Philonthus hepaticus ( Coleoptera , Staphylinidae ) in eastern Canada : are distribution gaps distinctive features or collecting artifacts ?

Philonthus hepaticus Erichson is reported for the fi rst time in eastern Canada, and for only the second time in Canada, from a specimen collected in New Brunswick. Th is discovery provides an opportunity to examine apparent distribution gaps in the range of some rove beetles found in the Maritime Provinces of Canada. Some of these gaps may be due to defi ciencies in collecting eff ort, while others may result from historic and prehistoric dispersal pathways, habitat fragmentation, or physiographic or climatic factors that allow species to exist in areas beyond their primary geographic range.


Introduction
Th e zoogeography of the Staphylinidae in Atlantic Canada is still imperfectly known, and knowledge of this speciose family in the region is still actively developing.Some Atlantic Canadian species exhibit striking apparent gaps in distribution.Th e Aleochari-nae are the most poorly known subfamily of the Staphylinidae, and as Majka and Klimaszewski (2008) pointed out, the confused and poorly understood systematics and taxonomy of the group, their small size, the specialized microhabitats they inhabit, and the external similarity of many species, have meant that they have been largely ignored in many faunistic, zoogeographic, ecological, and taxonomic studies.Majka and Klimaszewski (2008) provided 94 new provincial and state records of 53 species of North American aleocharines, which included many signifi cant range extensions.Consequently, apparent distribution gaps in the range of most aleocharines may simply be an artifact of collecting eff ort, or the lack of taxonomic resources to identify specimens.
However, even amongst the Staphylininae, arguably the best-known subfamily of rove beetles in North America, there are Atlantic Canadian species that exhibit significant distribution gaps.Some examples include Acylophorus caseyi Leng, which is known from Halifax and Waverley, Nova Scotia, and is otherwise recorded in eastern Massachusetts (a distribution gap of 685 km); Hemiquedius ferox (LeConte), which is known from Halifax and Crescent Beach, Nova Scotia, and is otherwise recorded in Paris, Maine (550 km); Quedius spelaeus spelaeus Horn, which is known from several sites in Hants County, Nova Scotia, and is otherwise recorded from Sullivan County, New York, (950 km) (Smetana 1965(Smetana , 1971) (Fig. 1); Gabrius ulpius Smetana, which is known from the Aspy River, Nova Scotia, and is otherwise recorded from Gorham, New Hampshire (860 km); Philonthus rufulus Horn, which is known from Sable Island, Nova Scotia and is otherwise recorded from southwestern Maine (880 km); and Philonthus thoracicus (Gravenhorst), which is known from Kouchibouguac National Park, New Brunswick, and is otherwise recorded in Paris, Maine (510 km) (Smetana 1995) (Fig. 2).

Results
In the present paper we add a further species to this roster, Philonthus hepaticus Erichson, 1840, on the basis of a specimen collected in Bouctouche, Kent County, New Brunswick (46° 25΄ 39.56˝ N, 64° 45΄ 50.35˝W) on 28 September 2007, by J.-P.Michaud.Th e specimen was recovered on a domestic pig (Sus scrofa Linnaeus) carcass that had decomposed for 22 days in an agricultural fi eld.For a comprehensive description of fi eld characteristics and of the methods used to collect specimens, see Michaud and Moreau (2009).Th is represents the fi rst record of this species in eastern Canada, and only the second Canadian record.Th e single previous Canadian record was a specimen collected in Vancouver, British Columbia, 3 August 1956 by B.F. and J.L. Carr (Smetana 1995).

Discussion
In terms of the bionomics of the species, Smetana (1995: 179) wrote that, "Philonthus hepaticus occurs in various kinds of rotting organic matter, such as dung (particularly horse and cow dung), rotting and fermenting fruit and vegetables, compost piles, grass cuttings, etc. Specimens were also taken by sifting litter and other forest fl oor debris, in seaweed and other beach debris and from litter along streams…." In general, P. hepaticus occurs across the United States from Massachusetts to northern California, on an arc roughly south of 41° N latitude, south to the states of Puebla and Veracruz in southern Mexico (19° N latitude).Consequently its discovery in eastern New Brunswick, approximately 680 km north of central Massachusetts where it has been previously recorded (Smetana 1995) is noteworthy (Fig. 3).Th is initial record should be followed by further research to determine the extent of this species' distribution in the province.
Philonthus hepaticus is a fully macropterous species capable of fl ight.Smetana (1995) noted that fl ight ability in the Philonthina is best developed in species that are predaceous on insects and their larvae (particularly Diptera), which are found in decompositional environments.Such species have sensitive olfactory chemoreceptors for detecting byproducts of decomposition, and fl y quickly and readily in search of food.Th ey are also ready crepuscular dispersers, and their highly developed fl ying ability has (in part) been instrumental in the vast ranges exhibited by many species of Philonthus.All this is likely to be true of P. hepaticus; however, it is also the case that with the exception of a couple of records (from British Columbia and Montana) the entire range of this species lies south of 41° N latitude, apparently indicating that despite the apparent dispersal abilities of this species, climatic, physiographic, ecological or other factors have limited the nothward extend of its distribution.In this regard it is noteworthy that the Northumberland Coastal Plain of the Atlantic Maritime Ecozone (where Bouctouche is situated) has the highest mean summer temperatures (together with isolated small pockets elsewhere), averaging + 19°C (1951-1980 values) of any region in Atlantic Canada (McCalla 1988).Perhaps this is a contributing factor that allows P. hepaticus to survive in this area.
Philonthus hepaticus has in common with the rove beetles listed above, a distribution that apparently stops in central or northern New England, and then resumes in the Maritime Provinces of Canada.In some instances, this distribution pattern may be an artifact of collecting history, but in the case of some species such as Q. s. spelaeus (Moseley et al. 2006) and P. rufulus, these distribution gaps appear to refl ect genuine disjunctions and indicate populations isolated from the balance of the range of the species.Th ere are many examples of such species amongst other families of Coleoptera.A  4). Majka and McCorquodale (2006) pointed out that some disjunct distributions in this region are similar to those of the coastal plain element of the Nova Scotian fl ora, plants which are found north to New England in the United States, whose distribution then resumes in southern Nova Scotia.Keddy and Wisheu (1989) proposed that the coastal plain fl ora arrived in southern Nova Scotia after the Wisconsinian glaciation by Philonthus hepaticus in eastern Canada: are distribution gaps distinctive features or collecting artifacts?353 migrating across Georges Bank to Browns Bank and thence to the mainland of the province.Klimaszewski et al. (2006) discussed the role of off shore glacial refugia like Georges Bank, and post-glacial island networks in the invertebrate colonization of Sable Island.It is possible that some roves beetles with such disjunct distributions could have dispersed to the Maritime Provinces via this pathway, accounting for such observed distribution patterns.Others may have dispersed to the region via continental pathways, and have subsequently been isolated from the balance of their respective ranges by changing environmental circumstances.Still others may not be disjunct at all (see below).
Are such disjunct distribution patterns real, or are they simply an artifact of collection eff ort?Only further research will resolve these questions.In particular, biodiversity research on Coleoptera in the state of Maine, a key area in discerning the faunistic relationships between New England and Atlantic Canada, has been fragmentary to date.Some of these distribution gaps (i.e., for species such as Quedius s. spelaeus, Philonthus rufulus, Ephalus latimanus, and Cicindela marginipennis) are clearly not simply artifacts of collecting eff ort.Th ey may be a result of a variety of factors including historic and prehistoric dispersal pathways, habitat fragmentation, and physiographic or climatic factors that allow species to exist in areas beyond their primary geographic range.Although many questions remain to be answered, such preliminary fi ndings point the way for profi table future biodiversity and zoogeographic research.