MALAWI CICHLIDS SARAH ROBBINS BSCI462 SPRING 2013
CICHLIDS Family of fish within the infraclass Teleostei Over 1600 species discovered, Up to 3000 species predicted Most commonly found in Africa and South America Popular in freshwater aquariums, also used as a food source
AFRICAN RIFT LAKES Found in East Africa s Great Rift Valley 3 Lakes with Genetically distinct Lineages Lake Tanganyika, Lake Victoria, and Lake Malawi Lakes are less than 1 million years old (Smith et. al. 2003) Cichlid populations in the lakes are genetically divided on very small geographic scales (Streelman et. al.2004) Environmental stochasticity is common and may be a driving force behind speciation and hybridization in the lakes (Streelman et. al. 2004)
GENETIC CLUSTERS From Loh et. al. (2013)
EXPLOSIVE SPECIATION Ideal Model System for Rapid Adaptive Radiation More than 500 species each in Lake Victoria and Lake Malawi Occurred in 3 bursts Danley and Kocher (2001) Stages of Malawi Radiation
CONVERGENT EVOLUTION Convergent evolution between Lakes Malawi and Tanganyika shows that cichlids solve ecological problems in similar ways (Albertson 2006).
SEXUAL SELECTION Male-male competition: defense of a mating area Female choice of bright color patterns
SEXUAL SELECTION Male-male competition: defense of a mating area Female choice of bright color patterns
SEX REVERSAL Recruitment of novel sex chromosomes to maintain sexual color dimorphism Resolution of conflict between sex determination and maintenance of color pattern Example from Roberts (2009): OB Phenotype
SPECIATION IMPLICATIONS Novel Sex Determiners may lead to reproductive isolation From Roberts (2009)
HYBRIDIZATION Hybridization may explain high levels of genetic diversity within populations and an increased number of speciation events. Smith 2003: Hybridization between two geographically isolated populations led to an intermediate species in an area that was between the two populations.
CONSERVATION THREATS Overfishing presents a significant threat to maintenance of cichlid populations in the wild
FUTURE DIRECTIONS Comprehensive study of speciation mechanisms in cichlids Genetic basis of pigmentation variation Sex Reversal vs. Sexual Selection Conservation efforts to preserve species with rapid population loss from overfishing Stricter regulations on fishing Increased species awareness Male-biased conservation of highly colored species
LITERATURE CITED Streelman JT, Gymrek SL, Kidd MR, Kidd C, Robinson RL, Hert E, Ambali AJ, Kocher TD. 2004. Hybridization and contemporary evolution in an introduced cichlid fish from Lake Malawi National Park. Molecular Ecology. 13: 2471-2479. Lande R, Seehausen O, van Alphen JJM. 2001. Mechanisms of rapid sympatric speciation by sex reversal and sexual selection in cichlid fish. Genetica. 112-113:435-443. SmithPF, Konings A, Kornfield I. 2003. Hybrid origin of a cichlid population in Lake Malawi: implications for genetic variation and species diversity. Molecular Ecology. 12: 2497-2504. Roberts RB, Ser J, Kocher TD. 2009. Sexual conflict resolved by invasion of a novel sex determiner in cichlids. Science. 326: 998-1001. Danley P, and Kocher TD. 2001. Speciation in rapidly diverging systems: lessons from Lake Malawi. Molecular Ecology. 10: 1075-1086. Albertson RC, Kocher TD. 2006. Genetic and Developmental Basis of Cichlid Tropic Diversity. Heredity. 97: 211-221. Genner, MJ and Turner GF. 2005. The mbuna cichlids of Lake Malawi: a model for rapid speciation and adaptive radiation. Fish and Fisheries. 6: 1-34. Knight ME, Van Oppen MJH, Smith HL, Rico C, Hewitt GM, and Turner GF. 1999. Evidence for male-biased dispersal in Lake Malawi cichlids from microsatellites. Molecular Ecology. 8: 1521-1527. Loh YH, Bezault E, Muenzel FM, Roberts RB, Swofford R, Baluenga M, Kidd CE, Howe AE, Di Palma F, Lindblad-Toh K, Hey J, Seehausen O, Salzburger W, Kocher TD, and Streelman JT. 2013. Origins of shared genetic variation in African cichlids. Mol Biol Evol. 4: 906-917.
PICTURE SOURCES http://www.cichlids.com/uploads/tx_usercichlids/user_pics/35 84/039_jp_6a453b2f5c.jpg http://www.nhnz.tv/images/nhnz%20programs/lifeforcefactaf-map.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/7/7e /Oreochromis_tanganicae_%28G%C3%BCnther%29.jpg/800px- Oreochromis_tanganicae_%28G%C3%BCnther%29.jpg