Can Sexual Selection Cause Divergence in Mating System-Related Floral Traits?

Abstract

Premise of the Research: The wide diversity of floral traits seen among plants is shaped by neutral and selective evolutionary processes. In outcrossing species, sexual selection from competing pollen donors is expected to be important for shaping mating system-related traits but empirical evidence is scarce. In a previous evaluation of experimental evolution lines crossed with either one or two pollen donors (monogamous, M, or polyandrous, P, lines) at early floral stages in mixed-mating Collinsia heterophylla (Plantaginaceae), P showed enhanced pollen competitive ability and reduced maternal seed set compared to M, in accordance with sexually antagonistic evolution of pollen. Here, we asked whether the presence of sexual selection during pollen competition affect mating system-related floral traits in the same lines. Methodology: We compared flowering start, timing of anther-stigma contact (as an indication of timing of self-pollination), timing of stigma receptivity and first seed set between M and P, and with a source line, S (starting material). The former three traits are later in outcrossers than in selfers of Collinsia. The latter trait was expected to be earlier in P than in M because of sexual selection for early seed siring of pollen. Pivotal Results: Artificial polyandry for four generations resulted in later flowering start and later anther-stigma contact in P compared to M, and the latter trait was intermediate in S. Thus, P appeared more 'outcrossing' than M. Stigma receptivity did not differ between lines. First seed set was earlier in P than in M, as expected from sexual selection. Conclusions: Our results from C. heterophylla experimental evolution lines suggest that a component of sexual selection during outcross pollination could enhance the patterns of floral divergence commonly found between outcrossers and selfers.

Softness of selection and mating system interact to shape trait evolution under sexual conflict

“…Also, does the softness of selection play a significant role in affecting trait evolution in hermaphroditic animals and plants? Since hermaphrodites, such as Caenorhabditis elegans (Carvalho et al 2014;Palopoli et al 2015) and the plant Collinsia heterophylla (Lankinen et al 2017;Lankinen and Strandh 2019), have been widely used to study the effect of sexual selection and sexual conflict in experimental evolution studies, we need to develop theoretical predictions for these systems.…”

“…2015) and the plant Collinsia heterophylla (Lankinen et al. 2017; Lankinen and Strandh 2019), have been widely used to study the effect of sexual selection and sexual conflict in experimental evolution studies, we need to develop theoretical predictions for these systems.…”

New genomic resources and comparative analyses reveal differences in floral gene expression in selfing and outcrossing Collinsia sister species

“…Moreover, there is an abundance of existing ecological and phenotypic data on Collinsia species related to niche breadth ( Randle et al 2009 ; Grant and Kalisz 2020 ), sexual interference, sexual conflict, and pollen traits ( e.g. , Lankinen and Madjidian 2011 ; Lankinen et al 2016 ; Lankinen and Strandh 2019 ; Malagon et al 2019 ; Madjidian et al 2020 ), pollination biology ( e.g. , Elle and Carney 2003 ; Kalisz and Vogler 2003 ; Kalisz et al 2004 ; Randle et al 2018 ), phenotypic plasticity ( Jorgensen and Arathi 2013 ; Spigler and Kalisz 2013 ), population differentiation ( Hazzouri et al .…”