Speciation in New Zealand

New Zealand is special… NZ has a wide range of microhabitats. We have been isolated from our nearest neighbouring land mass for about 80 million years. We have had many new species form during that time. This has occurred by: Speciation Dispersal – new immigrants arriving by air (many birds have flown in) and water (swimming here). These organisms are subjected to new selection pressures.

Geological events The Oligocene drowning New Zealand's landmass above water is just the tip of a much larger continent below sea level called Zealandia. Its visible shape has continued to change ever since it broke off from Gondwana more than 80 million years ago and drifted to its current position in the South Pacific.

Based on geological and biological evidence scientists agree that the deepest submergence occurred during the Oligocene, around 25 to 23 million years ago. In the 1960s, Sir Charles Fleming sketched maps that depicted Zealandia's changing shape and shrinkage.

The ‘drowning’ of the land would have caused many NZ flora and fauna to be lost. Only swampy low-lying land was emergent above the sea with small outposts of Gondwanaland survivors found in Coromandel, Waikato, Nelson and Otago, and the far North. No hills were higher than 300m above sea level. Extinction may have occurred with genetic bottlenecks for survivors: specifically wrens, ratites and kiwis.

The uplifting of the Southern Alps Watch Zealandia Occurred 5mya. Divided East/West- made a rain catchment in the West and drier rain shadow in the East. 25 to 15 million years ago the majority of New Zealand was covered by the ocean. As the Australian and Pacific tectonic plates began to collide with each the New Zealand crust came under pressure and the Alpine Fault was created.

The East/West division Led to allopatric and sympatric speciation within a small area with perhaps different selection pressures from neighbouring isolated pockets. Later retreats of glaciers will have left populations reproductively isolated and thus speciated.

Pleistocene Ice ages The Pleistocene period, which saw the climax of the New Zealand mountain-building movements, was the time of the world Ice Age. The Pleistocene period is often stated to have begun about 1 million years ago. New Zealand was of low enough latitude for its high mountains to be heavily glaciated during the Ice Age. Cooling resulted in glacial snouts protruding across the East Coast, dividing Canterbury and the more southern plains into isolated pockets of bush.

Changing climatic condition and microclimates open new niches such that sympatric speciation may occur for species living in the same area. Dispersal supplies constant new species that can take advantage of empty niches in NZ. Selection pressures will be different from point of origin for immigration species and will result in rapid speciation.

Predator-free NZ NZ birds evolved without predators. They lacked the normal fear response and are generally poor fliers. What did this mean when we first introduced predators? For conservation purposes we generally put vulnerable birds onto ‘predator free’ islands. What are the genetic consequences of this? - newly established popn has few individuals = founder effect issue. - parental popn has reduced numbers = bottleneck may result.

Conservation strategies The choice of which individuals to transfer. Optimum to transfer individuals with wide genetic base (reduce interbreeding). If parentage known, then choose unrelated individuals. As the popn increases in size: Isolated populations have isolated gene pools but individuals can be transferred between populations. Has the effect of increasing the effective gene pool to include all individuals of the species.

3. Strategy dealing with individuals that exhibit less favourable phenotypic traits. These individuals (possibly as the result of inbreeding and the homozygous occurrence of less favourable alleles) should be eliminated. In birds it might be possible to use these birds as surrogate parents so their non-breeding status need not reduce the population growth rate