Morfološke osobitosti pasivnog fleksornog mehanizma ptica s različitim rasporedom prstiju

Birds possess a mechanism which allows passive flexion of the digits of the hind limbs which consists of two components: “automatic digital flexor mechanism” (ADFM) and “digital tendon-locking mechanism” (DTLM). The aim of this paper was to establish the existence and specificities of those components in examples of birds with anisodactyl (domestic chickens) and zygodactyl (parrots) digit layout using standard anatomical dissection and histological methods. Spatial distribution of the parrots’ muscles with a central role in DTLM (M. flexor digitorum longus and m. flexor hallucis longus) was the same as the chickens’. The plantar position of the fourth digit, which makes the difference between the anisodactyl and the zygodactyl digit layouts, did not cause changes in the position and function of this flexor muscles. The domestic chickens’ tendon sheath ridges, as well as the tendon tubercles of the flexor muscles were less developed while the parrots’ tubercles and ridges were clearly defined and the differences in their morphology were visible. There were no chondrogenic elements or they were barely noticeable in the parrots’ tendons. A potential cause of these distinctions could be the difference in the load which the tendons endure due to the different biomechanical composition. The parrots primarily inhabit trees where they move agilely around by grasping the branches. The Galliformes have a much larger body mass which is a consequence of their life on the ground, so the flexor muscle tendons suffer a greater load than the parrots and the cartilage tissue embedded in the tendon itself could act to distribute the weight of the body borne by the foot and the tendonPtice posjeduju mehanizam koji im omogućuje pasivnu fleksiju prstiju noge, a sastoji se od dvije komponente: automatskog digitalnog fleksornog mehanizma (ADFM) i digitalnog mehanizma zatvaranja tetiva (DTLM). Cilj ovoga rada bio je ustanoviti postojanje i specifičnost ovih komponenti u predstavnika ptica s anizodaktilnim (domaća kokoš) i zigodaktilnim (papige) rasporedom prstiju, primjenjujući standardnu anatomsku sekciju i histološke metode. Prostorna organizacija mišića koji imaju središnju ulogu u DTLM-u (m. flexor digitorum longus i m. flexor hallucis longus) jednaka je u papiga i domaće kokoši. Plantarni položaj četvrtog prsta, što čini razliku između anizodaktilnog i zigodaktilnog rasporeda prstiju, nije uvjetovao promjene položaja i funkcije tih fleksornih mišića. Nabori tetivnih ovojnica i kvržice na tetivama fleksornih mišića bili su slabije razvijeni u domaće kokoši, dok su u papiga nabori i kvržice bili jasno definirani, a njihove morfološke razlike vidljive. Hondrogeni elementi nedostaju ili su jedva zamjetni u tetivama papiga. Mogući uzrok ovoj pojavi mogla bi biti razlika u opterećenju koje trpe tetive zbog različitih biomehaničkih prilika. Papige su primarno vezane za krošnje drveća gdje se vrlo spretno kreću prihvatom za grane. Kod galiformnih je ptica masa tijela znatno veća, što je posljedica prilagodbe životu na tlu, pa tetive fleksornih mišića trpe veće opterećenje nego kod papiga, dok hrskavično tkivo uklopljeno u samu tetivu može djelovati na raspodjelu mase tijela koje podnosi stopalo, pa samim tim i tetiva

Riverine wood-pasture responds to grazing decline

There is insufficient available information on structural changes within wood-pastures including their relationship to abiotic influences such as livestock grazing, flooding and available soil nutrients. In this paper, we address the links between important environmental variables and different stages of the wood-pasture cycle, with the aim of understanding fluctuations in this relationship and processes that follow changes in wood-pasture condition. We used satellite and aerial image interpretation to identify structural vegetation shifts over 44 years under significantly declining livestock numbers. We used ground truthing of 24 plots to assess the current field scenario and employed canonical correspondence analysis (CCA) to evaluate the relationship between plant communities and environmental influences. Three dominant structural vegetation types grassland, transitional vegetation with thorny shrubs and woody encroachment were surveyed and the following set of variables was chosen: grazing intensity, inundation frequency, elevation, soil total nitrogen, soil available phosphorus, soil potassium, soil magnesium, soil calcium, soil pH and soil carbon to nitrogen ratio. Interpretation of satellite images revealed dominance of wood-pasture in the past, which alternated structurally between more open and more closed physiognomies. CCA with ground truthing data and forward selection revealed grazing intensity as the predominant ecological driver modifying vegetation structure, as well as transitioning vegetation patterns between open herbaceous and closed woody cover. Each structural vegetation type demonstrated a collective distribution pattern and a close relationship to certain abiotic drivers, indicating strong interactions between soil parameters, grazing pressure and vegetation composition