first_img DNA from passenger pigeon museum specimens provided key new insights into this species’s demise. © Bailey Library and Archives, Denver Museum of Nature & Science In 2014, Wen-San Huang, an evolutionary biologist at National Taiwan Normal University (NTNU) in Taipei, and colleagues turned to DNA in an attempt to solve the mystery. Genetic material from four 19th century museum specimens revealed that the species had relatively low genetic diversity—meaning that most individuals were remarkably similar to each other—and that its numbers had fluctuated 1000-fold for millions of years. Hunting and habitat loss came during a time when the species was already declining, the team concluded, which pushed the birds over the edge.But the new study lays the lion’s share of the blame back on people. Beth Shapiro, a paleogenomicist at the University of California, Santa Cruz, and colleagues sequenced the complete genomes of two passenger pigeons, and analyzed the mitochondrial genomes—which reside in structures that power cells—of 41 individuals. The specimens came from throughout the bird’s range. In addition, they reanalyzed data from Hung’s group, and, for comparison, sequenced the bird’s closest living relative, the band-tailed pigeon. Sign up for our daily newsletter Get more great content like this delivered right to you! Country Four billion passenger pigeons once darkened the skies of North America, but by the end of the 19th century, they were all gone. Now, a new study reveals that the birds’ large numbers are ironically what did them in. The pigeons evolved quickly, but in such a way to make them more vulnerable to hunting and other threats.The pigeon’s fate may hold lessons for other animals under pressure from humans or other dangers, says A. Townsend Peterson, an evolutionary biologist at the University of Kansas in Lawrence who was not involved with the work.Scientists have long blamed hunting and deforestation for the passenger pigeon’s disappearance—the birds destroyed the very trees in which they nested—but biologists still couldn’t make sense of why they declined so quickly and completely. Passenger pigeons just couldn’t adapt to having smaller populations. 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 Four billion passenger pigeons vanished. Their large population may have been what did them in Like Huang’s study, Shapiro’s analysis found a remarkable lack of genetic diversity—given their population size—in passenger pigeons. Yet Shapiro’s team does not think this low genetic diversity resulted from populations fluctuations. Such fluctuations should affect all parts of the genome equally, but instead Shapiro and her colleagues saw concentrated pockets of low genetic diversity. What’s more, their analysis of the passenger pigeons’ mitochondrial genomes suggested that the bird’s population was stable for at least the last 20,000 years—countering the idea that the birds were already vulnerable when people began hunting them.Instead, the passenger pigeon’s huge population is what made it vulnerable, Shapiro’s team reports today in Science. The birds were able to adapt faster to their environment—and spread these changes quickly within their population—but this also caused all of them to be fairly genetically similar. And when a new threat—like human hunters and habitat loss—came around, they suddenly found their physiology and behavior were poorly suited for their declining numbers. Their population “went from being superbig to supersmall so fast they didn’t have time to adapt,” in part because they lacked the diversity to cope with this new way of living, Shapiro says.“This study suggests that the passenger pigeon’s most distinctive feature—its immense population size—left an enduring mark on its genome,” says Benjamin Van Doren, an evolutionary ecology graduate student at the University of Oxford in the United Kingdom not involved in the work.“[Shapiro] did a great job to support the idea that natural selection works efficiently in large populations,” says evolutionary biologist Shou-Hsien Li, Huang’s co-author on the 2014 paper and colleague at NTNU. But Li and Huang say the work merely reinforces their team’s view that the bird’s low genetic diversity reflects an already tumbling population.Some outside the camp agree with Shapiro’s interpretation, however. “The idea of wildly fluctuating passenger pigeon populations is deeply entrenched, Peterson says. But “I am persuaded by [Shapiro’s] argument, given this in-depth analysis of massive data resources.”Regardless, says Van Doren, the passenger pigeon’s precipitous decline is a “a cautionary tale [that] teaches us that successfully conserving species with large populations may require keeping their numbers higher than we might otherwise expect.” If their numbers start to sink, they may lack the ability to persist, even though the absolute number might not be very low. By Elizabeth PennisiNov. 16, 2017 , 2:00 PM JOEL SARTORE/National Geographic Creative Email Click to view the privacy policy. Required fields are indicated by an asterisk (*)last_img

Leave a Reply

Your email address will not be published. Required fields are marked *