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/LifeForce-

factAF-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