Question

How can you explain the bimodal distribution, with most soapberry bug individuals either having a long or a short proboscis several decades after the introduction of the non- native soapberry species. Focus on what selection pressures may have acted on this population and what the fitness of different individuals of varying phenotypes are in this population.

Answer 1

In general, soapberry bugs have variable beak lengths. The native host of soapberry bugs used to be round capsuled balloon vine prior to 1925 in Florida. The bugs fed on the fruits with long proboscis, as the fruits are round and food is available at a greater depth.

With the introduction of flat podded golden rain trees in Central Florida, the soapberry bugs started to feed the flat fruits for easy access of food. In due course, it was found that the population had members with reduced proboscis size.

In Southern Florida, the soapberry bugs continued to feed on the native species (baloon vines) and thus had longer proboscis.

This is a classical example of natural selection due to environment, i.e the length of the soapberry bugs fits their environment. The soapberry bugs in Central Florida with shorter beaks had easy access to food and better able to feed on small fruits, thus producing more progenies/ offsprings. Thus, they got selected in Central Florida due to better fitness.

Long probosis had the following disadvantages:

(1) low efficiency

(2) took longer time to develop

(3) long probosis posed problems to escape from predators