Umbra

Robert E. Schmidt & Robert A. Daniels, 2006, Hybridization in Umbridae in the Hudson River, New York, with Designation of Neotypes for Umbra limi and Umbra pygmaea., Zootaxa 1113, pp. 1-20 : 17-18

[[ Genus Umbra ]]

Biogeography

Umbra pygmaea dispersed into the Hudson drainage during or after recession of the Wisconsinan glacier (Schmidt 1986), reaching its present northernmost locality in the Wallkill River (Smith 1985), a Hudson River tributary. The lack of observations of U. pygmaea from the tidal Hudson River raises questions about how hybridization could have occurred. Manitou Marsh is situated 1.7 km north of the narrowest part of the Hudson River estuary (Fig. 1) and directly across the river from Popolopen Brook, a small tributary. The headwaters of Popolopen Brook interdigitate with headwaters of the Ramapo, Wallkill and Moodna Creeks (Woodbury Creek), known to have U. pygmaea populations (Smith 1985). Mearns (1898) and Greeley (1937) did not report U. pygmaea in Popolopen Brook. Recently (November 1997 & July 1998- J. Beemer, US Military Academy, pers. comm.), U. pygmaea was taken in Johnson Meadow Brook (Fig. 1), a Popolopen Brook tributary. The recent collections of U. pygmaea in the Popolopen Brook and lack of earlier specimens from the watershed suggest a recent invasion of the drainage, placing the species very close to Manitou Marsh.

Umbra limi dispersed north and east through the evolving Great Lakes after the Saint Lawrence outlet was opened (Underhill 1986) and eventually into Lake Champlain. Recent (probably 20th century) modifications to the Champlain Canal which connects Lake Champlain with the Hudson River system has encouraged dispersal of fishes through the canal system (Marsden et al. 2000, Plosila and LaBar 1981) and is a likely source of U. limi in the Hudson River.

Both species therefore have recently dispersed from their original native distributions, partially due to human modifications of the landscape. These species have retained the ability to reproduce throughout their Pleistocene isolation and hybridization has probably occurred within the last several decades. The fact that these two species hybridize might be expected given their close relationship, however the ability to reproduce is a plesiomorphic character (Rosen 1979) that, per se, has no taxonomic significance.

Morphology of the hybrids is very similar to that of the parental species which could indicate introgression. Examination of molecular characters could determine whether introgression has occurred. Rab et al. (2002), Kettler et al. (1986), and López et al. (2000) have provided a basis for further research.