SAMPLINGS 



Survival of the Rarest 



Tropical forests may be more resilient than 

 their reputations would have you believe. 

 The forests appear to bolster the tree spe- 

 cies most vulnerable to extinction: the 

 rare ones. 



Christopher Wills, an evolutionary biolo- 

 gist at the University of California, San 

 Diego, led a study in which international 

 teams took tree censuses on plots in seven 

 tropical forests around the globe. The team 



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Sing It to Me 



Juvenile (left) and adult male zebra finches 



Young male zebra finches learn to sing by 

 listening to adult tutors — often their fa- 

 thers — and by rehearsing endlessly. To get 

 a tune just right, a young bird must com- 

 pare the sounds it makes with its memo- 

 ries of the songs its tutor sang. The mem- 

 ories — or "sound templates" for bird- 

 song — must be stored somewhere in the 

 bird's brain, but where? Until now, investi- 

 gators have primarily searched parts of 

 the brain responsible for singing and song 

 learning. Now, Mimi L. Phan and David S. 



repeated the censuses 

 after five years for some 

 plots, after ten years for 

 others. Locally common 

 species, it turned out, 

 make up most of the 

 young trees in a given 

 age class, but locally rare 

 species have lower death rates. The net re- 

 sult is that rare trees become more com- 

 mon within their age class as time passes. 



Why might rare species survive preferen- 

 tially? Some avoid competing for the same 

 resources that more common species re- 

 quire. Others escape pathogens and preda- 

 tors that target their ubiquitous neighbors. 



Vicario, both neuroscientists at Rutgers 

 University in New Brunswick, New Jersey, 

 and a colleague have found evidence of a 

 template elsewhere: in a part of the brain 

 generally known as the NCM, which plays 

 a role in hearing. 



Phan and Vicario played a tutor's song to 

 young zebra finches for several weeks, then 

 switched it off for a month while the birds 

 matured. The neuroscientists then played a 

 selection of tunes that included the tutor's 

 song, the birds' own songs, and new songs, 

 while recording the electrical responses of 

 neurons in the birds' NCMs. By applying a 

 standard test of familiarity, the investigators 

 determined that the neurons in the NCM 

 recognized the tutor's song. What's more, 

 the birds that were most familiar with the 

 tutor's song reproduced it most accurately. 

 (PNAS 103:1088-93, 2006) — G.F. 



Tropical forest, Barro Colorado Island, Panama 



Fish Story in Reverse 



Smallest fish, a male anglerfish (Photocorynus spiniceps, shown above left at 

 actual size), is fused to the back of a much larger female. 



In January, ichthyologists announced they'd discovered the world's smallest vertebrate. 

 One female Paedocypris progenetica, a carp relative from Indonesian swamps, measured 

 just 7.9 millimeters. That's not so small, countered Theodore Pietsch, an ichthyologist at 

 the University of Washington in Seattle. In September he'd described Photocorynus spini- 

 ceps, a deep-sea-dwelling anglerfish from the Philippines, with males as small as 6.2 mil- 

 limeters. Males bite into females and fuse for life. They supply sperm; females supply eggs, 

 food, locomotion, and everything else. {Proceedings of the Royal Society B, forthcoming; 

 Ichthyological Research 52:207-36, 2005) —R.K. 



Evidence that nature favors diversity sug- 

 gests that tropical forests may be able to re- 

 cover fully and quickly from at least moder- 

 ate destruction. That's good news, but Wills 

 isn't celebrating. "If the forests are slashed 

 and burned," he warns, "all bets are off." 

 (Science 31 1 :527-31, 2006) 



— Samantha Harvey 



I m permafrost 



People living in the Far North have often 

 built their homes on solidly frozen earth. 

 But their heirs may have to contend with 

 wildly listing floors. Permafrost — soil 

 frozen for two or more years, with a thin 

 top layer that may seasonally thaw — 

 makes up about a quarter of the land 

 area in the Northern Hemisphere, roughly 

 4.1 million square miles. As the Earth 

 warms, however, permafrost is proving to 

 be anything but permanent. 



That's what David M. Lawrence of the 

 National Center for Atmospheric Research, 

 and Andrew G. Slater of the University of 

 Colorado, both climate scientists based in 

 Boulder, have found. They ran a powerful 

 computer model to predict the distribution 

 of the top eleven feet of permafrost under 

 various scenarios of greenhouse-gas emis- 

 sions. The model predicted that if emis- 

 sions remain high, as much as 90 percent 

 of the North's surface permafrost will thaw 

 by 2100. One consequence is that north- 

 ern soils may slowly dry out, contributing 

 somewhat — as may increased precipita- 

 tion — to a 28 percent rise in freshwater 

 runoff into the Atlantic Ocean. 



Perhaps even worse, thawed soils 

 could release methane and carbon diox- 

 ide into the air, intensifying the green- 

 house effect. Whether enough trees will 

 grow on the newly defrosted terrain to 

 mop up the excess carbon dioxide re- 

 mains to be seen. (Geophysical Research 

 Letters 32:L24401, 2005) —S.R. 



NATURAL HISTORY April 2006 



