Invasive history of NZ Daphnia populations
To infer the source of invasive Daphnia pulex/pulicaria in NZ, we
checked the possible routes of Daphnia pulex/pulicaria invasion.
It is thought that D. thomsoni (formerly D. carinata,Burns et al. 2017) and D. tewaipounamu are the only nativeDaphnia species in NZ, although there are several invasiveDaphnia . One recent invader, D. galeata, now common in
lakes throughout the North Island of NZ, may have been introduced to the
South Island during translocation of farmed Chinese grass carp
(Ctenopharyngodon idella ) for the purpose of weed control in
northern South Island waterways (Duggan and Pullan 2017). The presence
of D. pulex in some shallow constructed ponds in suburban
Auckland, North Island, has also been attributed to introductions of
grass carp (Branford and Duggan 2017). However, Chinese grass carp have
only been used for the weed control on the North Island and the northern
tip of the South Island, as water temperatures in southern NZ are
generally too cold for these fish. Therefore, it is highly unlikely that
grass carp were a major vector for the introduction of D.
pulicaria to the South Island.
Duggan et al. (2012) suggested introduced salmonids (trout, salmon) and
associated recreational fishing equipment as potential vectors forD. pulicaria on the South Island. The most common salmonid in NZ,
Chinook salmon (Oncorhynchus tshawytschca ), was initially
introduced from the Sacramento River, California, USA to South Island,
NZ, between 1901 and 1907. Salmon fishing in NZ has become popular since
the 1970s and has attracted many international tourists. The D.
pulicaria clone on the South Island has been known to produce
diapausing ephippia, which float on the water surface for long periods,
adhering to any surfaces they encounter, such as fishing equipment,
skin, fur, feathers, and clothing (Burns 2013). The movement of these
ephippia attached to recreational equipment, people, and wildlife may
facilitate the spread of D. pulicaria in lakes in the South
Island, NZ. In support of this, the invasion time estimated from the
molecular data is roughly consistent with transport during this period.
As noted above, the North Island Daphnia has only one nucleotide
difference on the COI gene compared to the JPN 1 clone that invaded
Japan (So et al. 2015), which suggests the possibility of a recent
transfer from Japan.