Heritable genetic variation and potential for adaptive evolution in asexual aphids (Aphidoidea)

Abstract

Aphid life cycles can encompass cyclical parthenogenesis, obligate parthenogenesis, obligate parthenogenesis with male production and an intermediate ‘bet‐hedging’ strategy where an aphid genotype will over‐winter by continuing to reproduce by parthenogenesis and by investment in sexually produced eggs. In this paper, we focus on aphid lineages that reproduce entirely parthenogenetically (asexual aphids), in contrast to those that have any sexual forms in the annual cycle. Using modern molecular techniques, aphid biologists have made many empirical observations showing that asexual lineages are widespread both geographically and temporally. Indeed, we are collectively beginning to gather data on the evolution and persistence of these lineages through time. Here we review aphid karyology and parthenogenesis, both essential for interpretation of the molecular and ecological evolution of aphid asexual lineages. We describe the growing list of studies that have identified aphid genotypes that are both temporally and geographically widespread. We then collate examples of molecular and chromosomal evolution in asexual aphids and review the literature pertaining to phenotypic evolution and ecological diversification of asexual aphid lineages. In addition, we briefly discuss the potential of bacterial endosymbionts and epigenetic effects to influence the evolution of asexual aphid lineages. Lastly we provide a list of aphid taxa believed to be obligately asexual. This will be a useful resource for those seeking parthenogenetic animals as study systems. In conclusion, we present guidelines for the use of the term clone in aphid biology and stress the need for well‐designed and well‐executed studies examining the potential of asexual aphid lineages for adaptive evolution. © 2003 The Linnean Society of London. Biological Journal of the Linnean Society, 2003, 79, 115–135.

The conversion of variance and the evolutionary potential of restricted recombination

“…Nevertheless, a variety of studies have found evidence for evolution and adaptation occurring in a surprisingly effective manner in asexual populations (eg Parker, 1979a;Williamson, 1981;Glazier, 1992;Christensen et al, 1992;Toline and Lynch, 1994;Andrade and Roitberg, 1995;Sunnucks et al, 1998;Weeks and Hoffman, 1998;Wilson et al, 1999Wilson et al, , 2003. These works cite such evidence as diverse and closely adapted clonal arrays (eg Parker, 1979a-c;Weeks and Hoffman, 1998;Wilson et al, 1999), natural clonal assemblages shown to have high (comparable to sexual) heritabilities for life history, morphological, and fitness-related traits (Stratton, 1991(Stratton, , 1992, and parthenogenetic genotypes that seem to outcompete sympatric sexual forms (eg Browne, 1992;Christensen et al, 1992;Weeks and Hoffman, 1998).…”

Post-Pleistocene radiation of the pea aphid complex revealed by rapidly evolving endosymbionts

“…Congruence with the diversification beginning some 16,000 years ago would imply a mutation rate on the order of 10 Ϫ5 per locus per year, roughly 10 Ϫ6 per locus per generation of pea aphids, corresponding to laboratory measures of microsatellite mutation rates in other insects (33). Mutation rates of microsatellites in aphids have not yet been estimated (34).…”

Genetic variability and adaptive evolution in parthenogenetic root-knot nematodes

“…Besides nematodes, a wide range of other asexual taxa have been shown to undergo rapid genetic changes, including, among others, crustaceans (Schö n et al, 2003) and insects (Wilson et al, 2003).…”