Ref ID : 112
John J. Gilbert; Further observations on developmental polymorphism and its evolution in the rotifer Brachionus calyciflorus. Freshwater Biology 10:281-294, 1980
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In laboratory experiments, long, Asplanchna-induced posterolateral spines of Brachionus calyciflorus were very effective in preventing their capture and subsequent ingestion by the predator Asplanchna sieboldi but provided no protection against predation by Mesocyclops edax. Young, short-spined B. calyciflorus were always captured after by adult A. sieboldi and were ingested in about 12 seconds. Adult, short-spined forms were captured on ca. 35% of occasions when attacked by this predator and were ingested in about 50 sec. Young and adult long-spined forms were captured by this predator on ca. 60% of occasions when attacked, but they both almost invariably escaped or were rejected 20-35 seconds after capture. Short- and long-spined B. calyciflorus adults were always captured when attacked by adult, female M. edax and were completely ingested in about 20 seconds and 30 seconds, respectively. Life-table experiments conducted with B. calyciflorus at several levels of the food organism, Aerobacter aerogenes, showed that neither the possession of long posterolateral spines nor the production of offspring with long posterolateral spines interfered with survivorship, fecundity, or reproductive potential. In the laboratory, the volumes of the amictic parthenogenetic eggs of B. calyciflorus cultured on Euglena or Aerobacter were significantly greater in individuals from populations maintaining long posterolateral spines than in comparable-sized individuals from populations maintaining short spines. Egg volume was generally independent of adult body length, but it was significantly greater in Brachionus fed on Euglena compared with Aerobacter. Possible reasons why B. calyciflorus does not produce long posterolateral spines in the absence of Asplanchna are discussed. Few organisms other than B. calyciflorus are known to develop novel defensive phenotypes in direct response to the presence of a predator. It is suggested that such developmental responses evolve only when two conditions apply: (1) the defensive structure is primarily effective against a single type of predator, and (2) the prey organism exhibiting the response has a short generation time.