Reproductie van amfibieën in systemen onder tijdsdruk: life history van legsel tot landschap

In this dissertation, we investigated life history variation in different stages of the anuran life cycle in a spatio-environmental context. Overall the thesis included a multi scale and multi life stage assessment of life history variation in frogs in response to gradients of environmental harshness and time stress in particular. For this, a range of different information sources is exploited in a Belgian and an Australian model species. Overall, reconstructed variation in life histories illustrate a wide variety of different potential strategies to respond to environmental gradients. In the Australian bleating froglet, Crinia pseudinsignifera, range-wide variation in several life-history traits such as potential number of reproductive years, growth trajectories and energy allocation towards reproduction showed strong associations with environmental harshness imposed by geographic differences in local climate and by differences in the exact climatic conditions these individuals experienced during their lifetime. The eco-geographic pattern was similar to results obtained from cold defined climatic harshness gradients, with increased body size and age in harsher climatic areas. On top of this range wide variation, energy allocation towards individual offspring shows variation within individual pool clusters. Variation in egg sizes within individual clutches was consistently large and suggested a shift in resource allocation. Larger eggs in more time stressed environments are most likely adaptive in the context of coping with time stress since larger eggs hatched earlier under common garden conditions. Research on Rana temporaria tadpoles collected from habitats along a pond permanence gradient in Flanders also revealed larval life history differentiation associated with habitat permanence. Reported differences were most likely genetic, with adaptive differentiation in development time persisting in the absence of acute time stress and the presence of genetic polymorphism in the habitats with the most variable hydroperiod. Tadpoles also responded plastically to a reduction in water level. The magnitude of this response was smaller in populations that already expressed fast development, hinting at the physiological limits of developmental acceleration. Additionally, more plastic populations could not produce development times as short as populations from pools with short hydroperiods that were least plastic. This highlights the potential advantage of specialization over plasticity when faced with predictable early yearly drought. Pool drying, associated with accelerated development, was also accompanied by increased oxidative damage upon metamorphosis. Additionally, similar levels of environmental stress did not automatically transfer into identical physiological stress levels, even among R. temporaria populations within the small region of Flanders. Results imply that tadpoles from ephemeral systems could have consistently lower stress potentially allowing them to fully exploit the short time frame for feeding and larval development. The physiological underpinnings, however, paint a relatively complex picture with populations from different habitat types characterized by different responses via different enzymes or pathways. Overall, we reported constitutive and induced variation in life history trajectories associated with environmental harshness and time constraints at different scales and in different life stages, which can be considered hopeful in the light of potential effects of global environmental change on these species. Further integration of physiological, ecological and evolutionary research to fully reconstruct the complex interactions between life history traits and the underlying physiological mechanisms that lie at the heart of life history variation in nature are needed. Additionally, relatively unexplored sources of information such as physiological data or historical museum datasets should be given more consideration.status: publishe