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- Chen, Hwei-yen, 1983-
(författare)
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Experimental Evolution of Life-history : Testing the Evolutionary Theories of Ageing
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ageing reduces fitness, but how ageing evolves is still unclear. Evolutionary theory of ageing hinges on the fundamental principal that the force of natural selection declines with age. This principle has yielded two important predictions: 1) the evolution of faster ageing in populations under high rate of extrinsic mortality; and 2) the evolution of faster ageing in a sex that experiences higher rates of extrinsic mortality. However, an emerging new theory argues that when the extrinsic mortality is not random but instead selects on traits showing positive genetic correlation with lifespan, increased mortality should lead to the evolution of increased lifespan. Such condition-dependent mortality is also expected to increase the robustness in the population, resulting in increased deceleration of mortality in late-life. Similarly, high sex-specific mortality can result in increased sex-specific selection on traits that have positive pleiotropic effects on lifespan in the affected sex. This thesis is based on two experimental evolution studies in Caenorhabditis remanei. The first experiment was designed to disentangle the effects of the rate (high or low) and the source (random or condition-dependent) of mortality on the evolution of lifespan and ageing. Reduced lifespan evolved under high rate of random mortality, whereas high condition-dependent mortality, imposed by heat-shock, led to the evolution of increased lifespan (Paper I). However, while female reproduction increased under condition-dependent mortality, male reproduction suffered, suggesting a role for sexual antagonism in maintaining genetic variation for fitness (Paper II). Besides, long lifespan and high fecundity evolved at a cost of slow juvenile growth rate in females (Paper III). Moreover, high condition-dependent mortality led to the evolution of lower rate of intrinsic mortality in late-life (Paper IV). The second experiment showed that evolution of sexual dimorphism in lifespan is driven by the factors that cause sex-specific mortality and cannot be predicted from differences in mortality rate alone. Specifically, high condition-dependent mortality renders males less prone to ageing than females despite higher rates of male mortality (Paper V). The strength of this thesis is the reconfirmation of the earlier findings combined with support for the new theory. Rather than further complicating the matter, the inclusion of the new ideas should help explain some empirical results that are inconsistent with the classic theory, as well as provide a more comprehensive picture of ageing evolution.
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| 2. |
- Hotzy, Cosima, et al.
(författare)
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Evolutionary history of sexual selection affects microRNA profiles in Drosophila sperm
- 2022
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Ingår i: Evolution. - : John Wiley & Sons. - 0014-3820 .- 1558-5646. ; 76:2, s. 310-319
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Tidskriftsartikel (refereegranskat)abstract
- The presence of small RNAs in sperm is a relatively recent discovery and little is currently known about their importance and functions. Environmental changes including social conditions and dietary manipulations are known to affect the composition and expression of some small RNAs in sperm and may elicit a physiological stress response resulting in an associated change in gamete miRNA profiles. Here, we tested how microRNA profiles in sperm are affected by variation in both sexual selection and dietary regimes in Drosophila melanogaster selection lines. The selection lines were exposed to standard versus low yeast diet treatments and three different population sex ratios (male-biased, female-biased, or equal sex) in a full-factorial design. After 38 generations of selection, all males were maintained on their selected diet and in a common garden male-only environment prior to sperm sampling. We performed transcriptome analyses on miRNAs in purified sperm samples. We found 11 differentially expressed miRNAs with the majority showing differences between male- and female-biased lines. Dietary treatment only had a significant effect on miRNA expression levels in interaction with sex ratio. Our findings suggest that long-term adaptation may affect miRNA profiles in sperm and that these may show varied interactions with short-term environmental changes.
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