Mitochondrial Molecular Adaptations and Life History Strategies Coevolve in Plants

Messenger RNA secondary structure prevents mutations at functionally important sites. Mutations at exposed sites would cause micro-adaptations, niche-specialization, and therefore, can be thought to promote K-strategists. Exposing, rather than protecting, conserved sites, is also potentially adaptive because they probably promote macro-adaptive changes. This presumably fits r-strategists: their population dynamics tolerate decreased survival. We found that helix-forming tendencies are greater at evolutionary conserved sites of plant mitochondrial mRNAs than at evolutionary variable sites in a majority (73%) of species–gene combinations. K-strategists preferentially protect conserved sites in short genes, r-strategists protect them most in larger genes. This adaptive scenario resembles our earlier findings in chloroplast genes. Protection levels at various codon positions also display disparity with respect to life history strategies of the plants. Conserved site protection increases overall mRNA folding stabilities for some genes, while decreases it for some others. This contrast exists between homologous genes of r- and K- strategists. Such compensating interactions between variability, mRNA size, codon position, and secondary structure factors within r- and K-strategists are most likely, molecular adaptations of plants belonging to the two extreme life history strategies. Our results suggest coevolution between molecular and ecological adaptive strategies

CONDITION-DEPENDENT LIFE HISTORY STRATEGIES

Many organisms evolve condition-dependent life history strategies to maximize their lifetime fitness in response to intrinsic and extrinsic processes. I investigated a sequentially flowering plant’s strategy to allocate resources to retain flowers versus grow existing basal fruits to a larger size, using the plant Yucca glauca. The sink strength hypothesis suggests basal fruits are nutrient sinks depriving distal flowers of resources and reducing their probability of retention. A low probability of retention of distal flowers can also be explained by the architectural effects hypothesis. This hypothesis posits inherent positional differences in structures along an inflorescence such as flower size and amount of vascular tissues decrease flower retention with increasing flower position, independent of the number of basal fruits. I experimentally showed that the presence of basal fruits decreased the probability of retention of distal flowers, which supports the sink strength hypothesis. Further, in the absence of fruits, plants retained distal flowers at a probability similar to that of basal flowers, which is inconsistent with the architectural effects hypothesis. Next, I developed a stochastic dynamic programming model to examine the conditions under which decreasing flower retention in response to existing basal fruits is optimal for sequentially flowering plants. The model predicts that plants should decrease flower retention with increasing number of basal fruits when large fruits produce more viable seeds than small fruits (fruit size-dependent viability benefit). Finally, I tested if a higher probability of flower abortion in the presence of basal fruits affects the life history strategy of insects that lay eggs in flowers. Yucca glauca flowers are egg-laying sites for seed-eating insect Tegeticula yuccasella. Flowers that have a high probability of being aborted are low quality egg-laying sites for T. yuccasella because all eggs in aborted flowers die. I experimentally showed that when basal fruits were present, T. yuccasella were less likely to lay eggs in flowers. These investigations help identify mechanisms underlying condition-dependent plant and animal life history strategies that contribute to intra-population variation in life history strategies. Adviser: Brigitte Tenhumber

Phytoplankton models and life history strategies

Phytoplankton models generally do not consider the initial phases of seed stocks and deal only with the vegetative growth phase, ignoring life history strategies. Some quantitatively important diatoms, such as species ofChaetoceros and Skeletonema, have special strategies with respect to the timing of the planktonic phase that cannot be explained purely on the basis of environmental clues. In Norwegian waters and elsewhere, the firstChaetoceros bloom of the growth season usually starts in mid March, initiated by C. socialis. Other Chaetoceros species appear in the water column later. Species of dinoflagellates like Alexandrium also bloom atcertain times of the year. In many cases, phytoplankton inocula originate from resuspension of bottom-dwelling spores or cysts rather than from residual planktonic vegetative cells, and it is probable that, in some species, inoculation events are controlled by endogenous biological clocks. The sequential appearance of different Chaetoceros species may be related to day-length-regulated germination of spores. Most Chaetoceros species have few generations, but they appear at opportunistic times in the plankton. In contrast, Skelelonema costatum and Scrippsiella trochoidea appear at any time of the year. Some modelling results can be improved by including the dynamics of phytoplankton seed stocks in the sediments

Life-history strategies of pike in a high-altitude loch in Scotland

Pike, Esox lucius, are present in Loch Callater at their highest altitude and most extreme habitat in the British Isles, with subarctic winter conditions and extended winter ice-cover. The response of pike in this environment is slower growth, due to a shorter growing season and the low availability of forage fish, giving the poorest reported length-at-age for pike in the British Isles. All pike were mature or had spawned in the same year, with gravid ovaries in April and normal recovering ovaries in June-July. As in other lochs with few prey fishes, the larger pike ate small items such as invertebrates

On the intertemporal allocation of consumption, mortality and life-history strategies

This paper studies the bio-evolutionary origin of time preference. By examining human life-history strategies, it demonstrates that time discounting and mortality reflect the age-variation in the value of survival, which in turn depends on future reproduction and production. Consistent with empirical findings, it also suggests that our biologically endowed time preference is positive, reaches its lowest at around age twenty and increases thereafter, and is higher when exchange transactions involve a reduction in present consumption than when they involve an increase in present consumption.

Evolution of life history strategies in Lophoziaceae

Includes abstract.Includes bibliographical references (leaves 117-135).This study used data from literature and data from the field to analyse the patterns of variation in life history characters among members of the liverwort family Lophoziaceae. A combination of Principal Component and Cluster analyses was used to analyse data from literature in testing for recurrent suites of life history variation among species of the family. Data from literature were also used to examine the relationship between mode of reproduction and reproductive system (sexuality) and between diaspore (spore or gemma) frequency and sexuality. Data from the field were used to establish diaspore (spore and gemma) sizes and their production per capsule or shoot and to test for relationships between diaspore size and production per shoot/capsule and also between diaspore sizes and proportion of germination

How ageing is shaped by trade-offs

The evolution of different life history strategies and thus different ageing patterns essentially depends on the nature of the underlying trade-offs between survival and reproduction. To fully comprehend ageing, we need to understand these trade-offs.ageing

Scaling of the risk landscape drives optimal life history strategies and the evolution of grazing

Consumers face numerous risks that can be minimized by incorporating different life-history strategies. How much and when a consumer adds to its energetic reserves or invests in reproduction are key behavioral and physiological adaptations that structure much of how organisms interact. Here we develop a theoretical framework that explicitly accounts for stochastic fluctuations of an individual consumer's energetic reserves while foraging and reproducing on a landscape with resources that range from uniformly distributed to highly clustered. First, we show that optimal life-history strategies vary in response to changes in the mean productivity of the resource landscape, where depleted environments promote reproduction at lower energetic states, greater investment in each reproduction event, and smaller litter sizes. We then show that if resource variance scales with body size due to landscape clustering, consumers that forage for clustered foods are susceptible to strong Allee effects, increasing extinction risk. Finally, we show that the proposed relationship between consumer body size, resource clustering, and Allee effect-induced population instability offers key ecological insights into the evolution of large-bodied grazing herbivores from small-bodied browsing ancestors.Comment: 9 pages, 5 figures, 3 Supplementary Appendices, 2 Supplementary Figure

Freshwater invertebrate life history strategies for surviving desiccation

In many regions, climate change is prolonging dry periods in rivers and wetlands, exposing freshwater invertebrates to increased periods of desiccation. Invertebrates show a range of strategies for surviving desiccation, but the effects of the degree of exposure to desiccation on the expression of particular traits is unknown. This review synthesizes existing information on the desiccation responses of freshwater invertebrates to examine the flexibility of these survival strategies and the relationship between strategies and the degree of desiccation to which individuals are exposed. It focuses on desiccation at the small spatial scales experienced by individuals and clarifies the terminology of resting stages present during desiccation. We provide a key to terminology used for different forms of dormancy, so that appropriate terms may be used. All invertebrate groups showed a range of strategies for surviving desiccation. Sometimes, different traits were expressed among different populations of a species; however, it is unclear how many species show multiple desiccation response strategies. Many crustacean taxa showed physiological dormancy responses to desiccation that enabled survival for long periods (years). Insects often rely on emigration from drying waterbodies as flying adults or on larvae occupying damp refuges on the benthos. Altered water regimes may alter the phenology of desiccation responses, potentially increasing local extinctions, even in species capable of prolonged dormancy because of constraints on life cycles. However, there is limited empirical evidence demonstrating the flexibility of, or limitations to, expression of these survival strategies and their potential fitness costs