Invasion Fosters Change: Independent Evolutionary Shifts in Reproductive Traits after Oxalis pes-caprae L. Introduction

Abstract

Biological invasions offer optimal scenarios to study evolutionary changes under contemporary timescales. After long-distance dispersal, exotic species have to cope with strong mate limitation, and shifts toward uniparental reproduction have been hypothesized to be selectively advantageous. Oxalis pes-caprae is a clonal tristylous species native to South Africa, and invasive in Mediterranean regions worldwide. It reproduces sexually and asexually but the importance of each strategy differs between ranges. Native populations reproduce mostly sexually while in invasive ones asexual reproduction is the prevailing strategy due to the dominance of pentaploid monomorphic populations. Nevertheless, two contrasting scenarios have been observed after introduction: transition toward clonality, and re-acquisition of sexuality fueled by multiple introductions of compatible mates. Here, we aimed to assess evolutionary changes of reproductive traits in O. pes-caprae invasive populations and evaluate whether these traits could be related with invasion success and prevalence of certain forms in the western Mediterranean basin. Sexual and asexual reproduction traits were quantified under optimal conditions in a common garden experiment including native and invasive sexual, predominately asexual, and obligated asexual individuals. Different reproductive, ecological, and genetic constraints created by long-distance dispersal seem to have generated different selective pressures in sexual and asexual traits, with our results supporting evolutionary changes in invasive populations of O. pes-caprae. Native plants had higher sexual fitness, while a transition toward clonality was clear for invasive forms, supporting clonal reproduction as a major trait driving invasion. Differences were also observed among invasive plants, with sexual forms having increased dispersal potential; thus, they are expected to be in advantage in comparison with predominantly asexual and obligated asexual plants, and may become widespread in the future. Historical processes, like the initial introduction of predominantly asexual forms followed by sexual forms more recently, could be in the origin of current distribution patterns of O. pes-caprae in the western Mediterranean. This study shows that invasion processes are very dynamic and that ecological and genetic constraints determined by the invasion process may originate different reproductive strategies that are likely to determine invasion success.

Spatial genetic structure and clonality of Prunus serotina Ehrh. during invasive spread into Scots pine forests

“…In P. serotina vegetative regeneration is viewed as strategy for long-term persistence in stochastic environments and sub-optimal light conditions (Auclair 1975;Closset-Kopp et al 2007). Based on our results and field observations we conclude that clonality per se is not a strategy allowing colonization, efficient space takeover or outcompeting of other species as was proven to be the case in other invasive species capable of vast clonal spread (Hollingsworth and Bailey 2000;Kollmann et al 2009;Budde et al 2010;Castro et al 2016). We rather consider that for black cherry, clonality mediates the transition from durable maintenance in a recipient habitat with sub-optimal conditions (low light availability) to the abundant seed production phase, which is one of the main contributors to the great invasiveness of black cherry.…”

“…The high values of the parameter R that characterizes the level of clonal structure clearly indicate generative reproduction as the main source of new recruitments. Some invasive species even show a transition into greater vegetative reproduction in an adventive range (Castro et al 2016), but this is not the case for black cherry. Considerable input of clonal individuals due to root suckers was noted only for the isolated population R, where the biggest genet of 13 ramets was detected.…”

“…In their theoretical model, Rafajlović et al (2017) indicated that dioecious clonal species may form a "asexual colonization wave" during colonization that efficiently supports the establishment of recent invaders, especially in situation of the biased sex ratio. In extreme conditions, clonality even enables wide colonization by one sex only (Budde et al 2011), and in the common garden experiment, Castro et al (2016) reported a transition into clonality in reproductive strategy in plants from the invasive range. All these studies clearly show that clonality is a very important trait in plant invaders.…”

Complex cytogeographical patterns reveal a dynamic tetraploid–octoploid contact zone

“…Additionally, differences in other traits, such as perenniality or asexual reproduction, could compensate for the minority cytotype disadvantage (e.g. Rodriguez 1996 ; Kao 2007 ; Castro et al 2016a ). In other polyploid complexes, traits such as the production of bulbs represented an advantage, enabling new cytotypes to persist at initial stages and spread within lower ploidy populations (e.g.…”

“… Kolář et al 2009 ; Trávníček et al 2010 ), production of unreduced gametes (e.g. Maceira et al 1992 ; Burton and Husband 2001 ; Ramsey 2007 ; Castro et al 2016a ) or recurrent occurrence of gene flow (e.g. Husband 2004 ; Kolář et al 2009 ; Castro et al 2011 ).…”