Evolutionary design of a flexible, seasonally migratory, avian phenotype: why trade gizzard mass against pectoral muscle mass?

Migratory birds undergo impressive body remodelling over the course of an annual cycle. Prior to long-distance flights, red knots (Calidris canutus islandica) reduce gizzard mass while increasing body mass and pectoral muscle mass. Although body mass and pectoral muscle mass are functionally linked via their joint effects on flight performance, gizzard and pectoral muscle mass are thought to be independently regulated. Current hypotheses for observed negative within-individual covariation between gizzard and pectoral muscle mass in free-living knots are based on a common factor (e.g. migration) simultaneously affecting both traits, and/or protein limitation forcing allocation decisions. We used diet manipulations to generate within-individual variation in gizzard mass and test for independence between gizzard and pectoral muscle mass within individuals outside the period of migration and under conditions of high protein availability. Contrary to our prediction, we observed a negative within-individual covariation between gizzard and pectoral muscle mass. We discuss this result as a potential outcome of an evolved mechanism underlying body remodelling associated with migration. Although our proposed mechanism requires empirical testing, this study echoes earlier calls for greater integration of studies of function and mechanism, and in particular, the need for more explicit consideration of the evolution of mechanisms underlying phenotypic design

Within-individual canalization contributes to age-related increases in trait repeatability: a longitudinal experiment in red knots

Age-related increases in the repeatable expression of labile phenotypic traits are often assumedto arise from an increase in among-individual variance due to differences in developmentalplasticity or by means of state-behavior feedbacks. However, age-related increases inrepeatability could also arise from a decrease in within-individual variance as a result ofstabilizing trait expression, i.e. canalization. Here we describe age-related changes in withinandamong-individual variance components in two correlated traits, gizzard mass andexploration behavior, in a medium-sized shorebird, the red knot (Calidris canutus). Increasedrepeatability of gizzard mass came about due to an increase in among-individual variance,unrelated to differences in developmental plasticity, together with decreases in withinindividualvariance, consistent with canalization. We also found canalization of exploration, butno age-related increase in overall repeatability, which suggests that showing predictableexpression of exploration behavior may be advantageous from a very young age onward.Contrasts between juveniles and adults in the first year after their capture provide support forthe idea that environmental conditions play a key role in generating among-individual variationin both gizzard mass and exploration behavior. Our study shows that stabilization of traitsoccurs under constant conditions: with increased exposure to predictable cues, individuals maybecome more certain in their assessment of the environment allowing traits to becomecanalized

Pancreatic cyst surveillance imposes low psychological burden

Background/Objectives: For the currently recommended pancreatic cyst surveillance to be feasible, participant adherence is a prerequisite. Our objective was to evaluate the psychological burden of pancreatic cyst surveillance from a participant's perspective. Methods: The present participant survey is part of an international cohort study (PACYFIC study, www.pacyfic.net), which prospectively records the outcome of surveillance of asymptomatic pancreatic cysts. Participants are invited to complete questionnaires before and during cyst surveillance. Results: 109 participants, 31 enrolled before and 78 during surveillance (median time since cyst diagnosis 16.5 (IQR 36) months), returned a total of 179 questionnaires. The majority indicated that surveillance reduces concerns of developing pancreatic cancer (82%), gives a sense of certainty (81%) and is a good method to detect cancer (91%). Participants already undergoing surveillance reported more negative aspects than those still to commence, like sleeping worse (30% vs 13%, P = 0.035), postponing plans (32% vs 13%, P = 0.031), and finding the follow-up burdensome (33% vs 13%, P = 0.044). Overall, the vast majority (94%) deemed advantages to outweigh disadvantages. Anxiety and depression scores were low (median Hospital Anxiety and Depression Scale 4 for anxiety (IQR 6), 2 for depression (IQR 5)). Conclusion: The psychological burden of pancreatic cyst surveillance is low. Therefore, participant adherence is expected to be high and annual surveillance seems feasible