Seasonal variation of genotypes and reproductive plasticity in a facultative clonal freshwater invertebrate animal (Hydra oligactis) living in a temperate lake

Abstract

Facultative sexual organisms combine sexual and asexual reproduction within a single life cycle, often switching between reproductive modes depending on environmental conditions. These organisms frequently inhabit variable seasonal environments, where favorable periods alternate with unfavorable periods, generating temporally varying selection pressures that strongly influence life history decisions and hence population dynamics. Due to the rapidly accelerating changes in our global environment today, understanding the population dynamics and genetic changes in facultative sexual populations inhabiting seasonal environments is critical to assess and prepare for additional challenges that will affect such ecosystems. In this study, we aimed at obtaining insights into the seasonal population dynamics of the facultative sexual freshwater cnidarian Hydra oligactis through a combination of restriction site‐associated sequencing (RAD‐Seq) genotyping and the collection of phenotypic data on the reproductive strategy of field‐collected hydra strains in a standard laboratory environment. We reliably detected 42 MlGs from the 121 collected hydra strains. Most of MLGs (N = 35, 83.3%) were detected in only one season. Five MLGs (11.9%) were detected in two seasons, one (2.4%) in three seasons and one (2.4%) in all four seasons. We found no significant genetic change during the 2 years in the study population. Clone lines were detected between seasons and even years, suggesting that clonal lineages can persist for a long time in a natural population. We also found that distinct genotypes differ in sexual reproduction frequency, but these differences did not affect whether genotypes reappeared across samplings. Our study provides key insights into the biology of natural hydra populations, while also contributing to understanding the population biology of facultative sexual species inhabiting freshwater ecosystems.

Warming increases survival and asexual fitness in a facultatively sexual freshwater cnidarian with winter diapause

“…Indeed, the higher asexual fitness of polyps exposed to higher temperatures might be at least partly consequence of their increased survival rate, although this effect was observed only in males, but not in females. Hence, temperature appears in a growing list of intrinsic and extrinsic factors that affect postreproductive survival in this species (age, size, genotype; Miklós et al, 2022 ; Ngo et al, 2021 ; Sebestyén et al, 2020 ). Exposure to high temperature could have resulted in higher survival for at least two different reasons.…”

“…Hence, the production of resting eggs appears to be an adaptation to survive freezing water through dormancy, and indeed, sexually reproducing individuals are found in nature during autumn, before the freezing of water surface occurs (Miklós et al, 2021 ; Sebestyén et al, 2018 ). Following sexual reproduction, hydra polyps experience a senescence‐like process and increased mortality risk, although some of them survive and revert to asexual reproduction (Tökölyi et al, 2017 ; Yoshida et al, 2006 ), depending on their age, size, and genotype (Miklós et al, 2022 ; Ngo et al, 2021 ; Sebestyén et al, 2020 ). Because of the presence of these asexual individuals, H. oligactis can reach huge population densities during late winter and early summer (Bryden, 1952 ; J.T.…”

“…| 3 of 12 TÖKÖLYI Sebestyén et al, 2018). Following sexual reproduction, hydra polyps experience a senescence-like process and increased mortality risk, although some of them survive and revert to asexual reproduction (Tökölyi et al, 2017;Yoshida et al, 2006), depending on their age, size, and genotype (Miklós et al, 2022;Ngo et al, 2021;Sebestyén et al, 2020). Because of the presence of these asexual individuals, H. oligactis can reach huge population densities during late winter and early summer (Bryden, 1952; J.T.…”

Warming increases survival and asexual fitness in a facultatively sexual freshwater cnidarian with winter diapause

“…Indeed, the higher asexual fitness of polyps exposed to higher temperature might be at least partly the consequence of their increased survival rate, although this effect was clearly observed only in males, while in females it was much more subtle. Hence, temperature appears in a growing list of intrinsic and extrinsic factors that affect post-reproductive survival in this species (age, size, genotype; Miklós et al, 2022;Ngo et al, 2021;Sebestyén et al, 2020). Exposure to high temperature could have resulted in higher survival for at least two different reasons.…”

“…Hence, the production of resting eggs appears to be an adaptation to survive freezing water through dormancy, and indeed, sexually reproducing individuals are found in nature during autumn, before the freezing of water surface occurs (Miklós et al, 2021;Sebestyén et al, 2018). Following sexual reproduction, hydra polyps experience a senescence-like process and increased mortality risk, although some of them survive and revert to asexual reproduction (Tökölyi et al, 2017;Yoshida et al, 2006), depending on their age, size, and genotype (Miklós et al, 2022;Ngo et al, 2021;Sebestyén et al, 2020). Because of the presence of these asexual individuals,H.…”