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Understanding fluctuating selection is important for our understanding of patterns of spatial and temporal diversity in nature. Host-parasite theory has classically assumed fluctuations either occur between highly specific genotypes (matching allele: MA) or from specialism to generalism (gene-for-gene: GFG). However, while MA can only generate one mode of fluctuating selection, we show that GFG can in fact produce both rapid 'within-range' fluctuations (among genotypes with identical levels of investment but which specialise on different subsets of the population) and slower cycling 'between ranges' (different levels of investment), emphasising that MA is a subset of GFG. Our findings closely match empirical observations, although sampling rates need to be high to detect these novel dynamics empirically. Within-range cycling is an overlooked process by which fluctuating selection can occur in nature, suggesting that fluctuating selection may be a more common and important process than previously thought in generating and maintaining diversity. [ABSTRACT FROM AUTHOR]

The genetic basis of infection in host-parasite interactions has traditionally been considered within the framework of either gene-for-gene (GFG) or matching-allele models. We present an alternative model, termed inverse-gene-for-gene (IGFG), where pathogen infectiousness is determined by parasite recognition of host signals and/or receptors or where there is active host searching by parasites. We show that coevolutionary dynamics under IGFG are both qualitatively and quantitatively different from those of the GFG model, and we suggest that this new approach may be applicable to a range of important host-parasite systems that are not currently catered for by the existing frameworks. [ABSTRACT FROM AUTHOR]