Are hermaphrodites better adapted to the colonization process in trioecious populations of Salix myrsinifolia?

Abstract

IntroductionSexual dimorphism in plants is characterized not only by the production of androecia vs. gynoecia (primary sexual characters) but also by a range of other morphological differences (secondary sexual characters) among sexual morphs. Males and females can also vary in traits such as individual leaf and flower size, the number of flowers, resource allocation and many others ([1,2] and references therein). Moreover, both sexes can be differentially influenced by biotic conditions such as parasitism and herbivory, which affect their competitive ability [3]. The latter is especially important [4] and even considered a potential force in the evolution of separate sexes from hermaphroditism [5]. Furthermore, differences in resource allocation and reproductive morphology may drive opposite sexes to specialization in different habitats (sexual specialization) and results in the spatial segregation of sexes [6]. It is likely that the phenomenon of spatial segregation of sexes may also be a result of inter-sexual competition, which may impact plants more significantly than intra-sexual competition [7].Size dimorphism is considered to be a result of different resource allocation in sexually dimorphic plants [8]. In general, females are considered to grow less due to a greater investment in reproduction, which was especially proven for woody plants [8][9][10][11]. Other factors, such as local mate competition, geitonogamy, and pollination vectors [12,13], can also influence the benefits of sex-size relations, depending on the species. Size itself positively correlates with flower production [14], the number of offspring [15] and survival probability [16,17] and therefore might serve as a good indicator of competitive abilities.Sex-dependent resource allocation is one of the evolutionary forces through which dioecy evolves via the gynodioecy pathway [18]. Although the evolution of separate sexes in plants has many advantages [19], drawbacks to sexual systems involving hermaphrodites have been recorded in several tree genera, mostly in Salix [20] and Acer [21][22][23], as well as in Taxus [24], Rhamnus and Populus [25]. Why is this turnover favorable if it is a step back in the evolution of sexual systems? It appears that introducing hermaphrodite individuals to previously dioecious populations may be favored in unstable conditions, such as under skewed sex ratios [26], landscape fragmentation [27], lack of pollinators [28], significant habitat alteration [29], or when the opportunities for cross-fertilization are rare, e.g., under the * Corresponding author. Email: p.mirski@uwb.edu.plHandling Editor: Aleksandra Samecka-Cymerman ORIGINAL RESEARCH PAPER Acta Soc Bot Pol 84(2): 167-175 DOI: 10.5586/asbp.2015.013 Received: 2014-11-17 Accepted: 2015-03-15 Published electronically: 2015 Are hermaphrodites better adapted to the colonization process in trioecious populations of Salix myrsinifolia?Paweł Mirski*, Emilia BrzoskoInstitute of Biology, University of Bialystok, Ciołkowskiego 1j, 15-245 Białystok, Poland Abstrac...

Genetic structure of dioecious and trioecious Salix myrsinifolia populations at the border of geographic range

“…First, the distribution of hermaphrodites in S. myrsinifolia follows the expansion front (Mirski 2016), but there was no advantage of this sex morph over males and females other than better colonization properties of self-compatible hermaphrodites (Mirski and Brzosko 2015). Even if only one hermaphrodite individual appears at the new site, it is capable of seed set through selfing (Mirski, pers.…”

“…He suspected that S. myrsinifolia hermaphrodites are characterized by bigger size, faster growth and higher reproductive potential. However, Mirski and Brzosko (2015) showed that hermaphrodites had intermediate values of morphological and reproductive traits between male and female individuals. They further showed that species with high reproductive potential (regardless of sex) produced hundreds of catkins containing several dozens or over hundreds of flowers.…”

“…It is a boreal Eurasian, entomogamous and anemochorous shrub or small tree (Meikle 1984;Mirski and Brzosko 2015). This species was rare in Poland at the beginning of the twentieth century (Skvortsov 1968;Chmelař and Meusel 1986); but a few decades later, it spread in the south and west of Poland, often on anthropogenic habitats (Zieliński 1976, Faliński 1998, Sugier et al 2011.…”

“…One of the polygamic species with co-existing dioecy and trioecy populations is the hexaploid dark-leaved willow, Salix myrsinifolia (Faliński 1998, Mirski and Brzosko 2015, Mirski 2016. It is a boreal Eurasian, entomogamous and anemochorous shrub or small tree (Meikle 1984;Mirski and Brzosko 2015).…”

Spatio-temporal dynamics of sex structure in trioecious and dioecious populations of Salix myrsinifolia

“…This species is typically dioecious, but on the southwestern margins of its range, it is frequently trioecious (Faliński 1998;Mirski and Brzosko 2015). In addition, this species recently became more numerous and commonly inhabited anthropogenic habitats (Faliński 2004).…”