Otoliths of five extant species of the annual killifish Nothobranchius from the East African savannah.

Bettina Reichenbacher,Martin Reichard

doi:10.1371/journal.pone.0112459

Abstract

This study presents, for the first time, a comprehensive dataset that documents the range of inter- and intraspecific otolith variation in aplocheiloid killifish, based on a total of 86 individuals representing five extant species of Nothobranchius PETERS, 1868, from East Africa: the sympatric pairs N. rubripinnis SEEGERS, 1986 and N. ruudwildekampi COSTA, 2009 (Eastern Tanzania), and N. orthonotus (PETERS, 1844) and N. furzeri JUBB, 1971 (Southern Mozambique), and two isolated populations of N. korthausae MEINKEN, 1973 (Eastern Tanzania). Otolith characters were analysed based on SEM images, and otolith morphometry was conducted using uni- and multivariate statistics. Two ancient clades of probably Early to Middle Miocene age in eastern Tanzania and southern Mozambique can be recognized based on otolith morphologies, which is consistent with previous work based on molecular data. The distinctive sulcus morphologies in the otoliths of sympatric species may be linked to species-specific hearing capabilities, perhaps constituting a case of character displacement in an area of secondary sympatry. The otoliths of the studied species of Nothobranchius are diagnostic at the species level, even in the case of closely related species diagnosable otherwise only by minor differences in coloration. The two populations of N. korthausae also displayed some differences in their otolith characters. The new data may facilitate future recognition of fossil species of Nothobranchius. As no fossil remains of extant aplocheiloid killifishes have yet been described, the discovery of fossil otoliths of Nothobranchius would significantly advance understanding of the evolutionary history of this interesting group of fishes.

Highlights

Otoliths are mineralized structures usually consisting of .90% aragonite embedded in a framework of proteins
The sagitta is especially important in the field of palaeontology, because fossil sagittae are much more abundant in the sedimentary archive than fossil fish skeletons [7]
The antirostrum is small and the excisura shallow or slightly incised in most of the otolith specimens from Tanzania, whereas the antirostrum is prominent and the excisura deeply incised in most otoliths of the species from Mozambique

Summary

Introduction

Otoliths are mineralized structures usually consisting of .90% aragonite embedded in a framework of proteins. The sagitta is the largest otolith, while the lapillus and the asteriscus are rather tiny structures [3,4]. The morphology and contour of the sagitta is well known to be a meaningful taxonomic character at the genus and species level in most teleosts. The lapillus and asteriscus may present informative characters for genus and species identification, but are rarely used for these purposes because of their usually small size [3,4,6]. Fossil lapilli can be found in sediments deposited in brackish or freshwater habitats and usually belong to species of the Otophysi; fossil lapilli or asterisci of other teleost groups are extremely rare [5]. Fossil sagittae are generally the most useful type of otolith for tracing the diversity of fossil fish faunas since the Cretaceous, when the radiation of Teleostei began [7,8]

Methods

Results

Conclusion