MELAS

Abstract -Natural hybridization is rare in the family Ictaluridae. Putative hybrids of the madtoms Noturus flavus and N. insignis were collected from Blackwater River, Monongahela River drainage, WV. Noturus flavus is native to the Monongahela River drainage, whereas N. insignis is nonnative. We quantified morphological differences among N. flavus, N. insignis, and putative hybrids by sheared principal components analysis of morphometric characters. Putative hybrids were intermediate in tooth patch dimensions, caudal fin pigmentation, length of the dorsal fin base, distance between the adipose/caudal notch and base of caudal fin, and position of anal fin. Hybridization between N. flavus and N. insignis is supported by morphological intermediacy, and may be linked to higher abundances of N. insignis or degraded habitat in the Blackwater River.

Introduction

Natural hybridization has been reported in several families of fishes, including catostomids (Hubbs and Hubbs 1947), cyprinids (Meagher and Dowling 1991), centrarchids (Hubbs and Bailey 1940), salmonids (Leary et al. 1983), cottids (Strauss 1986, Zimmerman and Wooten 1981), and percids (Hubbs and Strawn 1957, Page 1983). Natural hybridization is rare in the family Ictaluridae (Jenkins and Burkhead 1993, Taylor 1969), and includes bullhead hybrids Ameiurus melas Rafinesque x A. nebulosus Lesueur (Trautman 1981) and madtom hybrids Noturus exilis Nelson x N. miurus Jordan (Taylor 1969) and N. gyrinus Mitchill x N. miurus (Menzel and Raney 1973, Trautman 1948).

Natural hybridization may result from accidental egg/sperm contact, or mismating (Jenkins and Burkhead 1993). Accidental hybridization may occur when species spawn in close proximity, such as in nest-associated species (Johnston and Page 1992, Raney 1947) or when suitable spawning habitat is rare (Jenkins and Burkhead 1993). Rareness of one or both parental species may increase hybridization (Taylor 1969) and can result from population decline or an introduction event (Raesly et al. 1990). Habitat degradation may promote hybridization through its role in population decline or loss of spawning habitat. Additionally, habitat degradation may reduce water clarity and impair mate recognition.

Herein, we report natural hybridization between the stonecat, Noturus flavus (Rafinesque), and the margined madtom, Noturus insignis (Richardson), in the Blackwater River of the Monongahela River drainage, WV. Noturus flavus is native to the Monongahela drainage and widely distributed in the Mississippi River and Great Lakes drainages. Noturus insignis is native to Atlantic coast drainages, and probably introduced where it occurs in Big Sandy Creek and Blackwater River, WV (Jenkins and Burkhead 1993, Stauffer et al. 1995). Posterior extensions on the tooth patch, a lack of dark pigmentation on anal, caudal, and dorsal fin margins, and a lack of prominent posterior serrae on pectoral spines separate N. flavus from N. insignis. During field collection, individuals with reduced posterior extensions of the tooth patch were provisionally identified as putative hybrids.

Methods

A total of 20 N. flavus, 13 N. insignis, and 11 putative hybrids of N. flavus x N. insignis were collected for morphological study. All of the specimens, except for 13 N. flavus, were collected with rotenone from Blackwater River (Monongahela River drainage), Tucker County, WV, on 8 Sept 1997. The 13 additional specimens of N. flavus were collected from the Cheat River (Monongahela River drainage, Preston County) at Seven Islands, WV (11 individuals; 12 Sept 1980), and at Rowlesburg, WV (2 individuals; 18 Sept 1995). All individuals were preserved in 10% formalin for two weeks and transferred to 70% ethanol. For each individual, we recorded 22 distance measurements (nearest 0.1 mm using dial calipers). Sixteen morphometric characters formed a truss system of midsagittal landmarks modified from that of Strauss and Bookstein (1982), whereas an additional six distances measured head shape and body width (Fig. 1). Sagittal landmarks on the ventral surface of the head were excluded from the truss network due to low repeatability of measurements. Intermediate tooth patch dimensions were also excluded from analysis; their use in field identification of putative hybrids and in morphometric analysis would be logically circular. We recorded fin pigmentation and presence (prominent or moderate) or absence of posterior serrae on pectoral fin spines. Also, the angle of the adipose/caudal notch was estimated with a protractor.

Morphologic variation among individuals was quantified with sheared principal component analysis (SPCA) of morphometric characters (Bookstein et al. 1985, Humphries et al. 1981) with SAS code written by D. Swofford (Statistical Analysis Systems Institute, Inc., Cary, NC). Shape variation among N. flavus, N. insignis, and putative hybrids was depicted as plots of the sheared second principal component (SPC2) versus the sheared third principal component (SPC3). Multivariate analysis of variance (MANOVA) was used to examine morphometric (SPC2 x SPC3) clusters of N. flavus, N. insignis, and putative hybrids. Tukey-Kramer tests were conducted for multiple comparisons.

Results

Putative hybrids were intermediate in several morphometric variables that differed between purported parental species (Fig. 2). A MANOVA indicated significant differences among morphometric clusters of N. flavus, N. insignis, and putative hybrids, and Tukey-Kramer tests showed significant differences among all clusters along the SPC2 axis. Based on sheared principal component analysis of 22 distances, N. flavus had a longer dorsal fin base, and a shorter distance between the adipose/caudal notch and base of caudal fin (Table 1). Interorbital and internostril widths and nape length were shorter in N. flavus. Additionally, the position of the anal fin base of N. flavus was posterior to that of N. insignis, and intermediate in the putative hybrids.

Serrae on the posterior edge of the pectoral spine and pigmentation on margins of anal and dorsal fins varied among putative hybrids. Posterior serrae on pectoral spines were prominent in N. insignis and six putative hybrids, absent in N. flavus, and intermediate in five putative hybrids. Margins of the anal, caudal, and dorsal fins were pale in N. flavus and dark in N. insignis. The pale margin of the upper caudal lobe of N. flavus formed a subtriangular patch. Pigmentation patterns on caudal fin margins of putative hybrids were intermediate to those of N. flavus and N. insignis. Putative hybrids had a pale margin on the upper caudal lobe and a dark margin (ranging from dark gray to black) on the lower lobe. Dorsal fins had a black anterior margin and pale posterior margin in five hybrids, and a light margin with a dark interior in six putative hybrids. Anal fins of putative hybrids had a pale margin (interrupted by dark pigment in some individuals). The adipose/caudal notch formed an angle of 90-135° in N. flavus and nine putative hybrids, whereas a larger angle (> 135°) occurred in N. insignis and two putative hybrids.

Discussion

Hybrids often display intermediate morphology to parental species (Hubbs 1955, Neff and Smith 1979; but see Leary et al. 1983, Raesly et al. 1990). Putative hybrids were identified in the field by intermediate tooth patch dimensions. Our hypothesis of hybrid origin, however, is further supported by intermediate morphological characters of putative hybrids based on SPCA of 22 morphometric characters excluding tooth patch measurements. Also, pale margins of upper caudal lobes and dark margins of lower caudal lobes in putative hybrids depict an intermediate pigmentation pattern between pale caudal margins of N. flavus and dark caudal margins of N. insignis.

Noturus insignis was reported initially from the Monongahela River drainage, WV, in Big Sandy Creek (Taylor 1969), and subsequently in the Blackwater River in 1995 (Unpubl. data, West Virginia Division of Natural Resources, WVDNR). Assuming equal detection probabilities, surveys indicate that population sizes of N. insignis exceed those of N. flavus and putative hybrids in the Monongahela drainage, WV. Based on two surveys, abundances of N. flavus, N. insignis, and putative hybrids were 8, 22, and 11 adults, respectively (8 Sept 1997 survey of Blackwater River, includes specimens used herein) and 5, 73, and 8, respectively (31 August 1999 survey of Blackwater River, specimens discarded, unpubl. data, WVDNR). Abundance data of N. flavus from Blackwater River are consistent with findings from other sites within the Monongahela River drainage, where we have observed low abundances (

In addition to having higher abundances, adults of N. insignis are generally smaller than those of N. flavus. In species where males guard eggs, such as cottids (Downhower et al. 1983, Goto 1987), poeciliids (Ptacek and Travis 1997), and blenniids (Cote and Hunte 1989), females often prefer larger males. Given that N. flavus attains a larger size than N. insignis, it is possible that female N. insignis mismate with larger N. flavus males. Ranges of total lengths of N. insignis from the 1997 (84-150 mm) and 1999 (41-173 mm) surveys were lower than those of putative hybrids (97-180 mm and 152-206 mm, respectively) and N. flavus (89-196 mm, and 102-203 mm, respectively).

Accidental contact of gametes could explain hybridization between N. flavus and N. insignis. Longevity and sexual maturity differs between N. flavus (9 years, matures at 3-4 years; Walsh and Burr 1985) and N. insignis (4 years, and matures at 1-2 years; Jenkins and Burkhead 1993), but breeding habits are similar where males excavate nest cavities under rocks and guard eggs (Cochran 1996, Jenkins and Burkhead 1993, Walsh and Burr 1985). Also, habitat degradation may promote hybridization between N. flavus and N. insignis through reduction of suitable non-embedded substrate, thus increasing the tendency for spawning in close proximity and accidental contact of gametes. Trautman (1981) suggested that degraded habitat likely explained N. gyrinus x N. miurus hybrids. Water quality in the Blackwater River has decreased from acid mine drainage and from turbidity and sedimentation associated with logging and development. Poor water quality may disrupt mate recognition systems and promote mismating.

Hybrids may result from mismating or accidental contact of gametes, but further research is needed to identify causal factors. Studies that address alternative hypotheses such as mismating due to species differences in body size or abundance, mismating due to impaired vision from poor water quality, or accidental contact of gametes associated with spawning proximity may provide inference toward understanding hybridization between N. flavus and N. insignis in the Blackwater River, WV.

Acknowledgments

We thank Frank Jernejcic and Tom Oldham for assistance with field collections. Funding was provided from West Virginia Division of Natural Resources and U.S. Geological Survey, Biological Resources Division. Reference to trade names does not imply government endorsement of commercial products.

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STUART A. WELSH1,* AND DAN A. CINCOTTA2

1 US Geological Survey, West Virginia Cooperative Fish and Wildlife Research Unit, PO Box 6125, Morgantown, WV 26506. 2 West Virginia Division of Natural Resources, PO Box 67, Elkins, WV 26241. * Corresponding author - swelsh@wvu.edu.

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