Genetic differentiation in sympatric populations of the groundnut seed beetle Caryedon serratus (Coleoptera: Chrysomelidae): new insights from molecular and ecological data

Abstract

Abstract. The extent of genetic differentiation between native and groundnut-feedingforms of the groundnut seed beetle Caryedon serratus Olivier was studied. Sixteen samples(560 individuals of both sexes collected in four localities in Senegal) of C. serratus werereared from pods of four distinct host plants (Arachis hypogaea L., Bauhinia rufescens Lam.,Piliostigma reticulatum (DC) Hochst and Tamarindus indica L.), and five microsatellite lociwere analysed. Phylogenetic and statistical analyses indicated that host plants stronglyinfluence the degree of genetic differentiation between sampled individuals. Within hostplants, genetic differentiation was low. Genetic differentiation between hosts was highlysignificant (average u¼ 0.374) and geographical distances between localities did notinfluence the genetic structuration of C. serratus populations from a given host plant. Theresults of this study show that C. serratus could be under a host race formation process.Key words: Caryedon serratus, microsatellites, genetic differentiation, groundnut, hostplants, SenegalIntroductionHost race differentiation within populations, orgenetic differentiation in host use, is a widespreadphenomenon among insects and other invertebrates(Bush and Smith, 1998; Strauss and Zangler, 2002).Althoughthepossibilitythatitcanresultinsympatricspeciation is still debated, it may well be one of themajormechanismsthatledtopresent-daydiversityinherbivorous insects (Bernays and Chapman, 1994).One of the arguments against sympatric speciationvia host shift and host race formation is that theexistence of host races has not been demonstrated(Futuyma et al., 1993). However, establishing thebiological status of sympatric sister populationsutilizing different hosts is fairly straightforwardand objective. This does not necessarily imply thatthese host races have differentiated while insympatry, but such a demonstration is a necessarystep for investigating sympatric speciation viahost race formation. Recent studies (Bradshaw et al.,