Complex sex determination in the stinging nettle Urtica dioica

Abstract

The dioecious species Urtica dioica harbours wide variation in sex ratio of seeds. We conducted a series of crosses to analyse the genetic basis of sex determination in this species. Dutch populations of U. dioica contain low proportions of monoecious individuals beside male and female plants. Self-pollination of monoecious plants always yielded female, male and monoecious plants, generally in a ratio of one female to three male/monoecious individuals. This motivated us to write down a simple model in which gender is determined by one major sex-determination locus with four alleles. In the model males and monoecious plants have distinct genotypes but are both heterozygous at the sexdetermination locus. We first made crosses among progeny obtained after self-pollination of monoecious plants. These crosses showed that the monoecious trait generally showed Mendelian inheritance and was passed on to the next generation via both pollen and seeds. Further crosses between monoecious plants and plants from dioecious system indicated that alleles from the dioecious system are often dominant. However, many exceptions to our genetic model are observed which suggest that dominance is incomplete and/or that more genes are involved in sex determination. We discuss to what extent sex determination genes explain the strongly biased seed sex ratios and argue that additional genes, for instance genes for female choice, must also be involved.

The effects of rapid desiccation on estimates of plant genome size

“…Similarly, cryptic variation may exist in S. vulgaris, which is a highly cultivated species with many cultivars. As well, DNA content may differ by gender in species where gender is chromosomally determined (e.g., Doležel and Göhde 1995); however, in our study only U. dioica is known to express gender dimorphism, and sex is not chromosomally determined for this species (Glawe and de Jong 2009). Regardless of the explanation for real or apparent intraspecific variation, our study suggests that the casual choice of individual plants for testing may impact genome size estimates at a level comparable to tissue desiccation or other sources of variation.…”

Plant contributions to our understanding of sex chromosome evolution

“…2b), each involving sexually antagonistic 'trade-offs', because each must decrease the proportion invested in female flowers. Variable degrees of maleness are indeed seen in the monocotyledon Sagittaria latifolia, in the Alismataceae (Dorken & Barrett, 2004), Spinacia oleracea in the Chenopodiaceae (Onodera et al, 2011) and Urtica dioica (Glawe & de Jong, 2009). Similarly, when the ancestral state is hermaphroditism, evolution of dioecy often involves 'inconstant males' with partial female function (e.g.…”

The geometry of gender: hyper‐diversification of sexual systems in Urtica L. (Urticaceae)

“…Numerous theories have been proposed for the former (e.g. Greig‐Smith, ; Zuk, ; Freeman et al., ; Heemskerk et al., ; De Jong et al., ; Glawe and de Jong, , ; Shannon and Holsinger, ), but the latter phenomenon has escaped the attention of scientists. Apart from the study on Carex (Molina et al., ) few theories have so far been proposed for the latter, since a similarly complex integration of the segregation of unisexual flowers within the inflorescence has rarely been documented in flowering plants.…”

“…Most detailed studies concern U. dioica L. as the most well‐known and most widespread member of the genus (e.g. Greig‐Smith, ; Zuk, ; Freeman et al., ; Heemskerk et al., ; De Jong et al., ; Glawe and de Jong, , ; Shannon and Holsinger, ). Monoecy is often overlooked (especially in the taller species) due to the fragmentary nature of herbarium specimens, such as in “ Urtica pseudodioica ” (Navas, ), where specimens represent either apical sections of the inflorescence, which are purely female, or young plants, where only the male flowers are visibly developed (Weigend and Luebert, ).…”