Breeding systems of floral colour forms in theDrosera cistifloraspecies complex

Abstract

Variation in plant breeding systems has implications for pollinator‐mediated selection on floral traits and the ecology of populations. Here we evaluate pollinator contribution to seed production, self‐compatibility and pollen limitation in different floral colour forms of Drosera cistiflora sensu lato (Droseraceae). These insectivorous perennial plants are endemic to fynbos and renosterveld vegetation in the Cape Floristic Region of South Africa, and the species complex includes five floral colour forms (pink, purple, red, white and yellow), some of which are known to be pollinated by beetles. Controlled hand‐pollination experiments were conducted in 15 populations of D. cistiflora s.l. (two to four populations per floral colour form) to test whether the colour forms vary in their degree of self‐compatibility and their ability to produce seeds through autonomous self‐fertilization. Yellow‐flowered forms were highly self‐incompatible, while other floral colour forms exhibited partial self‐compatibility. Seed set resulting from autonomous selfing was very low, and pollinator dependence indices were high in all populations. Since hand cross‐pollination resulted in greater seed set than open pollination in 13 of the 15 populations, we inferred that seed production is generally pollen‐limited. Drosera cistiflora s.l. typically exhibits high levels of pollinator dependence and pollen limitation. This is unusual among Drosera species worldwide and suggests that pollinators are likely to mediate strong selection on attractive traits such as floral colour and size in D. cistiflora s.l. These results also suggest that the floral colour forms of D. cistiflora s.l. which are rare and threatened are likely to be vulnerable to local extinction if mutualisms were to collapse indefinitely.

Editorial: The Role of Flower Color in Angiosperm Evolution

“…Similarly, Johnson et al found that patterns of color variation in Drosera cistiflora, a species pollinated by beetles, are associated with different pollinator communities. Given that these beetle species discriminate among color forms (von Witt et al, 2020), the authors conclude that beetle pollinators are a significant factor in the evolution of D. cistiflora flower color. This is one of the first reports of flower color selection by beetles (see Streinzer et al, 2019).…”

How Much Pigment Should Flowers Have? Flowers With Moderate Pigmentation Have Highest Color Contrast

“…First, the flower pigmentation of numerous species exhibits considerable intraspecific variation [reviewed by Sapir et al (2021)]. Intraspecific flower color variation can be discrete (Schemske and Bierzychudek, 2007;Streinzer et al, 2019;von Witt et al, 2020;Buide et al, 2021) or continuous, e.g., covering the spectrum of white, pink and purple in Trifolium pratense (Figure 1), orchids (Sletvold et al, 2016;Dormont et al, 2019) and the Iris atropurpurea complex (Roguz et al, 2020). The amount of pigment that is synthesized is a quantitative trait, and therefore small changes in the pigment synthesis pathway can yield appreciable changes in color (Shrestha et al, 2014;.…”

Breeding systems of the Japanese‐endemic carnivorous sundew species Drosera makinoi and Drosera toyoakensis (Droseraceae)

“…250 species known worldwide (Fleischmann et al, 2018). Some Drosera flowers have characteristics that are considered adaptive for entomophily (Witt et al, 2020). Various insect species, including flower flies (El‐Sayed et al, 2016; Murza et al, 2006; Tagawa et al, 2018), bees (Wilson, 1995), and beetles (Anderson, 2010), have been recorded as effective pollinators, facilitating out‐crossing.…”

“…On the other hand, many Drosera are self‐compatible to make seeds by autogamy and do not depend on pollinators for reproduction (Murza & Davis, 2003; Pietropaolo & Pietropaolo, 1986; Sciligo, 2009). Witt et al (2020) suggested that the low pollinator dependence in Drosera is associated with the ephemerality of their habitats. The habitats of many Drosera species are seasonal wetlands, where attracting pollinators constantly would be difficult.…”