Abscisic acid and gibberellic acid-regulated responses of embryos and aleurone layers isolated from dormant and nondormant barley grains

Dormant and nondormant isogenic barley grains were obtained by maturing grains under short day (SD) or long day (LD) growth conditions, respectively. Hormonal responses of isolated embryos and aleurone layers from these grains were studied. Addition of abscisic acid (ABA) reduced germination rate and percentage of embryos, and induced Rab (ABA-responsive) mRNA in aleurone layers from both types of grain. Embryos and aleurone layers from dormant grains responded stronger to ABA than those from nondormant grains. Gibberellic acid (GA₃) increased the germination rate and percentage of embryos from dormant grains and counteracted the ABA-induced inhibition of embryo germination. GA₃ did not affect the amount of Rab mRNA in aleurone layers, suggesting that expression of the Rab gene has no direct correlation with germination. The stronger response of embryos and aleurone layers from dormant grains to ABA may not be explained by higher endogenous ABA levels, but might be due to differences in hormone signal transduction. Aleurone protoplasts from dormant grains had a higher cytosolic pH than those from nondormant grains. To inhibit the ABA-induced Rab mRNA, a much higher concentration of weak acid was required for aleurone layers from dormant grains than for those from nondormant grains. A possible difference in ABA signal transduction between dormant and nondormant grains is discussed.     

Spatial patterns in age- and colony-specific survival in a long-lived seabird across 14 contrasting colonies

Demographic rates such as recruitment and survival probability can vary considerably among populations of the same species due to variation in underlying environmental processes. If environmental processes are spatially correlated, nearby populations are expected to have more similar demographic rates than those further apart. Breeding populations and foraging ranges are spatially segregated in colonial seabirds, making them ideal for studying spatial patterns in demographic rates and their effects on local population dynamics. Here we explored variation in age-dependent survival probabilities across 14 colonies of Herring Gulls Larus argentatus breeding along the Dutch North Sea coast. We used long-term mark–recapture data of marked fledglings to estimate survival, and estimated spatial autocorrelation of survival probabilities. We assessed whether survival until recruitment age or until 10 years old (close to their expected lifespan) explained variation in population trajectories of each colony. Juvenile and adult survival showed a strong, but different, north-to-south gradient in survival probability, with lower juvenile but higher adult survival in northern colonies than southern colonies, whereas the spatial pattern of immature survival was less distinct. Neither recruitment nor the proportion of 10-year-old adults alive predicted whether a colony collapsed, declined, remained stable or increased. The distinct spatial pattern in survival suggests variation in regional food availability, which do not seem to drive local population dynamics. The absence of a link between survival and colony trajectories implies that connectivity between populations plays an important role affecting population dynamics.     

Context dependence of personalities: risk-taking behavior in a social and a nonsocial situation

Individuals of many species differ consistently in their behavioralreaction to mild novel challenges. Suites of these behaviorsare referred to as behavioral syndromes or personalities. Personalitytraits are often phenotypically and genetically correlated.Therefore, animal personalities are generally considered asbroad characteristics, with one underlying genetical and physiologicalmechanism that is expressed across situations and contexts.Because there are carryover effects between situations, animalsare not entirely flexible in their behavior in each situation.This may cause behaviors to seem nonadaptive in isolated situations.To test whether individuals with different personalities couldreact differently to changes in their environment, we studiedcontext dependence of personalities in the great tit (Parusmajor). We tested birds categorized as either fast or slow explorersfor their latency to come back to a feeding table after a mildstartle (risk-taking behavior) in a nonsocial followed by asocial context. We found that the relation between exploratorybehavior and risk-taking behavior depended on the social context.Females in general returned later in the social test, whilemale reaction to the presence of a conspecific was dependenton their behavioral type. Slow males thereby reacted to thebehavior of the companion and fast males did not. These resultsshow that although personalities have a rigid structure therelation between personality traits is context dependent. Theseresults are discussed in the perspective of the adaptive significanceand maintenance of personalities.