Monday, October 5, 2015

Update on the status of the remaining Hawaiian land snail species Part 3: Pupillidae and Succineidae

Norine W. Yeung and Kenneth A. Hayes

     In the third installment of our updates on the status of the Hawaiian land snail fauna we are covering the third and last of our Hawaiian Orthurethran families, the Pupillidae (Figure 1) and our only Elasmognathan representative, the Succineidae (Figure 2).

     The minute (<4 mm in shell height) Pupillidae belong in the Pupilloidea, and are thought to be Holarctic in origin, with a significant number of Pacific island land species.  The family level classifications differ among authors as do placement of genera with the Hawaiian species being treated as belonging to either in Pupillidae (Cowie et al. 1995) or Vertiginidae (Bouchet and Roucroi 2005).  There are 56 Hawaiian species in five genera (number of species in parentheses; Cowie et al. 1995): Lyropupa (22), Nesopupa (20), Pronesopupa (10), Pupoidopsis (1), Columella (3).  The sixth genus in Hawaii is represented by two non-native species, Gastrocopta servilis and G. pediculus (Cowie 1997).  Lyropupa is an endemic Hawaiian genus, Pronesopupa, Nesopupa and Pupoidopsis are distributed throughout the Pacific islands, and Columella has a global distribution.

     Twenty-five years ago Solem (1990) suggested that most of the Hawaiian “pupilloids” were extinct. However, our recent work has recovered multiple endemic taxa. Pronesopupa can be found in low elevation, non-native forests but the remaining Lyropupa and Nesopupa can only be found in upland native forests. Pupoidopsis hawaiiensis is likely extinct in Hawaii. Since 2010 we have recorded 23 species belonging to three Hawaiian genera (Nesopupa, Pronesopupa, and Columella). Ten additional species were recorded, but their native provenances are unknown as they are phylogenetically closer to North American Vertigo spp., a genus not recorded in Hawaii. Several of these unidentified species show conchological affinity to the endemic Hawaiian Lyropupa species, and it is possible that they are indeed undescribed native taxa. Based on preliminary molecular data, it is likely that all Hawaiian species should be referred to the Vertiginidae and not Pupillidae, but a full taxonomic revision of the group is needed.

     Most of the species recorded were from mid- and high-elevation forests and at most locations species appear abundant, with 10+ individuals easily found during our surveys. However for several species, only one or two individuals were found and additional surveys are needed to assess the conservation status of these species. Although we recovered numbers of species equivalent to nearly 58% of the described diversity, less than half of these have been referred to known described taxa, indicating that the historical diversity may have been much higher than initially estimated.

Family: Pupillidae/Vertiginidae
Subfamilies: Nesopupinae, Pupillinae, Vertigininae
Number of recognized species: 56
Number of species found in recent surveys: 23 (10 of unknown origins)
Historical distribution: Kauai, Oahu, Maui, Lanai, Molokai, Hawaii, Niihau, Kahoolawe
Current distribution: Kauai, Oahu, Maui, Molokai, Lanai, Hawaii
Conservation status: Threatened/Endangered

     Succineids have a global distribution primarily in damp areas close to fresh water (Pilsbry 1948, Barker 2001), but a few inhabit vegetated patches in dry areas (Baker 1965; Franzen 1985). In Hawaii, the 42 endemic species range from xeric coastal dunes to high elevation rainforests (Holland & Cowie 2007, 2009). The Succineidae originated in the Eocene in an unknown region (Tillier 1989), although their sister group, the Athoracophoridae, is thought to have originated within the Pacific Islands (Nordsieck 1986, Wade et al. 2006). Together the two families constitute the monophyletic Elasmognatha within the Stylommatophora, supported by molecular and morphological analyses (Dutra-Clarke et al 2001, Wade & Mordan 2001, Wade et al. 2006). The Succineidae are divided into two subfamilies (Succineinae and Catinellinae; Odhner 1950, Patterson 1971, Bouchet & Rocroi 2005), with both subfamilies represented in Hawaii (Cowie et al. 1995).

     The Hawaiian Succineidae have been reported to be one of the few families doing relatively well (Solem 1990), with many succineid species abundant in higher elevational forests. Recent surveys recovered twenty-six species from the six largest Hawaiian Islands. This represents more than half of the estimated diversity. However, similar to many other Hawaiian land snail families, fewer than half of these have been identified to recognized species, and a great deal of taxonomic revision is needed to fully understand the true levels of historical and current diversity.
     Initial phylogenetic analyses are consistent with previous reports of two major clades radiating in Hawaii (Holland and Cowie 2009), and a few taxa show a closer affinity to other Pacific islands than with Hawaiian endemics. All species recorded to date are single island endemics, with the exception of Succinea caduca. This pattern is inconsistent with previous records of many species spread across multiple islands, further suggesting that initial diversity estimates of Hawaiian Succineidae were too low.

Family: Succineidae
Subfamilies: Succineinae and Catinellinae
Number of recognized species: 42
Number of species found in recent surveys: 26
Historical distribution: Kauai, Oahu, Maui, Lanai, Molokai, Hawaii, Niihau, Kahoolawe
Current distribution: Kauai, Oahu, Maui, Molokai, Lanai, Hawaii
Conservation status: Threatened


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Figure 1: Representatives of the Hawaiian Pupillidae A) Vertigo sp., B) Pronesopupa sp.,C) Nesopupa sp., D) Vertigo sp., E) Pronesopupa sp. (scale bar = 1 mm)

Figure 2: Representatives of the Hawaiian Succineidae A) Catinella baldwini, B) Succinea lumbalis, C) Succinea spp. (scale bar = 1 cm)