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Recently diverged killifishes: Morphometry and caudal skeleton osteology of two members of the Aphanius dispar species group (Aphaniidae, Teleostei)

ELENI A. CHARMPILA1*, Azad Teimori2 and Bettina Reichenbacher1*
  • 1 Ludwig Maximilian University of Munich, Department of Earth and Environmental Sciences, Germany
  • 2 Shahid Bahonar University of Kerman, Department of Biology, Faculty of Sciences, Iran

The genus Aphanius (Nardo 1827) with 44 valid species currently identified, is characterized by its high level of adaptability to diverse environments, ranging from landlocked freshwater to brackish nearshore habitats and even hot sulfur springs (Teimori et al., 2014). Speciation events can originate when populations become reproductively isolated by natural barriers and such instances of population splitting have been proposed for Aphanius dispar (Reichenbacher et al., 2009). This species has been considered for a number of years now not to represent a monophyletic species (Hrbek and Meyer, 2003; Chiozzi et al., 2017). According to the molecular phylogeny presented in Freyhof et al. (2017) and Teimori et al. (2018), A. dispar actually represents a species group made up of four geographically isolated clades, consisting of six species in all: A. dispar (Rüppell, 1828), A. hormuzensis Teimori, Esmaeili, Hamidan & Reichenbacher 2018, A. stoliczkanus (Day 1872), A. ginaonis (Holly 1929), A. richardsoni (Boulenger 1907), and A. kruppi Freyhof, Weissenbacher & Geiger 2017. These species are distributed around the Red Sea and portions of the Arabian Sea, the Persian Gulf, the South-eastern sector of the Mediterranean Sea basin and the inland (fresh-)water bodies surrounding these areas. In this study we focus on A. stoliczkanus and A. hormuzensis. Their relatively recent diversification in the Persian Gulf area has rendered their identification on the basis of morphological and meristic characters difficult. Among the few diagnostic characteristics available are the numbers of dorsal fin rays in the case of A. stoliczkanus (6–9 as against 9–11 in the “true” A. dispar) and the distinctive otolith morphology of each species (Teimori et al., 2018). However, little quantitative data has been provided to support the contention that otolith morphology can be of taxonomic value in distinguishing between these species, and this factor could reduce acceptance of their validity. Moreover, the osteology of their skeletons has not been examined closely. In this study, differences between the skeletal elements of A. hormuzensis and A. stoliczkanus are examined, with a focus on the taxonomic value of the caudal skeleton. Specimens of A. stoliczkanus and A. hormuzensis were available from three sites in southern Iran, two located in the Hormuzgan Basin (Khurgu hot spring, Bandar e Hasineh lagoon) and the third in the Helleh Basin (Mirahmad hot spring). Specimens from the first two locations were identified as A. hormuzensis, while specimens from Mirahmad were assigned to A. stoliczkanus, based on the distribution of the species described in Teimori et al. (2012, 2018) and on qualitative otolith observation. In all, 90 specimens were examined. Specimens were photographed, transferred into separate tubes and stored in 70% ethanol. Sex was identified based on the pigmentation pattern displayed by the specimens. Morphometric measurements were made with a digital caliper to the nearest 0.1 mm. Total (TL) and standard lengths (SL), distances between snout tip and the points of emergence of dorsal (DL) and anal (AL) fins respectively, and the length of the base of the dorsal fin (DFB) were recorded. All measurements were standardized with respect to SL. Statistical analyses were performed separately for males and females, using PAST ver. 3.22. The measurements were normally distributed (Shapiro Wilk, p>0.05) except for DFB/SL in the case of male individuals from Khurgu and Mirahmad and females from Bandar. Welch’s t-test was used for comparisons between males and females within each population, while ANOVA was employed to compare differences between sexes across populations. Moreover, several specimens were X-rayed with a Faxitron system at the facilities of the Bavarian Natural History Collections in Munich (Fig. 1). Dorsal and anal fin rays (including the unbranched first and second rays), abdominal and caudal vertebrae (including the uroterminal centrum), number of anal fin pterygiophores and of preural vertebrae (PU) were counted. Numbers of neural (ns) and haemal spines (hs) of the preural vertebrae, and their positions relative to the caudal fin, were determined. The statistical analysis of the morphometric measurements revealed a significant difference between A. stoliczkanus and A. hormuzensis (Bandar, Khurgu) only in DFB (% of SL); this difference was significant for both males and females of the two species. Moreover, in the Bandar population there was a significant difference in the position of the anal fin, which in females was positioned further back on the body than in males. The Kruskal-Wallis test revealed a significant difference in the number of anal fin pterygiophores between Aphanius hormuzensis and A. stoliczkanus (1-5 in the first vs 1-3 in the latter). Additionally, specimens from Bandar had a more constant count of anal fin pterygiophores and preural vertebrae than the population from the Khurgu hot spring. In both A. hormuzensis populations the neural and haemal spines of the last preural centrum (usually PU5) extended as far as, or overlapped with the first procurrent rays of the caudal fin (Fig. 1B). In A. stoliczkanus, the neural or haemal spines (but rarely both of them contrary to A. hormuzensis) of the last preural centrum (PU4 or PU5) exhibited wide variation in their length or width among the specimens, and usually did not reach the procurrent rays of the caudal fin (Fig. 1D). Duplication of the neural spines of PU2 was the most common deviation from normal skeleton osteology among all populations investigated. In the case of A. stoliczkanus, the duplication of the haemal spine of PU2 was also observed. These results indicate that the studied populations of A. hormuzensis are characterized by a more robust caudal skeleton in comparison to A. stoliczkanus, because 4-5 (vs. 3) preural vertebrae are involved in supporting the procurrent rays of the caudal fin. This characteristic suggests improved swimming and maneuvering abilities for A. hormuzensis relative to A. stoliczkanus. In conclusion, the caudal skeleton osteology supports the species discrimination based on otolith morphology. Further investigation including staining procedures will be performed for a better illustration of these differences. Figure 1. X-ray of Aphanius hormuzensis (A) with close up of caudal skeleton (B) and X-ray of Aphanius stoliczkanus (C) with close up of caudal skeleton (D). e= epural, h= hypural plate, ph= parhypural.

Figure 1
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References

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Keywords: Aphanius, Iran, speciation, morphometry, Osteology

Conference: XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.

Presentation Type: Oral

Topic: MORPHOLOGY, ONTOGENY AND PALAEONTOLOGY

Citation: CHARMPILA EA, Teimori A and Reichenbacher B (2019). Recently diverged killifishes: Morphometry and caudal skeleton osteology of two members of the Aphanius dispar species group (Aphaniidae, Teleostei). Front. Mar. Sci. Conference Abstract: XVI European Congress of Ichthyology. doi: 10.3389/conf.fmars.2019.07.00077

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Received: 07 Jun 2019; Published Online: 14 Aug 2019.

* Correspondence:
Miss. ELENI A CHARMPILA, Ludwig Maximilian University of Munich, Department of Earth and Environmental Sciences, Munich, Germany, anna_helenachar@hotmail.com
Prof. Bettina Reichenbacher, Ludwig Maximilian University of Munich, Department of Earth and Environmental Sciences, Munich, Germany, b.reichenbacher@lrz.uni-muenchen.de