Rapid Divergence of Microsatellite Abundance Among Species of Drosophila

Abstract

Among major taxonomic groups, microsatellites exhibit considerable variation in composition and allele length, but they also show considerable conservation within many major groups. This variation may be explained by slow microsatellite evolution so that all species within a group have similar patterns of variation, or by taxon-specific mutational or selective constraints. Unfortunately, comparing microsatellites across species and studies can be problematic because of biases that may exist among different isolation and analysis protocols. We present microsatellite data from five Drosophila species in the Drosophila subgenus: D. arizonae, D. mojavensis, and D. pachea (three cactophilic species), and D. neotestacea and D. recens (two mycophagous species), all isolated at the same time using identical protocols. For each species, we compared the relative abundance of motifs, the distribution of repeat size, and the average number of repeats. Dimers were the most abundant microsatellites for each species. However, we found considerable variation in the relative abundance of motif size classes among species, even between sister taxa. Frequency differences among motifs within size classes for the three cactophilic species, but not the two mycophagous species, are consistent with other studied Drosophila. Frequency distributions of repeat number, as well as mean size, show significant differences among motif size classes but not across species. Sizes of microsatellites in these five species are consistent with D. virilis, another species in the subgenus Drosophila, but they have consistently higher means than in D. melanogaster, in the subgenus Sophophora. These results confirm that many aspects of microsatellite variation evolve quickly but also are subject to taxon-specific constraints. In addition, the nature of microsatellite evolution is dependent on temporal and taxonomic scales, and some variation is conserved across broad taxonomic levels despite relatively high rates of mutation for these loci.

The Genetic Structure ofDrosophila ananassaePopulations From Asia, Australia and Samoa

“…In general, heterozygosity and variance in repeat unit length are high in all populations (Table 1), similar to other Drosophila species for which dinucleotide repeat microsatellites have been assayed in natural populations (Hutter et al 1998;Noor et al 2000;Pascual et al 2000;Ross et al 2003;Orsini and Schlotterer 2004). We used a univariate ANOVA to test for differences among populations in levels of expected heterozygosity and variance in repeat unit.…”

Distribution of Microsatellites in the Genome ofMedicago truncatula: A Resource of Genetic Markers That Integrate Genetic and Physical Maps

“…This increase is correlated with the larger size of the soybean genome and also with the fact that the public genome sequence data for soybean is enriched in RFLP-derived genomic clones relative to the other species we analyzed. Although it is uncertain whether either of these factors is causal to the increased frequency of class I SSRs in soybean data, it is noteworthy that Ross et al (2003) have recently described the rapid divergence of microsatellite abundance among closely related species. Wierdl et al (1997;and more recently Kruglyak et al 1998;Katti et al 2001) proposed that the lower frequency of long vs. short SSRs may result from selection against mutagenic sites in the genome.…”

“…Unequal recombination between SSRs and slip-mispairing during DNA replication (Sia et al 1997) result in polymorphism rates that tend to be much greater than those observed for nonrepetitive DNA sequences. The high rate of mutation combined with low selection coefficients on variant alleles result in extreme allelic diversity at microsatellite loci (Ross et al 2003).…”

Genome size diversity in the family Drosophilidae

“…This species also specializes on particular host cacti endemic to the inhospitable Sonoran Desert, and offers the opportunity to address issues of adaptation to harsh dietary chemicals (Fogleman and Danielson 2002) and to thermal extremes (Stratman and Markow 1998). At this time a large microsatellite library is available (Ross et al 2003) that is being used to construct a genetic map for D. mojavensis. A cDNA library has also been constructed for use in producing a microarray.…”