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The adaptive function of touch-sensitive stigmas

Authors:
Shivani Krishna at Indian Institute Of Science Education and Research, Thiruvananthapuram
Shivani Krishna
Elsa M. Jos
Elsa M. Jos
Elsa M. Jos
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Hema Somanathan at Indian Institute Of Science Education and Research, Thiruvananthapuram
Hema Somanathan
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Abstract and Figures

Touch-sensitive movement in stigmas of angiosperm flowers is a phenomenon observable in a timescale of seconds or minutes. Despite its early documentation in a small fraction of angiosperm species, touch-sensitive stigmas (TSS) have been little studied. In this review, we examine its occurrence in the angiosperm phylogeny and investigate associations between plant reproductive traits and TSS. Prominent hypotheses regarding the evolution of TSS invoke the adaptive functions of outcrossing, pollination efficiency, and pollen germination. Using literature searches for species reported with TSS, we found that the distribution of TSS is phylogenetically clustered within the order Lamiales, while Bignoniaceae emerges as the family that abounds in TSS species. We found the strongest association with bisexuality in flowers. The other traits associated with TSS include self-incompatible mating system, dichogamy, large campanulate corollas, specialized pollination, and multiple ovules. Thus, we predict that TSS can be an effective reproductive strategy in conjunction with these specific traits.
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Plant Ecol (2023) 224:83–94
https://doi.org/10.1007/s11258-022-01281-2
The adaptive function oftouch‑sensitive stigmas
ShivaniKrishna· ElsaM.Jos· HemaSomanathan
Received: 19 August 2022 / Accepted: 29 November 2022 / Published online: 26 December 2022
© The Author(s), under exclusive licence to Springer Nature B.V. 2022
Abstract Touch-sensitive movement in stigmas of
angiosperm flowers is a phenomenon observable in
a timescale of seconds or minutes. Despite its early
documentation in a small fraction of angiosperm spe-
cies, touch-sensitive stigmas (TSS) have been little
studied. In this review, we examine its occurrence
in the angiosperm phylogeny and investigate asso-
ciations between plant reproductive traits and TSS.
Prominent hypotheses regarding the evolution of TSS
invoke the adaptive functions of outcrossing, pollina-
tion efficiency, and pollen germination. Using litera-
ture searches for species reported with TSS, we found
that the distribution of TSS is phylogenetically clus-
tered within the order Lamiales, while Bignoniaceae
emerges as the family that abounds in TSS species.
We found the strongest association with bisexuality in
flowers. The other traits associated with TSS include
self-incompatible mating system, dichogamy, large
campanulate corollas, specialized pollination, and
multiple ovules. Thus, we predict that TSS can be an
effective reproductive strategy in conjunction with
these specific traits.
Keywords Bignoniaceae· Floral traits· Plant
mating systems· Pollen transfer· Pollination
efficiency· Specialization
Introduction
Rapid closure of the leaves of mimosa, insect traps of
Drosera, and triggers of Catasetum orchids are exam-
ples of various rapid movement phenomena in plants
that have fascinated biologists for decades. Like many
other processes in the natural world, Darwin laid the
foundation for studies in plant movement (Darwin
1880). How plants have achieved such a diversity of
movement without the muscle features of animals
has attracted the attention of not only biologists but
also physicists and engineers interested in biomimetic
designs and bio-inspired materials (Burgert and Fratzl
2009; Forterre 2013; Martone etal. 2010; Werely and
Sater 2012).
Communicated by Scott Meiners.
Supplementary Information The online version
contains supplementary material available at https:// doi.
org/ 10. 1007/ s11258- 022- 01281-2.
S.Krishna(*)
Department ofBiology, Ashoka University, Sonepat,
Haryana, India
e-mail: shivani.krishna@ashoka.edu.in
E.M.Jos· H.Somanathan(*)
IISER-TVM Centre forResearch andEducation
inEcology andEvolution (ICREEE), School ofBiology,
Indian Institute ofScience Education andResearch
Thiruvananthapuram, Thiruvananthapuram, Kerala, India
e-mail: hsomanathan@iisertvm.ac.in
Present Address:
E.M.Jos
Department ofBiology andEcology Center, Utah State
University, Logan, UT84322, UnitedStates
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