Keywords

This volume is the fulfillment of a long-standing personal and scientific obligation to contribute to the history of studies of cichlid fishes. Noakes (herein “DLGN”) was personally involved in laboratory and fieldwork with cichlid fishes during his graduate studies on fish behavior (Noakes and Barlow 1973). Abate (herein “MEA”) has had the pleasure of studying cichlids (Abate et al. 2010) joined by many undergraduate researchers who were turned into cichlidophiles by the beauty and social complexity of these fish, even during their first unruly encounters with experimental design.

Chance often plays a role in what people come to appreciate in life as is the case for each of us when it comes to cichlids. For MEA, it was a random encounter one day outside of the Museum of Comparative Zoology, home to the Thayer Expedition’s vast collection of cichlid specimens from Brazil (see McConnell, this volume). There she struck up a conversation with Les Kaufman who introduced her to Karel Liem, cichlids, and phenotypic plasticity (Kaufman and Liem 1982). The coincidence of chance also brought DNLG to Halifax, Nova Scotia, Canada in December 2017 for the memorial service for Derek Iles, and the service itself made the cold of the season there less onerous. Anyone who knows anything about cichlids will be familiar with “Cichlid Fishes of the Great Lakes of Africa” by Geoffrey Fryer and Derek Iles (Fryer and Iles 1972). Their book was not the first word on cichlid fishes of African Great Lakes—but it certainly established those fishes on the international scientific stage. Their book was notable for several reasons. It combined detailed practical observations with strong theoretical insights. It was synthetic and progressive. They considered the broad scale of African Great Lakes (AGLs), and the even broader scale of species diversity, complexity, and evolution within those lakes. As they intended, their book drew attention to the incredible diversity of cichlid fishes in African Great Lakes, and the question of their evolution.

Descriptions of African cichlid fish species had accumulated in the major museums of England and Europe since the nineteenth century (Bloch 1801; Regan and Trewavas 1928; Trewavas 1928, 1946; Lowe 1955). There was a long history of discovery and descriptions of African cichlid fishes that increasingly drew attempts to account for the ecological and evolutionary mechanisms that might have produced such an extravagant example of speciation (Goldschmidt 1996). Standard evolutionary textbooks, mostly based on experience with ornithology (Mayr 1963), suggested rather dramatic geological cycles of changes in lake levels to account for what were clearly examples that did not conform to models of allopatric speciation. Sympatric speciation was anathema—history has had a lot to say about this. In the face of overwhelming ecological and genetic evidence, Ernst Mayr (2001, p. 181) eventually conceded that sympatric speciation did occur in cichlids in the African crater lakes.

This volume provides new interpretations of cichlid evolution from continental to regional scales in Africa and the Neotropics by using molecular genetics and genomics to understand the interplay of genomic structure and ecological factors (chapters by Wagner; Stiassny and Alter; Lopez-Fernandez; Torres-Dowdall and Meyer, this volume). The stunning polymorphism (e.g., Midas cichlid, see Fig. 2 of Torres-Dowdall and Meyer in this volume; Fig. 1) that we find so attractive has at the same time required a combination of new tools (van Rijssel et al.; Nyingi et al., this volume) to better distinguish species and assess species richness for more realistic models of evolution and conservation action plans. The melding of quantitative molecular and field monitoring techniques (Stiassny and Alter; Njingi et al., this volume) is now modeling the evolution of cichlid species far beyond what conventional morphometrics and meristics could have suggested.

Fig. 1
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Collection of cichlids in Nicaragua, 1969: how many species? (photo by Gerald Meral)

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Our personal contacts with cichlids have combined some elements of chance together with active choices, that led to remarkable opportunities and interactions with some of the most productive people in cichlid research. For MEA several of these encounters have been at cichlid symposia presented at EEEF, the biennial Ecological and Evolutionary Ethology Conference of Fishes (Fig. 2). We recognize and freely acknowledge our good fortune for all of this. Without exception, all the cichlid researchers that we have encountered over the years, including the many contributors to this volume from around the world, have been generous to a fault in sharing their time and insights into the behavior, ecology, and evolution of these incredible fishes.

Fig. 2
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Miles Keenleyside (Invited Chair of the Cichlid Symposium) with David Noakes and student award winners, Naomi Gardiner and Camille Leblanc, at the 2008 EEEF meeting held at Boston University. (photo by Maria Abate)

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DLGN has personally experienced the considerable progression of studies of cichlid fishes from the days when exploration, taxon discovery, and detailed description were the norm to the present day when cichlids have become some of the most significant model species for the study of fundamental processes in biology, particularly researching the evolution of parental behavior (Fig. 3) and other social behaviors (Balshine and Abate; Jordan et al.; Félix and Oliveira, this volume). The study of cichlid social behavior has been a long tradition (Noble and Curtis 1939); and now molecular genetics has increased the potential to identify the relative roles of natural, sexual, and kin selection in shaping the evolution of cichlid societies. It is worth noting that even Bill Hamilton, the greatest theoretical biologist of his era (Fig. 4), was attracted to the questions of the evolution of parental behavior in Amazonian cichlids (Henderson 2005). One of DLGN’s serious regrets (of a number) is that at the time when he knew Bill, he did not realize that Bill also had an earlier interest in cichlid fishes.

Fig. 3
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Spawning pair of rainbow cichlid, Archocentrus multispinosus (formerly Herotilapia multispinosa ) in laboratory aquarium. (photo by Jeffrey Baylis)

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Fig. 4
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Bill Hamilton, October 1994. (photo by David Noakes)

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Cichlids also provide remarkable insights into the sensory world of fishes because of their tremendous diversity and ecological adaptations (Gray; Webb et al.; Lobel et al.; Schulz-Mirbach and Ladich; Félix and Oliveira, this volume.) In these chapters, behaviors of the signaler and the receiver are dissected in terms of their underlying mechanisms, including functional neurogenomics, and their consequences within a species and at the community level. Cichlids are best known in this regard for their coloration, visual displays, and as a model for vertebrate visual ecology (Gray, this volume). Three chapters noted above are devoted to the study of mechanoreception and sound reception and production in cichlids as genomics, imaging techniques, acoustical research tools, and comparative studies have advanced their use for understanding the roles of the mechanosensory lateral line and auditory systems in mediating complex behaviors and how these sensory inputs influence evolution.

And yet the incredible ecological diversity of the cichlids continues to unfold as increasingly sophisticated theoretical approaches and analytical tools are focused on their evolution. We are pleased to include a chapter to summarize the long-term studies of Lake Tanganyika cichlids, pioneered by Hiroya Kawanabe (chapter by Takeyama, this volume), since the contributions of Japanese colleagues to cichlid field research have not been widely recognized. Our understanding of the ecology of cichlid fishes, particularly their respiratory ecology and trophic relationships, was built upon groundbreaking studies (e.g., Lowe-McConnell 1969; Fryer and Iles 1972). Contributions in this volume test some of the critical generalizations from those earlier studies on ecomorphology and take those areas of science in productive new directions to examine explanations involving trade-offs (chapter by Chapman) and feedback between internal and external drivers of variation (chapter by Hu and Albertson, this volume).

DLGN does not place any particular interpretation on the visit to Halifax and the memorial service for Derek Iles. It was the opportunity to meet members of his family and share their feelings about his remarkable life (Fig. 5). DLGN had known Derek for a number of years when he worked on marine fishes for the Department of Fisheries and Oceans Canada long after his work on cichlid fishes in Africa. But the coincidence of DLNG’s contacts with cichlids and events over time seems to be ongoing. For example, during the 2019 presentations to recognize the 50th anniversary of the Apollo 11 landing on the moon, DLNG was reminded that unlike a great many people in different countries he did not see those events when they happened. Together with Jerry Meral (“JM”), another graduate student from George Barlow’s laboratory, DLGN and JM were trapped in the “Soccer War” between El Salvador and Honduras during that week in 1969. Sitting in the airport in Tegucigalpa, Honduras and watching fighter aircraft take off to engage in the last aerial combat between piston-engine aircraft (Fig. 6), while two men walked on the moon. Driving from Berkeley, California to field sites in Nicaragua and just happening to be in the wrong place at the wrong time. Of course, eventually reaching Nicaragua and spending an incredible field season watching cichlid behavior in the crater lakes (Thorson 1976). It did take some time, however, before DLNG and JM became accustomed to seeing cichlids for sale in the local markets—and to eating cichlids in the restaurant in the hotel—after spending so much time in the research laboratory keeping fish alive and healthy as valuable research specimens (Fig. 1). For MEA, the chance of being in the wrong place at the wrong time in Nicaragua came in the middle of the night when lodgings in a forest reserve caught on fire (Fig. 7). It was a reminder of how fragile every day can be for the people who live in these remote places and make the field study of cichlids possible for those who come from afar.

Fig. 5
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Memorial service for Derek Iles, Halifax, Nova Scotia. (photo by David Noakes)

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Fig. 6
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Salvadoran Air Force Corsair aircraft that took part in the 1969 “Soccer War”, subsequently painted in USA color pattern. (photo by David Noakes)

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Fig. 7
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Lodgings ablaze in forest reserve, Nicaragua. (photo by Maria Abate)

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One of the fondest cichlid memories for DLGN is November 1980, sitting with ET, Ro, and Melanie in the British Museum, surrounded by bottles of museum specimens of cichlids and the proofs of ET’s monumental book on cichlids (Trewavas 1983) while having tea and chocolate (in the form of the number 80) to celebrate ET’s birthday. DLGN was truly fortunate to share time with ET and Ro at the international tilapia conference in Bellagio and hear them recount their wealth of personal observations of cichlids in Africa (Pullin and Lowe-McConnell 1982; Lowe-McConnell 2006).

In this volume, we have brought together people and their ideas that we think acknowledge the history and contributions of researchers who have studied cichlids and at the same time demonstrate the continued dynamic approaches and insights in this field. Of course, our debts to the major books by Baerends and Baerends-van Roon (1950), Greenwood (1974), ET (Trewavas 1983), Keenleyside (1991), and Barlow (2000) on cichlid fishes are obvious. The study of cichlids has progressed from the initial descriptive phase of discovery of new species and the documentation of the incredible diversity within this family to the most detailed analyses of molecular genetics. We are fortunate indeed to have the monumental historical contribution from Matthew McConnell to set the scene for our volume. We are especially pleased that we have contributions from colleagues in South America and Africa who bring very different perspectives on cichlids as native species (Natugonza et al.; Nyingi et al.; Agostinho et al., this volume).

The applications of molecular genetics to the study of almost every aspect of cichlid biology have at once revolutionized our understanding of cichlids and at the same time has led to new hypotheses to account for their behavior and evolution. Cichlids have now become model species, in their own right, for research on topics as diverse as neurobiology, sensory physiology, and environmental physiology. But we cannot ignore the increasing threats to native cichlids from their long history of being overfished (e.g., Lowe 1952) and the many other human activities that have disrupted habitat over the past few decades (chapters by Natugonza et al., Nyingi et al., this volume). Nor can we overlook the new threats of some cichlids themselves (Figs. 8 and 9) as invasive species often far beyond their native ranges (chapter by Agostinho et al., this volume).

Fig. 8
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Female spotted tilapia, Pelmatolapia mariae (formerly Tilapia mariae ), in a Florida canal. (photo by Jeffrey Baylis)

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Fig. 9
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Female Mossambique tilapia, Oreochromis mossambicus (formerly Tilapia mossambica ), retrieving free-swimming young back into her buccal cavity, in a Florida canal. (photo by Jeffrey Baylis)

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As readers will note, the styles of the chapters in this volume are quite different, a welcome consequence of the diversity of the authors as well as differences in the stories they present. Readers will no doubt also notice our dilemma in what remains a fundamental task for anyone studying cichlid fishes. How do we deal with the ever-changing taxonomy, systematics and scientific nomenclature (or should we even consider common names) in a volume that includes references that span decades? In most cases, there are no connections between publications and voucher specimens deposited in museum collections, so it would not be possible to resolve the questions with certainty.

Along with the species name as it appeared in the original reference, several chapters in this volume also included the updated valid name. In some cases, the most widely referenced species name or well known common name (e.g., convict cichlid) was used to clarify which species was being referenced. Hence, readers will find that the name of a particular species that was extracted from the contributed chapters for the volume’s subject index may be listed under its common, former or current name. While our approach to taxonomy was imperfect, we hope the volume is also useful for compiling findings for individual cichlid species over many years under its various names, which are summarized online in Eschmeyer’s Catalogue of Fishes (Fricke at al. 2020) with a cross-link from FishBase (Froese and Pauly 2020) where common names can be searched.

This volume includes many insights about the exciting and promising future of cichlid studies. It has been emphasized for at least 20 years that cichlids are model organisms for the study of evolution (e.g., Kornfield and Smith 2000); and now, with sequenced genomes and the recognition of different mechanisms underlying their highly varied phenotypes, some cichlids have also become model species for biomedical research. Compared to the typical lab rat or lab fish, the in-depth knowledge we have of cichlids in nature makes them a far more powerful model when it comes to understanding how gene–environment interactions influence the development of vertebrate traits including social behavior. With new molecular and imaging tools being used for cichlid studies, we not only have the opportunity to learn a lot more about cichlids but even some things about ourselves. This book will not be the last word on cichlids, but it certainly sets out what the next words will be for further discoveries of the mechanisms responsible for their complex traits and remarkable phenotypic variation (Parsons et al., this volume).