For 150 years there has been rivalry at every level - sporting, economic, religious and cultural.
And still, as our feature writers have discovered in the aftermath of the Christchurch earthquake, while there are ties that connect the two largest centres of population on this shaky isle, such things as globalisation and centralisation have done little to erode a very real independence.
The positive aspect of that appears to be that when Christchurch sneezes Dunedin does not necessarily catch a cold, reports Mark Price.
Dunedin firefighters, council staff, soldiers and media are there already. The city's builders are expected to follow.
Dunedin has been quick to lend a hand; no questions asked.
One way or another, Christchurch will form a much greater than normal part of Dunedin's consciousness over the coming weeks, months and years.
But, what is the normal relationship between the South Island's two biggest cities?Lincoln University geographer, and now Christchurch resident, Prof Ali Memon spent 20 years at the University of Otago.
This week, Prof Memon was one of the few able to say much about this little-studied relationship and about how events in one city might affect the other.
In the end, all he could point to, when pressed to help out, was the likely impact of the earthquake on Dunedin's labour market.
He expected Dunedin tradespeople would be called on to play a role in the rebuilding of Christchurch.
The history shows two quite distinctive cities growing in isolation from one another - separated by 360km of difficult terrain, religious suspicion and commercial rivalry.
And, while the political upheavals of the mid-1980s and the move to globalisation have had an effect in a few gradual and subtle ways, the change has not brought the two cities much closer together.
And, therefore, disaster in Christchurch has not left Dunedin in the lurch.
Take food for example.
Christchurch acts as a food distribution hub for the whole South Island with major factories based there that bottle milk and water, bake bread, and make other groceries.
Not surprising then that supermarkets here have had a few shortages of some products. But, problems have been minor and temporary.
Craig Nieper, owner of Centre City New World, says they are simply now sourcing items from Auckland or Wellington that would normally come from Christchurch.
And while Christchurch is a big producer of bread, Quality Bakers still has bakeries around the South Island, including in Dunedin and Invercargill.
Terry Brown, group marketing manager for Turners and Growers, says probably about half the fresh vegetables and fruit sold in Dunedin is grown in the southern half of the South Island and most will go directly through its Dunedin distribution centre to local supermarkets and stores.
Milk is the product for which Dunedin relies most heavily on Christchurch. Almost all milk for the South Island is bottled there and it is only because the Christchurch plants survived the earthquake that supplies to Dunedin have not been disrupted.
Otago Associate Professor Etienne Nel specialises in economic geography.
He notes the worldwide trend towards centralisation in the manufacturing of goods and provision of services.
"It's a question of the economies of scale whereby it is just more cost-effective to have large distributional hubs.
"Whether one's talking about air freighting or fresh produce supply, the scenario is pretty much the same.
"For example, in the United States years ago they moved into the concept of hub airports.
"It is just so much more logical to route everyone through a single hub and then send them out from there to another destination rather than attempt to have a spider web of flights all over the country."
Prof Nel says increased mechanisation also drives centralisation at the expense, for instance, of "local micro-bakeries".
"Something like mass production of ordinary regular bread probably isn't cost-effective anymore because the demand is so great that you need bigger production facilities."
The process of centralisation has left Dunedin producing very few packaged goods such as cereals, biscuits, flour, tinned and dry goods.
It leads to odd situations where Ettrick apples and Otago potatoes destined for Dunedin are transported to Christchurch first.
And it makes Dunedin more reliant on transport links, whether they be the road to Christchurch, the air-link to Auckland or the shipping-container service to Australia and beyond.
Green Party MP Sue Kedgley says centralised production and distribution is driven by supermarkets trying to drive down costs.
She argues it does not pay attention to the need to encourage local food production which is more resilient to disruption.
"Centralised distribution is more vulnerable to natural or global disasters such as earthquakes or oil prices," she says.
She is pressing for New Zealand to develop a national food security strategy as other countries are doing, to ensure that for the long term, New Zealand can feed its population "at all times and in all places".
The experience on this occasion is that foodwise, Dunedin can get by quite comfortably during a severe earthquake in Christchurch.
Thankfully, the extent to which Dunedin relies on Christchurch's health services was not put to the test.
Christchurch's hospital buildings came through in good shape. But had they been badly damaged the effects would have been felt in the South.
Southern DHB (Otago) chief operating officer Vivian Blake says: "Canterbury DHB is the largest tertiary referral centre for the South Island, so all DHBs are dependent on Christchurch for a number of specialty services, such as paediatric oncology".
Dr Robin Gauld, associate professor of health policy at the University of Otago, says the earthquake has thrown up some important issues about what would happen if Christchurch went down completely, and its health services with it.
"If Christchurch were to collapse, Dunedin would have to pick up the slack in the system."
That would be particularly the case where there was significant trauma.
Prof Gauld says the earthquake has struck at an interesting time in the debate over the siting of neurosurgery services, and does seem to underline the importance of Dunedin maintaining some capacity in that area of medicine.
"You need to have surge capacity; you need to have capacity at different points in the health system."
He considered it was a miracle that there had been so few serious injuries as a result of the 7.1-magnitude earthquake, given the many deaths in similar events overseas.
"If you had 500 people who had head injuries in Christchurch, they would have been overwhelmed."
The extent to which Dunedin relies on Christchurch for emergency communication also went untested.
Dunedin City Council civil defence manager Neil Brown says that while in an emergency the organisation has to plan to be without some external links, Dunedin does not have a critical dependency on any one city and alternatives can be found for most things.
Most radio stations broadcast out of Auckland or Wellington, at least overnight, but local staff can use a broadcast facility in the Dunedin civil defence operations building if needed, Mr Brown says. That happened a few years ago when there was a fire on the Pigroot, inland from Palmerston, and the public needed to be advised of a road closure.
Dunedin 111 calls to police, fire and ambulance services are no longer answered in Dunedin. They are dealt with in Christchurch, Auckland or Wellington.
However, emergency service spokesmen say if one communications centre has to close for a time, calls are automatically diverted to one of the two other centres - a process that already happens when staff are busy.
Inspector Kieren Kortegast, manager of the police south communications centre in Christchurch, considers centralisation has had more benefits than drawbacks.
Years ago, he says, calls went to the control rooms of local police stations, where staff had multiple tasks including looking after the public counter and sometimes helping with prisoners.
"The three centres have given us the power of pooling. There's a large number of staff and they're solely dedicated to emergency calls, general calls for service and dispatching patrol cars.
"The other issue is technology is horrendously expensive ... and you can't afford to equip 50 police stations."
In a period of two and a-half hours on the morning of the earthquake, the three police communications centres took 600 calls more than they normally would, says Insp Kortegast.
And because the Christchurch centre lost mains power and was running on a generator, police stations in Nelson, Timaru, Dunedin and Invercargill were put on stand-by, ready to dispatch their own patrols and take their own general calls if required.
Dunedin would have handled the city as well as the rural area from Oamaru to Queenstown.
This did not prove necessary but did work "seamlessly" a few months ago when the Christchurch centre had a total power outage and was down for a few hours.
"It's all planned for and practised."
Beyond food and emergency communications, Dunedin City Council economic development adviser Des Adamson could think only of Otago's reliance on Christchurch as the "gateway" for tourists.
"But generally speaking, we haven't got any major reliance on the city of Christchurch.
"We're reasonably well off in that goods and services side of things, I think."
Economic unit manager Peter Harris believes Dunedin's relationship with Christchurch is something "we take for granted" and the issue of the rights or wrongs of centralisation depend on individuals' world-views.
"The people who are talking about peak oil would say it's more likely to sort of reverse a little bit and production become more localised.
"But then, the challenge is that often the transport costs aren't necessarily a major part of the cost of a product.
"It's one of those debatable points."
He and others agree there is a tradeoff - cheaper-priced goods from efficient centralised production plants versus security of supply.
Prof Nel: "I think these are part of the risks of the modern economy".
"This is what happens where often there's quite a fine profit margin being traded off and when things do go wrong, the consequences are unfortunately reaped.
"It does expose your vulnerablilities should any break become extended."
Dr David Hayward, associate director of the University of Auckland's school of environment described the "drift" of head-office functions towards Auckland and across the Tasman as "just one very geographical facet of globalisation".
He suspects the "physical reality" of New Zealand means many functions need to remain in the South Island but "the inexorable logic towards concentration" will strengthen Christchurch's dominant position because of its size and central island location.
"And whether it's Christchurch, Auckland, Sydney or New York, once certain functions concentrate then they will create their own economic dynamics. It's what geographers and, more recently, economists refer to as agglomeration.
"Presumably it is especially disturbing for Dunedin since one logical outcome may be a hierarchy of a single South Island capital and then some provincial centres.
"Not a great prospect for Dunedin, I suppose."
BUSINESS LINKS
Otago Chamber of Commerce chief executive John Christie believes business links between the two cities are often unseen and Dunedin people will have been directly affected.
"I think we have more interaction with Christchurch than people perhaps fully understand."
He cites, as examples:
"There are several businesses from here that I know have operations and businesses that they conduct in Christchurch. It might be retailers from here that own retail stores in Christchurch.
"There are people in Dunedin who own property in Christchurch.
"There are investors that are part of consortiums that own commercial properties in Christchurch.
"There are business people here who contract for services out of Christchurch.
"There are businesses here who are part of networks or chains that also have operations in Christchurch either owned from here or owned elsewhere.
"There's a lot of consultancy done from Dunedin to Christchurch.
"There are probably a lot of [Dunedin] student flats owned by people in Christchurch who may now look to sell them to get cash back into their businesses or get equity back into other things closer to home."
Mr Christie believes while some Dunedin people will be adversely affected, others will be presented with opportunities.
"I know of one stockbroking firm that has picked up the overload out of that region until their office gets up and running again.
"There's some opportunity there for local business in terms of the supply of products and people to help rebuild infrastructure and housing.
"There will also be opportunities around providing services that Christchurch might not be able to provide for some time.
"If people were using Christchurch as a hub to distribute . . . they may review whether or not that is something that is in their long-term strategy now that there's been the earthquake."
- Additional reporting by Kim Dungey, Charmian Smith and Tom McKinlay
