Body size and fecundity are correlated in feather lice (Phthiraptera: Ischnocera): Implications for Harrison’s Rule : Relationship between size and fecundity in lice

1. Harrison’s rule, which predicts that large-bodied species of hosts have large-bodied species of parasites, has been documented in a wide diversity of parasites. 2. Harrison’s rule has been most thoroughly studied in avian feather lice, which escape from host defence (preening) by hiding in the feathers. Lice that are unable to hide are selectively removed by preening. Preening selects for small lice on small hosts, which have small feathers in which to hide. 3. Preening should not, however, select for large lice on large hosts. Instead, the larger size of lice on large hosts is thought to result from a positive relationship between size and fecundity, as shown for many other insects. 4. This study tested for a size–fecundity correlation within Columbicola columbae, the host-specific ‘wing louse’ of rock pigeons (Columba livia). 5. The results confirm a positive relationship between female body length and number of eggs laid. 6. The study thus supports a mechanism consistent with stabilising selection leading to the evolution of the Harrison’s rule pattern among species of Columbicola and their hosts.