The summer subsystem

Once a matching allo-infection of a summer host occurs, the successful spring alternator begins asexual reproduction, and it produces asexual individuals. Some of these individuals auto-infect the same host and they are called 'summer colonisers'. Others migrate in order to allo-infect another host, and they are called 'summer migrants'.

This asexual reproduction has two major effects. First, it permits very rapid reproduction, making the parasite an r-strategist that is able to produce a population explosion. It can then exploit an ephemeral food supply very effectively. Second, the asexual reproduction ensures that all the progeny are members of a single clone. This enables the summer colonisers to auto-infect their summer host without any problems of matching. Obviously, this auto-infection can be controlled only by the horizontal subsystem.

There is a major difference in the behaviour of colonisers and migrants. The colonisers auto-infect, and all auto-infection is matching infection. The migrants, however, must allo-infect, and they have the problem of finding a matching host. The probability of these allo-infections being matching infections will depend on the vertical subsystem. If a vertical subsystem is present, the majority of the summer migrants will fail to find a matching host, and they will be wasted. This wastage will be in the same proportion as the wastage of the spring alternators. Consequently, the vertical subsystem continues to dampen the population explosion of this r-strategist parasite throughout repeating cycles of allo-infection during the entire summer epidemic. The vertical subsystem will thus reduce the frequency of parasitism (see 8.6), in the summer host. It will also ensure that most matching allo-infections occur late in the season, and that, consequently, the injury from parasitism (see 8.6), is low in the majority of matched host individuals.

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