Kin discrimination in allelopathy and consequences for agriculture

Recent research has shown that plants can distinguish genetically-related individuals from strangers (kin recognition) and exhibit more cooperative behaviours towards these more related individuals (kin discrimination). The first evidence for this was found when Cakile edentula plants growing with half-sibs allocated relatively less biomass to roots than plants growing with unrelated individuals, indicating that kin recognition can reduce the intensity of competition (Dudley & File, 2007). Since then, kin discrimination has been shown to result in reduced competition for soil resources (Semchenko, Saar, & Lepik, 2014), light (Crepy & Casal, 2015) and pollinators (Torices, Gómez, & Pannell, 2018). On the other hand, allelopathy, plants producing chemical compounds that negatively affect performance of neighbour plants, has also been widely documented (Inderjit & Duke, 2003) and shown to profoundly affect local species coexistence and plant community structure (Meiners, Kong, Ladwig, Pisula, & Lang, 2012). In crops allelopathy can also be beneficial in suppressing weeds (Macías, Mejías, & Molinillo, 2019). In the current issue, Xu, Cheng, Kong, and Meiners (2021) published the first study to show that kin discrimination can also affect the balance between direct competition for resources and allelopathy, and this together may lead to improved weed suppression in rice.

Inheritance of breeding system in Cakile (Brassicaceae) following hybridization: implications for plant invasions

Background and Aims Hybridization is commonly assumed to aid invasions through adaptive introgression. In contrast, a recent theoretical model predicted that there can be non-adaptive demographic advantages from hybridization and that the population consequences will depend on the breeding systems of the species and the extent to which subsequent generations are able to interbreed and reproduce. We examined cross-fertilization success and inheritance of breeding systems of two species in order to better assess the plausibility of the theoretical predictions. Methods Reciprocal artificial crosses were made to produce F1, F2 and backcrosses between Cakile maritima (self-incompatible, SI) and Cakile edentula (self-compatible, SC) (Brassicaceae). Flowers were emasculated prior to anther dehiscence and pollen was introduced from donor plants to the recipient’s stigma. Breeding system, pollen viability, pollen germination, pollen tube growth and reproductive output were then determined. The results were used to replace the assumptions made in the original population model and new simulations were made. Key Results The success rate with the SI species as the pollen recipient was lower than when it was the pollen donor, in quantitative agreement with the ‘SI × SC rule’ of unilateral incompatibility. Similar outcomes were found in subsequent generations where fertile hybrids were produced but lower success rates were observed in crosses of SI pollen donors with SC pollen recipients. Much lower proportions of SC hybrids were produced than expected from a single Mendelian allele. When incorporated into a population model, these results predicted an even faster rate of replacement of the SC species by the SI species than previously reported. Conclusions Our study of these two species provides even clearer support for the feasibility of the non-adaptive hybridization hypothesis, whereby the colonization of an SI species can be assisted by transient hybridization with a congener. It also provides novel insight into reproductive biology beyond the F1 generation.

Efecto del sitio de procedencia sobre los atributos de las semillas de Cakile edentula (Brassicaceae), especie estabilizadora de duna costera

<p><strong>Background</strong>: The morphological traits and germinative behavior of seeds vary within a species in response to multiple factors. Knowledge of this variability is important in understanding adaptation of species to environmental conditions.</p><p><strong>Question</strong>: Does the provenance of seeds of <em>Cakile edentula</em> affect seed traits? Does the climate of the sites of origin of the seeds influence their variability? Does the presence of light affect seed germination?</p><p><strong>Study species</strong>: <em>Cakile edentula</em><em> </em>(Bigelow) Hook.</p><p><strong>Study site</strong>: Coastal dune vegetation on the northern coast of the Yucatan Peninsula in August and October 2017.</p><p><strong>Methods</strong>: Seeds of <em>Cakile edentula</em> were collected in different locations on the northern coast of the Yucatan Peninsula. Under laboratory conditions it was assessed whether the origin of the seeds influenced some traits such as seed mass, moisture content, viability and germinative behavior.</p><p><strong>Results</strong>: Seed provenance significantly affected seed mass and moisture content in <em>C</em>. <em>edentula</em>. Moreover, the seeds of <em>C</em>. <em>edentula</em> collected from hot and humid sites germinate quickly and in greater proportion than the seeds from warm and dry sites of the Yucatan Peninsula. The seeds of <em>C</em>. <em>edentula</em> germinate preferably in darkness, regardless site of provenance.</p><strong>Conclusions</strong>: Some seed traits of <em>C</em>. <em>edentula</em> are affected by the site of provenance. Evidence suggests that climatic variation is likely to influence the initial characteristics of the life history in this coastal dune species.

Hybridization can facilitate species invasions, even without enhancing local adaptation

The founding population in most new species introductions, or at the leading edge of an ongoing invasion, is likely to be small. Severe Allee effects—reductions in individual fitness at low population density—may then result in a failure of the species to colonize, even if the habitat could support a much larger population. Using a simulation model for plant populations that incorporates demography, mating systems, quantitative genetics, and pollinators, we show that Allee effects can potentially be overcome by transient hybridization with a resident species or an earlier colonizer. This mechanism does not require the invocation of adaptive changes usually attributed to invasions following hybridization. We verify our result in a case study of sequential invasions by two plant species where the outcrosser Cakile maritima has replaced an earlier, inbreeding, colonizer Cakile edentula (Brassicaceae). Observed historical rates of replacement are consistent with model predictions from hybrid-alleviated Allee effects in outcrossers, although other causes cannot be ruled out.

Differentiating the effects of pot size and nutrient availability on plant biomass and allocation

L. Hess and H. de Kroon (2007. J. Ecol. 95: 241–251) hypothesize that apparent plant responses to neighbour presence could be artifacts of pot-size manipulations. They posit that root size increases with pot size, regardless of nutrient concentration, while plant size increases with nutrient amount in the pot. Simple manipulations of pot size do not test this hypothesis, because larger pots contain more nutrients when nutrients are applied in solution at constant rate. We tested the effects of pot size on growth and allocation in two life stages of Cakile edentula (Bigel.) Hook. subsp. edentula var. lacustris while manipulating nutrient amount and concentration. Although pot size did affect growth and allocation, the patterns were not those predicted by the Hess and de Kroon hypotheses. In several treatments, total plant mass decreased with pot size. Root mass did not increase with pot volume independently of nutrients. Root mass increased with pot volume only when plants were given soluble fertilizer, and to a much greater extent in older plants. Contrary to predictions, root mass increased with pot size only in the treatment with high water-soluble fertilizer where plant size increased greatly with pot size. Root allocation showed a complex pattern of responses with plant life stage and nutrient treatments that were not predicted by the Hess and de Kroon hypotheses.