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Correlated evolution of neck length and leg length in birds.

ABSTRACT: Despite a diversity of about 10 000 extant species, the sophisticated avian 'body plan' has not much changed once it was achieved around 160 Ma after the origin of powered flight. All birds are bipedal having wings, a rigid trunk, a short and ossified tail, a three-segmented leg and digitigrade feet. The avian neck, however, has always been regarded as a classic example of high variability ranging from short necks in songbirds to extremely long, serpentine necks in herons. Yet, the wide array of small to very large species makes it difficult to evaluate the actual neck length. Here, we investigate the evolution of the vertebral formulae in the neck of birds and the scaling relationships between skeletal dimensions and body size. Cervical count in birds is strongly related to phylogeny, with only some specialists having an exceptional number of vertebrae in the neck. In contrast with mammals, the length of the cervical vertebral column increases as body size increases and, thus, body size does not constrain neck length in birds. Indeed, neck length scales isometrically with total leg length suggesting a correlated evolution between both modules. The strong integration between the cervical and pelvic module in birds is in contrast with the decoupling of the fore- and hindlimb module and may be the result of the loss of a functionally versatile forelimb due to the evolution of powered flight.

SUBMITTER: Bohmer C

PROVIDER: S-EPMC6549945 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

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Correlated evolution of neck length and leg length in birds.

Böhmer Christine C Plateau Olivia O Cornette Raphäel R Abourachid Anick A

Royal Society open science 20190508 5

Despite a diversity of about 10 000 extant species, the sophisticated avian 'body plan' has not much changed once it was achieved around 160 Ma after the origin of powered flight. All birds are bipedal having wings, a rigid trunk, a short and ossified tail, a three-segmented leg and digitigrade feet. The avian neck, however, has always been regarded as a classic example of high variability ranging from short necks in songbirds to extremely long, serpentine necks in herons. Yet, the wide array of ...[more]

PMID: 31218020

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Project description:Leg-length inequality results in an altered position of the spine and pelvis. Previous studies on the influence of leg asymmetry on postural control have been inconclusive. The purpose of this paper was to investigate the effect of structural leg-length discrepancy (LLD) on the control of posture.We studied 38 individuals (19 patients with structural LLD, 19 healthy subjects). The examination included measurement of the length of the lower limbs and weight distribution as well as a static posturography. All statistical analyses were performed with Statistica software version 10.0. Non-parametrical Kruskal-Wallis with Dunn's post test and Spearman test were used. Differences between the groups and correlation between mean COP sway velocity and the value of LLD as well as the value of LLD and weight distribution were assumed as statistically significant at p < 0.05.There was a significant difference in the asymmetry of weight distribution between the group of patients and the healthy subjects (p = 0.0005). Differences in a posturographic examination between the groups were not statistically significant (p > 0.05). Meaningful differences in mean COP velocity in mediolateral direction between tandem stance with eyes open and closed were detected in both groups (in controls p = 0.000134, in patients both with the shorter leg in a front and rear position, p = 0.029, p = 0.026 respectively). There was a positive moderate correlation between the value of LLD and the value of mean COP velocity in normal standing in mediolateral direction with eyes open (r = 0.47) and closed (r = 0.54) and in anterioposterior plane with eyes closed (r = 0.05).The fact that there were no significant differences in posturography between the groups might indicate compensations to the altered posture and neuromuscular adaptations in patients with structural leg-length inequality. LLD causes an increased asymmetry of weight distribution. This study confirmed a fundamental role of the sight in postural control, especially in unstable conditions. The analysis of mean COP sway velocity may suggest a proportional deterioration of postural control with the increase of the value of leg-length asymmetry.Trial registry: ClinicalTrials.gov NCT03048656 , 8 February 2017 (retrospectively registered).

Project description:BackgroundFibular hemimelia has been reported as the most common congenital longitudinal deficiency of the long bones. Previous studies have focused on the best treatment options for this congenital condition. There is very little to our knowledge in the literature focused on residual persisting malformations and leg length discrepancy after treatment.MethodsSeven patients presenting fibular hemimelia in eight fibulae received treatment between years 1988 and 2001. Pre-treatment average leg length discrepancy was 5.3 cm. All patients presented associated congenital deformities of the ipsilateral leg. Six patients received surgical treatment. Average post-treatment follow up was 9.7 years. Residual malformations and leg length discrepancy were recorded for all patients. It is a retrospective case series study at one institution by two of the presenting authors as senior surgeons.ResultsAverage leg length gained after successful bone lengthening in six patients was 5.06 cm. Although there was a significant functional improvement, a number of residual malformations and leg length inequality was recorded. Residual average leg length discrepancy of 3.1 cm was observed in five patients who completed surgical treatment. Five patients presented a limp. Residual anterior-medial bowing of the tibia was observed in four patients. Calf atrophy was present in all seven patients. Valgus deformity of the ankle was remained in two patients.ConclusionsTreatment of fibular hemimelia, even in cases graded as successful, showed to be accompanied by a number of persisting residual deformities and recurrent leg length inequality. Although the number of patients is limited, the high rate of this phenomenon is indicative of the significance of the report. The family and the patients themselves should have the right expectations and will be more co-operative when well informed about this instance. A report of common post-treatment residual deformities should be valuable in best possible treatment planning of fibular hemimelia.

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Correlated evolution of neck length and leg length in birds.

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Correlated evolution of neck length and leg length in birds.

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