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Vertebrate skin appendage early development is mediated by conserved molecular signaling composing a dynamical reaction-diffusion–like system. Variations to such systems contribute to the remarkable diversity of skin appendage forms within and among species. Here, we demonstrate that stage-specific transient agonism of sonic hedgehog (Shh) pathway signaling in chicken triggers a complete and permanent transition from reticulate scales to feathers on the ventral surfaces of the foot and digits. Resulting ectopic feathers are developmentally comparable to feathers adorning the body, with down-type feathers transitioning into regenerative, bilaterally symmetric contour feathers in adult chickens. Crucially, this spectacular transition of skin appendage fate (from nodular reticulate scales to bona fide adult feathers) does not require sustained treatment. Our RNA sequencing analyses confirm that smoothened agonist treatment specifically promotes the expression of key Shh pathway–associated genes. These results indicate that variations in Shh pathway signaling likely contribute to the natural diversity and regionalization of avian integumentary appendages.

The apparent biotic affinities between the mainland and the island in the Western Ghats–Sri Lanka biodiversity hotspot have been interpreted as the result of frequent migrations during recent periods of low sea level. We show, using molecular phylogenies of two invertebrate and four vertebrate groups, that biotic interchange between these areas has been much more limited than hitherto assumed. Despite several extended periods of land connection during the past 500,000 years, Sri Lanka has maintained a fauna that is largely distinct from that of the Indian mainland. Future conservation programs for the subcontinent should take into account such patterns of local endemism at the finest scale at which they may occur.

In “river dolphins add branches to family tree” (News of the Week, 30 Mar., p. [2531][1]), Dennis Normile discusses the molecular work of M. Nikaido and colleagues that indicates that river dolphins are old cetacean lineages that do not constitute a natural (that is, monophyletic) group ([1][2]). Nikaido et al. analyzed the insertion patterns for short interspersed elements (SINEs), which are transfer RNA-derived retroposons inserted throughout the genome, probably at random locations. Although it was not mentioned by Normile, we published the same conclusions based on different molecular analyses more than 8 months earlier ([2][3]). Using phylogenetic analyses of nucleotide sequences from three mitochondrial and two nuclear genes (from 19 cetacean species, including all river dolphins), we demonstrated with statistical significance that extant river dolphins form a polyphyletic group. We suggested that they are relict species whose adaptation to riverine habitats incidentally ensured their survival against major environmental changes in the marine ecosystem or the emergence of Delphinidae (true dolphins). A few months later, Hamilton et al. ([3][4]) published an analysis of three fragments of the mitochondrial genome (from 29 cetacean species), confirming our results. 1. [↵][5]1. M. Nikaido 2. et al. , Proc. Natl. Acad. Sci. U.S.A. 98, 7384 (2001). [OpenUrl][6][Abstract/FREE Full Text][7] 2. [↵][8]1. I. Cassens 2. et al. , Proc. Natl. Acad. Sci. U.S.A. 97, 11343 (2000). [OpenUrl][9][Abstract/FREE Full Text][10] 3. [↵][11]1. H. Hamilton, 2. S. Caballero, 3. A. G. Collins, 4. R. L. Brownell , Proc. R. Soc. London B Biol. Sci. 268, 549 (2001). [OpenUrl][12][Abstract/FREE Full Text][13] [1]: /lookup/doi/10.1126/science.291.5513.2531a [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #xref-ref-1-1 "View reference 1 in text" [6]: {openurl}?query=rft.jtitle%253DPNAS%26rft.stitle%253DProc.%2BNatl.%2BAcad.%2BSci.%2BUSA%26rft.issn%253D0027-8424%26rft.aulast%253DNikaido%26rft.auinit1%253DM.%26rft.volume%253D98%26rft.issue%253D13%26rft.spage%253D7384%26rft.epage%253D7389%26rft.atitle%253DRetroposon%2Banalysis%2Bof%2Bmajor%2Bcetacean%2Blineages%253A%2BThe%2Bmonophyly%2Bof%2Btoothed%2Bwhales%2Band%2Bthe%2Bparaphyly%2Bof%2Briver%2Bdolphins%26rft_id%253Dinfo%253Adoi%252F10.1073%252Fpnas.121139198%26rft_id%253Dinfo%253Apmid%252F11416211%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [7]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoicG5hcyI7czo1OiJyZXNpZCI7czoxMDoiOTgvMTMvNzM4NCI7czo0OiJhdG9tIjtzOjIyOiIvc2NpLzI5NC81NTQzLzc4Ny5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30= [8]: #xref-ref-2-1 "View reference 2 in text" [9]: {openurl}?query=rft.jtitle%253DPNAS%26rft.stitle%253DProc.%2BNatl.%2BAcad.%2BSci.%2BUSA%26rft.issn%253D0027-8424%26rft.aulast%253DCassens%26rft.auinit1%253DI.%26rft.volume%253D97%26rft.issue%253D21%26rft.spage%253D11343%26rft.epage%253D11347%26rft.atitle%253DIndependent%2Badaptation%2Bto%2Briverine%2Bhabitats%2Ballowed%2Bsurvival%2Bof%2Bancient%2Bcetacean%2Blineages%26rft_id%253Dinfo%253Adoi%252F10.1073%252Fpnas.97.21.11343%26rft_id%253Dinfo%253Apmid%252F11027333%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [10]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoicG5hcyI7czo1OiJyZXNpZCI7czoxMToiOTcvMjEvMTEzNDMiO3M6NDoiYXRvbSI7czoyMjoiL3NjaS8yOTQvNTU0My83ODcuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9 [11]: #xref-ref-3-1 "View reference 3 in text" [12]: {openurl}?query=rft.jtitle%253DProceedings%2Bof%2Bthe%2BRoyal%2BSociety%2BB%253A%2BBiological%2BSciences%26rft.stitle%253DProc%2BR%2BSoc%2BB%26rft.issn%253D0080-4649%26rft.aulast%253DHamilton%26rft.auinit1%253DH.%26rft.volume%253D268%26rft.issue%253D1466%26rft.spage%253D549%26rft.epage%253D556%26rft.atitle%253DEvolution%2Bof%2Briver%2Bdolphins%26rft_id%253Dinfo%253Adoi%252F10.1098%252Frspb.2000.1385%26rft_id%253Dinfo%253Apmid%252F11296868%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [13]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Nzoicm95cHJzYiI7czo1OiJyZXNpZCI7czoxMjoiMjY4LzE0NjYvNTQ5IjtzOjQ6ImF0b20iO3M6MjI6Ii9zY2kvMjk0LzU1NDMvNzg3LmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==