Diet quality and food limitation affect the dynamics of body composition and digestive organs in a migratory songbird (Zonotrichia albicollis)

Migrating songbirds interrupt their feeding to fly between stopover sites that may vary appreciably in diet quality. We studied the effects of fasting and food restriction on body composition and digestive organs in a migratory songbird and how these effects interacted with diet quality to influence the rate of recovery of nutrient reserves. Food limitation caused white-throated sparrows to reduce both lean and fat reserves, with about 20% of the decline in lean mass represented by a decline in stomach, small intestine, and liver. During refeeding on diets similar in nutrient composition to either grain or fruit, food-limited grain-fed birds ate 40% more than did control birds, and they regained body mass, with on average 60% of the increase in body mass composed of lean mass including digestive organs. In contrast, food-limited fruit-fed birds did not eat more than did control birds and did not regain body mass, suggesting that a digestive constraint limited their food intake. The interacting effects of food limitation and diet quality on the dynamics of body composition and digestive organs in sparrows suggest that the adequacy of the diet at stopover sites can directly influence the rate of recovery of body reserves in migrating songbirds and hence the pace of their migration.     

Bill morphology reflects adaptation to a fibrous diet in the kākāpō (Strigops: Psittaciformes)

We describe the upper portion of the bill sheath (rhinotheca) of the kākāpō (Strigops habroptilus) from three adult female specimens. The external buccal surface of the rhinotheca is deeply concave with a prominent palatal stop and hardened chevrons creating a ‘milling apparatus’ that the kākāpō uses to grind food. The palatal stop presents a working face of 40–50?mm². The internal surface of the rhinotheca mirrors the overlying premaxilla and provides a distinct thickened abutment consistent with resistance against the increased workload of the mandibles (gnathotheca) due to the kākāpō’s fibrous diet and chewing style. Along the midline, the rhinotheca at the abutment is up to 5.6?mm thick, compared with as thin as 2.1?mm elsewhere on the midline. The closely related Nestor parrots have less developed palatal stops, chevrons and abutments on their rhinothecas consistent with their lower preference for fibrous plant material. The form of the rhinotheca agrees with the kākāpō’s feeding ecology as a generalist herbivore that grinds locally available fibrous material to assist digestion.     

Molecular evolution modeled as a fractal Poisson process in agreement with mammalian sequence comparisons

The fractal doubly stochastic Poisson process (FDSPP) model of molecular evolution, like other doubly stochastic Poisson models, agrees with the high estimates for the index of dispersion found from sequence comparisons. Unlike certain previous models, the FDSPP also predicts a positive geometric correlation between the index of dispersion and the mean number of substitutions. Such a relationship is statistically proven herein using comparisons between 49 mammalian genes. There is no characteristic rate associated with molecular evolution according to this model, but there is a scaling relationship in rates according to a fractal dimension of evolution. The FDSPP is a suitable replacement for the homogeneous Poisson process in tests of the lineage dependence of rates and in estimating confidence intervals for divergence times. As opposed to other fractal models, this model can be interpreted in terms of Darwinian selection and drift.      

Differentiation pathway of Peyer's patch precursors of IgA plasma cells in the secretory immune system

Others have shown that Peyer's patch (PP) precursor cells can seed the small intestine with IgA plasma cells, whose appearance after cell transfer requires an interval of a week. The location of the precursor cells during this period is the subject of the present investigation in which the fate of radiolabeled murine PP cells was studied after intravenous transfer into primary and secondary recipients. In short-term single-transfer experiments, few radiolabeled PP blasts were found in the small intestine and only a small proportion of these contained IgA. Radiolabeled PP blasts were approximately equally distributed between mesenteric lymph nodes (MN) and peripheral lymph nodes (PN). However, a higher proportion of those which went to MN than of those which went to PN was subsequently capable of settling in the small intestine of secondary recipients and a higher proportion of those arriving in the intestine was found to contain IgA. Thus, MN were distinctly superior to PN as an intermediate site for the maturation of PP-derived IgA plasma cell precursors capable of seeding the small intestine, even when these had been injected intravenously. Treatment of PP cells with antiserum to IgA prior to their injection into primary recipients interfered with the homing of IgA precursor cells to the small intestine of secondary recipients, indicating that the precursors are already producing IgA while still in the PP. IgA-containing, radiolabeled PP cells were found in the subcapsular sinus of MN within 30 min of intravenous injection, suggesting that these cells are capable of extravasating from blood and reaching the lymph within the intestine long before they are ready to remain in the intestine as plasma cells. These results imply that the superiority of MN over PN as an intermediate site for the proliferation and differentiation of PP IgA precursor cells into IgA plasma cells capable of seeding the small intestine is due to the location of the MN in the pathway of circulation of mucosal B cells.     

Genetic Control of RNA Polymerase I-Stimulated Recombination in Yeast

We examined the genetic control of the activity of HOT1, a cis-acting recombination-stimulatory sequence of Saccharomyces cerevisiae. Mutations in RAD1 and RAD52 decrease the ability of HOT1 to stimulate intrachromosomal recombination while mutations in RAD4 and RAD50 do not affect HOT1 activity. In rad1 delta strains, the stimulation of excisive recombination by HOT1 is decreased while the rate of gene replacement is not affected. In rad52-8 strains the ability of HOT1 to stimulate both excisive recombination and gene replacement is decreased. All of the recombinants in the rad52-8 strains that would be categorized as gene replacements based on their phenotype are diploids apparently derived by endomitosis and excisive recombination. Studies on rad1 delta rad52-8 strains show that these mutations interact synergistically in the presence or absence of HOT1, resulting in low levels of recombination. The rate of gene replacement but not excisive recombination is stimulated by HOT1 in rad1 delta rad52-8 strains. Taken together, the results show that HOT1 stimulates exchange using multiple recombination pathways. Some of the activity of HOT1 is RAD1-dependent, some is RAD52-dependent, and some requires either RAD1 or RAD52 as suggested by the synergistic interaction found in double mutant strains. There is also a component of HOT1 activity that is independent of both RAD1 and RAD52.