A new westward migration route in an Asian passerine bird

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Correlates of molt in golden lion tamarins (Leontopithecus rosalia)

In this paper we describe the timing and correlates of molt for a native population of golden lion tamarins (Leontopithecus rosalia). We conducted 820 examinations of 267 adult tamarins over a 7.75 year period to determine the annual molting cycle in this population. Dorsal molt was an annual event for most individuals in the study population; however, 10% of sampled individuals apparently molted twice in a 12 month period. Duration of molt was estimated at 5–6 weeks. The proportion of samples in which tamarins were in molt was significantly greater during the wet season than the dry season and positively correlated with mean monthly precipitation and minimum temperature but not tamarin births, suggesting an environmental component to timing of molt. We found no sex differences in the occurrence of molt during wet or dry seasons. However, the relative frequency of samples in molt was significantly less for gravid females than for nongravid females. In four polygynous groups, socially dominant females gave birth before subordinate females, and younger reproductive females completed molt before older reproductive females. © 1995 Wiley-Liss, Inc.     

Interactive effects of temperature and concentration of the flavonol rutin on growth, molt and food utilization of Manduca sexta caterpillars

A factorial experiment tested the effects of varying concentrations of the flavonol rutin and daytime temperatures of 20 and 30°C on growth, molting and food utilization efficiencies of third instar tobacco hornworms (Manduca sexta (L.)). Cool temperature prolonged both the growth (=feeding) and non-feeding periods and consequently the relative consumption rates (RCR) and relative growth rates (RGR). Temperature had no impact on the amount of food consumed and the utilization indices of efficiency of conversion of ingested food and efficiency of conversion of digested food to larval biomass. But rutin was more concentrated in the frass of the larvae at the warm temperature. With increasing levels of rutin in the diet, the efficiency of conversion of ingested food tended to decline. Rutin reduced RCR and RGR. At the cool temperature, rutin increased the time spent in the first portion of the non-feeding period disproportionately. Analysis of growth rate intervals within the growth period indicated that at the cool temperature rutin had no discernible impact over the first half of the growth period, during which developmental competence to molt is likely achieved. Overall, these results indicate an overlap in the growth and molting phases and suggest that rutin interferes with physiological processes at the time of molt initiation, with these effects magnified at a cool temperature.     

Regulatory mechanisms for the development of the migratory phenotype: Roles for photoperiod and the gonad

This article is part of a Special Issue “Energy Balance”.     

Sterols and steroids in a freshwater crustacean (Proasellus meridianus): hormonal response to nutritional input

For crustaceans that eat shredded plant material in freshwater habitats, the amount and the composition of food greatly vary over time because of the seasonal succession of plant fragments and algal biomass. The acquisition of elements necessary for growth, immune defense, and reproduction depends largely on this variation in food type and availability. In particular, sterols that are required as cellular membrane components and as precursors of ecdysteroids (molting hormones) must be acquired through food because crustaceans do not synthesize the steroid nucleus de novo. The present study examined the possible link between nutrition, sterols, and ecdysteroids in an isopod, Proasellus meridianus. In a first step, quantitative and qualitative analyses of sterols of P. meridianus were performed by gas‐chromatography/mass spectrometry. The results suggested that members of P. meridianus are able to convert dietary plant sterols into cholesterol required for growth and reproduction. In a second step, by manipulating food availability and using an enzyme immuno‐assay, we showed that ecdysteroid content in males and females (ovigerous or not) of P. meridianus decreased significantly after a starvation period. A nutritional input following this starvation period triggered an increase in the ecdysteroid contents of these animals. The comparable ecdysteroid responses to food pulses in males and females suggested that a nutritional control on steroid hormones regulated growth or gametogenesis rather than egg maturation. Thus, it appears that P. meridianus possesses an efficient stop‐and‐go endocrine system that may have been selectively favored in response to seasonal pulses of food.     

Sexual selection,feather wear,and time constraints on the pre‐basic molt explain the acquisition of the pre‐alternate molt in European passerines

Avian feathers need to be replaced periodically to fulfill their functions, with natural, social, and sexual selection presumably driving the evolution of molting strategies. In temperate birds, a common pattern is to molt feathers immediately after the breeding season, the pre‐basic molt. However, some species undergo another molt in winter‐spring, the pre‐alternate molt. Using a sample of 188 European passerine species, Bayesian phylogenetic mixed models, and correlated evolution analyses, we tested whether the occurrence of the pre‐alternate molt was positively associated with proxies for sexual selection (sexual selection hypothesis) and nonsexual social selection (social selection hypothesis), and with factors related to feather wear (feather wear hypothesis) and time constraints on the pre‐basic molt (time constraints hypothesis). We found that the pre‐alternate molt was more frequent in migratory and less gregarious species inhabiting open/xeric habitats and feeding on the wing, and marginally more frequent in species with strong sexual selection and those showing a winter territorial behavior. Moreover, an increase in migratory behavior and sexual selection intensity preceded the acquisition of the pre‐alternate molt. These results provide support for the feather wear hypothesis, partial support for the sexual selection and time constraints hypotheses, and no support for the social selection hypothesis.     

Great tits (Parus major) reduce body mass in response to wing area reduction: a field experiment

Flight performance is crucial in determining whether a smallbird will survive an attack by a predator. Given the importanceof body mass in determining flight performance, it has beensuggested that birds should strategically regulate body massas a response to predation risk. However, all experiments upto now have been carried out with captive birds, comparing experimental to control birds. Here we present data from thefirst experiment in the field using a within-individuals experimentaldesign. The wing area of wild great tits, Parus major, wasreduced by reversibly taping primaries five to seven. Thisallowed for the same individual to alternatively act as controlor experimental bird. Great tits reduced body mass (but not pectoral muscle width) during episodes of wing area reduction,lending support to the view that the reduction in body massexperienced by birds during molt is a strategy rather thanthe result of energetic stress. Theoretical models establishingthe different trade-offs that determine optimal body mass should therefore take into account this important life-history episode.     

Onset and duration of gray seal (Halichoerus grypus) molt in the Wadden Sea,and the role of environmental conditions

Surveys of gray seals (Halichoerus grypus) during the molt period, when they are abundant on land, can be used to monitor changes in population size, but accurate interpretation of results requires an understanding of the molt process and how it may vary between years. This study investigates variability in onset (start date) and duration of visible molt by gray seals in the Wadden Sea, and the influence of environmental conditions on the onset. Molt was monitored in nine captive seals and observed molt phases were applied to wild seals over seven annual molt periods between 2004 and 2010, monitored using aerial photography. The onset of visible molt varied significantly between years, for example it differed 28 d between 2008 and 2009. Model selection by AIC retained one environmental variable that correlated with molt onset; however, its effect was inconsistent within the molt season and did not explain some of the apparent observed annual variation. Hence, the main causes of interannual variability in the onset of molt remain unclear and warrant further study. Researchers should account for annual variability in the onset of molt when interpreting survey results based on molt counts.