Comparative demographic analysis in contrasting environments of Magnolia dealbata: an endangered species from Mexico

The study of population regulation and demography in natural habitats is critical for the conservation of rare and endangered species. We address the impact of cattle exclusion on the demographics of Magnolia dealbata (Magnoliaceae), an endangered species according to IUCN and Federal Mexican laws. Sixteen permanent plots were established, eight of which were enclosed to livestock, in the mountain cloud forest in Coyopolan, Mexico, which has the largest population of M. deadlbata. Censuses of the plots were undertaken annually during three annual cycles to record seed number, recruitment, mortality, and growth (defined as length and diameter at breast height). The effects of two treatments (with and without livestock exclusion) on the dynamics of M. dealbata were investigated using transition matrix models and life table response experiment (LTRE) analysis. Contrary to expectations, there was no significant effect of cattle exclusion on population growth rates (λ). Furthermore, the λ, estimated from the mean transition matrix for both treatments was greater than one. The transitions with the highest elasticity values were similar between the two treatments, while reproductive stage contributed more to differences in population growth rate and were less variable than the non-reproductive stage. LTRE analysis showed that treatment differences had little effect on λ. Livestock exclusion appears to lead more to differences in the arrangement of the values of the transition matrix than to the rate of population growth for M. dealbata.     

Does benefit justify research with children?

The inclusion of children in research gives rise to a difficult ethical question: What justifies children's research participation and exposure to research risks when they cannot provide informed consent? This question arises out of the tension between the moral requirement to obtain a subject's informed consent for research participation, on the one hand, and the limited capacity of most children to provide informed consent, on the other. Most agree that children's participation in clinical research can be justified. But the ethical justification for exposing children to research risks in the absence of consent remains unclear. One prevalent group of arguments aims to justify children's risk exposure by appealing to the concept of benefit. I call these ‘benefit arguments’. Prominent versions of this argument defend the idea that broadening our understanding of the notion of benefit to include non‐medical benefits (such as the benefit of a moral education) helps to justify children's research participation. I argue that existing benefit arguments are not persuasive and raise problems with the strategy of appealing to broader notions of benefit to justify children's exposure to research risk.     

Which data should be tracked in forward-dynamic optimisation to best predict muscle forces in a pathological co-contraction case?

The choice of the cost-function for predicting muscle forces during a movement remains a challenge, especially in patients with neuromuscular disorders. Forward dynamics-based optimisations mainly track joint kinematics or torques, combined with a least-excitation criterion. Tracking marker trajectories and/or electromyography (EMG) has rarely been proposed. Our objective was to determine the best tracking objective-function to accurately predict the upper-limb muscle forces. A musculoskeletal model was created and EMG was simulated to obtain a reference movement – a shoulder abduction. A Gaussian noise (mean = 0; standard deviation = 15%) was added to the simulated EMG. Another noise – corresponding to the actual soft tissue artefacts (STA) of experimental shoulder abduction movements – was added to the trajectories of the markers placed on the model. Muscle forces were estimated from these noisy data, using forward dynamics assisted by six non-linear least-squared objective-functions. These functions involved the tracking of marker trajectories, joint angles or torques, with and without EMG-tracking. All six approaches used the same musculoskeletal model and were solved using a direct multiple shooting algorithm. Finally, the predicted joint angles, muscle forces and activations were compared to the reference values, using root-mean-square errors (RMSe) and biases. The force RMSe of the approach tracking both marker trajectories and EMG (18.45 ± 12.60 N) was almost five times lower than the one of the approach tracking only joint angles (82.37 ± 66.26 N) or torques (85.10 ± 116.40 N). Therefore, using EMG as a complementary tracking-data in forward dynamics seems to be promising for the estimation of muscle forces.     

Probable evolution of the coelacanth's reproductive style: lecithotrophy and orally feeding embryos in cichlid fishes and in Latimeria chalumnae

Synopsis The living coelacanth is a livebearer. Yolk seems to be the main source of nutrients and of oxygen to the embryo (fetus). Long before birth, young may also possibly feed orally on histotrophe secretion and egg debris. This type of reproduction evolved, as in most other fishes, from oviparity. The Carboniferous coelacanth Rhabdoderma exiguum had eggs of much lesser yolk volume and may represent an earlier form of oviparity with hiding, guarding or brooding type of parental care. The Jurassic coelacanth Holophagus (Undina) and the Cretaceous Axelrodichthys appear to have already evolved the internal-bearing style. Much of this evolutionary sequence is similar to that in cichlids. Ancestral cichlids are substrate tenders and nesters, with small eggs, little yolk and a feeding larva with indirect development. Mouthbrooding cichlids evolved a few, large eggs with denser yolk, direct development and, ultimately, orally feeding embryos while yolk is still in ample supply. Mixed feeding from yolk and orally ingested food in cichlids and in coelacanths is shown to be an enhanced mode of food delivery to the embryos over that from each source separately, in order to produce directly a better developed or larger young at the time of release, i.e. independence. Increase in egg size is regarded as an environmentally induced, altered pattern of yolk synthesis and an initial component of the epigenetic mechanism leading towards greater specialization. Carotenoids are incorporated within the yolk to assist the oxidative metabolism of the developing embryo.