Macrhybopsis pallida 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 : 517-520

Macrhybopsis pallida Gilbert & Mayden sp. nov.

Pallid Chub

Figs. 1 D, 2; Table 1.

Hybopsis aestivalis .— Suttkus 1961: 233 –234 (review of Mississippi fish book; first reported from Florida) . Yerger & Suttkus 1962: 327 (additonal Florida records). Smith-Vaniz 1968: 40 (in part; Alabama) . Mettee 1970: 11 –12 ( Choctawhatchee River drainage, Florida and Alabama) . Yerger 1978: 12 –13 (general account; listed as threatened in Florida; photograph is of Macrhybopsis etnieri ). Wallace 1980: 180 (in part; brief account; distribution map of M. aestivalis complex).

Extrarius n. sp. cf aestivalis . — Gilbert & Yerger 1992: 133 –137, fig. (general account; Florida distribution map; listed as rare in Florida).

Extrarius aestivalis .— Boschung 1992: 52 (in part; brief discussion of systematics; in list of Alabama fishes).

Macrhybopsis aestivalis .— Mettee et al. 1996: 218 –219, lower fig. (in part; general account; localities mapped for all species of M. aestivalis complex in Alabama).

Macrhybopsis sp. cf. M. aestivalis “C”.— Boschung & Mayden 2004: 209 –210, pl. 21C (diagnosis; distribution; systematics; distribution map in part, Alabama).

Holotype. UF 73313, a 50.5 mm SL female from Choctawhatchee River, at U.S. highway 84 bridge, east of Clayhatchee , Dale and Houston counties, Alabama, T. C. Lewis and H. A. Beecher (field no. HAB 76), 10 January 1975.

Paratypes. The following paratypes, comprising 44 lots and 666 total specimens, are listed here in abbreviated fashion by state, county, and river drainage, followed by museum catalogue number and numbers of specimens. Complete locality data appear in Appendix 1.

Alabama: Escambia River : (Escambia Co.) UF 44666 (68), UF 73320 (10); TU 15948 (6), TU 81354 (9); UAIC 1823.03 (2) , UAIC 10855.04 (1 [illustrated female from presumably larger series, ex Boschung & Mayden 2004: pl. 21C]).

Blackwater Bay [Yellow River system]: (Covington Co.) TU 73150 (1), TU 72958 (1); UAIC 4188.03 (1).

Choctawhatchee River: (Dale Co.) UF 73336 (29), UF 73488 (2); (Dale/ Houston cos.) UF 73468 (1); (Houston Co.) UAIC 3508.11 (14).

Florida: Escambia River: (Escambia Co.) UF 9333 (11), UF 53534 (2), UF 54366 (4), UF 130433 (8), UF 130470 (1), UF 138618 (2), UF 143879 (4), UF 150156 (1), UF 171841 (3), UF 171848 (9); (Escambia/Santa Rosa cos.) UF 75361 (2), UF 75441 (2), UF 172372 (8); (Santa Rosa Co.) UF 73352 (1), UF 73438 (15), UF 145534 (6), UF 145898 (36).

Blackwater Bay [Yellow River system]: (Okaloosa Co.) UF 57640 (5), TU 79682 (2), TU 82620 (5), TU 83078 (11), TU 101906 (4), TU 102299 (1).

Choctawhatchee River: (Holmes Co.) UF 55457 (21), UF 75477 (1), TU 20811 (28), UAIC 3126.13 (196 originally, now 166), USNM 437191 (5), UMMZ 250265 (5), ANSP 200787 (5), MCZ 171824 (5), KU 41376 (5), UT 44.13095 (5) (six series immediately preceding all ex UAIC 3126.13), UAIC 3195.06 (12) UAIC 4449.08 (4), TU 102794 (32); (Washington Co.) UAIC 3191.02 (84).

Diagnosis. A species of the Macrhybopsis aestivalis complex, as described in the generic diagnosis. Macrhybopsis pallida ( Fig. 1 D) is characterized by 4-4 pharyngeal teeth; seven anal rays; two pairs of prominent maxillary barbels; anal opening situated midway between pelvic and anal-fin origins; dorsal-fin origin situated directly above pelvic-fin origins; body largely devoid of pigment, the melanophores typically tiny; genital papillae well developed.

Other diagnostic characters include a relatively elongate and slender body, with a relatively deep caudal peduncle, the depth of which may be as much as two-thirds the greatest depth of body; pectoral fins in both sexes usually long and pointed, often extending posteriorly to or past pelvic-fin origins; belly immediately anterior to pelvic fins lacking scales; nuptial tubercles on pectoral fins of breeding males uniserial.

Macrhybopsis pallida is one of the most morphologically distinctive members of the M. aestivalis complex. It is the only eastern species to possess two pairs of maxillary barbels and seven anal rays, and the intermediate position of the anal opening relative to the origins of the pelvic fins and anal fin is shared only with M. etnieri among the nine species comprising the entire species complex.

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-fin rays 8; anal-fin rays usually 7 (rarely 6 or 8); pectoral-fin rays usually 14 and often 15 (range 13– 16); pelvic-fin rays usually 8 (rarely 7); lateral-line scales usually 36–38 (range 35–39); predorsal scales usually 16–17, often 15–18 (range 14–19); body-circumferential scale rows above and between lateral lines usually 11, occasionally 10 or 12 (range 9–13); body-circumferential scale rows below and between lateral lines incomplete, the scales always missing from mid-belly area anterior to pelvic fins; total caudal-peduncle scale rows uniformly 12 (five scale rows above and below lateral lines on each side of caudal peduncle); total vertebrae usually 37, often 36 or 38; more posterior maxillary barbel longer and more prominent; dorsal fin bluntly pointed at tip; anal fin broadly rounded and never pointed at tip; pectoral fins pointed, sometimes extremely so, often extending posteriorly to or past pelvic-fin origins; head moderately rounded and moderately flattened ventrally; mouth inferior and horizontal, not as wide as head; lips moderately fleshy, not thickened posteriorly; eyes oval in shape and relatively large, the diameter nearly equal to distance from anterior margin of orbit to tip of snout; genital papillae well developed as conical or cylindrical extensions in both sexes; four or five rudimentary gill rakers on upper limb of outer (anteriormost) gill arch, the rakers usually absent from lower limb of arch; pharyngeal teeth short, thin, and hooked, with little or no grinding surface; nuptial tubercles present in membrane immediately posterior to first pectoral-fin ray in nuptial males; pectoral-fin rays 2–10 thickened in nuptial males, and containing large, conical, recurved uniserial tubercles; tiny tubercles sometimes present on rays of dorsal and pelvic fins of high nuptial males.

Females attain a significantly larger size than males. The largest specimen examined is a 51.5 mm SL female (UF 172372) from the Escambia River, at the state highway 4 bridge on the Escambia and Santa Rosa county line, collected on 14 May 1986 . Only two other females of comparable size are known: the 50.5 mm holotype (UF 73313), collected on 10 January 1975, and another 50.5 mm specimen (UF 57640), collected on 6 June 1961. The largest male examined, 37.5 mm SL (TU 102299), was collected on 9 June 1977 from the Yellow River, Okaloosa County, Florida. Males with well developed nuptial tubercles have been seen as small as 28.5 mm SL (TU 101906) .

Comments. Macrhybopsis pallid a does not bear a close physical resemblance to any other eastern members of the M. aestivalis species complex, and is unique among eastern species in possessing two pairs of maxillary barbels and seven anal rays, together with an overall pallid appearance, an unusually slender body coupled with a comparatively deep caudal peduncle, and an apparently smaller average body length.

Macrhybopsis pallid a shares with Macrhybopsis australis the combination of two pairs of maxillary barbels and seven anal rays. However, there is morphological and genetic evidence to indicate that these species are not closely related. Macrhybopisis pallida shares, along with M. etnieri , an intermediate position of the anus (situated midway between the origins of the pelvic and anal fins) and comparably developed genital papillae. These characters, which are unique among members of the M. aestivalis complex, undoubtedly were factors in Eisenhour’s assumption of a close relationship between these two species ( Eisenhour, 2004: figs. 16–17). Despite this, genetic data (discussed elsewhere in this paper) indicate unequivocally that M. pallida and M. etnieri are not intimately related, and that the former instead is sister to M. boschungi .

Distribution. Macrhybopsis pallida is endemic to the Escambia, Blackwater, and Choctawhatchee river drainages of southeastern Alabama and western panhandle Florida. This region is home to at least a dozen endemic fish species (some still undescribed) bearing a close phylogenetic relationship to species occurring in the adjacent Mobile Bay basin of Alabama and Mississippi (Clemmer 1971; Williams 1975; Swift et al. 1986; Suttkus & Bailey 1993; Mettee et al. 1996, Boschung & Mayden 2004; Pera & Armbruster 2006).

Habitat. Macrhybopsis pallida inhabits shallow unimpounded rivers of the western Florida panhandle and adjacent parts of Alabama. Bottoms of these streams are comprised of sand and gravel, combined with occasional small rubble, and water clarity ranges from relatively clear to moderately turbid. In recent years sections of these streams have become impacted by fine silt carried down from upstream, which is presumed to have had a negative impact on populations of this species.

Conservation status. Macrhybopsis pallida is an uncommon species, apparently the rarest of the five eastern members of the M. aestivalis complex. Although the total number of museum specimens examined (667) is substantial, this figure is misleading in many respects. Bailey et al. (1954) did not include the species in their analysis of Escambia River fishes in Alabama and Florida, which, combined with a small number of earlier samples, totaled approximately 30 fish collections available at that time. The first collection to include M. pallida appears to have been a series of 11 specimens (UF 9333), collected by William McLane in October, 1954, from the Escambia River near Pine Barren, Florida. Suttkus (1961) was the first to document the existence of the species, and Yerger & Suttkus (1962: 327) were first to record the species from Florida, although the McLane collection was not cited in either of those publications.

Beginning in the 1950’s, fish collecting in eastern Gulf slope drainages of Alabama and Florida increased exponentially, and although the number of collections made from this region has not been precisely tabulated, this surely is now well into the hundreds. Considering this, the 44 total collections in which Macrhybopsis pallida has been included are not very many. Thirty of these collections comprise fewer than ten individuals, and of the total 667 specimens, 429 have come from seven collections. Breaking this down further, 381 specimens (all young-ofthe-year individuals taken during the fall) are from only four collections (UAIC 3126.13, UAIC 3191.02, UF 44666, and UF 145898]).

Further evidence of the species’ rarity is evidenced from intensive sampling efforts by United States Geological Service personnel, between 2001 and 2003, in the lower reaches of the Escambia River south of the Florida-Alabama state line. This project was for the specific purpose of determining the current status in Florida of six rare fish species occurring in the drainage, including Macrhybopsis pallida . Small-fish sampling was accomplished using 30-foot bag seines with fine-meshed cod ends, with sampling effort equally divided between day and night collections. Stream levels were very low throughout the sampling period, and collecting conditions were ideal. The three most common cyprinid species encountered were Cyprinella sp. cf venusta and Notropis texanus (4,000–5,000 total combined specimens), followed by Hybopsis sp. cf winchelli (ca. 500 total specimens). Although collected in far fewer numbers, the four dominant percid species occurring in the main-stem Escambia River ( Percina nigrofasciata , Percina austroperca , Percina vigil , and Ammocrypta bifascia ) were found in normal concentrations. Only 57 specimens of Macrhybopsis pallida (the largest 31.1 mm SL) were obtained in six collections, of which 36 were from one collection (UF 145898) on 30 September 2003. The combination of ideal collecting conditions, effective sampling gear, and relative abundance of other fish species with superficially similar ecological requirements, would lead to the expectation that M. pallida should have been found in far greater numbers than it actually was.

It is worth noting that shoal areas where seining collections were made during the 2001–2003 sampling period contained heavy silt loads, which conceivably could have negatively impacted a small, bottom-dwelling species such as M. pallida . If so, however, it might have been expected that other benthic species, especially one such as Ammocrypta bifascia , would have been equally affected. Also, this does not adequately explain the continued longterm rarity of M. pallida , at least during the past 60 years.

Etymology. The species name pallida is in reference to the generally pallid body pigmentation characteristic of this 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.