Preface: Advances in cichlid research II: behavior, ecology and evolutionary biology

Hydrobiologia DOI 10.1007/s10750-017-3111-9 ADVANCES IN CICHLID RESEARCH II Preface: Advances in cichlid research II: behavior, ecology and evolutionary biology Stephan Koblmüller Tetsumi Takahashi . R. Craig Albertson . Martin J. Genner . Kristina M. Sefc . Received: 27 December 2016 / Revised: 23 January 2017 / Accepted: 26 January 2017 Ó Springer International Publishing Switzerland 2017 With currently 1703 valid species, 195 of which have been described only in the last ten years (Eschmeyer & Fong, 2017), and several hundreds more that still await formal description, cichlid fishes are among the most species-rich families of freshwater fish. They are naturally distributed from southern North America to southern South America (570 species), across most of Africa (1100 species), in southern Iran (1 species), Madagascar (29 species), and the Indian sub-continent (3 species) (Eschmeyer & Fong, 2017). They are famous for their extraordinary diversity and rapid Guest editors: S. Koblmüller, R. C. Albertson, M. J. Genner, K. M. Sefc & T. Takahashi / Advances in Cichlid Research II: Behavior, Ecology and Evolutionary Biology S. Koblmüller (&)
K. M. Sefc Institute of Zoology, University of Graz, Universitätsplatz 2, 8010 Graz, Austria e-mail: R. C. Albertson Department of Biology, University of Massachusetts, Amherst, MA, USA M. J. Genner School of Biological Sciences, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK T. Takahashi Institute of Natural and Environmental Sciences, University of Hyogo, Yayoigaoka 6, Sanda, Hyogo 669-1546, Japan speciation, and are well established as a prime model system in evolutionary biology research (e.g., Turner, 2007; Santos & Salzburger, 2012; Brawand et al., 2014; Henning & Meyer, 2014). A multitude of publications on cichlid fish has furthered not only our understanding of the factors and processes that underlie the diversification of this exceptional fish family, but also our knowledge of the evolution of biological diversity in general. Considering the importance of cichlids, a special issue was devoted to behavioral, ecological, and evolutionary biological research on cichlid fish in 2011 (Koblmüller et al., 2011). We were overwhelmed by the enthusiastic response to our call for contributions and the positive feedback by the readers of this first special issue on cichlid research. Since then, we have continued a series of special issues on cichlid fishes, which was hosted by Hydrobiologia since 2015 (Koblmüller et al., 2015). The importance of these volumes is underscored by recent reminders of the anthropogenic threats to cichlid-dominated habitats (e.g., Seehausen et al., 1997; Tweddle et al., 2015; Abila et al., 2016; Cohen et al., 2016). The prospect of oil drilling in the Great Lakes of East Africa in particular (Abila et al., 2016) is a chilling reminder of the sensitivity of these fishes and their ecosystems, and motivates us to inform the scientific and general public about the importance of these fascinating and unique species. The current special issue presents a collection of seventeen papers that tackle various aspects of cichlid 123 Hydrobiologia behavior, ecology, evolutionary biology and genomics. Together, they advance our knowledge of the mechanisms generating and maintaining the tremendous diversity within this freshwater fish family. Naturally, the studies included in this special issue do not fully represent all fields of research that have contributed to what we know about cichlids and their evolution. Nonetheless, they do represent rich and diverse knowledge, which we are happy to share with the readers of Hydrobiologia. Below, the papers are briefly summarized in the order in which they appear in this special issue. East African Great Lakes The East African Great Lakes’ biodiversity has awed scientists since the beginning of its exploration (e.g., Boulenger, 1899; Worthington, 1937). These lakes are renowned biodiversity hotspots, hosting a remarkable set of radiations of both invertebrates and fishes, of which the largely endemic cichlid species flocks, counting several hundred species each, are the most famous and species rich (Turner et al., 2001; Koblmüller et al., 2008; Salzburger et al., 2014). Twelve papers included in this special issue target various aspects of evolution, ecology, and behavior in cichlids of the East African Great Lakes. Takahashi-Kariyazono et al. (2017) investigated the evolution of c-type lysozyme, an enzyme involved in the innate immune system, during the adaptive radiation of East African cichlid fish. Based on Southern blot and sequence-based analyses, they found that while all Lake Tanganyika cichlid species investigated have only one copy of the c-type lysozyme gene, haplochromine cichlids from Lake Victoria and Lake Malawi have two and four copies, respectively. Furthermore, many of the inferred amino acid substitutions were found to change the charge of amino acid residues, changing the optimum pH for enzymatic activity. These findings are suggestive for an important role of lysozyme gene duplications and amino acid replacements in defense mechanisms against bacteria in environments with different salt concentrations, pH, or temperature, and a particular role of these genes in the radiation of the extremely species-rich tribe Haplochromini. An important issue in studies of population differentiation and speciation relates to the timing of divergence events, and how these relate to past environmental changes. Four studies on Lake 123 Tanganyika cichlid fish address the role of habitat fragmentation and changing lake levels on patterns of population genetic differentiation, divergence, and hybridization. Winkelmann et al. (2017) asked if divergence of rock-living and shell-living ‘‘ecomorphs’’ of Telmatochromis temporalis could have been driven by the availability of new habitat that followed the last major rise in lake level that took place approximately 100 kya. Using information within mitochondrial DNA sequences, they were able to determine that local ecomorph divergence and local population expansions most likely post-date the lakelevel rise. Thus, the results are consistent with divergent evolution into ecomorphs taking place in response to the availability of new habitat, consistent with theory of ‘‘ecological opportunity’’ as a promoter of adaptive radiation. Koblmüller et al. (2017) investigated the phylogeographic structure in two closely related species of the genus Altolamprologus. Using mitochondrial and nuclear DNA sequences, they found (a) that divergence between these two species was fairly recent (approximately 100 kya) and proceeded with little if any gene flow, (b) that a geographically restricted divergent haplogroup originated from ancient introgression, and (c) that habitatinduced population fragmentation contrasts with weak phylogeographic structure, a pattern consistent with low levels of periodic gene flow mediat (...truncated)