High genetic variability despite haplodiploidy in primitive sawflies of the genusCephalcia (Hymenoptera, Pamphiliidae)

Abstract

Abstract. Hymenoptera are haplodiploid and usually display very low genetic variation. Most data concern social or parasitic Apocrita, while the little information available for the primitive phytophagous species of the suborder Symphyta is contradictory. The present study is related to seven species of the genus Cephalcia, living in coniferous forests of Northern Eurasia and sharing spruce (Picea sp. pl.) as host plant. Individuals from 22 populations belonging to Cephalcia abietis, C. alashanica, C. arvensis, C. erythrogaster, C. fallenii, C. fulva, C. klugii from Europe and China were surveyed for genetic variation at 28 loci using enzyme electrophoresis. Pairs of sibling species were recognized within C. arvensis and C. fallenii, corresponding to different phenological and morphological forms. In the latter case, reproductive isolation in sympatry occurs despite low genetic distance (D --0.059). Large genetic distances and fixed alternate alleles were observed between Chinese and European populations of C. abietis and C. arvensis. Expected heterozygosity of Cephalcia populations (0.197, SD 0.064) is significantly higher than that of other Symphyta (Tenthredinoidea) (average H~xp 0.059, SD 0.032) (two-tailed Mann-Whitney test, Z = 4.39, p <0.01). These data suggest that haplodiploidy per se does not reduce the genetic variation in most Cephalcia populations. Most of the factors that can lower the potential for genetic diversity in a haplodiploid genetic system are not so effective in Cephaleia populations, which seem to be comparable to diplodiploid insect populations in diversity. In a few isolated populations the large number of fixed loci and the large genetic distances may support the predicted faster rate of fixation, as a consequence of haplodiploidy.

Populational genetic structure and sociogenetic structure of cocoon masses of Digelasinus diversipes (Kirby, 1882) (Hymenoptera: Symphyta: Argidae)

“…However, the effective population size is also influenced by the sex ratio (Crozier, 1976;Hedrick and Parker, 1997) and by the mating system (Berkelhamer, 1983;Owen, 1985), and the levels of heterozygosity have been found to be distinct among species of the same social level (Owen, 1985). Data presented here show high levels of heterozygosity in Symphyta, as found by Sheppard and Heydon (1986), Rosenmeier and Packer (1993), and Boato and Battisti (1996). These data suggest that haplodiploidy per se does not seem to be responsible for the low levels of genetic variability in Hymenoptera.…”

“…For the purpose of comparing these data with those previously reported in the literature, Table 4 presents an average value of the mean heterozygosity for Hymenoptera (Metcalf et al, 1975;Wagner and Briscoe, 1983;Crespi, 1991;Owen et al, 1992;Shoemaker et al, 1992; and unpublished data of our laboratory) and for Symphyta (Graur, 1985;Sheppard and Heydon, 1986;Woods and Guttman, 1987;Rosenmeier and Packer, 1993;Boato and Battisti, 1996).…”

“…This group is traditionally considered an exception in terms of genetic variation, showing values similar to diploidiploid insects (Graur, 1985;Sheppard and Heydon, 1986;Woods and Guttman, 1987;Rosenmeier and Packer, 1993;Boato and Battisti, 1996). This unexpected high genetic variation observed in Symphyta has been attributed to factors such as wide variation in the physical environment, continuous larvae feeding on plant tissues, full exposure to selection at all developmental stages, and overlapping generations (Woods and Guttman, 1987;Boato and Battisti, 1996).…”

Genetic differentiation among geographic populations of Gonatocerus ashmeadi, the predominant egg parasitoid of the glassy-winged sharpshooter, Homalodisca coagulata

“…Berkelhamer (1983) demonstrated that Hymenoptera were associated with low gene diversity values 0.037 (3.7%) vs. 51 diploid insects 0.135 (13.5%). On the other hand, Sheppard and Heydon (1986) demonstrated mean expected gene diversity values of 0.121 to 0.144 (12.1 to 14.4%) in sawflies and Boato and Battisti (1996) demonstrated a mean expected gene diversity value of 0.197 (19.7%) in Cephalcia populations. Though a direct comparison of mean expected gene diversity values can not be made between enzyme electrophoreses studies and PCR methods incorporating SSR, in the present study with G. ashmeadi we observed individual mean expected gene diversity values ranging from 2.9 to 14.3%, but a total genetic diversity value (Ht) of 23.1% for the field populations.…”

“…In general, genetic variation of Hymenoptera as measured by isozyme electrophoresis is approximately one-third of that found in diploid insects (Berkelhamer 1983;Graur 1985;Unruh et al 1986;Powell and Walton 1989;Owen 1993;Unruh and Woolley 1999), though there have been limited reports of high genetic diversity (Sheppard and Heydon 1986;Boato and Battisti 1996). Berkelhamer (1983) demonstrated that Hymenoptera were associated with low gene diversity values 0.037 (3.7%) vs. 51 diploid insects 0.135 (13.5%).…”