Question

The example on begonias (Section 10.6) illustrated that organisms are frequently caught between opposing agents of selection. Each of the following examples also illustrates a tug-of-war between several agents of natural selection. For each example, hypothesize about what selective patterns may maintain the trait described and what selective patterns may oppose it.

a. What selective patterns may maintain a male moose's annual antler growth?
b. What selective patterns may oppose Douglas fir trees growing to over 60 feet tall?
c. What maintains cellulose-digesting microorganisms in a termite's gut?
d. What opposes maple trees losing their leaves in autumn?
e. What maintains a male moth's huge antennae?
f. What opposes a barnacle permanently attaching to a rock?

Answer 1

Natural selection operates through various agents that can either maintain or oppose a particular trait. Examples include the growth of moose antlers, Douglas fir height, microorganisms in termite guts, leaf detachment in maple trees, size of moth antennae, and barnacle attachment.

Step-by-step explanation:

Male moose display annual antler growth, which can be maintained by sexual selection, where larger antlers may attract mates and help in combat with rivals. However, the energy cost to grow antlers and the increased visibility to predators can oppose this trait. Douglas fir trees growing over 60 feet may capture more light and better compete with other plants, but factors like wind damage and resource limitation can oppose such growth. Cellulose-digesting microorganisms are maintained in termite guts due to mutualism, as they enable termites to digest wood, but dietary changes can disrupt this relationship. Maple trees losing leaves in autumn is opposed by the energy loss in growing new leaves, but the prevention of water loss in winter and potential snow damage supports this trait. Male moths with huge antennae benefit from better pheromone detection to find mates but may be hindered by increased energy demands and predation risk. Lastly, barnacles permanently attach to a rock face selection for stability and feeding efficiency but might be opposed by environmental changes like pollution or reduced water flow affecting their food supply.