Genetic distinctiveness of the Waikawa Island mouse population

A paper by Ellie Bradley and colleagues has just been published on the haplotype diversity of the Waikawa Island mouse population. Ellie, a student at Massey University, wanted to know if the mouse population on the island were genetically different from the mainland population. The results of the research would have important implications for future rodent control programmes on the island.

Waikawa Island, an island near Mahia Peninsula in the Hawkes Bay, is an important refuge for the New Zealand seabirds including the New Zealand shore plover (Thinornis novaeseelandiae), the New Zealand dotterel (Charadrius obscurus) and white-faced storm petrel (Pelagodroma marina) – as well as two New Zealand endemic lizards, the common skink (Oligosoma polychroma) and common gecko (Woodworthia maculata).

When DOC started their shore plover recovery progamme the island was rat free, although mice are abundant. Unfortunately rats colonised the island, probably by swimming over from the mainland. Their presence was detected when DOC found dead shore plover chicks with signs of rat predation. The shore plovers could survive in the presence of mice but rats were a serious threat.

In 2014 DOC tried to eliminate rats from the island but their efforts were hindered by the mice competing for baits and masking smells used by predator-detection dog. For a rat eradication to be successful the mice population needed to be controlled and a mice eradication programme would only be effective if the probability of mice recolonising the island was low. Removing mice would also benefit other native species on the island.

Ellie's team used genetics and morphology to compare the mouse population on Waikawa Island to the adjacent mainland population and found that Waikawa Island mice are morphologically and genetically distinct from those sampled on the mainland. The study indicates low movement of mice between mainland and island – good news for any possible eradication programme.


Genetic distinctiveness of the Waikawa Island mouse population indicates low rate of dispersal from mainland New Zealand

Ellie Bradley, Steven A. Trewick, Mary Morgan-Richards

New Zealand Journal of Ecology(2017) 41(2)



In New Zealand, mice in reserves can complicate the control of mammalian predator invasion by masking scent and eating baits. Eradicating mice allows predator invasions to be more readily detected and managed, but removal of mice is only feasible if recolonisation is rare. We used genetics and morphology to assess whether the mouse population on Waikawa Island was isolated from the mainland population. A sample of mitochondrial DNA sequences revealed that at least four female mice must have founded the Waikawa population, but that gene flow between island and mainland mice is limited. Although no variation in DNA sequences of exon 1 of the nuclear gene vitamin K 2,3-epoxide reductase subcomponent 1 was detected, the common allele is not associated with resistance to anticoagulant rodenticides such as warfarin. Body size comparisons revealed the island population as distinct, possibly due to age structure differences. We infer low levels of successful dispersal between the mainland and Waikawa Island mice populations and suggest eradication might be sustainable in the long-term if protection against rodent invasion is maintained.