Fluctuating sexual dimorphisms in an eco-physiological trait across environmental gradients in non-vascular plants

D Nicholas McLetchie, Department of Biology, University of Kentucky, Lexington, KY, Rose A Marks, Department of Horticulture, Michigan State University, East Lansing, MI, Juliana da Costa Silva e Costa, Universidade Federal de Minas Gerais, Brazil and Andrea Pereira Luizi-Ponzo, Universidade Federal de Juiz de Fora, Brazil

Background/Question/Methods: The occurrence of sexual dimorphisms (SDs) is oftentimes assumed to be a species characteristic, being present in all populations of a sexual dimorphic species. Sexual dimorphisms are common among many animal species, but SDs also occur in plants where they are rarely as obvious as in animals. In addition, SDs might scale up to affect population sex ratios and consequently sexual reproduction. Based on previous results showing that morphological SD fluctuate, we used a thalloid and a leafy liverwort (Marchantia inflexa and Plagiochila porelloides) to investigate variation in a SD physiological trait (water-stress recovery) and to link this dimorphism to population sex ratios. We subjected male and female plants from multiple populations to a water stress event (compete drying at relevant vapor pressure deficit levels) and then determined a plant’s recovery response after rehydration using a measure of the efficiency of photosystem II (Fv/Fm). We also estimated sex ratios of each population using random transects.
Results/Conclusions: The interaction of sex and population had a significant effect on recovery in both species. More specifically, recovery was higher for females than male (a dimorphic response) in some populations, but not in other populations. In M. inflexa, the variation in the dimorphic response was due to male variation and occurred in the less exposed sites. However, in P. porelloides the dimorphic response occurred in the more exposed sites. Thus, SDs need not be a characteristic of a species, and conclusions of the presence of SDs in species, based on one or a few populations, should be interpreted with caution. Detailed studies across populations of other species are needed to test for the commonness of fluctuations in SDs. Such species can be used to test the specific causes and consequences of SDs among plants and to identify trade-offs between water-stress recovery and other traits, including physiological and life history traits. There was no obvious link between the pattern of water-stress recovery and population sex ratios, suggesting that the patterns of male and female water-stress recovery were not a good predictor of population sex ratios.