Gecko sex chromosomes arose independently 22 times
A comparison of 22 gecko species and 2 outgroups finds that 22 separate sex-determination systems arose independently from only 17 ancestral chromosomes. Other studies reveal evolution reusing and reversing earlier solutions: a family tree of 50 crab species points to many returns from sideways to forward walking; 5 museum bones separate two extinct Galápagos tortoise lineages; and dodder remodelled a gene acquired from its host while keeping it functional.
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New systems from the same chromosomes
Zhang Guojie and colleagues at Zhejiang University compared 22 gecko species with 2 outgroups. Their phylogenetic analysis finds that 22 separate sex-determination systems arose independently from only 17 ancestral chromosomes. Sequence divergence places most origins between 7 and 12 million years ago, and the sample covers about 70 per cent of known gecko sex-chromosome origins. The timing of five origins around Middle Miocene cooling is consistent with the interpretation that climate could have been a trigger, but that mechanism remains untested. Because the sample does not include every known origin, incomplete sampling could also affect the apparent timing cluster.[1]
A second life for DNA from the past
Alexander Ochoa and Adalgisa Caccone at Yale University recovered DNA from 5 museum bones of extinct giant tortoises from San Cristóbal and Santa Fe islands. Computational filtering separated two lineages even though less than 1 per cent of the genome could be read in some specimens; increasing extinct genome segments through selective breeding of living hybrids remains an expectation rather than a measured conservation outcome. Separately, Koh Aoki and colleagues at Osaka Metropolitan University traced CYP81Q, a gene dodder acquired from a host. Mobile genetic elements remodelled it over millions of years and added a new intron, while the gene retained its function of producing sesamin. The transfer points to the order Lamiales, but the donor species remains unknown.[2], [3]
Crabs return to walking forwards
A team including Junya Taniguchi and Yuuki Kawabata of Nagasaki University observed 50 crab species in circular arenas designed to resemble their native settings. Of these, 35 mostly walked sideways and 15 forwards. Phylogenetic reconstruction points to one origin of sideways walking in true crabs followed by many returns to forward movement. The sideways-walking branch contains more species, but this comparison does not establish that the gait produced greater diversity.[4]
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