Flóra Sebestyén

Bio: Flóra Sebestyén is an academic researcher from University of Debrecen. The author has contributed to research in topics: Hydra oligactis & Asexual reproduction. The author has an hindex of 4, co-authored 8 publications receiving 51 citations.

Effects of food availability on asexual reproduction and stress tolerance along the fast–slow life history continuum in freshwater hydra (Cnidaria: Hydrozoa)

Abstract: Life history theory predicts that reproduction and somatic maintenance are negatively related, but the strength of this relationship is expected to depend on food availability. In this study, we investigated asexual reproduction (budding rate) and oxidative stress tolerance as two opposing facets of life history trade-offs in 17 strains of five freshwater hydra species under experimentally simulated low, medium, and high food availability. Stress tolerance was quantified by exposing animals to exogenous H2O2, which mimics reactive oxygen species arising in vivo. The five species differed in life history traits (low budding rate and high stress tolerance in Hydra vulgaris and H. circumcincta and the opposite in H. oligactis and H. viridissima; low budding rate combined with relatively low stress tolerance in H. oxycnida). Stress tolerance and asexual reproduction increased with food, but there were clear interspecific differences in this relationship. Across all strains, stress tolerance and budding rate were significantly negatively related on the low and medium, but not the high food level. These results suggest that resource allocation trade-offs are involved in determining life history traits in hydra; populations/species can be broadly positioned on a fast–slow life history continuum, and response to variation in food varies along this continuum.

Age-dependent plasticity in reproductive investment, regeneration capacity and survival in a partially clonal animal (Hydra oligactis).

Abstract: Asexual reproduction diversifies life-history priorities and is associated with unusual reproduction and somatic maintenance patterns, such as constant fertility with age, extensive regeneration ability and negligible senescence While age-dependent plasticity in relative allocation to sexual versus asexual reproductive modes is relatively well studied, the modulation of somatic maintenance traits in parallel with age-dependent reproduction is much less well understood in clonal or partially clonal animals Here, we asked how age-dependent investment into sexual and asexual reproduction co-varies with somatic maintenance such as regeneration in a partially clonal freshwater cnidarian Hydra oligactis, a species with remarkable regeneration abilities and experimentally inducible sex We induced gametogenesis by lowering temperature at two ages, 1 or 4 weeks after detachment from an asexual parent, in animals of a male and a female clone Then we measured phenotypically asexual and sexual reproductive traits (budding rate, start day and number of sexual organs) together with head regeneration rate, survival and the cellular background of these traits (number of reproductive and interstitial stem cells) for 2 or 5 months Younger animals had higher asexual reproduction while individuals in the older group had more intensive gametogenesis and reproductive cell production In parallel with these age-dependent reproductive differences, somatic maintenance of older individuals was also impacted: head regeneration, survival and interstitial stem cell numbers were reduced compared to younger polyps Some of the traits investigated showed an ontogenetic effect, suggesting that age-dependent plasticity and a fixed ontogenetic response might both contribute to differences between age groups We show that in H oligactis asexual reproduction coupled with higher somatic maintenance is prioritized earlier in life, while sexual reproduction with higher maintenance costs occurs later if sex is induced These findings confirm general life-history theory predictions on resource allocation between somatic maintenance and sexual reproduction applying in a partially clonal species At the same time, our study also highlights the age-dependent integration of these resource allocation decisions with sexual/asexual strategies Accounting for age-related differences might enhance repeatability of research done with clonal individuals derived from mass cultures

Reproductive mode, stem cells and regeneration in a freshwater cnidarian with postreproductive senescence

Abstract: In many basal metazoans both somatic and reproductive functions are performed by cellular derivatives of a single multipotent stem cell population. Reproduction can drain these stem cell pools, imposing a physiological cost with subsequent negative effects on somatic maintenance functions. In the freshwater cnidarian Hydra oligactis both asexual (budding) and sexual reproductive modes (production of resting eggs) are present, and both of these are dependent on a common pool of interstitial stem cells. Resting eggs tolerate abiotic conditions which neither the parental animals, nor asexual offspring can survive (e.g. freezing). Therefore, when facing unfavorable conditions and increased mortality risk, hydra polyps are expected to show higher differentiation of interstitial stem cells into germ cells (i.e. sexual reproduction), compared to other cell types needed for selfmaintenance or asexual reproduction. Here, by comparing sexually and asexually reproducing individuals to non-reproductives, we studied the physiological costs of reproduction (size of interstitial stem cell pools, their somatic derivatives and regeneration rate, which is dependent on these cell types) in H. oligactis polyps from a free-living Hungarian population prior to the onset of winter. Sexual individuals (but not asexuals) were characterized by significantly smaller interstitial stem cell pools, fewer somatic derivatives (nematoblasts involved in food capture) and lower regeneration ability compared to non-reproductives. We also found a negative correlation between germ cell counts and stem cell numbers in males (but not in females). These results show that the physiological costs of reproduction are higher for sexual individuals. They also suggest that increased differentiation of stem cells into gametes might limit investment into somatic functions in hydra polyps. Exhaustion of cellular resources (stem cells) could be a major mechanism behind the extreme post-reproductive senescence observed in this species.

Phenotypic plasticity rather than genotype drives reproductive choices in Hydra populations.

Abstract: Facultative clonality is associated with complex life cycles where sexual and asexual forms can be exposed to contrasting selection pressures. Facultatively clonal animals often have distinct developmental capabilities that depend on reproductive mode (e.g., negligible senescence and exceptional regeneration ability in asexual individuals, which are lacking in sexual individuals). Understanding how these differences in life history strategies evolved is hampered by limited knowledge of the population structure underlying sexual and asexual forms in nature. Here we studied genetic differentiation of coexisting sexual and asexual Hydra oligactis polyps, a freshwater cnidarian where reproductive mode-dependent life history patterns are observed. We collected asexual and sexual polyps from 13 Central European water bodies and used restriction-site associated DNA sequencing to infer population structure. We detected high relatedness among populations and signs that hydras might spread with resting eggs through zoochory. We found no genetic structure with respect to mode of reproduction (asexual vs. sexual). On the other hand, clear evidence was found for phenotypic plasticity in mode of reproduction, as polyps inferred to be clones differed in reproductive mode. Moreover, we detected two cases of apparent sex change (males and females found within the same clonal lineages) in this species with supposedly stable sexes. Our study describes population genetic structure in Hydra for the first time, highlights the role of phenotypic plasticity in generating patterns of life history variation, and contributes to understanding the evolution of reproductive mode-dependent life history variation in coexisting asexual and sexual forms.

Life History Evolution

Abstract: Life history biology sits on the interface between genetics and ecology, and both have made important theoretical and empirical contributions to our understanding. However, the connections between the disciplines have not always been as close as they might have been and this book takes some useful steps towards remedying this. It gives an excellent review of life history theory, and integrates this well with results from the empirical literature. After an 11-page introduction, Roff sets out ‘a framework for analysis’ in which he covers the necessary elements of quantitative and population genetics. This includes clear definitions of fitness in a range of circumstances, from density independent populations in constant environments through to the more complex situations of density and frequency dependence and environments that are spatially or temporally stochastic. Trade-offs are then examined, including a valuable analysis of potential pitfalls in studying them and ways that these can be avoided. The author then deals in turn with evolution in constant environments; stochastic environments and ‘predictable environments’. The last of these covers situations where there is environmental variation, but at least some information is available to allow individuals to make an adaptive response. The final chapter identifies 20 topics for future study. Some will find the book too dominated by theory. Others (but probably not readers of Heredity!) will find it contains too much genetics. But Roff does an excellent job of making the theory accessible, covering the essential issues and pointing to original sources for the details. Theory is related to a significant number of empirical studies, although there is room for another book reviewing the empirical literature on life histories in detail, and Roff’s book would provide a robust skeleton on which to hang this. To make my own assessment, I examined in detail Roff’s discussion of the question of fitness measures for density dependent populations in stochastic environments – an area in which I have been involved. I could not fault him – all the key references were there and the issues were made very clear without the more esoteric mathematics. I also examined some areas that I was less familiar with, and again the text was clear and easy to read. My only real criticism of the book would be that its very long chapters (more than 130 pages in one case) makes it difficult to find things. It would have been simple to address this by including the section headings on the contents pages. A minor personal quibble would be that the book usually expresses problems in terms of the intrinsic rate of increase, r, and the characteristic (Lotka) equation. A matrix formulation is often more tractable and is easier to generalise to density dependent populations and stochastic environments, so expanding on the relationship between the two would have been useful. But overall this is an excellent book. It brings together the key theory in a single place. It gives an invaluable route into the literature, with a bibliography of 1600 or so items. These features, and its identification of topics that need further study should make an important contribution to moving the field forward.

Age-dependent plasticity in reproductive investment, regeneration capacity and survival in a partially clonal animal (Hydra oligactis).

Abstract: Asexual reproduction diversifies life-history priorities and is associated with unusual reproduction and somatic maintenance patterns, such as constant fertility with age, extensive regeneration ability and negligible senescence While age-dependent plasticity in relative allocation to sexual versus asexual reproductive modes is relatively well studied, the modulation of somatic maintenance traits in parallel with age-dependent reproduction is much less well understood in clonal or partially clonal animals Here, we asked how age-dependent investment into sexual and asexual reproduction co-varies with somatic maintenance such as regeneration in a partially clonal freshwater cnidarian Hydra oligactis, a species with remarkable regeneration abilities and experimentally inducible sex We induced gametogenesis by lowering temperature at two ages, 1 or 4 weeks after detachment from an asexual parent, in animals of a male and a female clone Then we measured phenotypically asexual and sexual reproductive traits (budding rate, start day and number of sexual organs) together with head regeneration rate, survival and the cellular background of these traits (number of reproductive and interstitial stem cells) for 2 or 5 months Younger animals had higher asexual reproduction while individuals in the older group had more intensive gametogenesis and reproductive cell production In parallel with these age-dependent reproductive differences, somatic maintenance of older individuals was also impacted: head regeneration, survival and interstitial stem cell numbers were reduced compared to younger polyps Some of the traits investigated showed an ontogenetic effect, suggesting that age-dependent plasticity and a fixed ontogenetic response might both contribute to differences between age groups We show that in H oligactis asexual reproduction coupled with higher somatic maintenance is prioritized earlier in life, while sexual reproduction with higher maintenance costs occurs later if sex is induced These findings confirm general life-history theory predictions on resource allocation between somatic maintenance and sexual reproduction applying in a partially clonal species At the same time, our study also highlights the age-dependent integration of these resource allocation decisions with sexual/asexual strategies Accounting for age-related differences might enhance repeatability of research done with clonal individuals derived from mass cultures

High regenerative capacity is a general feature within colonial dendrophylliid corals (Anthozoa, Scleractinia).

Abstract: The regenerative capacity of cnidarians plays an essential role in the maintenance and restoration of coral reef ecosystems by allowing faster recovery from disturbances and more efficient small-scale dispersal. However, in the case of invasive species, this property may contribute to their dispersal and success in nonnative habitats. Given that four Indo-Pacific members of the coral genus Tubastraea have invaded the Atlantic, here we evaluated the ability of three of these species (Tubastraea coccinea, Tubastraea diaphana, and Tubastraea micranthus) to regenerate from fragments of undifferentiated coral tissue to fully functional polyps in response to differences in food supply and fragment size. For comparative purposes, another colonial dendrophylliid (Dendrophyllia sp.) was included in the analyses. All dendrophylliids displayed regenerative ability and high survival rates that were independent of whether or not food was supplied or fragment size. However, regeneration rates varied between species and were influenced by fragment size. Temporal expression of key genes of the regenerative process (Wnt and FGF) was profiled during whole-body regeneration of T. coccinea, suggesting a remarkable regenerative ability of T. coccinea that points to its potential use as a laboratory model for the investigation of regeneration in colonial calcified anthozoans.

Reproductive mode, stem cells and regeneration in a freshwater cnidarian with postreproductive senescence

Abstract: In many basal metazoans both somatic and reproductive functions are performed by cellular derivatives of a single multipotent stem cell population. Reproduction can drain these stem cell pools, imposing a physiological cost with subsequent negative effects on somatic maintenance functions. In the freshwater cnidarian Hydra oligactis both asexual (budding) and sexual reproductive modes (production of resting eggs) are present, and both of these are dependent on a common pool of interstitial stem cells. Resting eggs tolerate abiotic conditions which neither the parental animals, nor asexual offspring can survive (e.g. freezing). Therefore, when facing unfavorable conditions and increased mortality risk, hydra polyps are expected to show higher differentiation of interstitial stem cells into germ cells (i.e. sexual reproduction), compared to other cell types needed for selfmaintenance or asexual reproduction. Here, by comparing sexually and asexually reproducing individuals to non-reproductives, we studied the physiological costs of reproduction (size of interstitial stem cell pools, their somatic derivatives and regeneration rate, which is dependent on these cell types) in H. oligactis polyps from a free-living Hungarian population prior to the onset of winter. Sexual individuals (but not asexuals) were characterized by significantly smaller interstitial stem cell pools, fewer somatic derivatives (nematoblasts involved in food capture) and lower regeneration ability compared to non-reproductives. We also found a negative correlation between germ cell counts and stem cell numbers in males (but not in females). These results show that the physiological costs of reproduction are higher for sexual individuals. They also suggest that increased differentiation of stem cells into gametes might limit investment into somatic functions in hydra polyps. Exhaustion of cellular resources (stem cells) could be a major mechanism behind the extreme post-reproductive senescence observed in this species.