Abstracts (first author)
Ration dependent allocation to growth and reproduction in an annual killifish
Animals with indeterminate growth experience a life history trade-off in resource allocation between reproduction and growth throughout their lives. Adaptations to erratic conditions of temporal pools in African savannas make annual killifish Nothobranchius furzeri (Cyprinodontiformes) a species with an extremely rapid growth. We tested hypothesis that their resource allocation is also very plastic. Specifically, we studied their ability to track resource abundance by allocation of resources between the growth and reproduction. We experimentally manipulated the diet ration at six treatment groups. Two groups received the same ration throughout the experiment (low-low, high-high). The ration of other two groups was switched in the middle of the experiment (low-high, high-low). Finally, another two groups (low-†, high-†) were sacrificed during the ration switch to enable control for size and fecundity with respect to age and size differences among groups. Female size and fecundity were significantly different between the two rations already in the first part of the experiment and remained different throughout the experiment. In the treatments with the switched ration, growth cessation (high to low ration) and growth acceleration (low to high) were observed. The low-high treatment fish fully compensated the size difference of fish fed high ration throughout the experiment and no decrease in fecundity as a cost of compensatory growth was detected. Overall, only current ration affected female allocation to reproduction, the initial ration had no effect. This demonstrates that growth rate and fecundity of N. furzeri females rapidly track changes in resource availability. A decreased growth rate when resource availability is low can be readily compensated when conditions are improved, with no long-term effect on their reproductive potential. Such adaptation is advantageous in the erratic environments with highly variable level of resource availability and competition.
An invasive species reverses the roles in a host-parasite relationship
Host-parasite relationships are often characterized by coevolutionary dynamics of parasite adaptations to exploit their host, and counter-adaptations in the host to avoid the costs imposed by parasitism. Such dynamic can be severely affected by introduction of a non-native species. We used a unique reciprocal host-parasite relationship between European bitterling fish, Rhodeus amarus, and European unionid mussels to study the effect of an invasive mussel species on bitterling oviposition behaviour and its consequences. Bitterling lay their eggs into gills of live mussels and, in turn, mussel larvae parasitize fish. The European bitterling colonized most of Europe relatively recently and parasitize all sympatric European mussels, which are evolutionarily naive and have not evolved strong defences (egg rejection) against bitterling parasitism. The parasitic larvae of European mussels are unable to utilize the bitterling, although readily parasites most other European fishes. The Chinese pond mussel, Anodonta woodiana, recently colonized European freshwaters from the region of high abundance and diversity of Asian bitterling species where it evolved strong adaptations against bitterling parasitism. We found that European bitterling behaviourally responded to A. woodiana as to a potential host, but failed to use it properly for oviposition (one population) or used it but all the eggs were lost due to rejections by the mussel (second population). Another experiment revealed that parasitic larvae of A. woodiana can develop on the European bitterling successfully, and hence effectively reversed the host-parasite relationship between the bitterling and mussels. We also discuss potential long-term consequences on population dynamics of the bitterling fish.