybrid swarm appeared when wild Grevillea glabella swapped pollen with three species in gardens nearby. Wattles also cross easily. A superweed is spawned when coast wattle (Acacia sophorae) and sallow wattle (A. longifolia) meet. In the Yarra Valley near Melbourne Cootamundra wattles (A. baileyana) in gardens and wild silver wattles (A. dealbata) ‘are hybridising like mad all over the place’, explained botanist Lincoln Kern, who worries about Warrandyte State Park where hybridisation is now ‘rampant’. Around Sydney Cootamundra wattles also cross with threatened downy wattles (A. pubescens). Wattles are merging in so many places that major evolutionary change is now under way. It’s not what the Wattle Day League had in mind when they extolled these plants a century ago.

  Eucalypt hybrids also arouse alarm. Rohan Cuming told me about the trials of growing eucalypt seed taken from old swamp gums (Eucalyptus ovata) on the Mornington Peninsula for revegetation work. ‘The seedlings look fine,’ he said. ‘But after three or four months they start to look a bit weird. They go a bit blue and the stems look a bit different.’ These individuals, a tenth of the batch, he discards as obvious blue gum (E. globulus) hybrids. He is then left wondering about the integrity of the rest. ‘You can’t tell the seeds apart, you can’t even tell the seedlings. You’ve got to grow enough plants to cull some of them.’

  Many strange mergers are made. The rushes growing south of Perth include crosses between two eastern Australian species (Juncus usitatus × J. polyanthemus), and hybrids between an African and native rush (Isolepis prolifera × I. cernua). Victorian sweet pittosporum is crossing with a native tree – banyalla (Pittosporum bicolor) – and also with New Zealand kohuhu (P. tenuifolium) grown in gardens. Other hybrids are arising among correas, tea-trees (Leptospermum laevigatum × L. myrsinoides), paperbarks (Melaleuca armillaris × M. ericifolia), coprosmas (Coprosma quadrifida × C. repens) and willowherbs (Epilobium), promising a tangled future. They appear most often in Victoria, where the bush is whittled down to fragments and native gardening boasts a long history, ensuring ample opportunities for pollen to stray. Sometimes they turn very invasive, a recent article, ‘Hybridization as a stimulus for the evolution of invasiveness in plants?’, listing dramatic examples overseas. Lantana is one amazing example of an invasive hybrid.

  In the Bunya Mountains near Toowoomba giant bunya pines and hoop pines (Araucaria cunninghamii) tower like sentinels above the jungle gloom. When the winding road up the range was realigned in the 1970s, the bare banks were planted with young hoop pines taken from a state forestry nursery that had done breeding trials. The seed came from all over the hoop pine’s range, which runs from New South Wales right up to the highlands of New Guinea. Hoop pines are ancient beyond reckoning, the genus (Araucaria) dating back to dinosaur days. The scattered stands cloistered today on mountain shoulders and tropical islands are genetically isolated.
But in the Bunya Mountains today hoop pines from New South Wales are probably trading pollen with Queensland and New Guinea trees (all inside a national park). Here’s another issue to ponder. We’ve looked at hybrids between species, but what ensues when individuals from the same species but from distant locales are brought together?

  Botanist Julia Playford nominates two possibilities: underdominance and hybrid vigour (heterosis). They mirror what prevails when different species cross. When plants from afar come together they may differ so much genetically they bear little or no seed. But when plants from nearby regions meet, hybrid vigour may produce – for a generation or two, or permanently – robust new strains. The inferior recessive genes that weaken natural populations are masked by new dominant genes. Vegetable growers rely on hybrid vigour to produce robust crops, although subsequent generations are weaker because recessive genes come to the fore again. This can happen in the wild as well.

  Underdominance and hybrid vigour may be affecting many plants. Geraldton wax (Chamelaucium uncinatum) is now rare around Perth, and cultivated forms are stealing away from gardens and probably pollinating the last wild plants, which may either be setting less seed or begetting hybrids. With so many native plants grown in gardens and forestry plots the prospects for genetic rearrangement are endless. Darwin’s nurseries sell plenty of ‘local’ native plants but nearly all of their stock – of more than fifty species – comes from Queensland. The mat-rushes (Lomandra longifolia) grown along Victoria’s highways are also sourced largely from interstate. ‘They’ve got broader, more rigid leaves,’ notes Geoff Carr. He worries about a rare subspecies of yellow gum (Eucalyptus leucoxylon bellarinensis) near Geelong that could be hybridised away by related forms grown in nearby parks. Another rarity at risk is the macadamia nut (Macadamia integrifolia), which lingers on in rainforest pockets in southern Queensland, close to plantations where cross-pollination must go on. The farmed breeds were concocted in Hawaii from a few nuts taken over a century ago. They were bred to produce thin shells around their nuts (for ease of harvesting) which hungry rainforest rats find easier to breach.

  Seed used in regeneration projects is often sourced from far away. Alcoa replanted coalmine spoil near Anglesea, Victoria, with myrtle wattle (Acacia myrtifolia), a local shrub, but used Western Australian seed. The wattles, now growing in their thousands, are taller, longer-leaved, and flower earlier than local plants, with which they probably swap pollen. I’ve also heard of coast wattles grown on New South Wales beaches from South Australian seed.

  Genetic issues are contentious in aquaculture. Many fish stockers look upon different strains of yellowbelly and other fish as resources for breeding trials and not as evolutionary lineages to respect. They mix up breeding fish deliberately or accidentally. Brad Pusey is critical of some Queensland Fisheries work. ‘They don’t give a rat’s arse where the fish come from.’ The Pioneer River near Mackay was stocked with sooty grunters (Hephaestus fuliginosus) bred by mixing fish from several catchments, including the Gulf-flowing Walsh River. But the Walsh River form may prove to be a separate, unnamed species. Fish that won’t mate in the wild are forced into it by hatcheries. Said Brad, ‘They hormonally induce spawning in the female, then they just grab the male and squeeze the milt out of him. There’s no love in it.’ He fears there are many cryptic fish species in north Queensland awaiting discovery, but which hatcheries may be obliterating.

  Redclaw crayfish were first farmed in the 1980s, genetic work began in the 1990s, and already there are new strains that grow 9.5 per cent faster. The Gilbert and Flinders Rivers yield the ‘best’ redclaw, and their progeny will end up everywhere. Queensland Fisheries hopes to create orange-coloured sleepy cod for sale to Asia, and ‘semi-domesticated’ yellowbelly with a taste for dried food. The CSIRO is breeding up bigger Sydney rock oysters, and attempts were made to hybridise tiger prawns. Weird things are entering our waters. Sydney’s Cataract Dam is full of trout cod and Murray cod hybrids, derived from fish that were stocked there long ago, although neither cod belongs locally.

  Australia and Asia share many native plants, and their gene pools can now meet. The native mung bean (Vigna radiata) in northern forests – a vine with tiny blackish seeds – is probably exchanging pollen with Asian cultivars on farms; these grow upright (for easy harvesting) and bear big green seeds. Other plants that straddle both continents include street trees such as weeping fig (Ficus benjamina) and albizia (Albizia lebbeck); garden plants like sword fern (Nephrolepis cordifolia) and maidenhairs (Adiantum); crops such as taro (Colocasia esculenta) and water chestnuts (Eleocharis dulcis); and even weeds such as pigweed (Portulaca oleracea) and pennyweed (Centella asiatica). When I see wild maidenhair near a city, I don’t know if it’s a native plant, a foreign escapee or an inter-continental hybrid. One day we may even see Asian shitake mushrooms (Lentinula edodes), now farmed as vegetables, crossing with the native species (L. lateritia) in our rainforests.

  With so much biotic movement around Australia, populations that appear perfectly natural may well be carrying genes from far away. I’m thinking of all the native seeds riding around on muddy farm machinery, frogs on fruit, caterpillars on pot plants, spiders and beetles in firewood, turtles and parrots escaping as pets, tadpoles moved by frog-breeders, and so much more. Most such movements go unnoticed, but I wonder how often insects and seeds fall off cars when they enter national parks. I wonder about the speargrass seeds in my socks. Only rarely do subtle genetic mixings come to light. Most of Perth’s galahs have red eye-rings marking them out as escapees from the east (western birds are grey-ringed). Studies show that the eastern Australian strain of Ross River virus has taken over around Perth, magnifying health problems. And in Preston, Melbourne, progeny of brown tree-frogs (Litoria ewingii) imported from Tasmania for a pond have spread across six suburban blocks and will soon meet up with local brown tree-frogs and trade genes.

  The gene scene will become a lot messier in future. Nurseries will keep stocking native plants sourced from far away. Plant breeders will concoct more extravagant hybrids. I’ve read about ‘super eucalypts’ – ‘elite clones’ of flooded gums (Eucalyptus grandis) and river red gums (E. camaldulensis) bred in South America that put on wood much faster than anything natural. In replanting schemes more and more non-local seed will be sown. Fish hatcheries and stockers will keep blurring their broods. Populations will lose their regional character as species homogenise. It’s all part of the trend towards global homogenisation, in ecology as well as culture. Gene pools are merging everywhere. Africa’s ostriches, impalas and white rhinoceros have been scrambled, and African wild cats are mating with escaped pets. North America’s bison and trout are a mess. In New Zealand even crickets carried over mountains in firewood are hybridising.

  There’s another matter to consider: inbreeding. When forests are replanted the seeds are often sourced from a few old trees, including remnant eucalypts in paddocks. While the idea of perpetuating the last old-growth giants has appeal, it’s genetically unsound. Isolated trees are often self-fertilising, their young weak and inbred. Seed should be sourced widely from vigorous trees. The same ideal applies in hatcheries. Fish are so fecund that a lazy hatchery can produce hundreds of thousands of nearly identical fingerlings from a few large females. When released into rivers they swamp wild populations and lower genetic diversity, producing populations ill-equipped to cope with change. Inbreeding should be a dire problem for Victoria’s koalas, but so far they remain hardy and fecund.

  The problems with kangaroos, koalas and mesic shift discussed earlier emerged in part because Aborigines were thrown off their lands. Genetic issues are usually different, but not always. In Western Victoria there’s a critically endangered subspecies of pied currawong (Strepera graculina ashbyi) that may already be a footnote to history, swallowed up by hybridisation (introgression) with the common form of pied currawong (S. graculina nebulosa). Sooty-slate, not black, and with not much white on the wing, it was isolated from the rest of its kind
by the grassy plains running west of Melbourne. Stephen Garnett and Gabriel Crowley wrote of its plight: ‘Introgression may have escalated as a result of increases in tree density across western Victoria since the late 18th century after Aboriginal burning regimes were abandoned, but before deliberate tree-clearing was universal.’ In other words, Aboriginal fires kept the populations apart by keeping trees off the plains, fostering the evolution of a distinct form. Isolation is usually a prerequisite to separate evolution. Only hybrid currawongs survive today. Garnett and Crowley suggest that ‘reimposition of a grassy barrier east of the Grampians will allow resumption of earlier evolutionary trends’. But if the pale form arose because of land management, is its conservation important? Only, I suspect, if we value the role people play in ecosystems. Some experts believe that whole eucalypt species, and even certain lizards (Ctenotus), evolved because of Aboriginal fire.

  Another point to ponder is whether we should breed more adaptability into wild populations. If the world is warming up and animals and plants locked away in national parks aren’t coping, should we bring in stock from further north, bearing genes for warmer climes? Farmers want salt-tolerant eucalypts, and scientists hope to breed up jarrah trees (Eucalyptus marginata) that resist root rot (Phytophthora cinnamomi), a devastating exotic disease. J.A. McComb and colleagues have posed questions that apply more broadly: ‘Are we willing to see this type of genetic engineering in our natural ecosystems? Is the damage from Phytophthora and other pathogens so great that we would be willing to make the natural ecosystem, to some extent, un-natural?’ Questions like these will keep arising. Is conservation about preserving the past or preparing for the future?

  Intervention is sometimes essential. Norfolk Island had its own reddish subspecies of boobook owl (Ninox novaeseelandiae undulata), but by 1985 only one remained. To cheat extinction the last bird was paired with a New Zealand boobook (genetically its closest relative). The hybrids are slowly multiplying. When a species is rare, genetic purity may matter less than extinction. Far better to save something than nothing. It’s a consideration for all those endangered marsupials now confined to small islands.