Biomechanics of prey capture in selected newts

The uptake of food is one of the crucial activities in animal life and is often a complex affair requiring coordinated activity of many body parts whose anatomical and dynamic relationships must be tightly integrated to gather food energy in a particular environment. Accordingly, the structural and functional configuration of the food uptake apparatus as well as feeding kinematics are strongly influenced by the biophysical demands of the medium where feeding occurs (i.e. water vs. air). These biophysical demands on the feeding system as a whole are different and to a large extant opposing. Only few tetrapod species, especially within amphibians and reptiles, have found a way to cope with the conflicting demands in both media and can harvest food in water and on land. Most amphibians show in principle a two-phasic life history, metamorphosing from an aquatic larva to a more or less terrestrial stage that normally is not subject to further noteworthy modifications. By contrast, most metamorphosed European newts (family Salamandridae) show a multiphasic lifestyle: they change their habitat from terrestrial to aquatic and again terrestrial every year. These habitat shifts demand major morphological and physiological changes of almost every organ system. This project is designed to detect how these newts cope with the conflicting biophysical demands of water and air to successfully capture prey in both environments. A certain degree in behavioral plasticity is known and seems to be fundamental in nearly all semiaquatic tetrapods that change between terrestrial and aquatic food uptake. Only some newt species, however, are known to undergo morphological modifications when they change seasonally between both environments. We hypothesize that also the feeding apparatus as a whole is modified during such a habitat shift in the European newts selected for this study. These modifications might include, besides the labial lobes, the hyobranchial skeleton, the hyobranchial musculature, and the lingual mucosa. Furthermore, we will test whether the feeding kinematics, as well as the neuromotor control of selected muscles, are tuned to the demands of the respective prey capture mode. These modifications of the feeding system might improve the prey capture performance in both media, possibly leading to an improved uptake of food-energy which would positively affect individual fitness in a given environment. By contrast, the prey-capture system of newts that forego morpho- functional changes when shifting habitat represent a compromise to the conflicting demands of water and air; this probably reduces feeding performance in both media - compared to species that undergo morpho-functional modifications.

The uptake of food is crucial for animal life and adaptations of the feeding biology to specific environments are essential for survival. In vertebrates, food uptake strategies are very diverse but differ mostly between aquatic and terrestrial environments due to the very different physical properties of water and air. Amphibious animals that can efficiently exploit food sources in aquatic and terrestrial environments, however, greatly benefit from it by widening their trophical spectrum. On the other hand, they are faced with the problem of very different physical circumstances between water and air that make an efficient uptake of food most challenging. In this project, I aimed to study morphological and functional changes of the feeding system in salamanders characterized by seasonal aquatic?terrestrial transitions, namely newts. The results show that newts have solved the functional problems associated with environmental transitions by quickly adapting their prey?capture strategy to the new environment and show the importance of behavioral flexibility to cope with environmental changes. In fact, prey capture on land and prey capture in water differ substantially from each other but the transition from the one capture mode to the other is achieved by only subtle changes of single movement patterns. Additionally, it was shown that similar functional problems can be solved by using different biomechanical strategies. Specifically, in different salamanders, different movement patterns are used to induce a fast water flow into the mouth to capture elusive prey. In conclusion, the data obtained from this project contribute to our knowledge of how form, function, and behavior are integrated and modified during environmental transitions, what finally also furthers our understanding of functional aspects of evolutionary processes