Variation in sexual dimorphism in a wind‐pollinated plant: the influence of geographical context and life‐cycle dynamics

Abstract

Understanding the mechanisms causing phenotypic differences between females and males has long fascinated evolutionary biologists. An extensive literature exists on animal sexual dimorphism but less information is known about sex differences in plants, particularly the extent of geographical variation in sexual dimorphism and its life-cycle dynamics.Here, we investigated patterns of genetically based sexual dimorphism in vegetative and reproductive traits of a wind-pollinated dioecious plant, Rumex hastatulus, across three lifecycle stages using open-pollinated families from 30 populations spanning the geographic range and chromosomal variation (XY and XY 1 Y 2 ) of the species.The direction and degree of sexual dimorphism was highly variable among populations and life-cycle stages. Sex-specific differences in reproductive function explained a significant amount of temporal change in sexual dimorphism. For several traits, geographical variation in sexual dimorphism was associated with bioclimatic parameters, likely due to the differential responses of the sexes to climate. We found no systematic differences in sexual dimorphism between chromosome races.Sex-specific trait differences in dioecious plants largely result from a balance between sexual and natural selection on resource allocation. Our results indicate that abiotic factors associated with geographical context also play a role in modifying sexual dimorphism during the plant life-cycle.

Ancestral and neo‐sex chromosomes contribute to population divergence in a dioecious plant

“…Indeed, common garden glasshouse studies of the R. hastatulus populations used in our study indicate geographical clines associated with abiotic adaptation to climatic variables in a variety of sexually dimorphic traits (Puixeu et al. ). It therefore seems probable that the sex chromosomes are enriched for genes participating in these traits.…”

“…Alternatively, a disproportionate level of genetic differentiation on the X can arise from increased local adaptation on X chromosomes (Lasne et al 2017;Presgraves 2018). Indeed, common garden glasshouse studies of the R. hastatulus populations used in our study indicate geographical clines associated with abiotic adaptation to climatic variables in a variety of sexually dimorphic traits (Puixeu et al 2019). It therefore seems probable that the sex chromosomes are enriched for genes participating in these traits.…”

The ecology, evolution, and genetics of plant reproductive systems

“…For example, Puixeu et al . (, in this issue pp 1108–1120) investigate the role of environmental heterogeneity in determining the degree of sexual dimorphism in a dioecious system, highlighting strong correlates of abiotic climate conditions with patterns of sexual dimorphism. Several papers in this Special Issue address questions about the interaction of flowers with their environment, especially their pollen vectors.…”

Genetic Diversity and Population Structure in Bryophyte With Facultative Nannandry

“…It might occur when (4) the probability to encounter a sexual partner is low and the need to keep sexual partners nearby is high, as for example in the bone-eating marine worm Osedax or anglerfishes ( Vollrath, 1998 ; Pietsch, 2005 ; Vrijenhoek et al, 2008 ; Rouse et al, 2015 ): in these cases males evolved into rudimentary creatures, which are permanently attached to a normal-sized female. In contrast to well-known examples from the animal kingdom, the evolution of sexual dimorphism in plants has been much less studied ( Geber et al, 1999 ; Puixeu et al, 2019 ), although gender dimorphism occur in approximately 6–10% of all angiosperms ( Geber et al, 1999 ; Vamosi et al, 2003 ) and in more than half of all moss taxa ( Vanderpoorten and Goffinet, 2009 ; Frey and Kürschner, 2011 ). Male dwarfism, also called nannandry, has evolved several times independently in unrelated moss families ( Vanderpoorten and Goffinet, 2009 ; Hedenäs and Bisang, 2011 ) and can either be obligate or facultative, i.e., males growing only as dwarfs or occurring as normal-sized males as well.…”