Current Biology Magazine yet fully integrate the devastation Quick guide How do cuckoo fool caused by the asteroid strike with that ? Cuckoo catfish invade caused by the longer-running Deccan Cuckoo catfi sh nests during spawning where Trap eruptions in India”. they quickly deposit their own eggs Although generally I enjoyed the which then are mistakenly collected book, I cannot agree that paleontology Martin Reichard by the female cichlid. Observations has become a true science only in in captivity show that groups of the past 40 years. This period marks Why ‘cuckoo’ catfi sh? The cuckoo catfish can overwhelm the discovery of many exceptionally ‘cuckoo’ part of the name references spawning pairs of cichlids, disrupting preserved new dinosaur that the cuckoo bird. Like their bird spawning and attempting to eat the constitute the basis for changing our counterparts, cuckoo catfi sh smuggle cichlid’s eggs. Male cichlids respond understanding of dinosaur biology. their eggs into the care of foster aggressively to intruding catfish, Discovery of a fact or truth about nature parents. This reproductive strategy but repeated intrusions by groups is itself part of the science and often of relinquishing parental duties to of cuckoo catfish eventually enable constitutes the most fascinating aspect foster parents — known as brood them to with the cichlids. The to the public. No one would doubt the parasitism — has evolved on several catfish release batches of about 10 signifi cance of discovering the Higgs independent occasions in unrelated eggs at a time. When catfish eggs boson in physics. Paleontologists should groups. In a few species, are released, female cichlids may not be bothered by being called ‘stamp it has developed to the point that inadvertently collect some of them collectors’, a term that is itself unfairly parents can no longer raise their own in their mouths as they quickly try used for many scientifi c disciplines that offspring — termed obligatory brood to pick up their own eggs, which are are often dealing with complex natural parasitism. at risk of being eaten by intruding phenomenon and rely on endless catfish. observations and the collection of Why are cuckoo catfi sh special? important samples. The current trend Among vertebrates, only a few bird Why don’t cichlids avoid catfi sh in the study of paleontology is almost lineages have evolved obligatory eggs? Catfi sh chicanery does not certainly characterized by an integration brood parasitism. Social insect (ants, include egg visual mimicry. Catfi sh of biological and geological progress bees, wasps and also some beetles) eggs are markedly different in and the application of new technologies are invertebrate examples. Uniquely shape and are smaller than the eggs that produce revolutionary ideas about among brood parasites, the cuckoo of their hosts (Figure 1). Recent dinosaur biology, yet nothing would be catfi sh ( multipunctatus) experiments suggest that cichlid as exciting to both paleontologists and has evolved brood parasitism even hosts that coexist with cuckoo catfi sh the public alike as the revolutionary though its relatives show no parental in Lake Tanganyika may be able to discoveries themselves. care. The cuckoo catfi sh is a member selectively reject cuckoo catfi sh eggs, of a small group of squeaker catfi shes but how host females discriminate REFERENCES (family ) from Lake cuckoo catfi sh eggs is still unknown. Tanganyika, with approximately ten Strikingly, mouthbrooders from other 1. Wang, M., O’Connor, J.K., Xu, X., and Zhou, Z. (2019). A new scansoriopterygid and locally endemic species. With the African lakes seem helpless once the loss of membranous wings in theropod exception of the cuckoo catfi sh, all infected with catfi sh eggs. So far, too dinosaurs. Nature 569, 256–259. 2. Nyakatura, J.A., Melo, K., Horvat, T., other squeaker catfi sh species (in few host species have been studied Karakasiliotis, K., Allen, V.R., Andikfar, A., Lake Tanganyika and elsewhere) to see whether this is a general Andrada, E., Arnold, P., Lauströer, J., Hutchinson, reproduce by scattering their eggs pattern, but it seems that — as in J.R., et al. (2019). Reverse-engineering the locomotion of a stem amniote. Nature 565, during mating and provide no care to cuckoos and their host birds— a 351–355. their young. coevolutionary ‘arms race’ operates 3. O’Connor, J.K. (2019). The trophic habits of early birds. Palaeogeogr. Palaeocl. 513, 178–195. between cuckoo catfi sh and Lake 4. Pan, Y., Zheng, W., Sawyer, R.H., Who is parasitized? The cuckoo Tanganyika cichlids, while catfi sh Pennington, M.W., Zheng, X., Wang, X., catfi sh exploits the parental are one evolutionary step ahead of Wang, M., Hu, L., O’Connor, J., Zhao, T., et al. (2019). The molecular evolution of feathers care of mouthbrooding cichlids. cichlids from all other locations. with direct evidence from fossils. Proc. Natl. Haplochromine cichlids have Acad. Sci. USA 116, 3018–3023. 5. Lindgren, J., Sjövall, P., Thiel, V., Zheng, W., undergone spectacular species What is the fate of the host brood? Ito, S., Wakamatsu, K., Hauff, R., Kear, B.P., radiations in the African Great Lakes Having a cuckoo catfi sh as a step- Engdahl, A., Alwmark, C., et al. (2018). Soft-tissue (Tanganyika, Malawi and Victoria), sibling is fatal for baby cichlids. evidence for homeothermy and crypsis in a Jurassic ichthyosaur. Nature 564, 359–365. and this diversifi cation is thought to Catfi sh eggs hatch earlier than those 6. Schoene, B., Eddy, M.P., Samperton, K.M., Keller, have been facilitated by their strong of cichlids. However, unlike avian C.B., Keller, G., Adatte, T., and Khadri, S.F.R. (2019). U-Pb constraints on pulsed eruption of parental habits. These cichlids lay cuckoo chicks, which often evict host the Deccan Traps across the end- their eggs in a specially prepared offspring from the nest, baby cuckoo mass extinction. Science 363, 862–866. nest, and female mouthbrooders catfi sh devour the host embryos, one collect their eggs immediately after by one, over several days (Figure 1). Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of spawning to incubate them in their Cichlid embryos have a large yolk Sciences, P.O. Box 643, Beijing 100044, China. mouths for a period of about three sac, a nutrient-rich energy supply E-mail: [email protected] weeks. to sustain their long incubation in

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the parent’s mouth, and this serves as food for the parasitic catfi sh. By the end of oral incubation all host embryos have usually been consumed and cuckoo catfi sh may resort to cannibalism. Cuckoo catfi sh embryos are well equipped for consuming the offspring of their host. They develop quicker than cichlids and their wide mouth is armed with formidable embryonic teeth, evidently an adaptation to their unusual biology. After weeks devoted to their care and protection, the female cichlid releases the young catfi sh from her mouth instead of her own offspring. Ironically, catfi sh eggs not collected by a cichlid when spawned (and perhaps even those that were rejected) might get a second chance to infect a mouthbrooding cichlid later on. Catfi sh eggs can hatch and develop outside the cichlid’s mouth. As the maternal instincts of female cichlids are strong, mouthbrooding females often indiscriminately collect stray heterospecifi c offspring they encounter, which, at least in captivity, can include cuckoo catfi sh. Figure 1. The cuckoo catfi sh and embryos of its hosts. Top left: cuckoo catfi sh embryos feed on embryos of their host, latching on to the head of a Are all mouthbrooding cichlids hatched cichlid and gradually swallowing the entire embryo (top left; 6 days post fertilization). Top right: the eggs of the cuckoo catfi sh are round and considerably smaller than the oval, nutrient- exploited? In Lake Tanganyika rich eggs of their hosts. Bottom: an adult cuckoo catfi sh. Photo credits: M. Brent Hawkins (top) where the cuckoo catfi sh is endemic, and Radim Blažek (bottom). only six cichlid species have been confi rmed as cuckoo catfi sh hosts, But how could this all have started Tanganyika, the time has now come to with 1.4–15% of brooding females in the fi rst place? Unlike in birds and tease apart the details of this remarkable infected in these species. Notably, insects, cuckoo catfi sh parasitism association using a combination of fi eld this estimate is based on a single could not have initially evolved through and lab experiments. study at one location. As cuckoo brood parasites exploiting hosts Where can I fi nd out more? catfi sh are distributed throughout Lake within their own species, because Blažek, R., Polacˇ ik, M., Smith, C., Honza, M., Tanganyika (which is 673 km long), this group of catfi sh lacks parental Meyer, A., and Reichard, M. (2018). Success of cuckoo catfi sh brood parasitism refl ects it remains to be seen how prevalent care. Instead, these catfi sh appear to coevolutionary history and individual experience cuckoo catfi sh parasitism is in other opportunistically join cichlid spawning of their cichlid hosts. Sci. Adv. 4, eaar4380. parts of the lake. pairs as egg predators, providing a Cohen, M.S., Hawkins, M.B., Knox-Hayes, J., Vinton, A.C., and Cruz, A. (2018). A laboratory In captivity, mouthbrooding possible route to parasitism through study of host use by the cuckoo catfi sh cichlids from other African lakes are the spatial and temporal overlap of Synodontis multipunctatus. Environ. Biol. Fish. 101, 1417. commonly infected at a much higher spawning. Alternatively, the strong Cohen, M.S., Hawkins, M.B., Stock, D.W., and rate than Tanganyikan cichlids. On maternal instinct of cichlids to collect Cruz, A., (2019). Early life-history features average, one third of clutches were stray offspring may have led to the associated with brood parasitism in the cuckoo catfi sh, Synodontis multipunctatus (Siluriformes: infected in non-Tanganyikan cichlids, exploitation of mouthbrooding cichlids Mochokidae). Phil. Trans. R. Soc. B 374, but with great variation among host by catfi sh. 20180205. Polacˇ ik, M., Reichard, M., Smith, C., and Blažek, R. species. Natural cuckoo catfi sh hosts, Our understanding of cuckoo catfi sh (2019). Parasitic cuckoo catfi sh exploit parental in contrast, are parasitized much less brood parasitism, and its evolutionary responses to stray offspring. Phil. Trans. R. Soc. frequently, typically at a rate of 6–15% origins, is still rudimentary but the B 374, 20180412. Sato, T. (1986). A brood parasitic catfi sh of of broods. This rate is comparable to species promises to bring fresh new mouthbrooding cichlid fi shes in Lake that in Lake Tanganyika, suggesting insight into our understanding of Tanganyika. Nature 323, 58–59. that cichlids coexisting with cuckoo how brood parasitism can evolve Institute of Vertebrate Biology, Academy of catfi sh have evolved mechanisms and persist. More than 30 years after Sciences of the Czech Republic, Kveˇ tná 8, to mitigate the success of catfi sh the fi rst discovery of the cuckoo Brno, Czech Republic. parasites. catfi sh reproductive strategy in Lake Email: [email protected]

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