Table 1.
Summary of key terms used within this study and a description of their implementation within the mathematical models. Full details on the mathematical implementation of each mechanism are given in the electronic supplementary material.
| mechanism | biological definition | model representation |
|---|---|---|
| vertical transmission (VT) | the passage of the microbe from the host mother (sometimes the father) to its offspring | a percentage of offspring from carrier mothers inherit the microbe |
| environmental acquisition | asocial acquisition of independently proliferating microbes available in the environment, habitat and/or host diet | a probability that non-carrying individuals acquire the microbe following birth but prior to sexual maturity. Independent of population-level carrier density; this is a steady-state characteristic within the models |
| horizontal transmission (HT) | the non-vertical passage of microbes among hosts, may include larval conspecific feeding or sexual transmission | a probability of carriers transmitting to non-carriers, calculated as a multiple of the total carrier frequency; therefore, HT is dependent on population-level carrier density |
| mixed modes of transmission (MMT) | any combination of transmission modes including VT, HT and environmental acquisition by which microbes can be acquired by hosts | any stable carrier frequency which occurs because of more than one (exclusive) mechanism of microbial transmission |
| fitness | measured as individual reproductive success, and equal to the contribution to the gene pool of the next generation made by individuals of the specified genotype/phenotype | the probability of an individual surviving to sexual maturity relative to the non-carrier level (0.5 means half the number of individuals survive, whereas 2 indicates twice as many individuals survive) |
| dispersal | when individuals move from one site to another to mature or breed | a percentage (2%) of each population is exchanged at random each generation; this occurs following uptake/acquisition and fitness but prior to mating |
| host mate choice | the process that occurs whenever the effects of traits expressed in one sex lead to non-random matings with the opposite sex; either (i) assortative mating, i.e. preference for similar characteristics (microbial carrier/ non-carrier), or (ii) preference for a consistent phenotype, i.e. for microbial carriers | n-choice framework—the choosing sex samples n potential mates; if a preferred type is found, then mating occurs or else mating is with the n-th sampled individual |