In bottom sediments of lakes and streams, organic matter is broken down by heterotrophic microorganisms and ammonia is released. Under aerobic conditions, specialized bacteria convert ammonia to nitrate (nitrification). This nitrate, together with nitrate from other sources, diffuses into the deeper sediments, where it may undergo anaerobic conversion to nitrogen gas (denitrification). These sediments typically contain oligochaete worms that live with their heads buried and their tails waving back and forth in the overlying water. Plastic columns were packed with freshly collected stream sediments and then  covered  with  layers  of  nitrate enriched  water.  A similar  set  of  columns  was packed with sediment that had been sterilized and then covered with either nitrate-enriched water or distilled water. Oligochaete  worms  were  collected  and  acclimated  to  20°(C)Following  acclimation,  worms  were  rinsed  in  distilled water and then added to three sediment columns. The columns were incubated in the dark at 20°C and monitored every three days for changes in the concentration of nitrate in the overlying water. Nitrate concentrations in each of the experimental treatments were plotted against time, as shown in the graph below

It can be concluded from the figure that

#Question id: 4985

#Unit 11. Evolution and Behavior

The loss of ventral spines by modern freshwater sticklebacks is due to natural selection operating on the phenotypic affects of Pitx1 gene

#Question id: 4984

#Unit 11. Evolution and Behavior

A hypothetical mutation in a squirrel population produces organisms with eight legs rather than four. Further, these mutant squirrels survive, successfully invade new habitats, and eventually give rise to a new species. The initial event, giving rise to extra legs, would be a good example of

#Question id: 4983

#Unit 11. Evolution and Behavior

As rat pups mature, the growth of their snouts and tails outpaces growth of the rest of their bodies, producing the appearance of sexually mature males. It is found that sexually mature female rats prefer to mate with mutant, sexually mature males that possess snouts and tails with juvenile proportions. Which of the following terms is (are) appropriately applied to this situation?

#Question id: 4982

#Unit 11. Evolution and Behavior

Bagworm moth caterpillars feed on evergreens and carry a silken case or bag around with them in which they eventually pupate. Adult female bagworm moths are larval in appearance; they lack the wings and other structures of the adult male and instead retain the appearance of a caterpillar even though they are sexually mature and can lay eggs within the bag. This is a good example of

#Question id: 4981

#Unit 11. Evolution and Behavior

An organism has a relatively large number of Hox genes in its genome. Which of the following is not true of this organism?

#Question id: 4980

#Unit 11. Evolution and Behavior

If an increase in dicynodont species diversity (i.e., number of species) occurred soon after the Permian extinction, and if it occurred for the same general reason usually given for the increase in mammalian diversity following the Cretaceous extinction, then it should be attributed to