Greater reproductive assurance of asexual plant compared with sexual relative in a low‐density sympatric population: Experimental evidence for pollen limitation

Abstract

High reproductive assurance is regarded as a key advantage of uniparentally reproducing organisms for establishing a new population. This demographic benefit should especially be relevant for plants with autonomous apomixis, that is those which produce seeds completely independently from mates and pollinators. Indeed, many autonomous apomicts occupy larger distributional ranges when compared to their sexual relatives, showing geographical parthenogenesis patterns. However, uniparental reproduction advantage has only rarely been quantified in natural populations and results provided a mixed support, partly because allopatric sexual and asexual populations were exposed to different environmental and pollination conditions causing considerable between‐population variation in the level of reproductive assurance. Here, we compared the level and stability of reproductive assurance between sexual self‐incompatible and asexual autonomously apomictic plants of Hieracium alpinum (Asteraceae) cultivated in a sympatric low‐density population with two levels of spatial clumping of sexual plants. Overall, we found that the realized seed set (i.e. proportion of well‐developed seeds per capitulum) of asexuals was ca. 3 times greater than that of sexuals (83% vs. 27%), whereas the variance of this trait expressed as coefficient of variation was ca. 4 times smaller in asexuals compared with sexuals (19% vs. 83%). Solitary sexual plants had more than 2 times lower realized seed set when compared to clumps composed of two spatially close (20–30 cm) sexual plants (13% vs. 34%). Our study provides experimental evidence for benefit of uniparental reproduction of asexuals in a sympatric situation when the availability of mates is limited. This, together with unpredictability of pollinator environment could provide autonomous apomicts with an ultimate demographic superiority during colonization reflected in geographical parthenogenesis observed in this species.

Why Do Hybrids Turn Down Sex?

“…Even though gynogens do need mates and fertilization (egg and sperm fusion), we show that they can still benefit from reproductive assurance if male gametes are not always able to transmit their genomes (in which case sexual females have limited reproductive outputs). Traditionally, reproductive assurance has been associated with mate scarcity because of reduced population sizes or biased sex-ratios [46, 47, 48, 49]. Here, we argue that mates may not be lacking, but mates able to transfer their genetic material may be because of disruptions to the union of maternal and paternal genomes.…”

Geographical Parthenogenesis in Alpine and Arctic Plants

“…The GP pattern was referred to as a better colonization ability and a more stable reproductive system of apomicts [ 38 ]. In sympatrically cultivated apomictic and sexual populations, apomicts had much higher fertility, which was explained by mate limitation acting for sexuals, but not for apomicts [ 91 ]. However, colonization history may influence GP patterns.…”

Genome Size, Cytotype Diversity and Reproductive Mode Variation of Cotoneaster integerrimus (Rosaceae) from the Balkans

“…As a consequence of bypassing meiosis and lack of genome recombination, apomicts have a genetic structure identical to the maternal plant, thus creating clonal populations. Apomictic polyploids show a greater colonization ability by occupying more extreme ecological niches and persisting in larger distribution areas (geographic parthenogenesis, [14]) than their diploid sexual relatives [16][17][18]. Although genetically uniform, apomicts acquire genetic variation over time via accumulation of spontaneous mutations and via residual sexuality fostering diversity within clonal populations [19][20][21].…”