The buck in the milkweed: evidence of male–male interference among pollinaria on pollinators

Abstract

SummaryDirect physical confrontation among conspecifics for access to mates is a form of sexual selection well known among animals, but not thought to take place in plants. Consequently, no structures are known that can be considered as weapons that evolved under such confrontation. Pollinaria of milkweeds may physically compete for access to attachment points on the pollinators' body, and occasionally pollinaria may link onto pre-existing pollinaria on a pollinator resulting in concatenation.We hypothesized that concatenation may result in interference between proximal and distal pollinaria, and that features of nonconcatenating pollinaria might be attributed to prevention of concatenation. We tested this by analyzing pollen donation efficiency, experimental manipulation of the phenotype and the phylogenetic patterns of co-occurrence of traits.It is shown that concatenation was able to diminish the reproductive performance of proximal pollinaria, that horns on pollinaria prevented concatenation, and that horn acquisition was correlated with a loss of concatenation. The experimental removal of horns in species that did not concatenate caused reversion to concatenation.The present work could be the first evidence of male physical struggles and of the acquisition of weapons related to these struggles, that are analogous to those known in animals.

Slow stamen movement in a perennial herb decreases male–male and male–female interference

“…The spatial separation of anthers by stamen movement is similar to tetradynamous stamens (Conner et al 2003; Kudo 2003) and didynamous stamens (Ren and Tang 2010). However, research on male – male interference has received attention only recently, such as in Asclepiadaceae (Cocucci et al 2014) and Saxifragaceae (Ren and Tang 2012, Ren and Bu 2014). …”

Using theories of sexual selection and sexual conflict to improve our understanding of plant ecology and evolution

“…1). In plants, where hermaphroditism is the most common breeding system, sexual selection can occur before pollination, when traits favouring pollinator attraction or optimal attachment on pollinators can increase pollen transfer to conspecific stigmas (Delph and Ashman 2006; Biernaskie and Elle 2007; Cocucci et al 2014). Even though mating is done by proxy, involving a vector for pollen transfer, there is opportunity for both sexes or sexual functions to enhance their reproductive success (e.g.…”

“…Moreover, recent studies indicate new mechanisms of sexual selection in plants, e.g. competition for optimal placement on the pollinator (Cocucci et al 2014) and early male flowering in dioecious species as a means to compete for access to ovules of high-quality female plants (Forrest 2014). Thus, mechanisms of sexual selection may have been overlooked that can help us explain ecology and evolution of plant traits.…”

Sexually antagonistic evolution caused by male-male competition in the pistil

“…It is also widely acknowledged that these selective forces can occur in hermaphrodites (Schärer et al 2014). In plants the significance of sexual selection and sexual conflict is debated (Moore and Pannell 2011;Lankinen and Karlsson Green 2015), but there is an increasing interest to apply these ideas also to plants (Bernasconi et al 2004;Delph and Ashman 2006;Lankinen et al 2006;Willi 2013;Cocucci et al 2014).…”