Recurved Taraxacum phyllaries function as a floral defense: experimental evidence and its implication for Taraxacum evolutionary history

Abstract

Florivores directly decrease the reproductive success of plants by consuming pollen and seeds; thus, plants often have defense mechanisms against florivory. Here, we show that the recurved phyllaries of an agamospermous hybrid dandelion, Taraxacum japonicum · officinale, function as a physical barrier to slug florivory. We allowed Lehmannia valentiana, a European slug naturalized in Japan, to feed on eight pairs of the hybrid dandelion and T. japonicum, a Japanese species with erect phyllaries. Consequently, the slugs only damaged T. platycarpum flowers. The slugs either moved back from recurved phyllaries or spent more than twice as long on recurved than on erect phyllaries. When we removed the recurved phyllaries, the slugs stayed on hybrid and T. japonicum phyllaries for equal lengths of time. In addition to recurved outer phyllaries, the hybrid dandelion has erect inner phyllaries that are longer than those of T. japonicum, which effectively conceal the florets at night protecting them from slug florivory. Using the taxonomic literature, we have confirmed that recurved phyllaries evolved in many species in several parts of Europe, but are rare in East Asia. These findings suggest that European dandelions acquired recurved phyllaries as a defense mechanism under antagonistic coevolution with florivorous slugs, but this coevolution did not occur in East Asia.

Withering corolla remains on the calyx tube enhance reproductive success in Oxalis stricta L.

“…However, the ecological difference between senescence and abscission, especially concerning the function of the corolla remains, has not yet been studied. Although the corolla remains might also have other functions, such as protecting the inner floral parts from the entry of airborne pathogens(van Doorn & van Meeteren, 2003) and frugivorous animals (e.g., slugs;Wu & Yahara, 2017), we conclude that the ecological function of thermal maintenance for seed maturation is thought to be universal in many plant lineages that include plants with withering corolla remains. Thus, our study on the corolla remains presents a new aspect of thermal ecology in flowers that was not previously mentioned in the literature.…”

“…As flowers bear important reproductive organs, such as pistils and stamens, they are assumed to have evolved certain adaptive traits (Abdusalam & Tan, 2014), such as protection from airborne pathogens and frugivorous animals (van Doorn & van Meeteren, 2003;Wu & Yahara, 2017). Therefore, in this study, we sought to investigate whether the withering remains of corollas that are retained on the calyx tube have any ecological significance.…”

“…In plants, several traits can affect reproductive fitness after flowering, including pollinator attraction (Ida & Kudo, 2003 ; Kudo, 1995 ; Moyroud & Glover, 2016 ; Overland, 1960 ), herbivory defense (McCall & Irwin, 2006 ; Wu & Yahara, 2017 ), prevention of pollen loss (Bynum & Smith, 2001 ; von Hase, Cowling, & Ellis, 2006 ; Prokop, Jersáková, Fančovičová, & Pipíška, 2019 ), protection against pathogens (van Doorn & van Meeteren, 2003 ), and thermal regulation of the pistil (Abdusalam & Tan, 2014 ; Liu, Zhang, Ji, Zhang, & Wang, 2017 ; van der Kooi, Kevan, & Koski, 2019 ). Additionally, as indicated by van der Kooi et al.…”

“…However, the ecological function of the withered petals or corolla remains, and the reason why they remain attached to the calyx tube after pollination and during the fruiting period, have yet to be examined in detail. As flowers bear important reproductive organs, such as pistils and stamens, they are assumed to have evolved certain adaptive traits (Abdusalam & Tan, 2014 ), such as protection from airborne pathogens and frugivorous animals (van Doorn & van Meeteren, 2003 ; Wu & Yahara, 2017 ). Therefore, in this study, we sought to investigate whether the withering remains of corollas that are retained on the calyx tube have any ecological significance.…”