Macrhybopsis boschungi Gilbert & Mayden

Gilbert, Carter R., Mayden, Richard L. & Powers, Steven L., 2017, Morphological and genetic evolution in eastern populations of the Macrhybopsis aestivalis complex (Cypriniformes: Cyprinidae), with the descriptions of four new species, Zootaxa 4247 (5), pp. 501-555 : 512-514

Macrhybopsis boschungi Gilbert & Mayden sp. nov.

Mobile Chub

Figs. 1 B, 2; Table 1

Hybopsis hyostomus . — Gilbert 1891: 155, 157 (in part; records from Tuscaloosa, Alabama).

Hybopsis aestivalis . — Cook 1959: 129 –130 (in part; general account; considered very rare in Mississippi).

Extrarius aestivalis .— Mayden 1989: 14 (in part; chub clade; phylogeny based on cranial osteology).

Extrarius sp. cf aestivalis .— Boschung 1989: 50 (Tombigbee River distribution map; diagnoses of two undescribed species in Mobile Bay basin; ecological notes).

Macrhybopsis aestivalis .— Boschung 1992: 52 (in part; Alabama). Mettee et al. 1996: 218 –219 (in part; distribution map, description and account of species complex in Alabama).

Macrhybopsis sp. (“Mobile chub”).— Eisenhour 2004: 37, 47 (in part; phylogenetic tree involving other members of genus).

Macrhybopsis sp. cf M. aestivalis “A” (Gulf Chub).— Boschung & Mayden 2004: 209, plate 21A (general account [refers in part to Macrhybopsis tomellerii ]; color illustration).

Holotype. UF 175766 (ex UT 44.2312), 57.0 mm SL female, Cahaba River , at U.S. highway 80 bridge, 16 km W of Selma, Dallas Co., Alabama, D. A. Etnier and class, 17 May 1981.

Paratypes. The following paratypes, comprising 34 lots and 617 total specimens, are listed here in abbreviated fashion by state, river system, and county, followed by museum catalogue number and numbers of specimens. Complete locality data appear in Appendix 1.

Catalogue numbers accompanied by an asterisk (*) denote lots originally containing specimens of both Macrhybopsis boschungi and M. etnieri , where the species were sampled syntopically.

Alabama: Cahaba River : (Bibb Co.) UAIC 1443.06 (1), UF 116293 (1)* (mixed lot also includes four M. etnieri [UF 15434]) ; UAIC uncat. (2)* (mixed lot also includes four M. etnieri [UAIC 7198.02]); UMMZ 250267 (2)* (mixed lot includes 28 M. etnieri [ UMMZ 250266 ]); (Dallas Co.) UT 44.2312 (76 originally, now 41), UF 175767 (5) , USNM 437193 (5), UMMZ 250263 (5), ANSP 200789 (5), TU 204138 (5), MCZ 171826 (5), KU 41378 (5) (preceding seven lots of paratopotypes all ex UT 44.2312); UAIC 7188.01 (20), UAIC 7189.04 (62), UAIC 10845.03 (1 [illustrated female specimen, fig. 1B; ex Boschung & Mayden 2004: pl. 21A]); (Perry Co.) UAIC 962.06 (5) , UAIC 1437.19 (2), UAIC 5819.01 (1), UAIC 6430.04 (1), UAIC uncat. (5)* (mixed lot also includes 18 M. etnieri [UAIC 6791.03]), UAIC uncat. (2)* (mixed lot also includes seven M. etnieri [UAIC 6799.02]), UAIC uncat. (20)* (mixed lot also includes ten M. etnieri [UAIC 7194.03]).

Coosa River: (Elmore Co.) UF 116296 (5).

Tallapoosa River: (Macon Co.) UAIC 1516.04 (2), UT 44.1949 (2), UF 116295 (13); (Montgomery Co.) UF 116297 (3).

Tombigbee River: (Pickens Co.) UAIC 4330.03 (192); (Tuscaloosa Co.) USNM 36715 (3), USNM 43531 (18).

Alabama River: (Mobile Co.) UF 20859 (16), UF 20862 (5).

Mississippi: Tombigbee River: (Clay Co.) UF 28985 (7); (Lowndes Co.) UT 33.1204 (150).

Diagnosis. A species in the Macrhybopsis aestivalis complex, as described in the generic diagnosis.

Macrhybopsis boschungi ( Fig. 1 B) resembles the allopatrically distributed M. tomellerii ( Fig. 1 E), with which it shares a lightly spotted body; a single pair of moderately long maxillary barbels; 4-4 pharyngeal teeth; eight anal rays; anal opening distinctly closer to anal-fin origin than pelvic-fin origin (ca. 70 percent of intervening distance); genital papillae extremely reduced; and similar scale counts (usually 36–37 lateral-line scales and 11 rows of scales above and between the lateral lines on opposite sides of body) (Table 1).

The above two species are distinguished by consistent differences in head morphology, most notably a longer snout in M. boschungi (which exceeds the postorbital length) versus a shorter snout in M. tomellerii , the length of which equals the postorbital length). A second difference (not readily evident from gross examination or in poorly preserved specimens) may be expressed as an imaginary line extending upward from the angle formed by juncture of the lachrymal groove and posterior flap of snout, which in M. boschungi runs forward of the nares but in M. tomellerii intersects the anterior margin of the nares.

M. boschungi and M. tomellerii together bear a superficial resemblance to eastern populations of M. hyostoma ( Fig. 1 A), from which they differ most obviously in having a less heavily spotted body.

M. boschungi differs from M. etnieri ( Fig. 1 C) in pharyngeal-tooth count (4-4 vs. 1,4-4,1); position of anal opening about two-thirds (70 percent) of distance between pelvic and anal-fin origins (vs. midway); dorsal-fin positioned directly above pelvic fins (vs. distinctly posterior); a less heavily spotted body; and longer maxillary barbels.

M. boschungi differs from M. pallida ( Fig. 1 D) in having a single pair of maxillary barbels (vs. two pairs); eight anal rays (vs. seven); position of anal opening about two-thirds of distance between pelvic and anal-fin origins (vs. midway); a slightly more heavly spotted body. (vs. essentially pallid ); and a greater average body size, as discussed in the individual species accounts.

Description. Characters listed in the Diagnosis are not repeated here, unless additional clarification is required. Variation in meristic characters is presented in Table 1.

Dorsal rays 8; anal rays 8 (rarely 7); pectoral rays usually 15 (occasionally 14 or 16); pelvic rays usually 8 (rarely 7); lateral-line scales usually 36–37 (range 35 to 39); body-circumferential scale rows above and between lateral lines on opposite sides of body usually 11, occasionally 12 (range 10 to 13); scales sometimes present on belly preceding anal fin, more often incomplete or absent (about 75 percent of time); total body-circumferential scale rows (when complete) 25 to 28; predorsal scales irregularly distributed and poorly defined, usually numbering 15 to 18 (rarely 14 or 19); total vertebrae usually 36, sometimes 35 or 37 (very rarely 34).

Dorsal fin angular and slightly falcate, the anteriormost rays (when depressed) extending about same distance posteriorly as posteriormost rays; head moderately rounded dorsally and moderately flattened ventrally; mouth inferior and horizontal, its width about 60 percent of head width; lips moderately fleshy, not thickened posteriorly; eyes oval in shape and relatively large, the diameter about 60 percent of preorbital distance.

A small percentage of specimens of M. boschungi examined (11 of 84 [13 percent]) possessed a complete bridge of scales across the belly, a character never observed in any of the 83 individuals examined of M. tomellerii . In addition, M. boschungi exhibits a slight downward shift in predorsal-scale counts (Table 1).

Females attain a larger maximum size than males. The largest specimen examined (UF 175766 [the holotype]), is a 57.0 mm SL female from the Cahaba River, Dallas County, Alabama, 17 May 1981. The largest male examined, 47.2 mm SL (UT 44.2312), is from the same collection.

Comments. Similarities and relationships of Macrhybopsis boschungi and other species, especially the morphologically similar M. tomellerii , are discussed in the account of M. tomellerii .

Distribution. Macrhybopsis boschungi is endemic to the lower Mobile basin of Alabama and northeastern Mississippi, where its upstream range limits are sharply delineated by the Fall Line ( Fig. 2 ). As discussed subsequently, it is replaced above the Fall Line by Macrhybopsis etnieri , to which it is not intimately related.

Habitat. Macrhybopsis boschungi inhabits the larger, moderately clear to turbid rivers and the lowermost parts of their major tributaries below the Fall Line in the Mobile Bay basin. In such areas water currents are moderate to strong and the bottom is comprised of a combination of gravel, sand and silt.

Conservation Status. Although this species has occasionally been collected in large numbers, ongoing stream modifications and habitat alteration throughout the lower Mobile Bay basin do not bode well for its future. In particular, construction of the Tenn-Tom waterway, which has changed the original free-flowing Tombigbee River into a series of standing pools, has served to eliminate this species from a major portion of its original geographic range. This species should be closely monitored throughout remaining parts of its range.

Etymology. Named for the late Dr. Herbert T. Boschung, Emeritus Professor of Biology at the University of Alabama, for his many contributions over the years to southeastern ichthyology in general and the state of Alabama in particular, including co-authorship of Fishes of Alabama ( Boschung & Mayden 2004).

It should be noted here that the vernacular name “Mobile Chub” used here differs from the name “Gulf Chub” applied by Boschung & Mayden (2004: 209; plate 21A). Considering its geographical distribution, we consider the former name to be more appropriate for the species.

Figures

FIGURE 1. Species of Macrhybopsis aestivalis species complex from eastern North America. A) Macrhybopsis hyostoma, UAIC 11060.03, Female, 34 mm SL, Alabama, Limestone County, Elk River, 28 September 1994. B) Macrhybopsis boschungi, UAIC 10845.03, Female, 50 mm SL, Alabama, Dallas County, Cahaba River, 12 July 1993. C) Macrhybopsis etnieri, UAIC 11053.01, Female, 44 mm SL, Alabama, Bibb County, Cahaba River, 24 June 1994. D) Macrhybopsis pallida, UAIC 10855.04, Female, 36 mm SL, Alabama, Escambia County, Conecuh River, 15 July 1993. E) Macrhybopsis tomellerii, UAIC 11364.03, Female, 51 mm SL, Mississippi, Covington County, Pascagoula River drainage, 18 February 1994.

FIGURE 2. Distribution of southeastern species of Macrhybopsis east of the Mississippi River. Individual species are identified by symbol and color. Circles with half blue and half red represent locations where M. boschungi and M. etnieri occur syntopically.