Reproductive success and genetic diversity in newts

In recent years, an array of new, DNA-based genetic markers have led to a wealth of information on wild populations, but their use together with experimental ecological approaches has been so far mostly neglected. Amphibians are particularly amenable to studies at the level of populations, and currently receive significant public attention by playing a key role in wetland conservation and by a controversially discussed global population decline. The present proposal uses the urodele amphibian Triturus vulgaris (the common newt) as a model species to investigate the influence of habitat quality on the maintenance of within-species genetic diversity in isolated populations. What makes this project novel is the combination of semi-natural breeding ponds ("mesocosms"), for which environmental conditions can be manipulated, with the use of microsatellite DNA methods to identify the parental origin of each offspring produced. The aims of the proposed project have the following four dimensions: (I) to determine the genetic parentage of each individual in experimental newt populations using microsatellite markers, (II) to document the influence of ecological conditions on within-population patterns of reproductive success, (III) to investigate under differential ecological regimes whether individuals with higher genetic diversity are more successful in reproduction than more inbred individuals, (IV) to test the hypothesis that the genetic erosion of isolated amphibian populations is accelerated by suboptimal environmental conditions during breeding. The main characteristics of the present proposal are a collaboration with a world-wide leading working group, modern methodological approaches, experiments whose outcome are of primary interest for both the scientific and a more general audience, and a balanced combination of desk, laboratory, and field work.

The project covered a wide range of topics in amphibian ecology and behaviour. Do females mate with more than one male and if so, how do they choose their preferred male? We used genetic fingerprinting to reveal paternity in both species. Smooth newts choose their mates by the height of their dorsal crest. After insemination by two males, however, the paternity success was mostly determined by the degree of relatedness between the parents. Less related males were more successful. Interactions between egg and sperm cells (compatibility) taking place within the females` reproductive tract seem to play a major role in determining paternity in the common newt. Additional studies in the common toad showed that 30% of egg strings laid in a natural population had two fathers. Multiple paternity increases with male density. Under high density, females can not choose a mate but are subject to male harassment. How populations of pond breeding amphibians are structured and whether migration between subpopulations occurs is difficult to investigate by traditional direct methods. By using indirect, genetic methods, however, it could be shown in an assemblage of breeding ponds of crested and marbled newts that individuals of one pond generally form genetically distinct units. Migration between ponds is influenced by population size with small populations being more likely to receive immigrants form large populations than vice versa. For the management of existing populations, this implies that as many ponds as possible should be preserved, rather than only a fraction of seemingly more important (e.g. larger) ponds. By using the technique of radio tracking the migratory behaviour and the terrestrial habitats of alpine crested newts and common toads was investigated. The results gave new insights in the habitat requirements of the species in alpine environments. In the common toad, vertical migrations over several 100 m in elevation could be confirmed for the first time in adult amphibians. Both studies indicate that effective amphibian conservation may require large areas and will therefore be more demanding than so far assumed.