Summary:

In fire-prone environments, the evolution of plant life-histories is thought to be strongly influenced by fire regimes and environmental conditions. Fire management practices should therefore be informed by a better understanding of how fire related life-history traits have been shaped by environmental changes throughout evolutionary history. Perennial plant species in fire-prone environments have developed a wide range of adaptations to fire, which differ in the source of new recruits following fire events. Resprouting species can survive fires regenerating vegetatively from protected buds. In contrast, individuals of “obligate seeder” species are killed by fire: the population will only persist through seeds stored either in the soil or in the canopy (serotiny). To better explain such diversity of strategies, we used a optimization modeling approach (Tonnabel et al. 2012) to predict how fire regime and environmental conditions influence fire life history evolution (in particular serotiny). We then confront the predictions with data about relationships between life-history traits and environment collected for the genus Leucadendron (Proteaceae) in the South-African fynbos. We use comparative analyses approaches to test whether the evolution of particular fire-adaptations is linked to occurrence in specific environments (i.e. fire regimes, precipitation, temperature...) across a newly reconstructed phylogeny. This analysis reveals that fire adaptations arose several times during the evolutionary history of the Leucadendron. As predicted, we find that the evolution of serotinous obligate seeders is associated with the evolution of ecological niches where water limitation is weaker than for all other strategies. Such findings can help understand which species will probably be most vulnerable to climate change that is supposed to lead to dryer conditions in the South-African fynbos.

Summary:

The genus Austrolebias consists of over 30 species of freshwater annual killifish. These fish reside in ephemeral pools across a wide region of South America including parts of Brazil, Uruguay, Paraguay, Argentina and Bolivia. Austrolebias possess a peculiar and interesting life-history. Males and females dive together into the muddy substrate of the pond and deposit their gametes. Later, these adults are often seen dying in shallow water as the ponds completely evaporate during the beginning of the dry season. The eggs then go through several stages of diapause until hatching is triggered by the earliest wet season rains, after which the fish grow rapidly and the process is repeated. The large geographic range of Austrolebias means that the genus is subject to considerable variation in climate. I reveal which climate variables are most important in determining the distribution of Austrolebias by using data collated from my own collection trips, primary literature, online biodiversity databases as well as the records of amateur collectors. Larger species of Austrolebias can be up to 13cm in length, the smallest only 4cm. Recent phylogenetic work has shown that large species have been derived from small species in at least 3 separate instances. I use phylogenetic independent contrasts to investigate whether any bioclimatic variables can explain this variation in size. In addition, species distribution models (SDMs) are built using Maxent and subsequently compared using ENMTools in order to identify whether those species that are morphologically similar possess a similar climatic niche. The nature of the Austrolebias life cycle suggests that it is sensitive to climate change. Current SDMs are compared to 2050 SDMs using the HadCM3 model with multiple emission scenarios to predict the future range shifts of Austrolebias in order to discern the effect climate change will have on this genus.

Summary:

Maturation is a key life history transition, due to the importance of age and size at maturity in determining fitness. Understanding how maturation phenotypes evolve requires an appreciation of the underlying ontogenetic mechanisms, including the maturation threshold, which determines when an individual ‘decides’ to mature. Maturation thresholds are poorly understood, and little is known about how phenotypically plastic or genetically variable they are, but the parthenogenetic crustacean Daphnia is the ideal organism in which to study their evolution. Statistically modelling the maturation process shows that the maturation threshold is a developmentally plastic trait in response to variable resource availability, and more closely resembles a process with a rate than a discrete switch. The idea that the threshold is better thought of as a rate than a switch is further supported by gene expression changes during maturation. The maturation threshold also differs between genotypes and species of Daphnia, and clone-specific maternal effects in the development and growth rate interact to produce phenotypically plastic adult phenotypes. Furthermore, experiments studying the fitness consequences of maturation variation showed that Daphnia magna genotypes initiating maturation at smaller sizes had a higher intrinsic rate of population increase, but this size did not correlate well with competitive success when five clones were directly competed with each other, suggesting that interactions with other factors were influencing fitness. Maturation thresholds in Daphnia do not appear to be based on a single fixed state, but are responsive to environmental variation. The presence of heritable variation and transgenerational effects in these developmentally plastic traits suggests that they have an important role in the evolution of age and size at maturity.