Virulence Dynamics and Regional Structuring of Puccinia striiformis f. sp. tritici in France Between 1984 and 2009

Understanding of long-term virulence dynamics of pathogen populations in response to host resistance gene deployment is of major importance for disease management and evolutionary biology. We monitored the virulence dynamics of Puccinia striiformis f. sp. tritici, the causal agent of wheat stripe rust, over 25 years in France. Virulence dynamics was explained by estimates of area associated with resistance genes carried by farmers' cultivars. The epidemics assessed through disease severity significantly correlated with the number of P. striiformis f. sp. tritici isolates collected each year, used to describe virulence dynamics. In the south, the dominance of the Mediterranean pathotype 6E16 and the cultivation of a susceptible cultivar were associated with an epidemic from 1997 to 1999. In the north, five epidemics occurred due to successive acquisition of virulence to the resistance genes Yr7, Yr6, Yr9, Yr17, and Yr32, either by acquisition of the virulence in the previous dominant pathotype or by incursion or selection of one or two new pathotypes. Frequency of pathotypes with Vr7 and Vr6 declined with the reduction in the cultivation of corresponding Yr gene cultivars, whereas the virulence Vr9 persisted longer than the cultivation of Yr9 cultivars. Although the first pathotypes carrying Vr9 decreased, this virulence persisted in other pathotypes even in the absence of Yr9 cultivars. At the regional level, Yr9 cultivars in the north caused a shift from high Vr6 frequency to high Vr9 frequency whereas, in the central region, where Yr9 cultivars were rare, Vr6 remained prevalent.

Delayed grammatical acquisition in first language development

Recent research comparing simultaneous and successive acquisition of bilingualism suggests that successive acquisition is affected by age-related changes possibly as early as age (of onset of acquisition) 3–4. Since children are typically exposed to colloquial varieties, the primary linguistic data can lack properties of formal varieties during early years. If, however, the acquisition of a given property is delayed until age 5 or later, the acquired knowledge may rather resemble that of L2 learners. This happens in the acquisition of French interrogatives where certain inversion constructions do not occur in Colloquial French. Native speakers acquire them after the age of 5, and they behave like L2 learners in using or judging them. A grammaticality judgment test reveals a broad range of variability in their ratings of constructions which are ungrammatical in Standard French. Their grammar is afflicted by the kind of persistent optionality familiar from L2 acquisition.

Cues to Decreasing Resistance to Extinction in Successive Acquisitions and Extinctions

Four groups of rats were used in a successive acquisition and extinction situation to determine which conditions, if any, produce a decrease in resistance to extinction across successive acquisitions and extinctions. Two groups experienced long N-R transitions (time from extinction to the subsequent acquisition) with all remaining transitions being short. The short transitions were: R-R (time between acquisition trials), R-N (time from the end of an acquisition until the subsequent extinction), and N-N (time between extinction trials). Two groups experienced long R-N and short N-R, N-N, and R-R transitions. Rats in one long N-R transition and one long R-N transition group had acquisitions and extinctions delineated by distinctive cues (blinking lights during acquisition or extinction trials). The other two groups had no such cues. The disparity in N-N versus N-R transition times combined with additional visual cues during extinction produced decreasing resistance to extinction across successive extinctions.

Successive Acquisitions and Extinctions with Goldfish (Carassius Auratus) in a Swimway Situation

Goldfish were trained in a successive acquisition and extinction shuttle-swimway situation. Groups of 12 fish experienced alternating days of acquisition and extinction, extinction following immediately after each daily acquisition session, and acquisition following immediately after each daily extinction session. None of the groups produced decreasing resistance to extinction across extinctions within eight successive acquisitions and extinctions. A group of fish given 16 successive acquisitions and extinctions with alternating days of acquisition and extinction learned to decrease swimming speeds after eight successive extinctions. However, these fish also decreased acquisition speeds across the last 8 successive acquisitions.