Eine neue Form von Züchtungsschalen für Gewebekulturen,besonders geeignet für Bestrahlungsversuche

Ohne Zusammenfassung     

Apomixis und umweltbedingte Variation beiPoa pratensis L

Ohne ZusammenfassungMit 13 Textabbildungen.     

Evolutionary rescue in randomly mating,selfing, and clonal populations

Severe environmental change can drive a population extinct unless the population adapts in time to the new conditions (“evolutionary rescue”). How does biparental sexual reproduction influence the chances of population persistence compared to clonal reproduction or selfing? In this article, we set up a one‐locus two‐allele model for adaptation in diploid species, where rescue is contingent on the establishment of the mutant homozygote. Reproduction can occur by random mating, selfing, or clonally. Random mating generates and destroys the rescue mutant; selfing is efficient at generating it but at the same time depletes the heterozygote, which can lead to a low mutant frequency in the standing genetic variation. Due to these (and other) antagonistic effects, we find a nontrivial dependence of population survival on the rate of sex/selfing, which is strongly influenced by the dominance coefficient of the mutation before and after the environmental change. Importantly, since mating with the wild‐type breaks the mutant homozygote up, a slow decay of the wild‐type population size can impede rescue in randomly mating populations.     

Longevity of orders is related to the longevity of their constituent genera rather than genus richness

Longevity of a taxonomic group is an important issue in understanding the dynamics of evolution. In this respect a key observation is that genera, families or orders can each be assigned a characteristic average lifetime (Van Valen in Evol Theory 1:1–30, 1973). Using the fossil marine animal genera database (Sepkoski in Bull Am Paleontol 363, pp 563, 2002) we here examine the relationship between longevity of a higher taxonomic group (orders) and the longevity of its lower taxonomic groups (genera). We find insignificant correlation between the size of an order and its longevity, whereas we observe large correlation between the lifetime of an order and the lifetime of its constituent genera. These observations suggest that longevity of taxonomic groups is heritable intrinsically or on the grounds of environmental preferences.