Aspects of the population structure of the sand martin flea,Ceratophyllus styx, in Britain

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Abstract
Overwintering populations of 2 sspp. of the sand martin flea, C. s. styx (Rothschild) and C. s. jordani (Smit), (Insecta:Siphonaptera) were screended for morphological variation of the genitalia and for electrophoretically detectable variation at a polymorphic aminopeptidase locus. C. s. jordani populations were characterized by a low length/breath ratio of the male clasper, a more pronounced indentation of the posterior edge of sternum VII from females, and by a low frequency of the Ap-1s allele, C. s. jordani was characteristic of northern populations, C. s. styx of southern. Significant internest heterogeneity in allele frequencies within sand martin colonies was noted and the 3 nest populations showed significant deviations from Hardy-Weinberg expectations. These observations ar consistent with overwintering nest populations being founded from small numbers of fleas. Further work is required to examine the possibility of hybridization between the subspecies where they occur sympatrically.