Megadromus speciosus (Picton ground beetle) is found in just a few forest remnants, in northern South Island New Zealand.[1][2] The species is typically found under stones and logs, and in areas with deep leaf litter.[2] The habitat is heavily influenced by the presence of wild pigs, which have caused extensive damage to the soil surface and understorey vegetation, particularly at Port Underwood.[2] The species also shows a preference for undisturbed native vegetation.[2]
The species is confined to isolated populations in the Marlborough Sounds, northern South Island, New Zealand.[2] Specifically, it is found at Port Underwood Saddle and Arapawa Island.[2] The Arapawa Island population appears to be more secure, while the Port Underwood population is under threat from habitat degradation.[2] A historical report suggested the presence of the species on Blumine Island, but this was not confirmed in recent surveys.[2] Niche modelling used to study the distribution of this genus found that 50% of the predicted range of Megadromus speciosus is within the New Zealand protected areas network.[3]
Morphology
Megadromus speciosus is described as a large, stout-bodied beetle with a length of 23-26 mm.[2] The dorsal surface of the head and pronotum is greenish, while the elytra have a coppery-purple sheen.[2] Male genitalia are distinct, with an enlarged mesotibia and a forked left paramere.[2] The morphological conservatism within the genus makes species identification challenging without examining genitalia.[2]
Taxonomy
Megadromus speciosus was described in 2007 by Peter Johns from specimens collected from Nothofagus forest near Picton (Port Underwood).[1] The genus Megadromus is part of the Carabidae family, which comprises large, flightless beetles.[2]
Genetic analysis of mitochondrial DNA sequences (COI and ND1 genes), show that M.speciosus is distinct from other related species, with significant sequence divergence.[2]
Conservation status
Under the New Zealand Threat Classification System, this species is listed as "Relict" with the qualifiers of "Range Restricted" and "Biologically Sparse".[4][1] The species is formally protected under the Wildlife Amendment Act (1980) and has been included in various conservation ranking systems due to its vulnerability to habitat modification and introduced predators.[2]
The primary threat to Megadromus speciosus is habitat degradation caused by wild pigs, especially at Port Underwood Saddle.[2] The pigs have extensively damaged the soil surface and understorey vegetation, which are critical for the species' survival.[2]
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