Astrapogon

Baldwin, Carole C., Mounts, Julie H., Smith, David G. & Weigt, Lee A., 2009, Genetic identification and color descriptions of early life-history stages of Belizean Phaeoptyx and Astrapogon (Teleostei: Apogonidae) with Comments on identification of adult Phaeoptyx, Zootaxa 2008, pp. 1-22 : 15-21

Astrapogon

Identification. Astrapogon specimens in our samples form 3 distinct genetic lineages corresponding to the three known species ( Fig. 7 ). Intraspecific variation ranges from 0.00–1.30% nucleotide substitutions per site as opposed to 15.62–20.06% for interspecific variation ( Table 6). We identified adult A. puncticulatus and A. stellatus through counts of pectoral-fin rays and gill rakers in adults ( A. puncticulatus typically with 16 pectoral-fin rays and 12–13 lower-limb gillrakers; A. stellatus usually with 15 pectoral-fin rays and 11 lowerlimb gill rakers—Böhlke & Randall 1968). By process of elimination, the third clade, comprising only larvae, is A. alutus .

A. alutus N=3 A. puncticulatus N=18 A. stellatus N=7 A. alutus 0.72% (0.62–0.93)

A. puncticulatus 19.11% (18.44–20.06) 0.39% (0.00–1.30) A. stellatus 16.06% (15.62–16.62) 17.13% (16.60–18.23) 0.29% (0.00–0.62) Larvae and Juveniles ( Figs. 8 , 9 ). Astrapogon larvae can be distinguished from larvae of other apogonids by the heavily pigmented (often black) first dorsal and pelvic fins, and usually by the trunk melanophores, which, when expanded, cover most of the body and variously obscure the pale orange chromatophores beneath. (Note: reared juvenile specimens are available for A. puncticulatus and A. stellatus but not for A. alutus ; we incorporate notes on the juveniles within the appropriate sections below.)

Astrapogon alutus: Three larvae, 5–6 mm SL. First dorsal and pelvic fins heavily pigmented, with large dark spots (interradial membranes of first dorsal fin almost black in one 5-mm SL specimen) and yellow chromatophores. Second dorsal and anal fins mostly clear, one or two melanophores extending from trunk onto bases of fins. Caudal fin with no pigment in one 5 mm specimen, with one orange chromatophore at base of one ray in dorsal lobe in the other 5 mm specimen, and with several orange chromatophores at bases of central and ventral rays in 6 mm specimen. Posterior end of caudal peduncle clear, trunk pigment ending abruptly on anterior part of peduncle. Background color of head and body yellow and orange. Large melanophores present on head and body. Snout, jaws, cheek, temporal region, and lateral surface of gut with melanophores. A dense cap of melanophores visible over swimbladder.

Astrapogon puncticulatus: Size range of larvae 7.5–12 mm SL; size range of juveniles 10–14.5 mm SL. First dorsal and pelvic fins heavily pigmented in larvae, almost black but with some yellow pigment on or between fin elements. Second dorsal fin mostly clear, one or two melanophores usually extending from trunk onto base of fin. Anal fin primarily clear, a melanophore usually extending from trunk onto base of fin and one melanophore usually present at base of anterior part of fin—sometimes on one side of body only. Caudal fin usually with a few orange chromatophores at bases of central rays. In reared specimens 12 mm SL and larger, heavy pigment present on second dorsal and anal fins, but both fins with distinctive clear areas; second dorsal usually without pigment along distal edges of all rays, posteriormost one or two rays, and near proximal base of posterior fin rays; these clear areas roughly forming a semicircle around pigmented portion; anal fin with similar clear areas in most specimens. Caudal fin in reared specimens mostly dark; distal tips of all rays and proximal portions of central (and sometimes additional) rays clear. In larvae, posterior end of caudal peduncle with three melanophores in vertical bar. In one 9-mm SL larva this bar of melanophores separated by a small but distinct gap from the pigment immediately anterior to it; in another 9 mm specimen this small gap present on left side of body only. Background color of head and body mostly orange, some yellow pigment above swimbladder. Large melanophores present on head, usually including top of head, snout, jaws, cheek, and temporal region; head pigment sometimes including four conspicuous lines of pigment radiating from eye—one dorsally, two posteriorly, and one ventrally. Large melanophores present on body but conspicuously absent on dorsal trunk just anterior to first dorsal fin, just behind second dorsal fin, and posterior to gut; when trunk melanophores in expanded state, these areas conspicuously paler than remainder of trunk. In one of smallest larvae available, 8.5 mm, trunk lacking melanophores except two beneath first dorsal fin and one on caudal peduncle. In a 7.5-mm specimen, trunk melanophores contracted but present in typical number and pattern for A. puncticulatus . Reared juveniles usually darker in overall body color than larvae and exhibiting less orange coloration; pale areas as described above still evident in most juveniles. Lines of pigment radiating from eye observed in larvae usually visible in juveniles. Cap of melanophores usually visible over gut and swimbladder as in larvae.

Astrapogon stellatus: One larva, 7 mm SL; four juveniles reared from wildcaught larvae, 10–13 mm SL. In the larva, first dorsal and pelvic fins heavily pigmented, almost black but with some yellow pigment on or between fin elements. Second dorsal and anal fins mostly clear, trunk melanophores extending onto base of fin. In reared specimens, second dorsal and anal fins each with a blotch of melanophores set within and usually entirely surrounded by pale remainder of fin. In specimens with greatly expanded melanophores, basal fin pigment sometimes merging slightly with the blotch of melanophores on fin. Caudal fin without melanophores in larva but with a few scattered orange chromatophores at bases of central and ventral rays. In reared specimens caudal fin with two large, rounded melanophores at base of fin and one or two smaller melanophores above upper spot and below lower; fin rays clear centrally; two concentrations of melanophores present posteriorly (appearing either as two patches of small spots or as two large pigmented blotches), one on upper caudal lobe and one on lower. Tips of fin rays clear. Background color of head and body mostly orange in larval specimen, some yellow anteriorly; no chromatophores on body in reared specimens. Large, greatly expanded melanophores covering head and body in larva. Trunk nearly chocolate brown in reared specimens, with expanded but distinct melanophores in other two reared specimens. Posterior end of caudal peduncle in larva with at least two melanophores in vertical bar and with a clear area anterior to those spots. Caudal peduncle uniformly dark in chocolate brown reared specimens, with small clear area anterior to bar of melanophores on posterior end of caudal peduncle in other reared specimens. Snout, jaws, cheek, temporal region, and lateral surface of gut with melanophores. A dense cap of melanophores visible over gut and swimbladder in larva.

Comparisons: Larvae of A. puncticulatus differ from the other species in usually having three areas on the trunk that conspicuously lack melanophores: just anterior to origin of first dorsal fin, just posterior to second dorsal fin, and just above anterior end of anal fin (just posterior to the gut). These gaps can be seen in specimens in which the trunk melanophores are contracted ( Fig. 8 E) or expanded ( Fig. 8 D). The gap behind the second dorsal fin is sometimes small ( Fig. 8 F) because of an additional melanophore on the dorsal portion of the caudal peduncle, and in one unusual specimen ( Fig. 8 G), so few melanophores are present that there is no conspicuous pattern of gaps. Larvae of A. stellatus sometimes exhibit less distinctive pale areas in similar but slightly different locations than those in A. puncticulatus ( Fig. 8 C): the gap anterior to origin of first dorsal fin is a bit more forward, the gap at posterior end of second dorsal fin is below the fin (vs. behind it), and the gap above anal fin is above the anterior third of the fin (vs. above the most anterior point of the fin). Larvae of A. puncticulatus have an overall paler appearance than larvae of A. alutus and A. stellatus ; this is, in part, because the pale areas described above reveal more of the pale orange background body color but also because the trunk melanophores, even when expanded, are generally smaller or lighter than those in the other species. Most A. puncticulatus larvae lack a clear area on the caudal peduncle anterior to the posterior bar of melanophores, a feature present in the larval A. stellatus ; the entire peduncle is clear in 5- and 6-mm SL specimens of A. alutus . A small clear gap is present on the caudal peduncle in two 9-mm SL specimens of A. puncticulatus , however, suggesting that it could be present in early ontogenetic stages of all three species.

It is not possible with our limited larval Astrapogon material to definitively diagnose larvae of A. alutus and A. stellatus . Astrapogon alutus differs from the other species in having yellow and orange body coloration vs. primarily orange. However, the largest (and only) larvae of A. alutus we have collected are 5 and 6 mm SL, and the smallest larvae of A. puncticulatus and A. stellatus are 8.5 and 7 mm SL, respectively. Accordingly, the differences in body coloration could be attributable to differences in size or developmental stage.

Astrapogon alutus is unique in having no melanophores on the caudal peduncle, and A. stellatus has a bar of melanophores posteriorly on the caudal peduncle preceded by a clear area. Those differences may reflect variation typical of early larval stages: in a series of Astrapogon larvae from a single collection (all approximately 6 mm SL) not identified using DNA but representing either A. alutus or A. stellatus based on trunk pigmentation, the pigment on the caudal peduncle is highly variable: pigment is absent on the caudal peduncle in one specimen, bears a single spot on one side and several on the other in another specimen, has a posterior bar of pigment and a clear area preceding it in several specimens, and has the peduncle entirely pigmented in another.

Juveniles of A. puncticulatus differ from those of A. stellatus in the patterns of pigment on the second dorsal, anal, and caudal fins: in A. puncticulatus , the second dorsal and anal fins have a large blotch of pigment with clear areas forming roughly a semicircle around the posterior end of the blotch; in A. stellatus , the pigment blotch on the second dorsal and anal fins is smaller and completely surrounded by clear areas. Caudal-fin pigment of juvenile A. puncticulatus comprises a horizontally elongate oval centered on the proximal portion of the fin, whereas in A. stellatus the caudal fin has two large, rounded melanophores at the base of the fin and two concentrations of melanophores further out on the fin. Identification of juvenile A. alutus is needed to determine if the fin pigment in A. puncticulatus or A. stellatus , or both, is diagnostic.

Comments on previous identifications of Astrapogon larvae. Lara (2006:1391) provided illustrations of two specimens of A. stellatus , 5.7 and 7.8 mm SL. The 5.7 mm specimen looks very similar to both our 6 mm specimen of A. alutus and 7 mm specimen of A. stellatus except that it lacks a clear area on the caudal peduncle. Lara’s 7.8 mm specimen of A. stellatus bears the distinctive pale areas in front of the first dorsal fin, beneath the posterior portion of the second dorsal fin, and above the anterior third of the anal fin characteristic of some of our larval A. stellatus . As noted above, A. puncticulatus has similar pale areas, but it is never as uniformly covered with melanophores as in Lara’s specimen and our A. stellatus . Lara (2006:1389) illustrated five larval and juvenile specimens of A. puncticulatus . The pale areas characteristic of A. puncticulatus appear to be present in the 5.6, 8.6, and 14.3 mm specimens (her figures A, B, D). The 10.5 mm larva (her figure C) appears to have small melanophores anterior to the first dorsal fin and several melanophores behind the second dorsal fin. The absence in that specimen of pigment on the first dorsal and pelvic fins is odd and unlike that of any larval Astrapogon specimen we have examined. Possibly there is geographical variation in pigment patterns of Astrapogon between Florida (where Lara’s specimens were obtained) and Belize. The 16.8 mm juvenile (her figure E) appears to have the clear area on the proximal part of the posterior half of the second dorsal fin typical of A. puncticulatus and a similar band on the anal fin.

Lara (2006) did not indicate how she identified the larval stages of Astrapogon prior to their developing the full complement of gill rakers and pectoral-fin rays, and her descriptions contain some errors. In her description of A. stellatus larvae, Lara (2006:1390) noted that, by 5mm, most of the body is heavily pigmented except for the dorsal third, but her illustrations of 5.7 and 7.8 mm specimens depict heavy pigmentation on the dorsal third—consistent with our specimens of A. stellatus . She also indicated (2006:1390) that “D1 & P1 fins darkly pigmented,” but the pectoral fin is clear in her illustrations and presumably she meant the pelvic fins: as she correctly noted later in the description, the first dorsal and pelvic fins are heavily pigmented. Likewise, in the description of A. puncticulatus , she noted that small larvae have large melanophores on the head and anterior half of the body, but her illustration of a 5.6 mm specimen reveals large melanophores on the posterior half of the body as well. Large melanophores are present posteriorly in our specimens. She mistakenly indicated the presence of heavy pigment on the pectoral fin as in A. stellatus .

One image of A. puncticulatus was located on the internet ( Victor 2008). The 9.2-mm SL larva from San Blas, Panama, agrees well in pigmentation with our A. puncticulatus .

Figures

FIGURE 7. Neighbor-joining tree derived from Cytochrome Oxidase 1 sequences showing three genetically distinct lineages of Belizean Astrapogon.

FIGURE 8. Astrapogon larvae: (A) Astrapogon alutus, 5 mm SL, 6041; (B) Astrapogon alutus, 6 mm SL, 6040; (C) Astrapogon stellatus, 7 mm SL, 6038; (D) Astrapogon puncticulatus, 9.5 mm SL, 4449; (E) Astrapogon puncticulatus, USNM 393909, 12 mm SL, 5396; (F) Astrapagon puncticulatus, USNM 393407, 13 mm SL, 7125; (G) Astrapagon puncticulatus, 8.5 mm SL, 7262.

FIGURE 9. Astrapogon juveniles: (A) Astrapogon puncticulatus, USNM 393404, 14 mm SL, 5488, reared specimen; (B) Astrapogon stellatus, USNM 393413, 10 mm SL, 6449, reared specimen; (C) Astrapogon stellatus, USNM 393413, 13 mm SL, 6450, reared specimen.