Davacarus gressetti Hunter

Davacarus gressetti Hunter

(figure 3A)

Material examined. PARATYPES: South Georgia: female, King Edward, 12–14 November 1963, ex nest of shoemaker (Proceilaria aequinoctialis); male, Bird Island (54‡30’S, 38‡00’W), Macaroni Creek, 9 April 1963, ex nest greyheaded albatross, coll. H. B. Clagy. In OSAL.

Other material examined. Îles Crozet: female, Île de la Possession, Baie du Navire near Port Alfred (46‡25’S, 51‡48’E), 2 July 1968, ex Poa cookii tussock on peat, coll. L. Davies. In OSAL. Heard Island: female, deutonymph, two males, Spit (53‡07’S, 73‡30’E), King Penguin, Pringlea, 21 October 1985, coll. H. Burton. In ANIC.

Diagnosis. Brown davacarid mites with weakly reticulate podonotal shields; simple, relatively short opisthosomal setae: seven to eight setae on each mesonotal shield, 10 pairs of setae on the ventrianal shield; sternal setae st1 on small platelets. Anterior opisthosomal gland (gld1) on small platelet with two pores; all glands sessile. Endogynium (figure 3A) with strut-like base and a pair of lozenge-shaped processes with sparse punctae.

Remarks. Davacarus gressetti was based on a series of 43 females, 46 males and 29 nymphs from collections on the western subantarctic Bird Island (54‡00’S, 38‡00’W), at the north-western extreme of South Georgia Island and from Royal Bay (54‡30’S, 36‡00’W) on the eastern side of the main island. The holotype female is from the nest of a black-browed albatross, and most of the rest of the series was from the nests of other seabirds (grey-headed and wandering albatross, dove prion, diving petrel and shoemaker), under rocks in a gentoo penguin rookery or in tussock grass. Subsequent collections have turned up D. gressetti on subantarctic islands far to the east (Île de la Possession, Heard Island), also in association with seabirds or grass tussocks. Only minor morphological variation seems to occur among these disparate populations on small oceanic islands, suggesting the existence of phoretic dispersal on seabirds. Such behaviour has not been shown in other Cercomegistina, but may have evolved in response to deteriorating climate in Antarctic populations during the Tertiary.