LOCAL MALADAPTATION IN THE ANTHER-SMUT FUNGUSMICROBOTRYUM VIOLACEUMTO ITS HOST PLANTSILENE LATIFOLIA: EVIDENCE FROM A CROSS-INOCULATION EXPERIMENT

Abstract

Abstract.-Conventional wisdom holds that parasites evolve more rapidly than their hosts and are therefore locally adapted, that is, better at exploiting sympatric than allopatric hosts. We studied local adaptation in the insect-transmitted fungal pathogen Mierobotryum violaceum and its host plant Silene latifolia. Infection success was tested in sympatric (local) and allopatric (foreign) combinations of pathogen and host from 14 natural populations from a metapopulation. Seedlings from up to 10 seed families from each population were exposed to sporidial suspensions from each of four fungal strains derived from the same population, from a near-by population « 10 km distance), and from two populations at an intermediate « 30 km) and remote « 170 km) distance, respectively. We obtained significant pathogen X plant interactions in infection success (proportion of diseased plants) at both fungal population and strain level. There was an overall pattern of local maladaptation of this pathogen: average fungal infection success was significantly lower on sympatric hosts (mean proportion of diseased plants = 0.32 ± 0.03 SE) than on allopatric hosts (0.40 ± 0.02). Five of the 14 fungal populations showed no strong reduction in infection success on sympatric hosts, and three even tended to perform better on sympatric hosts. This pattern is consistent with models of time-lagged cycles predicting patterns of local adaptation in host-parasite systems to emerge only on average. Several factors may restrict the evolutionary potential of this pathogen relative to that of its host. First, a predominantly selfing breeding system may limit its ability to generate new virulence types by sexual recombination, whereas the obligately outcrossing host S. latifolia may profit from rearrangement of resistance alleles by random mating. Second, populations often harbor only a few infected individuals, so virulence variation may be further reduced by drift. Third, migration rates among host plant populations are much higher than among pathogen populations, possibly because pollinators prefer healthy over diseased plants. Migration among partly isolated populations may therefore introduce novel host plant resistance variants more often than novel parasite virulence variants. That migration contributes to the coevolutionary dynamics in this system is supported by the geographic pattern of infectivity. Infection success increased over the first lO-km range of host-pathogen population distances, which is likely the natural range of gene exchange.

Testing for local host–parasite adaptation: an experiment with Gyrodactylus ectoparasites and guppy hosts

“…In the following sections we expand on the potential explanations for local Gyrodactylus maladaptation, as well as the relative importance of ecological history and evolutionary lineage as drivers of host-parasite co-evolution. Although parasites are generally expected to have an evolutionary advantage over hosts (Ebert, 1994;Saarinen and Taskinen, 2005) due to their short generation time and potentially high host specificity, parasites have not always shown signatures of local adaptation to their sympatric hosts (Kaltz et al, 1999;Oppliger et al, 1999;Koskela et al, 2000;Lemoine et al, 2012;Roth et al, 2012;Konijnendijk et al, 2013;Sternberg et al, 2013). Our study reduced the methodological limitations of many previous studies, and our data indicate that Gyrodactylus does not generally show strong local adaptation to their sympatric guppy hosts.…”

Local Adaptation, Resistance, and Virulence in a Hemiparasitic Plant-Host Plant Interaction

“…In studies of plants and their pathogens (Parker 1985(Parker , 1991, plants and herbivores (Mopper et al 1995), snails and their trematode parasites (Lively 1989;Manning et al 1995;Lively and Jokela 1996), fish and their trematodes (Ballabeni and Ward 1993), and Daphnia and their microsporidian parasites (Ebert 1994), the parasites were more infectious to sympatric hosts than to allopatric hosts. In contrast, evidence for local adaptation was not found by Kaltz et al (1999), who studied a fungal parasite (Microbotryum violaceum) of Silene latifolia; by Parker (1989), who studied a fungal parasite of mayapple (Podophyllum peltatum); or by Imhoof and Schmid-Hempel (1998), who studied a trypanosome of bumblebee (Bombus terrestris). In most of these cases, the generation time and reproductive output of the parasite species have been higher than those of the respective host species.…”

Population structure of a parasitic plant and its perennial host

“…In the freshwater snail-trematode interaction the parasites are locally adapted to their hosts (Lively, 1989) and also have higher migration rates than their hosts (Dybdahl and Lively, 1996). In the dioecious plant-fungal pathogen interaction the parasites are not locally adapted to their hosts (Kaltz et al, 1999) and show less gene flow than their hosts (Delmotte et al, 1999).…”