The parasitic caterpillars of Maculinea (Lepidoptera: Lycaenidae) need to be adopted and nursed by ants of the genus Myrmica (Hymenoptera: Formicidae). Each Maculinea species is locally associated with one or a few main and often several secondary host species. To determine whether the parasite-host associations bear marks of cophylogenetic constraints, we reconstructed phylogenies of Maculinea and Myrmica using DNA sequence data. We searched for evidence of cospeciation with a tree-independent (ParaFit) and tree-based (TreeFitter) method. This did not reveal any indication of phylogenetic host tracking in Maculinea. This agrees with earlier insights, which emphasise that as most of the potential host ant populations are never infested by Maculinea, the selective pressure of the butterflies on Myrmica is likely to be slight. Each Maculinea species also specialises on one or a few host plant species before adoption by ants. We suggest that Maculinea species have a substantial potential to accommodate evolutionarily to geographically changing ranges of potential Myrmica hosts, available at the oviposition sites of the butterflies. We use recently published evidence on geographically varying host ant species to discuss a suite of plausible scenarios of adaptive shifts to new Myrmica host species. and Gunther Jansen, Kari Vepsäläinen, Riitta Savolainen.
Parasites with high host specificity maximally depend on their hosts, which should increase the likelihood of coevolution. However, coevolution requires reciprocal selection exerted by the host and the parasite, and thus a considerable level of parasite virulence. In species of the monogenean ectoparasite genus Gyrodactylus consecutive generations are confronted with a single host, which may constrain the evolution of virulence. Transmission, which is often important in the ecology of Gyrodactylus species, may have the opposite effect, but may also lead to the avoidance of coevolutionary arms races. We investigated the potential outcome of coevolution between Gyrodactylus gasterostei Gläser, 1974 and its host, the three-spined stickleback (Gasterosteus aculeatus L.) by determining the strength of genotype by genotype (G×G) interactions on two levels: within and between sympatric and allopatric host populations. To do so, we compared the parasite's infection dynamics on laboratory-reared sympatric (Belgian) and allopatric (German) hosts. We found that a parasite line successfully infected a range of sympatric host genotypes (represented by families), while it failed to establish on allopatric hosts. Phylogeographic studies suggest that neutral genetic divergence between the host populations cannot explain this dramatic difference. Provided that this result can be generalised towards other parasite lines, we conclude that coevolution in this host-parasite system is more likely to lead to local adaptation on the population level than to G×G interactions within populations.
To explore local adaptation in wild populations at a fine spatial scale we characterized the genetic variability of eight closely located populations of Drosophila subobscura and its associations with microhabitat environmental conditions. Three different genetic markers were assessed: chromosomal inversions, a SNP of mitochondrial ND5 gene and nuclear microsatellites. Population genetic analyses of chromosomal variability revealed significant genetic differentiation between these populations. Gene arrangement frequencies on the E chromosome contributed most to these differences. We also investigated role of mito-nuclear epistasis in mitochondrial genome differentiation and revealed weak linkage disequilibrium (LD) exclusively between O3+4 inversion arrangement and mitochondrial DNA haplotype I in two populations. In addition, the trend in the LD between OST chromosomal arrangement and haplotype II was general in the total sample. Microsatellite analysis revealed an absence of stochastic processes, like census reduction, upon population differentiation. Only a small amount of the genetic variation is related to geographic distance, while most (97%) is attributable to other factors and in some degree to microhabitat variables (temperature, humidity). The analysis of these factors revealed they effect inversion arrangement frequencies, especially E1+2+9, EST and OST. Even though this model organism is known for its high mobility and mostly large effective population size, the results presented here reveal that local adaptations can occur even at a small spatial scale. We propose that locally adapted alleles within chromosomal inversions, as well as joint selective pressures acting on mitochondrial and nuclear genomes, are responsible for the observed adaptation to microhabitat conditions.