Ameiotic recombination in asexual lineages of Daphnia

Abstract

Despite the enormous theoretical attention given to the evolutionary consequences of sexual reproduction, the validity of the key assumptions on which the theory depends rarely has been evaluated. It is often argued that a reduced ability to purge deleterious mutations condemns asexual lineages to an early extinction. However, most well characterized asexual lineages fail to exhibit the high levels of neutral allelic divergence expected in the absence of recombination. With purely descriptive data, it is difficult to evaluate whether this pattern is a consequence of the rapid demise of asexual lineages, an unusual degree of mutational stability, or recombination. Here, we show in mutation-accumulation lines of asexual Daphnia that the rate of loss of nucleotide heterozygosity by ameiotic recombination is substantially greater than the rate of introduction of new variation by mutation. This suggests that the evolutionary potential of asexual diploid species is not only a matter of mutation accumulation and reduced efficiency of selection, and [corrected] it underscores the limited utility of using neutral allelic divergence as an indicator of ancient asexuality.

Fig. 1.

Map locations of LOH in linkage groups I, II, and III for the LIN mutation-accumulation lines. The ancestral diploid state for each linkage group is shown on the left, with heterozygous (informative) loci denoted by black type and uninformative loci in gray type. Numbers to the left denote map distances (centimorgans), and numbers to the right indicate marker names. Loci revealing LOH are denoted with arrows, and numbers of individuals experiencing a particular LOH profile are given below each profile. Arrows pointing right denote loss of the shorter allele, and those pointing left denote loss of the longer allele.