Comparison of populations of the Rhipicephalus simus group: R. simus, R. praetextatus, and R. muhsamae (Acari: Ixodidae).

Abstract

Integrated biological, ecological, and morphological studies were carried out on Rhipicephalus simus Koch group ticks from Africa and Arabia. Crossbreeding studies were undertaken using three geographically isolated populations: two strains initially designated “ R. simus ” from northeastern Africa and from southern Africa, plus Rhipicephalus muhsamae Morel & Vassiliades from western Africa. All stages of each reared strain were examined using scanning electron microscopy. Over 3,500 specimens in 338 field collections from Africa and Arabia were examined for ecological analysis. Material identified hitherto as“ R. simus ” from northeastern, eastern, central, and southern Africa consists of two distinct taxa. R. simus sensu stricto occurs in central and southern Africa, roughly south of latitude 8°S. Ticks from northeastern and eastern Africa (Egypt, Sudan, Ethiopia, Somalia, Kenya, Uganda, and most of Tanzania) are now designated as Rhipicephalus praetextatus Gerstaecker, previously regarded as a junior synonym of R. simus . The third species, R. muhsamae , occurs in western Africa from Senegal eastwards into Sudan, Uganda, and Ethiopia. At its eastern limits, its distribution overlaps with that of R. praetextatus . A few offspring were produced from R. muhsamae × R. simus and R. praetextatus × R. simus matings. In R. simus male × R. praetextatus female crosses, either a few males only or no progeny were produced. Behavioral, genetic, and cytoplasmic differences apparently contribute to reproductive isolation in these species. Morphological differences among these three species are most marked in immature stages and in female genitalia. Differential diagnostic criteria for each stage of these taxa are given.