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.

Seasonal variation in sexual readiness in a facultatively sexual freshwater cnidarian with diapausing eggs

“…Collecting polyps at distinct locations increases the chances that multiple genotypes are sampled (based on a previous study, this population contains multiple genotypes, but there is also a relatively high rate of clonality; Miklós et al. 2021). Polyps found on each location were put in a Falcon tube in lake water and brought to the laboratory in a cool box on the day of collection.…”

“…Each of them served as a founder polyp for a distinct strain, because individuals collected at the same location often belong to different genotypes (J. Tökölyi & M. Miklós, unpublished data ; Miklós et al. 2021). Both wild‐collected polyps and their asexual offspring were kept individually in 6‐well plates, with 5 mL M‐solution per well.…”

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

“…During sexual reproduction, persistent/diapausing eggs are produced which tolerate desiccation and freezing (Steele et al, 2019). Based on our observations, however, in some of the natural populations, asexually and sexually reproducing individuals occur simultaneously before the unfavourable periods and adults can survive the unfavourable periods in large numbers (Miklós et al, 2021; MM & JT, personal observations). Therefore, the contribution of sexual individuals with diapausing eggs to the genetic structure and seasonal population dynamics of this species is unclear, as this has not been studied so far.…”

“…Asexual buds detached from experimental animals were used to genotype strains. They were dried using silica gel and stored at room temperature to preserve DNA quality (see Miklós et al, 2021). Genomic DNA from H. oligactis individuals was isolated using a standard mammalian nucleic acid extraction protocol (detailed description of used method, see in supplementary of Miklós et al, 2021; (Supplementary Methods 1)).…”

“…Details of the library preparation protocol can be found in the supplement of Miklós et al, 2021; (Supplementary Methods 1). Quality and quantity of the library were checked with Bioanalyzer (High-Sensitivity DNA Kit).…”