Aphanius irregularis, Yoğurtçuoğlu & Freyhof, 2018

Yoğurtçuoğlu, Baran & Freyhof, Jörg, 2018, Aphanius irregularis, a new killifish from south-western Anatolia (Cyprinodontiformes: Aphaniidae), Zootaxa 4410 (2), pp. 319-330 : 321-327

Aphanius irregularis , new species

( Figs. 1–4 )

Holotype. FFR 08653, male, 35 mm SL; Turkey: Denizli prov.: spring Kaklık, 37°51.36'N 29°23.11'E; Baran Yoğurtçuoğlu , 30 Sept. 2017.

Paratype. FFR 08654, 14, 22–42 mm SL; same data as holotype. FSJF 3460 , 3 , 29–31 mm SL; FSJF 3461 , 10 , 25–30 mm SL; Turkey: Denizli prov.: spring Kaklık , 37°51.36'N 29°23.11'E .

Diagnosis. Males of A. irregularis are distinguished from males of all other species of the A. anatoliae group by having irregularly-set and shaped dark-brown flank-bars, most bars being fused to each other, interrupting the silvery interspaces forming vertical rows of silvery blotches (vs. flank bars regularly set and spaced) and flank with silvery spots or fields of silvery vermiculation (vs. no silvery spots or vermiculation on flank). Aphanius irregularis is closely related and also geographically proximate to A. maeandricus . Except the irregularly-set and shaped flank bars, it is distinguished from this species by having a wide, dusty grey or black anal-fin margin, often interrupted in small individuals, in males (vs. a narrow black anal-fin margin) as well as a vermiculate brown colour pattern, usually with a mid-lateral series of short stripes, in females (vs. many small, black dots in A. maeandricus ). Also, male A. irregularis often but not always have one or a few white blotches in the middle of the dorsal fin (vs. always absent in A. maeandricus ). Aphanius irregularis is distinguished from A. saldae , A. splendens , A. sureyanus and A. transgrediens by the flank and back being completely covered by scales (vs. scales reduced in various degrees, especially on the back) and from these species as well as from A. fontinalis by having a black dorsal-fin base (vs. white). Male A. irregularis are also distinguished from males of other species of the A. anatoliae group by a combination of characters: Aphanius irregularis have a wide, dusty-grey or black anal-fin margin (a narrow black anal-fin margin in A. anatoliae , A. marassantensis , A. iconii , A. meridionalis ) and a black dorsal-fin base (vs. white or hyaline in all species except A. iconii ) followed by a narrow, white line or a series of white spots (vs. a wide white or hyaline band in A. iconii ).

Description. See Figures 1–4 for general appearance and Table 1 for morphometric data of holotype and 13 paratypes. Dorsal head profile straight or convex. Dorsal profile straight or slightly convex from nape to dorsal-fin origin. Ventral profile convex. Body deeper than wide, compressed. Body deepest at about dorsal-fin origin. Greatest body width at pectoral-fin base or at middle of belly in female. Lower jaw gently upturned, oriented about 45° to body axis. Caudal peduncle compressed laterally, 1.2 in holotype, 1.2–1.3 in paratypes, times longer than deep. Pectoral fin rounded, reaching half or full of distance between pectoral- and pelvic-fin bases. Pelvic fin not reaching to anus, very small or absent in some individuals. Anal-fin origin below vertical of 2 nd or 3 rd branched dorsal-fin ray. One scale between pelvic-fin bases. Anus situated just in front of anal-fin origin, tissue around genital papillae swollen and papillae hidden between scales in nuptial females. Dorsal and anal fins with convex posterior margin. Dorsal and anal fins roundish in both sexes. Tip of longest dorsal-fin ray reaching to a vertical of middle of last branched anal-fin ray in female, to tip of anal fin or to a point slightly before in male. Caudal fin slightly rounded. Largest individual examined 42 mm SL.

Dorsal fin with 9½ (7), 10½ (2), or 11½ (1) branched rays. Anal fin with 9½ (3) or 10½ (7) branched rays. Caudal fin with 8+8 (1), 9+8 (10) or 9+9 (3) branched rays. Pectoral fin with 9–11 branched rays and pelvic fin small, (rarely absent) with 5–6 rays. Trunk and head entirely scaled. Scales cycloid. Flank with 25 (3), 26 (3), 27 (4), 28 (4) scales along lateral series. Between dorsal- and pelvic-fin origins 10-11 scale rows. Caudal peduncle with 6-8 circumpeduncular scales. Lateral line absent. Teeth tricuspid, median tip longer than laterals.

Coloration. See Figures 1–4 for general appearance. Preserved males: belly and ventral side of head yellowish grey, back and flank plain dark- or pale-grey, often with few, usually vertically elongated yellowish blotches in males larger than 25 mm SL. Smaller males with yellowish background and irregularly set and shaped, dark-grey or black bars on flank, much wider than interspaces, often fused to each other forming rows of vertically elongated yellowish blotches. Caudal-fin base black in some individuals, white in others, two wide black bands on caudal fin. Pectoral fin hyaline. Pelvic fin hyaline with a black margin or tip in some individuals. Dorsal-fin base black, a narrow white line or some small irregularly set white spots or lines at or slightly above dorsal-fin base, absent in some individuals. Dorsal fin above white line usually black, with a second whitish line or few white blotches in middle of dorsal fin in some individuals, distal half of dorsal fin pale grey in non-breeding males. Anal fin usually whitish or yellowish with a wide dusty-black margin and two black bands. Anal-fin margin and black bands often irregularly set and shaped.

Live males: Cheeks, ventral side of head and belly silvery. Back brown. Flank silvery with irregularly set and shaped, dark-brown bars, much wider than interspaces, most bars being fused to each other, interrupting silvery interspaces and forming vertical rows of silvery blotches. Flank with minute silvery spots or fields of silvery vermiculation. Bars in nuptial males almost black, yellowish-brown in stressed and non-breeding males. Dorsal-fin base black, a narrow white line or some small irregularly set spots or lines at or slightly above dorsal-fin base, not found to be absent in live individuals. Fin patterns agree with preserved males.

Live and preserved females: Background colour yellowish brown or grey when preserved, silvery-grey in live. Top of head and back pale brown. Cheek, ventral side of head, belly and flank silvery-grey or pale-brown. Flank with a dark-brown or black vermiculate pattern. In most females, a mid-lateral row of short stripes, often an adjacent row of short stripes or horizontally elongated blotches above and below mid-lateral stripes on caudal peduncle. No diamond-shaped black blotch at middle of caudal-fin base. All fins hyaline, grey with a grey hue in preserved individuals. Dorsal, caudal and anal fins with a pale-grey band shortly above base in live.

Distribution and conservation. The spring Kaklık is located at the intersection of the Menderes and Gediz Grabens in the south-western Turkey ( Özler 2015). The water issuing from the karstic aquifer has been impounded in a semi-artificial pond ( Fig. 5 ) for recreational purpose and here the core population of A. irregularis occurs. One of the outlets flows directly into the Kaklık Cave and has given rise to travertine formation within the cave ( Fig. 6a ), by its carbonate-sulphur rich water. Kaklık Cave is a local tourist attraction and a small park is maintained around the area. The other outlet of the pond flows to a swimming pool that is actively used by the visitors to the cave.

Aphanius irregularis is only known from one, very small population found in the spring itself as well as occasionally in some of the small natural pools within the cave ( Fig. 6b ). However, no records confirmed the existence of the species out of this semi-closed system despite a field survey carried out in nearby ditches and streams.

Aphanius irregularis might be a threatened species. The cave is a protected natural area and has been open to tourism since 2002, with controlled entrance permission and guards being permanently present at the site. However, this could not be regarded as a “species conservation” action. For example, the management of the site had completely cleaned the pool of Characean algae in 2014, the only spawning substrate of A. irregularis ; there is no awareness of this unique species at that site. As a first step for conservation, the species needs to be brought to the attention of the site managers, with a discussion as to how the site can be managed so as not to impact the species negatively.

Etymology. The species name, “ irregularis ”, is given for the irregular settings of the male colour pattern, which is unique in Anatolian Aphanius . An adjective.

Remarks. The identity of the Kaklık Aphanius had remained unclear since it was first found in 2012. Pichler et al. (2014) suggest that it could be a new species based on six microsatellite markers, a mitochondrial marker encoding the d-loop, Amplified Fragment Length Polymorphism (AFLP) and geometric morphometric analysis. Geiger et al. (2014) identified the Kaklık Aphanius as A. maeandricus , another species from the Büyük Menderes River drainage, due to the low molecular distance between both (0.7% K2P distance; M. Geiger, pers. comm.).

Aphanius maeandricus ( Fig. 7 ) inhabit the springs around Işıklı and Dinar ( Fig. 8 ). While belonging to the Büyük Menderes today, Işıklı and Dinar springs as well as Kaklık spring had not been connected to the river until the late Quaternary ( Kazanci et al. 2009, M. Ekmekçi, pers. comm.). The progressive development of the Büyük Menderes Graben compromised of two successive groups of events. The first one controlled the Early–Middle Miocene formation of the Büyük Menderes drainage, and incongruent strata existing between this period and the Quaternary indicate a time interval of folding, uplift and severe erosion. The second events included several pulses of deformation, which covered the rapid deposition of alluvial deposits in the Holocene and ultimately the migration of the Büyük Menderes Graben depocenter to the present-day position ( Gürer et al. 2009). The Büyük Menderes must have captured the Kaklık spring and the Işıklı and Dinar spring complex between the end of the Günz glacial (about 820 000 years ago) and the end of Würm glacial (about 10 000 years ago) ( Kazanci et al. 2009). If the Büyük Menderes captured the springs at the beginning of its extension, the springs must have been connected for 820,000 years, with four successive isolation-reconnection events, in parallel with the four glacial epochs, or fewer times or not, if the capture occurred later.

A similar low molecular distance (0.5%, Geiger et al. 2014) is found between Aphanius fontinalis from the Lake Yarışlı and A. sureyanus from the Lake Burdur. The timing of the epeirogenic events isolating these two species is similar to the Büyük Menderes case. The Lake Burdur was shallower and wider than today during the early Pleistocene and became narrower and deeper during the Würm glaciation (10,000 –110,000 years ago) separating from the Yarışlı Lake during this time ( Erol 1984).

After the connection of the springs by the Büyük Menderes River, we suspect that Aphanius invaded the river from Kaklık or from Işıklı. Indeed, we have no real argument to favour a scenario in which Aphanius invaded the Büyük Menderes from either of these springs. As there is a small but significant molecular distance between the populations, we suspect that after the initial invasion of one spring by the other, both populations became isolated again during a subsequent glaciation event. This isolation subsequently led to speciation.

Interestingly, there are no recent records of Aphanius from the Büyük Menderes River, except of A. fasciatus from the estuarine area. Aphanius had been found in the 20 th century at Yenicekkent, Sarayköy and Akçay ( Güçlü et al. 2013; Hrbek et al. 2002; Neer et al. 2008) ( Fig. 8 ) in the Büyük Menderes drainage. Despite the recent fieldwork at these sites, none of the records could be confirmed and no voucher materials are available from these records. Although the Aphanius at these points are thought to be A. maeandricus , this needs to be confirmed.

The geological scenario discussed above has resulted in peripatric speciation in which a new species is formed from an isolated peripheral population. The primary characteristics of peripatric speciation, as proposed by Coyne & Orr (2004), are that one of the populations is much smaller than the other and the effects of selection (e.g. sexual) and genetic drift by the limited population size are strong. This is clearly the case in A. irregularis . In addition, the Kaklık spring can be regarded as an extreme habitat even for Aphanius , having high sulphur concentration, high temperature and oxygen-poor conditions, and most likely these extremes had been more severe in the past ( Gulecal-Pektas & Temel 2017). Gavrilets (2003) suggests that drifted alleles underlying selection also increase fitness through pleiotropic effect, for example those driving the colour pattern in Kaklık, and strong selection for local adaptation is likely to speed up speciation. This kind of acceleration in divergence can also be contributed by the very small gene pool which should be more severely influenced by each of the individual mutations.

The molecular and developmental mechanisms underlying colour-pattern formation e.g. stripes vs. spots or intermediate shapes, have been recently documented and modelled in closely related Danio species and their mutant phenotypes ( Parichy 2003; Singh & Nüsslein-Volhard 2015). In zebrafish, Danio rerio , the dissociation of stripes into a spotted pattern is based on one of few mutations in one gene only ( Watanabe et al. 2006) and we suspect this to be the case also in A. maeandricus and A. irregularis . However, the knowledge on the relationship between colour pattern formation and the evolution of species is still very poor. Captive-bred generations have proven the colour patterns of A. maeandricus and A. irregularis to be stable and not variable or phenotypically plastic.

Figures

FIGURE 1. Aphanius irregularis, FFR 08653, holotype 35 mm SL, Turkey: Kaklık spring.

FIGURE 2. Aphanius irregularis, FFR 08654, left side from top: males 25, 24 and 25; right side from top: females, 40, 32 and 30 mm SL; mm SL; Turkey: Kaklık spring.

FIGURE 3. Aphanius irregularis, from the top: FFR 08654, female, paratype, 52 mm SL; FFR 08653, male, holotype, 35 mm SL; Turkey: Kaklık spring.

FIGURE 4. Aphanius irregularis, not preserved, captive individuals; from the top: female lacking pelvic fin; male, both about 30 mm SL); Turkey: Kaklık spring.

FIGURE 5. Kaklık spring: Pool holding the core population of A. irregularis.

FIGURE 6. Kaklık spring: a, outflow of the semi-artificial pond entering the cave and the travertine formations; b, natural pond located just at the entrance of the cave.

FIGURE 7. Aphanius maeandricus, from the top: FSJF, female, 40 mm SL, male, 30 mm SL; Turkey: Işıklı spring.

FIGURE 8. Records of A. irregularis (type locality only) and A. maeandricus.