Factors Mediating Host-Associated Differentiation in Insect Communities
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Host-Associated Differentiation (HAD) is a form of ecologically mediated speciation by which two or more populations of the same parasite species become genetically distinct due to each population associating with a different host species (Abrahamson et al., 2003; Stireman et al., 2005). Different host species may exert significantly different selection pressures on their parasites. If these selection pressures are strong or linked to any trait important to insect reproduction then they can generate reproductive isolating barriers between parasite populations associated with different host-plant species. Once reproductively isolated, parasite populations associated with different host species may accumulate genetic differences due to genetic drift and/or disruptive selection for adaptive alleles. Since most insects are plant or animal parasites (Price, 1980), HAD may explain the vast species diversity we observe in insects (Funk et al., 2002). It is still unclear how common HAD is and which traits of a given parasite/host systems are most likely to explain it. Essentially, any ecological factor that decreases either the probability that mating will occur between members of different host-associated parasite populations or that results in outbreeding depression between these parasite populations may constitute a reproductive isolating barrier that can result in HAD (Feder & Filchak, 1999).........