Stephen Dalton; NHPA 



Beneath the bark of a rotting tree, below, a female 

 pseudoscorpion carries developing embryos in an 

 external brood sac. Despite its vivid colors, 

 a harlequin beetle, right, blends into the bark of 

 a tree in a Venezuelan rainforest 



Edward S. Ross 



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pete to fertilize her eggs. Female promis- 

 cuity makes paternity hard to establish. 



Fortunately, DNA fingerprinting now 

 offers a direct way to measure a male's 

 success in fertilizing the eggs of his mate. 

 By cloning DNA from the beede-riding 

 pseudoscorpions, we were able to identify 

 two regions of DNA that were particularly 

 useful for tracing relationships between 

 individuals. These probes enabled us to 

 test our oscillating-selection hypothesis. 

 We needed beetles from recently fallen 

 trees, but few fig trees fell in Soberania 

 Park that season. We traveled to French 

 Guiana, where, we were told, we might 

 find sufficient numbers of harlequins to 

 complete the study. In the Kaw Mountains 

 southeast of Cayenne, we found harle- 

 quins in abundance, collected breeding 

 pseudoscorpions from beneath the beetles' 

 wing covers, and reared their offspring. 



Back in Panama, we found that DNA 

 fingerprints of these families demon- 

 strated that in the beetle environment sex- 

 ual selection does favor large male size. 

 Only very large males are able to monop- 

 olize beetles. Yet even within this elite, the 

 DNA fingerprints revealed a strong, posi- 

 tive relafionship between size and fertil- 



42 Natural History 3/94 



ization success. To study the relafionship 

 between male size and reproductive suc- 

 cess in trees, we now need to develop ad- 

 ditional DNA probes that will allow us to 

 determine paternity among large numbers 

 of putative sires. 



Taking a break from the long hours in 

 the molecular lab, we spent a day in the 

 forest, returning to the tree where we had 

 seen the two harlequins fight a year before. 

 A small male beetle, newly emerged from 

 his pupal chamber, was resting on the 

 trunk. All around him, pseudoscorpions 

 were emerging from beneath the bark. 

 One by one, they pinched his abdomen 

 and disappeared on board. That night, we 

 knew, the beetie would abandon the old 

 tree and set out on his maiden flight. Al- 

 ready overgrown with saplings, the re- 

 mains of the fig tree would soon rot away 

 completely, returning its precious nutri- 

 ents to the soil. 



Somewhere in Soberania Park another 

 old fig ti^ee will crash to the forest floor, but 

 for the harlequin, for the beetle-riding 

 pseudoscorpion, for an entire community 

 of arthropod species, the death of this 

 magnificent tree will present an indispens- 

 able ecological opportunity. O 



