Macrhybopsis tomellerii 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 : 520-522

Macrhybopsis tomellerii Gilbert & Mayden sp. nov.

Gulf Chub

Figs. 1 E, 2; Table 1

Hybopsis aestivalis . — Cook 1959: 129–130 (in part; general account; considered very rare in Mississippi). Douglas 1974: 100– 101 (in part; general account; Louisiana distribution map [Lake Pontchartrain and Pearl River drainage records only]; illustration is of Macrhybopsis hyostoma ).

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

Macrhybopsis aestivalis .— Ross 2001: 177 –179 (in part; general account; Mississippi distribution map [Pearl and Pascagoula drainage records only]; photograph).

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 (general account [refers in part to Macrhybopsis boschungi ]; color illustration).

Macrhybopsis sp. cf aestivalis (Coastal Chub).— Boschung & Mayden 2004: plate 21D (color illustration [also see preceding reference]).

Holotype. UF 28146 (47.1 mm SL female), Pearl River, ca. 0.8 km. south of Sunrise , on unmarked road, T11N, R9E, Secs. 25 and 30, Leake Co. Mississippi, Carter R. Gilbert et al., 22 June 1980.

Paratypes. The following paratypes, comprising 24 lots and 567 total specimens (including nine paratopotypes), 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.

Louisiana: Pearl River : (Washington Psh.) TU 45061 (30, ex original lot of 192 specimens), TU 62 182 (30, ex original lot of 2058 specimens).

Mississippi: Pearl River: (Leake Co.) UF 237859 (9) (paratopotypes, ex UF 28146). ( Simpson Co. ) TU 57271 (30, ex original lot of 141 specimens).

Pascagoula River: (Covington Co.) UAIC 11364.01 (1 [illustrated female specimen ex Boschung & Mayden 2004: pl. 21D]; present fig. 1E); (Forrest Co.) UAIC 6391.02 (9), UAIC 6392.02 (2), UAIC 6393.02 (5), UAIC 6412.02 (12), UAIC 6413.06 (6). (Jones Co.) INHS 79942 (6), INHS 76268 (81), TU 57445 (63), UT 44.1206 (159). (Lauderdale Co.) UT 44.2317 (20). (Smith Co.) TU 53791 (87 originally, now 57), UF 237864 (5), USNM 437190 (5), UMMZ 250264 (5), ANSP 200786 (5), MCZ 171824 (5), KU 41375 (5) (preceding six lots ex TU 53791). (Stone Co.) UAIC 893.02 (3). (Wayne Co.) TU 15395 (17).

Two additional lots (total of 21 specimens), not designated paratypes, from the Lake Pontchartrain drainage of Louisiana, are not included here but are listed in Appendix 1.

Diagnosis. A species in the Macrhybopsis aestivalis complex, as described in the generic diagnosis. Macrhybopsis tomellerii ( Fig. 1 E) resembles the allopatrically distributed M. boschungi ( Fig. 1 B), 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 closer to anal-fin origin than pelvic-fin origin (ca. 70 percent of intervening distance); 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 shorter snout in M. tomellerii (about equal to postorbital length) versus a longer snout in M. boschungi , the length of which exceeds 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. tomellerii intersects the anterior margin of the nares but in M. boschungi runs forward of the nares.

M. tomellerii and M. boschungi 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. tomellerii 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 beweeen pelvic and anal-fin origins (vs. midway); genital papillae extremely reduced; dorsal fin positioned directly above pelvic fins (vs. distinctly posterior); a less heavily spotted body; and longer maxillary barbels.

M. tomellerii differs from M. pallida ( Fig. 1 D) in having a single pair of maxillary barbels (vs. two pairs of barbels); anal rays 8 (vs. 7); position of anal opening about two-thirds (70 perecent) of distance between pelvic and anal-fin origins (vs. midway); a slightly more heavily spotted body (vs. body 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 and often 16); pelvic rays usually 8 (rarely 7); lateral-line scales usually 36–37 (range 35 to 38); body circumferential scale rows above and between lateral lines on opposite sides of body usually 11, occasionally 12 (range 10 to 12); scales never present on belly; predorsal scales irregularly distributed and poorly defined, usually numbering 16 to 20 (rarely 15 or 20); 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, the diameter about 60 percent of preorbital distance.

None of the 83 specimens of M. tomellerii from which meristic data were taken possessed a complete bridge of scales across the belly, as opposed to a small percentage of the superficially similar M. boschungi (eleven of 84 specimens [13 percent] having this feature). In addition, M. tomellerii appears to exhibit a slight upward shift in predorsal-scale count and a slight downward shift in total vertebrae count (Table 1).

The largest specimen examined (TU 53791) is a 50.7 mm SL female from the Leaf River, Smith County, Mississippi, collected on 5 October 1960. The largest identified male, 47.5 mm, is from the same collection. This information is presented with some qualification, however, in contrast to that for the other four species in this study. First, the above specimens are from a fall collection made well past the late-spring or early-summer breeding season, which made accurate sex determination less certain than for material collected earlier during the year. Second, the total number of specimens of M. tomellerii examined, although comparable to the numbers for other species included in this study, represents only a fraction of the total existing in museum collections (primarily Tulane University). Also, the size difference in sexes reported for this species is less than for the other four eastern species. These factors suggest that information reported here on maximum body size may be subject to modification.

Comments. Based on close similarity in overall appearance and geographically contiguous distributions, M. tomellerii and M. boschungi were initially thought to be conspecific. Genetic analysis has revealed, however, that the relationship of M. tomellerii and M. boschungi is not intimate. The latter is sister to the morphologically dissimilar M. pallida , whereas M. tomellerii does not show an intimate relationship to any other eastern species, including evidence of direct decent from Macrhybopsis hyostoma (see section on Relationships and Historical Biogeography).

Detailed comparisons of M. tomellerii and M. hyostoma populations from the lower Mississippi Valley are clearly in order, especially as regards genetic data. Eisenhour’s (1997, 2004) morphological analysis included material of M. hyostoma from the lower Mississippi, but his findings cannot be readily correlated with those obtained here for M. tomellerii . Eisenhour presumed all eastern Gulf slope populations of “ M. hyostoma ” from Lake Pontchartrain to the lower Mobile Bay basin to be specifically identical, and data from those areas were accordingly combined. Based on overall numbers of distribution records of M. hyostoma from the mainstem lower Mississippi River and closely adjacent tributaries ( Douglas 1974: 101; Pflieger 1975: 138; Burr & Warren 1986: 89; Robison & Buchanan 1988: 182; Etnier & Starnes 1994: 193; Ross 2001: 178), adequate material should be available for analysis.

Distribution. Macrhybopsis tomellerii is confined to the Pearl and Pascagoula river drainages of Mississippi and southeastern Louisiana, and presumably also the adjacent Lake Pontchartrain drainage of these two states ( Fig. 2 ).

Western limits of the geographic range of Macrhybopsis tomellerii have yet to be precisely defined. The two samples available for this study from the Lake Pontchartrain drainage (total of 21 specimens [ INHS 79456 , UF 14731]) are identified as this species, and the records are accordingly plotted on the spot-distribution map. Since genetic information is lacking for material from this drainage, it was considered prudent to exclude these specimens from the list of paratypes.

Habitat. Macrhybopsis tomellerii inhabits large, moderately clear to turbid rivers and lowermost parts of their major tributaries in the Pearl, Pascagoula, and Lake Pontchartrain drainages of Mississippi and Louisiana. Conditions in these areas are similar to those favored by the superficially similar M. boschungi in lower parts of the adjacent Mobile Bay basin.

Conservation status. Macrhybopsis tomellerii has, in years past, sometimes been collected in substantial numbers. Although suitable habitats have undoubtedly been subjected to negative modifications, as yet none are believed to have had dramatic impacts on the overall status of the species. The species should be monitored on a regular basis.

Etymology. Named for Joseph R. Tomelleri , biological illustrator living in Leawood, Kansas, whose unsurpassed and meticulously rendered color illustrations of North American freshwater fishes have graced the pages of numerous scientific publications (including the present one), as well as books such as Fishes of the Central United States ( Tomelleri & Eberle 1990) and Fishes of Alabama ( Boschung & Mayden 2004).

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.