Individual variation and the biomechanics of maneuvering flight in hummingbirds.

An animal's maneuverability will determine the outcome of many of its most important interactions. A common approach to studying maneuverability is to force the animal to perform a specific maneuver or to try to elicit maximal performance. Recently, the availability of wider-field tracking technology has allowed for high-throughput measurements of voluntary behavior, an approach that produces large volumes of data. Here, we show how these data allow for measures of inter-individual variation that are necessary to evaluate how performance depends on other traits, both within and among species. We use simulated data to illustrate best practices when sampling a large number of voluntary maneuvers. Our results show how the sample average can be the best measure of inter-individual variation, whereas the sample maximum is neither repeatable nor a useful metric of the true variation among individuals. Our studies with flying hummingbirds reveal that their maneuvers fall into three major categories: simple translations, simple rotations and complex turns. Simple maneuvers are largely governed by distinct morphological and/or physiological traits. Complex turns involve both translations and rotations, and are more subject to inter-individual differences that are not explained by morphology. This three-part framework suggests that different wingbeat kinematics can be used to maximize specific aspects of maneuverability. Thus, a broad explanatory framework has emerged for interpreting hummingbird maneuverability. This framework is general enough to be applied to other types of locomotion, and informative enough to explain mechanisms of maneuverability that could be applied to both animals and bio-inspired robots.

Weathering the storm: parental effort and experimental manipulation of stress hormones predict brood survival.

BACKGROUND: Unpredictable and inclement weather is increasing in strength and frequency, challenging organisms to respond adaptively. One way in which animals respond to environmental challenges is through the secretion of glucocorticoid stress hormones. These hormones mobilize energy stores and suppress non-essential physiological and behavioral processes until the challenge passes. To investigate the effects of glucocorticoids on reproductive decisions, we experimentally increased corticosterone levels (the primary glucocorticoid in birds) in free-living female tree swallows, Tachycineta bicolor, during the chick-rearing stage. Due to an unprecedented cold and wet breeding season, 90 % of the nests in our study population failed, which created a unique opportunity to test how challenging environmental conditions interact with the physiological mechanisms underlying life-history trade-offs. RESULTS: We found that exogenous corticosterone influenced the regulation of parental decisions in a context-dependent manner. Control and corticosterone-treated females had similar brood failure rates under unfavorable conditions (cold and rainy weather), but corticosterone treatment hastened brood mortality under more favorable conditions. Higher female nest provisioning rates prior to implantation were associated with increased probability of brood survival for treatment and control groups. However, higher pre-treatment male provisioning rates were associated with increased survival probability in the control group, but not the corticosterone-treated group. CONCLUSIONS: These findings reveal complex interactions between weather, female physiological state, and partner parental investment. Our results also demonstrate a causal relationship between corticosterone concentrations and individual reproductive behaviors, and point to a mechanism for why naturally disturbed populations, which experience multiple stressors, could be more susceptible and unable to respond adaptively to changing environmental conditions.

Estrogens protect male mice from obesity complications and influence glucocorticoid metabolism.

BACKGROUND: Although the prevalence of obesity is higher among women than men, they are somewhat protected from the associated cardiometabolic consequences. The increase in cardiovascular disease risk seen after the menopause suggests a role for estrogens. There is also growing evidence for the importance of estrogen on body fat and metabolism in males. We hypothesized that that estrogen administration would ameliorate the adverse effects of obesity on metabolic parameters in males. METHODS: Male and female C57Bl/6 mice were fed control or obesogenic (DIO) diets from 5 weeks of age until adulthood. Glucose tolerance testing was performed at 13 weeks of age. Mice were killed at 15 weeks of age and liver and adipose tissue were collected for analysis of gene expression. A second cohort of male mice underwent the same experimental design with the addition of estradiol pellet implantation or sham surgery at 6 weeks. RESULTS: DIO males had greater mesenteric adipose deposition and more severe increases in plasma glucose, insulin and lipids than females. Treatment of males with estradiol from 6 weeks of age prevented DIO-induced increases in adipose tissue mass and alterations in glucose-insulin homeostasis. We also identified sex differences in the transcript levels and activity of hepatic and adipose glucocorticoid metabolizing enzymes. Estrogen treatment feminized the pattern of DIO-induced changes in glucocorticoid metabolism, rendering males similar to females. CONCLUSIONS: Thus, DIO induces sex-specific changes in glucose-insulin homeostasis, which are ameliorated in males treated with estrogen, highlighting the importance of sex steroids in metabolism. Given that altered peripheral glucocorticoid metabolism has been observed in rodent and human obesity, our results also suggest that sexually dimorphic expression and activity of glucocorticoid metabolizing enzymes may have a role in the differential metabolic responses to obesity in males and females.

Toward a more natural breast: the interpolated thoracoepigastric pedicle in breast reconstruction.

A method of reconstructing the breast mound after mastectomy using a superiorly based thoracoepigastric pedicle is presented. The advantages of the method are its relative simplicity and its definition of the inframammary fold. It often obviates the need for inflatable expanders. The prime disadvantage is the scar left on the abdominal donor site.

The frequency of local recurrence and microsatellites as a guide to reexcision margins for cutaneous malignant melanoma.

A retrospective study was undertaken of local, regional, and distant recurrences in 346 patients with primary melanomas of tumor thickness less than 1.0 mm that were excised with margins of normal skin varying between 0.1 cm and 5.0 cm or more. Prospective histopathologic examination of 284 melanomas for the presence of microsatellites was also performed and their effect upon the frequency of local recurrence was studied. Margins of excision did not influence the frequency of local, regional, or distant metastases. Four recurrences of in situ superficial spreading melanoma occurred, however, when very narrow margins of excision (0.5 cm or less) were employed. Microsatellites were uncommon with tumors less than 3.0 mm in thickness (2.8% of all tumors of less than 3.0 mm in thickness, taken together), but relatively frequent in association with thicker tumors (37%). Melanomas with microsatellites were associated with a greater frequency of local clinical metastasis than those without (14% vs. 3%). Removal of more than 1.0 cm of normal skin around a melanoma of less than 1.0 mm in thickness does not further reduce rates of recurrence of any type. The use of margins of 0.5 cm or less for melanomas with a radial growth phase does appear to result in an increased frequency of local recurrence of the primary melanoma with an epidermal in situ component. These recurrences can be prevented by the removal of 1.0 cm of normal skin around such a melanoma. Microsatellites constitute a risk factor for local recurrence, but are a relatively uncommon phenomenon at tumor thickness less than 3.0 mm.

Midline cervical cleft. A case report.

The midline cervical cleft is a rare congenital anomaly. This article describes clinical, operative and histological aspects of this rare lesion.