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.     

Survival of Barrow's goldeneyes during remigial molt and fall staging

Postbreeding survival of waterfowl is rarely quantified, despite potential for constraints during this stage of the annual cycle that may subsequently affect population dynamics. We estimated survival of radio-marked adult male Barrow's goldeneyes (Bucephala islandica) during remigial molt and fall staging at Cardinal and Leddy Lakes in the Boreal Transition Zone of northwestern Alberta, Canada. Daily survival rate (DSR) was high during remigial molt (DSR = 0.9987, 95% CI: 0.9967–1.0000), corresponding to a 39-day period survival rate (PSR) of 0.95 (95% CI: 0.88–1.00). During fall staging, DSR was markedly lower (DSR = 0.9938, 95% CI: 0.9898–0.9978), corresponding to a PSR of 0.68 (95% CI: 0.53–0.87) over the 62-day period between the end of remigial molt and fall migration. Half of fall staging mortalities observed on Cardinal Lake were directly attributed to hunting. We conclude that remigial molt is a period with high survival in the annual cycle of Barrow's goldeneyes at our study sites. However, in light of low fall staging survival, Barrow's goldeneye harvest management strategies should be carefully evaluated with intent to reduce risk of localized high mortality at significant staging sites in western Canada. © 2013 The Wildlife Society.     

Developmental trait evolution in trilobites

We performed a tree-based analysis of trilobite postembryonic development in a sample of 60 species for which quantitative data on segmentation and growth increments between putative successive instars are available, and that spans much of the temporal, phylogenetic, and habitat range of the group. Three developmental traits were investigated: the developmental mode of trunk segmentation, the average per-molt growth rate, and the conformity to a constant per-molt growth rate (Dyar's rule), for which an original metric was devised. Growth rates are within the normal range with respect to other arthropods and show overall conformity to Dyar's rule. Randomization tests indicate statistically significant phylogenetic signal for growth in early juveniles but not in later stages. Among five evolutionary models fit via maximum likelihood, one in which growth rates vary independently among species, analogous to Brownian motion on a star phylogeny, is the best supported in all ontogenetic stages, although a model with a single, stationary peak to which growth rates are attracted also garners nontrivial support. These results are not consistent with unbounded, Brownian-motion-like evolutionary dynamics, but instead suggest the influence of an adaptive zone. Our results suggest that developmental traits in trilobites were relatively labile during evolutionary history.     

盐度波动对中国对虾稚虾蜕皮、生长和能量收支的影响

采用实验生态学方法研究了在盐度为20的条件下,4个盐度波动幅度（2、4、6、8）对中国对虾稚虾蜕皮和生长的影响.结果表明：中国对虾的蜕皮率为13.3%～15.4%,处理间差异未达到显著水平;盐度波动幅度为4的情况下,对虾的特定生长率最大,用在生长上的能量最高,用于呼吸的能量最低,生长迅速;盐度波动幅度为2的情况下,中国对虾的摄食量最低;盐度波动幅度为2和4的情况下,对虾的食物转化效率最高;不同处理中国对虾用在蜕皮上的能量差异不显著.盐度波动幅度过大不利于中国对虾稚虾的生长,但对蜕皮无影响.     

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.     

Cloning, expression, and localization of a molt-related beta-N-acetylglucosaminidase in the spruce budworm, Choristoneura fumiferana

A beta-N-acetylglucosaminidase cDNA (CfGlcNAcase) was cloned from the spruce budworm, Choristoneura fumiferana. Western blotting analysis of developmental CfGlcNAcase expression revealed high levels of expression of the gene on the last day of the 5th instar larvae and the first day in the 6th instar larvae, followed by a decrease to background levels during the intermolt of the 6th instar. CfGlcNAcase was detected again from the last day of the 6th instar to day 2 of pupal stage. CfGlcNAcase expression was induced by tebufenozide at 24 h post treatment and remained at high levels until 72 h. Immunohistochemical localization analysis of CfGlcNAcase indicated that CfGlcNAcase was present in the molting fluid, epidermis, trachea, and hemolymph in prepupae during the transformation from larva to pupa. CfGlcNAcase cDNA was expressed into a recombinant protein in bacterial and baculovirus systems and the protein expressed in the baculovirus system had a higher chitinolytic activity than in the bacterial system and appeared to be secreted.     

Diapause avoidance induced by low temperature in the yellow-spotted longicorn beetle, Psacothea hilaris

The diapause-averting effect of low temperature on pre-diapause larvae was examined in the yellow-spotted longicorn beetle, Psacothea hilaris. Larvae that had been reared under diapause-inducing conditions (25 °C , L12:D12) were temporarily exposed to 10 °C for various periods, and returned to the initial condition. Diapause was not averted by chilling for 15 days irrespective of the age of the larvae at chilling. After a 30-day chilling treatment, all of the 40- and 60-day-old larvae averted diapause, while diapause was averted in only one-third of the 10- and 20-day-old larvae. None of the pre-diapause larvae chilled for 60 days entered diapause irrespective of the age at chilling. With diapause avoidance, larvae that overwintered in earlier instars can start growing in earliest spring without any arrest; this phenomenon probably subserves the synchronization of larval development in a population.