Palirhoeus Explained

Palirhoeus is a monospecific genus of beetle found on islands in the Sub-Antarctic Indian Ocean.^[1]

Taxonomy

Palirhoeus eatoni is the only species within the genus Palirhoeus. This weevil species^[2] was described in 1876 by the British entomologist C. O. Waterhouse who placed it in the genus Ectemnorrhinus.^[3] In 1971, Chilean-New Zealand entomologist Guillermo Kuschel created the monospecific genus Palirhoeus.

Description

Palirhoeus eatoni is a weevil in the tribe Ectemnorhinini with seven larval instars.^[4] Adult females are on average larger (4.4 mm) than males (3.9mm).^[5] Adults are black or dark brown with a slight metalic sheen. Thorax has keel-like ridge.

Biology

Palirhoeus eatoni lives on the shoreline (in the littoral zone),^[6] where it feeds on marine algae and lichens. The species is tolerant of cold but cannot survive freezing. This beetle is unusual in that it needs to osmoregulate to survive in both fresh and seawater.

Distribution

This weevil species lives on islands in the Sub-Antarctic Indian Ocean: Heard Island, Crozet, Kerguelen, Prince Edward and McDonald Islands. A genetic signature of isolation by distance in this species suggests that it disperses via rafting.

Conservation status

Palirhoeus eatoni is found on two of the islands in the Prince Edward island group, i.e. Marion Island (with mice) and Prince Edward Island (without mice) but as they are not eaten by mice the individuals from the different populations on the two islands cannot be distinguished on body size.^[7] However, weevil samples collected over 50 years show signs of morphological change in this species (reduction in body size) associated with climate change.^[8]

Notes and References

1. KLOK . C. JACO . CHOWN . STEVEN L. . 2003 . Resistance to temperature extremes in sub-Antarctic weevils: interspecific variation, population differentiation and acclimation . Biological Journal of the Linnean Society . 78 . 3 . 401–414 . 10.1046/j.1095-8312.2003.00154.x . 0024-4066.
2. van der Merwe . M. . Chown . S. L. . Smith . V. R. . 1997 . Thermal tolerance limits in six weevil species (Coleoptera, Curculionidae) from sub-Antarctic Marion Island . Polar Biology . en . 18 . 5 . 331–336 . 10.1007/s003000050196 . 1997PoBio..18..331V . 1432-2056.
3. Waterhouse . C. O. . 1876 . Description of a new species of Ectemnorrhinus from Kerguelen Land . Entomologist's Monthly Magazine . 13 . 51–52.
4. Chown . S. L. . 1993-01-01 . Instar number and mass of Palirhoeus eatoni (C. O. Waterhouse) and Bothrometopus randi Jeannel (Coleoptera: Curculionidae) from subantarctic Marion Island . Coleopterists Bulletin . English . 47 . 1 . 69–73 . 0010-065X.
5. Chown . S. . Klok . C. . 2001 . Habitat use, diet and body size of Heard Island weevils . Polar Biology . en . 24 . 9 . 706–712 . 10.1007/s003000100281 . 2001PoBio..24..706S . 1432-2056.
6. Baird . Helena P. . Shin . Seunggwan . Oberprieler . Rolf G. . Hullé . Maurice . Vernon . Philippe . Moon . Katherine L. . Adams . Richard H. . McKenna . Duane D. . Chown . Steven L. . 2021 . Fifty million years of beetle evolution along the Antarctic Polar Front . Proceedings of the National Academy of Sciences . en . 118 . 24 . 10.1073/pnas.2017384118 . free . 0027-8424 . 8214695 . 34108239. 2021PNAS..11817384B .
7. Treasure . Anne M. . Chown . Steven L. . 2014 . Diez . Jeffrey . Antagonistic effects of biological invasion and temperature change on body size of island ectotherms . Diversity and Distributions . en . 20 . 2 . 202–213 . 10.1111/ddi.12153 . 2014DivDi..20..202T . 1366-9516. free .
8. A morphological analysis of weevils from sub-Antarctic Prince Edward Islands: an assessment of ecological influences . University of Pretoria . 2007-08-24 . Thesis . Lindie . Janse van Rensburg. 2263/27500 .