Data for: Effects of parental age on salt stress tolerance in an aquatic plant

Parental age influences components of offspring fitness in many species.
The ability to tolerate stress also affects fitness, but less is known
regarding changes in offspring stress tolerance with increasing parental
age, especially in plants. We examined first and fifth-born clonal
offspring (using birth order as a proxy for parental age), and compared
their fitness in several sub-lethal concentrations of salt (NaCl), to
investigate the interactive effects of birth order and salt stress on the
offspring of the aquatic plant Lemna minor L. We found that increasing
salt concentration reduced reproduction particularly at early ages, which
detrimentally affected fitness, as measured by the intrinsic rate of
natural increase. Fifth offspring had greater fitness than first
offspring, potentially due to the hump-shaped relationship between
offspring fitness and birth order observed in other studies on Lemna, with
fifth offspring near the peak of the hump. We found no interactive effect
of birth order and salt concentration on offspring fitness; however, there
were interactive effects on the time to first reproduction and the size of
fronds. Specifically, first offspring exposed to increasing salt
concentrations exhibited longer delays to first reproduction and grew to a
greater size, while fifth offspring showed little change in either
variable with increasing salt concentration. Thus, variation in birth
order affected offspring response to salt stress, although not in terms of
fitness. These results help illuminate factors impacting the age-specific
strength of natural selection and stress responses, and may be
environmentally relevant in the context of environmental salinization.