Academic journal article The American Midland Naturalist

Possible Large-Scale Hybridization and Introgression between Longnose Gar (Lepisosteus Osseus) and Shortnose Gar (Lepisosteus Platostomus) in the Fox River Drainage, Wisconsin

Academic journal article The American Midland Naturalist

Possible Large-Scale Hybridization and Introgression between Longnose Gar (Lepisosteus Osseus) and Shortnose Gar (Lepisosteus Platostomus) in the Fox River Drainage, Wisconsin

Article excerpt

INTRODUCTION

Hybridization and introgression betsveen species are relatively common within the bony fishes (Teleostei) and occur across many different families and orders (Hubbs, 1955; Scribner et al, 2001). Hosvever, hybridization has only recently been documented for the more primitive ray-finned fishes (Holostei, sensu Grande, 2010), specifically the gars (Lepisosteidae). Hybrids betsveen Alligator Gar (Atractosteus spatula) and Longnose Gar (Lepisosteus osseus) were reported first from captivity (Herrington et al., 2008) and then later from the wild (Bolin et al., 2017). These hybrids displayed intermediate morphology and had mitochondrial DNAfrom one or the other parental species and were uncommon in the wild, representing less than 1% of the total gars encountered. More recently, tsvo possible hybrids of Longnose Gar and Shortnose Gar (L. platostomus), observed in captivity but originally captured from Green Bay, Lake Michigan, have been reported based on the fish displaying Shortnose Gar morphology but having Longnose Gar mitochondrial DNA (Farley et al., 2018). Suspected Longnose and Shortnose Gar hybrids have also been reported from the wild from the upper Mississippi River in Wisconsin and Minnesota (Schmidt, 2015) and in Iowa and Missouri (Robert Hrabik, Missouri Department of Conservation, retired, pers. comm.), the Missouri River and tributaries in Missouri (Hrabik, pers. comm.), and the Platte River, a tributar)' of the Missouri River, in Nebraska (Sipiorski, 2011; Hrabik et al, 2015).

Longnose and Shortnose Gar commonly occur together in large lakes and rivers in southern Wisconsin (Becker, 1983; Lyons et al, 2000). They are usually easily distinguished in the field by their snout shape; the Longnose Gar has a relatively long and thin snout usually without, but occasionally with, spotting on the dorsal surface, and the Shortnose Gailias a relatively short and broad snout without spotting (Stiukus, 1963; Wiley, 1976; Grande, 2010). Both species are found in the Fox River drainage, including the upper and lower Fox River and its major tributary (the Wolf River) and several relatively large riverine lakes (Poygan, Winneconne, Butte des Morts, Winnebago, and Little Butte des Morts), all of which drain to Green Bay in the Lake Michigan Basin (Fig. 1). Both species are also found in the adjacent Mississippi River Basin, including the Mississippi River and its major tributaries, such as the Chippewa and Wisconsin rivers, with the mainstem of the latter flowing within 2 km of the upper Fox River.

In 2004 anglers reported catching unusual looking gar from the Fox River drainage. These fish had relatively short and broad snouts that were covered with large circular spots and looked superficially like Spotted Gar (L. oculatus), a species not known from Wisconsin. Subsequent pilot sampling and analyses of gar from the Fox River drainage indicated that gar with this spotting pattern were common, including many fish with snout dimensions intermediate between typical Longnose and Shortnose Gar. Scale, fin ray, and gill raker counls on a subset of specimens demonstrated that the spotted forms were not Spotted Gar and were most taxonomically consistent with Shortnose Gar (Stiukus, 1963; Wiley, 1976; Etnier and Starnes, 1993; Ross, 2001; Grande, 2010); however, their atypical appearance suggested they might be hybrids or introgressed individuals (hereafter "hybrids ') between Longnose Gar and Shortnose Gar. These results prompted expanded sampling and analyses of gar from both the Fox and Wisconsin/Mississippi river drainages. The goal of this work was to assess whether hybrids were indeed present. Specific objectives of the increased sampling were to determine the characteristics, distribution, and relative abundance of Longnose Gar and Shortnose Gar and their possible hybrids in southern Wisconsin.

Materials and Methods

Gar sampling look place from 2004-2017 (Table 1) and was piggybacked onto summer daytime nearshore fish community eleclrofishing or seining in the two drainages (Lyons et al, 2001). …

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