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watched for any signs of reproductive 

 compatibility. Because so few studies like 

 this have been done, we didn't know ex- 

 actly what to expect. 



Snapping shrimps are good candidates 

 for such a matchmaking experiment. They 

 breed year-round, and when pairs are in- 

 compatible, they tend to be aggressive, so 

 we could look at both behavioral interac- 

 tions and fertility. Under experimental 



conditions, almost none of the transisth- 

 mian pairs produced eggs. Some of our 

 look-alike pairs were quite tolerant of each 

 other, but others were extremely aggres- 

 sive, snapping repeatedly and sometimes 

 pulling off claws. We were able to show 

 that these behavioral incompatibiliries 

 were also reflected on a molecular level. 



The evolutionary theory of the molecu- 

 lar clock holds that certain kinds of mole- 



Before plate tectonics forged the land 

 bridge between North and South 

 America, marine creatures such as the 

 snapping shrimp Alpheus armatus moved 

 freely between what are now the 

 Caribbean Sea and the Pacific Ocean. 

 Today this species is found only 

 in the Caribbean. 



Alex Kerstitch 



67 



