|
ИСТИНА |
Войти в систему Регистрация |
Интеллектуальная Система Тематического Исследования НАукометрических данных |
||
Adaptationist approach to construction of evolutionary scenarios. Mammalian flapping flight as an exampleтезисы доклада Тезисы
- Автор: Panyutina A.A.
- Сборник: Organisms in nature – evolutionary perspective and ecological significance. Fourth International Workshop, Linde in Brandenburg
- Тезисы
- Год издания: 2019
- Место издания: Humboldt-Universität
- Первая страница: 19
- Последняя страница: 20
- Аннотация: Interactions of an organism with the environment are performed at a plurality of different levels: mechanical, ecological, physiological etc. Analyzing the interaction framework at each of these levels and comparing it in different organisms, we can reconstruct an outline of the evolution of adaptations. To understand the functioning and the formation of morphological forms of macroscopic organisms, mechanical interactions are most demonstrative. Considering an organism as a mechanical system, we can understand how one or another of its structures are responsible for the interaction with the environment and for optimal fitness. Based on knowledge of these interactions, we can build lines of successive adaptations on the grounds of the mechanical properties of the structures of organisms under comparison. Subsequently, relying on the environmental paleodata and knowledge of phylogenetic relations, we can reconstruct those evolutionary scenarios of morphological transformations that meet the ecological conditions of the formation of specific groups, as well as their initial morphological basis. In this case strict adherence to mechanical consistency and functionality allows us to develop scenarios with uninterrupted adaptation to the environment and justification for improving the fitness of each subsequent evolutionary stage.As a result of this approach, it becomes possible to address the key problems of evolutionary biology, for holistic consideration of which paleontological data is sorely insufficient.In animals, the locomotor apparatus, which is a purely mechanical system, is best suited for solving such problems of all organ systems. Moreover, it is the evolution of the locomotor apparatus that is the most challenging to interpret in terms of preserving the fitness of transitional forms during major evolutionary transformations associated with the change of the locomotor environment, such as the land or air conquest.We have reconstructed an evolutionary scenario for the flight formation in the bat lineage of mammals. The forelimbs were analyzed in detail as the major basis for the mechanical model; however, the hind limbs and the features of the axial skeleton were addressed as well for completeness. For the model, data on the structure of muscles, bones and ligaments of tree shrews, colugos and bats, as well as auxiliary data on a number of other groups of mammals were used.As a result, a series of successive morphological transformations has been built, which should have taken place during the formation of a flapping flight. The series includes the following locomotive forms: terrestrial-arboreal, arboreal-gliding, and active-flying. All transformations at each evolutionary transition were considered both at the preadaptation stage and at the stage of full-fledged functioning.As a key structural transformation that paved the way for a flapping flight in mammals, we have identified the transition of the extremities from the parasagittal plane to the frontal one (deparasagittalization). Mechanical conditions for this transition arise when dwelling the biotope of a mature forest with large tree-to-tree distances. At the initial stage of the transition from the terrestrial-arboreal niche to arboreal-gliding, the main skeletal segments of the limbs operated predominantly in the parasagittal plane. As the parachuting and then gliding from tree to tree developed, the elements of the shoulder girdle began to acquire more and more horizontal position bringing the limb to the frontal plane. This repositioning contributed to the wingspan. The ability to spread the limbs apart plays also an important role in running up large-diameter tree trunks, as it helps keeping the body closer to the trunk in order to reduce the torque which tends to overturn the body.As a result, locomotor specialization is formed, equally beneficial for two ways of traveling at once: gliding flight and quadrupedal ascent on thick trees with the forelimbs set widely apart. The most vivid example of such a specialization in recent mammals is Dermoptera. As a result of such locomotor specialization, the acquisition of the ability of limbs to move from parasagittal to frontal position and back again, that is to move up and down in the transverse plane, turns out to be a preadaptation to the next step in the chain of specializations – the development of flapping motions. With the development of air-borne locomotion, the role of the clavicle as a strut for the forelimb increases. The clavicle acquires distinct articular surfaces with the scapula and the sternum, and becomes an analogue of the avian coracoid. Some specialization of this kind is already expressed in the clavicles of various groups of gliding mammals, among which it reaches its maximum in the colugo. In bats the clavicle is the most complete analogue to the coracoid of birds.Rearrangements of the hind limb mobility are much less radical, since the hip joint of placental mammals initially allows for much greater freedom of movement than the shoulder joint. However, at the stage of improving the gliding apparatus some special accommodations were formed in it. Inter alia, the dorsal bony lip of the acetabulum, which normally restricts the rise of the femur in the transverse plane, is reduced to varying extent in all mammalian gliders.Reorientation of the main mobility and the load of the limbs is accompanied by changes in the topography of the skeletal muscles. Depending on the main directions of the external forces acting in locomotion, the mass of muscles acting in the corresponding direction increases and the mass of other muscles decreases. In the shoulder girdle, in quadrupedal locomotion, retractors and, to a lesser extent, protractors play the main role, whereas when gliding locomotion becomes more and more developed, the adductors begin to dominate gradually taking away part of the mass from retractors. During the development of flapping flight, quadrupedal locomotion becomes secondary, and the adductors gain dominance in the muscular system; in fact retractors are forced out by adductors, and protractors are forced out by abductors.If analyzed thoroughly from the adaptationist point of view, almost the entire set of specific musculoskeletal features of bats can be interpreted through an intermediate specialization to arboreal-gliding locomotion. Most of the features acquired at this stage were key preadaptations for the further development of flapping flight.With this approach, the structure of organisms gives the key not only to evaluation of the environmental constraints, but also to understanding the ecological and evolutionary perspectives of a particular structural type.
- Добавил в систему: Панютина Александра Андреевна