Ancient hookups between different species may explain Lake Victorias stunning diversity of

first_img Ancient hookups between different species may explain Lake Victoria’s stunning diversity of fish Ole Seehausen, an evolutionary biologist at the University of Bern who has studied cichlids for more than 25 years, wondered whether hybridization could have generated the genetic raw material. In earlier research, his team collected cichlids from the rivers and lakes surrounding Lake Victoria and partly sequenced each species’s DNA to build a family tree. Its branching pattern indicated that Lake Victoria’s cichlids are closely related to a species from the Congo River and one from the Upper Nile River watershed, the group reported last year in Nature Communications.A close look at all their genomes suggested the two river species hybridized with each other long ago. Seehausen proposed that during a warm spell about 130,000 years ago, water from tributaries of the Malagarasi River, itself a tributary of the Congo, temporarily flowed into Lake Victoria, bringing Congo fish into contact with Upper Nile fish.To explore the cichlids’ genetic history in more detail, Seehausen and postdocs Matt McGee, Joana Meier, and David Marques have now sequenced 450 whole cichlid genomes, representing many varieties of 150 species from the area’s lakes, and from the Congo, Upper Nile, and other nearby watersheds. Clues in the genomes suggest multiple episodes of mixing took place. Periods of drying have repeatedly caused Lake Victoria to disappear, and Seehausen and his team propose that fish in the remaining waterways evolved independently until wetter periods reunited them. This “fission-fusion-fission” process restored genetic diversity each time.About 15,000 years ago, three groups of fish, themselves products of the ancient hybridizations, came together in Lake Victoria as it filled again. Their ancestry provided the “standing variation” that natural selection could pick from to help the fish adapt to a vast range of niches, producing the cichlid bounty seen today. “Hybridization may turn out to be the most powerful engine of new species and new adaptations,” Seehausen says.”It’s mind-blowing,” says Dolph Schluter, an evolutionary biologist at The University of British Columbia in Vancouver, Canada. “All the variation required for speciation is already there” in the hybrids.Studies of other species also suggest standing variation can speed evolution. Biologists trying to understand how marine stickle-backs adapted so quickly to living in freshwater have discovered that a crucial gene variant was already present—in low percentages—in the fishes’ marine ancestors. At the meeting, researchers offered similar stories of standing variation jump-starting diversification, for example enabling long-winged beetles to evolve into short-winged ones on the Galápagos Islands. “I’ve never seen so many talks where you have evidence that genes are borrowed from old variation and further evolution is somehow facilitated by that,” Schluter says.Andrew Hendry, an evolutionary biologist at McGill University in Montreal, Canada, cautions colleagues not to completely dismiss new mutations in rapid species diversification: “What’s not clear to me is whether [the role of ancient hybridization] is a general phenomenon,” he says.Regardless, “The implications for conservation are blaring,” says Oliver Ryder, who heads conservation genetics efforts at the San Diego Zoo in California. Endangered species are currently managed as reproductively isolated units, and conservationists are reluctant to bolster populations by breeding the threatened animal with related species or populations. Eight years ago, however, a controversial program that mated Florida panthers with Texas cougars helped rescue the former from extinction. Studies such as Seehausen’s, says Ryder, suggest that in the long run, hybridization is important to preserving a species’s evolutionary potential. Sign up for our daily newsletter Get more great content like this delivered right to you! Country Country * Afghanistan Aland Islands Albania Algeria Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia, Plurinational State of Bonaire, Sint Eustatius and Saba Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d’Ivoire Croatia Cuba Curaçao Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guatemala Guernsey Guinea Guinea-Bissau Guyana Haiti Heard Island and McDonald Islands Holy See (Vatican City State) Honduras Hungary Iceland India Indonesia Iran, Islamic Republic of Iraq Ireland Isle of Man Israel Italy Jamaica Japan Jersey Jordan Kazakhstan Kenya Kiribati Korea, Democratic People’s Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People’s Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macao Macedonia, the former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Martinique Mauritania Mauritius Mayotte Mexico Moldova, Republic of Monaco Mongolia Montenegro Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Norway Oman Pakistan Palestine Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Qatar Reunion Romania Russian Federation Rwanda Saint Barthélemy Saint Helena, Ascension and Tristan da Cunha Saint Kitts and Nevis Saint Lucia Saint Martin (French part) Saint Pierre and Miquelon Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Serbia Seychelles Sierra Leone Singapore Sint Maarten (Dutch part) Slovakia Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands South Sudan Spain Sri Lanka Sudan Suriname Svalbard and Jan Mayen Swaziland Sweden Switzerland Syrian Arab Republic Taiwan Tajikistan Tanzania, United Republic of Thailand Timor-Leste Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States Uruguay Uzbekistan Vanuatu Venezuela, Bolivarian Republic of Vietnam Virgin Islands, British Wallis and Futuna Western Sahara Yemen Zambia Zimbabwe WAIMEA, HAWAII—In the shallow waters of Lake Victoria, the world’s largest tropical lake, swim some 500 species of cichlid fish with a dizzying variety of appearances, habitats, and behaviors. Genomic studies have shown they arose from a few ancestral species in just 15,000 years, a pace that has left researchers baffled about how so much genetic variation could have evolved so quickly. Now, extensive sequencing of cichlids from around Lake Victoria suggests much of it was there at the start, in the cichlids’ ancestors. Ancient and more recent dallying between cichlid species from multiple watersheds apparently led to genetically diverse hybrids that could quickly adapt to life in the lake’s many niches.Reported last week at the Origins of Adaptive Radiation meeting here, the work is “a tour de force, with many lines of evidence,” says Marguerite Butler, a functional morphologist at the University of Hawaii in Honolulu. It joins other research suggesting that hybridization is a powerful force in evolution. “What hybridization is doing is allowing the good stuff to be packed together,” Butler says.Some of Lake Victoria’s cichlids nibble plants; others feed on invertebrates; big ones feast on other fish; lake bottom lovers consume detritus. Species vary in length from a few centimeters to about 30 centimeters; come in an array of shapes, colors, and patterns; and dwell in different parts of the lake. Mutations don’t usually happen fast enough to produce such variety so quickly. “It’s been really hard to figure out what’s going on,” says Rosemary Gillespie, an evolutionary biologist at the University of California, Berkeley. By Elizabeth PennisiAug. 9, 2018 , 12:35 PMcenter_img (CLOCKWISE FROM LEFT): TIM ALEXANDER (2); MORITZ MUSCHICK Lake Victoria is home to hundreds of cichlid species, diverse in both appearance and behavior. Email Click to view the privacy policy. 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