Exaptation and vulnerability to introduced mammal herbivores on Balearic endemic flora

Aim: Introduced mammal herbivores are predicted to negatively affect insular flora. However, disentangling which particular traits (1) developed from exaptations and (2) are functional to avoid herbivory remains mainly unknown. This study aims to assess if the flora of continental islands with historic native herbivores are exapted to the introduction of new mammal herbivores and to predict the potential vulnerability of endemic species from islands where mammal herbivores have not been introduced. Location: Balearic Islands. Taxon: 96 Balearic endemic plant species. Methods: We investigated whether the endemic flora on continental islands maintains functional traits that resist introduced mammal herbivores by analysing the chemical and morphological traits related to plant resistance of five individuals for each of 98 species. Also, we measured plant-size variables to assess plant escape strategies. Overall, we combined these traits with the accessibility to goats. Predictive models were generated for species that inhabit islands where goats have not been introduced to assess their potential vulnerability. Results: Endemic species may defend against new herbivores (e.g. goats) if they contain highly toxic compounds (alkaloids, glycosides, coumarins), spinescent and urticating structures, or specific plant architecture (low plant size, high specific leaf area). If such traits are absent, the species may become extinct—unless they inhabit areas inaccessible to goats. On continental islands, some endemic species are expected to resist the introduction of herbivores, while others may be significantly affected. Main Conclusions: From the ancient connection with the mainland, exaptations may allow the plants to resist the presence of introduced herbivores. However, non-exapted species could be threatened by the introduction of non-native ungulatesDireccio General de Politica Universitaria i Recerca (Govern de les Illes Balears) FPI/1925/2016Spanish Government CGL2015-70449-REuropean Union (NextGenerationEU

Incomplete partitioning of pollinators by Linum suffruticosum and its coflowering congeners

This work was supported by funding from The Royal Society (Research Grant 13525) and the Spanish Ministry of Science and Innovation (grant PID2021-127264NB-I00 by MCIN/AEI/10.13039/501100011033 ERDF A way of making Europe) to R.P.B. The fieldwork of R.P.B. was supported by a postdoctoral grant funded by US NSF to W.S.A. (DEB-0444754) and the postdoctoral JDC program from the Spanish Ministerio de Ciencia e Innovacion. The open access funding was provided by Universidad de Granada/CBUA.PremiseLinum suffruticosum shows variations in pollinator fit, pollen pickup, and local pollinators that predict pollen deposition rates. The species often coflowers with other Linum species using the same pollinators. We investigated whether L. suffruticosum trait variation could be explained by local patterns of pollinator sharing and associated evolution to reduce interspecific pollen transfer. MethodsPollinator observations were made in different localities (single species, coflowering with other congeners). Floral traits were measured to detect differences across populations and from coflowering species. Reproductive costs were quantified using interspecific hand pollinations and measures of pollen-tube formation, combined with observations of pollen arrival on stigmas and pollen-tube formation after natural pollination in allopatric and sympatric localities. ResultsThe size and identity of the most important pollinator of L. suffruticosum and whether there was pollinator sharing with coflowering species appeared to explain floral trait variation related to pollinator fit. The morphological overlap of the flowers of L. suffruticosum with those of coflowering species varied, depending on coflowering species identity. A post-pollination incompatibility system maintains reproductive isolation, but conspecific pollen-tube formation was lower after heterospecific pollination. Under natural pollination at sites of coflowering with congeners, conspecific pollen-tube formation was lower than at single-species localities. ConclusionsTrait variation in L. suffruticosum appears to respond to the most important local pollinator. Locally, incomplete pollinator partitioning might cause interspecific pollination, imposing reproductive costs. These reproductive costs may generate selection on floral traits for reduced morphological overlap with coflowering congeners, leading to the evolution of pollination ecotypes.Royal Society 13525Spanish Ministry of Science and Innovation by MCIN/AEI PID2021-127264NB-I00National Science Foundation (NSF) DEB-0444754Universidad de Granada/CBU

Pollen as the link between floral phenotype and fitness

Pollen plays a key role in plant reproductive biology. Despite the long history of research on pollen and pollination, recent advances in pollen‐tracking methods and statistical approaches to linking plant phenotype, pollination performance, and reproductive fitness yield a steady flow of exciting new insights. In this introduction to the Special Issue “Pollen as the Link Between Phenotype and Fitness,” we start by describing a general conceptual model linking functional classes of floral phenotypic traits to pollinationrelated performance metrics and reproductive fitness. We use this model as a framework for synthesizing the relevant literature, highlighting the studies included in the Special Issue, and identifying gaps in our understanding and opportunities for further development of the field. The papers that follow in this Special Issue provide new insights into the relationships between pollen production, presentation, flower morphology, and pollination performance (e.g., pollen deposition onto stigmas), the role of pollinators in pollen transfer, and the consequences of heterospecific pollen deposition. Several of the studies demonstrate exciting experimental and analytical approaches that should pave the way for continued work addressing the intriguing role of pollen in linking plant phenotypes to reproductive fitness.Swedish Research Council 2021-04777Spanish Government PID2021-127264NB-I00Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) 308107/2021-7Austrian Science Fund (FWF) T-118

Evolution of distyly breakdown in Palicoureeae Robbr. & Manen and Psychotrieae Cham. & Schltdl. (Rubiaceae)

Distyly is a floral polymorphism with reciprocal placement of male and female structures, heteromorphic selfincompatibility, and other ancillary traits. However, breeding system breakdowns and loss of polymorphism are common. Here we traced the diversification of breeding strategies in the type genera of tribes Palicoureeae and Psychotrieae and discussed the evolution of distyly in a phylogenetic framework. We used literature and field information for breeding systems transitions in 46 species of Palicourea and Psychotria. Beyond distyly, we found four additional breeding systems, including monomorphism with herkogamy, homostyly (without herkogamy), monoecy and dioecy. Breeding transitions arose independently and were mostly derived from distyly. Only two species presented monomorphism as an intermediate state into gender specialization. It was not possible to evaluate the origin and evolutionary pathways for distyly in Psychotria and Palicourea as a whole, since distyly seems to be ancestral to their diversification. Breeding transitions in Psychotria and Palicourea appeared to be phylogenetically and biogeographically independent and occurred mostly in islands or isolated forest fragments, with distinct divergence times. Breeding transitions were not related to changes in ploidy. We propose that evolution of breeding transitions in Psychotria and Palicourea represent phylogenetically independent strategies to reproductive assurance in isolated or disturbed habitats.Fundacao de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG) APQ-02138-15 001Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) 306551/2014-4 474516/2013-0 477885/2012-

Natural selection on plant resistance to herbivores in the native and introduced range

. When plants are introduced into new regions, the absence of their co-evolved natural enemies can result in lower levels of attack. As a consequence of this reduction in enemy pressure, plant performance may increase and selection for resistance to enemies may decrease. In the present study, we compared leaf damage, plant size and leaf trichome density, as well as the direction and magnitude of selection on resistance and plant size between non-native (Spain) and native (Mexico) populations of Datura stramonium. This species was introduced to Spain about five centuries ago and constitutes an ideal system to test four predictions of the enemy release hypothesis. Compared with native populations, we expected Spanish populations of D. stramonium to have (i) lower levels of foliar damage; (ii) larger plant size; (iii) lower leaf trichome density that is unrelated to foliar damage by herbivores; and (iv) weak or no selection on resistance to herbivores but strong selection on plant size. Our results showed that, on average, plants from non-native populations were significantly less damaged by herbivores, were less pubescent and were larger than those from native populations. We also detected different selection regimes on resistance and plant size between the non-native and native ranges. Positive selection on plant size was detected in both ranges (though it was higher in the non-native area), but consistent positive selection on relative resistance was detected only in the native range. Overall, we suggest that changes in selection pressure on resistance and plant size in D. stramonium in Spain are a consequence of ‘release from natural enemies’

Local climate and vernalization sensitivity predict the latitudinal patterns of flowering onset in the crop wild relative Linum bienne Mill.

Background and aims: The timing of flowering onset often correlates with latitude, indicative of climatic gradients. Flowering onset in temperate species commonly requires exposure to cold temperatures, known as vernalization. Hence, population differentiation of flowering onset with latitude might reflect adaptation to the local climatic conditions experienced by populations.Methods: Within its Western range, seeds from Linum bienne populations (the wild relative of cultivated L. usitatissimum) were used to describe the latitudinal differentiation of flowering onset to determine its association with the population´s local climate. A vernalization experiment, including different crop cultivars, was used to determine how vernalization accelerates flowering onset, and the vernalization sensitivity response among populations and cultivars. Additionally, genetic differentiation of L. bienne populations along the latitudinal range was scrutinized using microsatellite markers.Key results: Flowering onset varied with latitude of origin, with southern populations flowering earlier than their northern counterparts. Vernalization reduced the number of days to flowering onset, but vernalization sensitivity was greater in northern populations compared to southern ones. Conversely, vernalization delayed flowering onset in the crop, exhibiting less variation in sensitivity. In L. bienne, both flowering onset and vernalization sensitivity were better predicted by the population´s local climate than latitude itself. Microsatellite data unveiled genetic differentiation of populations, forming two groups geographically partitioned along latitude.Conclusions: The consistent finding of latitudinal variation across experiments suggests that both flowering onset and vernalization sensitivity in L. bienne populations are under genetic regulation and might depend on climatic cues at the place of origin. The association with climatic gradients along latitude suggests that the climate experienced locally drives population differentiation of the flowering onset and vernalization sensitivity patterns. The genetic population structure suggests that past population history could have influenced the flowering initiation patterns detected, which deserves further work.Keywords: climate change; crop wild relative; flax; flowering phenology; genetic differentiation; latitudinal gradients; local adaptation; vernalization

Natural selection on plant resistance to herbivores in the native and introduced range

Citation: Valverde PL, Arroyo J, Nú ñ ez-Farfá n J, Castillo G, Calahorra A, Pérez-Barrales R, Tapia-Ló pez R. 2015. Natural selection on plant resistance to herbivores in the native and introduced range. AoB PLANTS 7: plv090; doi:10.1093/aobpla/plv090 Abstract. When plants are introduced into new regions, the absence of their co-evolved natural enemies can result in lower levels of attack. As a consequence of this reduction in enemy pressure, plant performance may increase and selection for resistance to enemies may decrease. In the present study, we compared leaf damage, plant size and leaf trichome density, as well as the direction and magnitude of selection on resistance and plant size between non-native (Spain) and native (Mexico) populations of Datura stramonium. This species was introduced to Spain about five centuries ago and constitutes an ideal system to test four predictions of the enemy release hypothesis. Compared with native populations, we expected Spanish populations of D. stramonium to have (i) lower levels of foliar damage; (ii) larger plant size; (iii) lower leaf trichome density that is unrelated to foliar damage by herbivores; and (iv) weak or no selection on resistance to herbivores but strong selection on plant size. Our results showed that, on average, plants from non-native populations were significantly less damaged by herbivores, were less pubescent and were larger than those from native populations. We also detected different selection regimes on resistance and plant size between the non-native and native ranges. Positive selection on plant size was detected in both ranges (though it was higher in the non-native area), but consistent positive selection on relative resistance was detected only in the native range. Overall, we suggest that changes in selection pressure on resistance and plant size in D. stramonium in Spain are a consequence of 'release from natural enemies'

Sources of variation in reciprocal herkogamy in the distyly floral syndrome of Linum tenue (Linaceae)

Premise of research. Distyly is a floral polymorphism involving reciprocal herkogamy shaped by selection for pollen transfer efficiency. The variation of the floral organs involved in pollen transfer can be individually affected by environmental and genetic sources of variance, but the organ development will be canalized to minimize reciprocal inaccuracy between anthers and stigmas, as this is the focus of selection. Methodology. We measured floral organ and cell length of both morphs of distylous Linum tenue (Linaceae) at different developmental stages of field- and glasshouse-grown plants. We analyzed the results to measure reciprocal inaccuracy and identify sources of variance. Pivotal results. Flowers from the field were larger than those from the glasshouse owing to both environmental and genetic (population) factors. Pistil and stamen length in adult flowers correlated with flower size, but reciprocal herkogamy was mostly invariant to the size of individual floral organs. The length of short floral organs showed greater maladaptive bias, while the length of tall organs showed greater imprecision. During development, the pistils of pin flowers grew at a faster rate than those of thrum flowers, mostly owing to cell elongation, while cell division was more important for male organ height. Conclusions. Distyly in L. tenue involves the interaction of multiple coordinated developmental and environmental mechanisms, leading to limited but predictable patterns of variance in the expression of reciprocal herkogamy

Pollen as the link between floral phenotype and fitness

Pollen plays a key role in plant reproductive biology. Despite the long history of research on pollen and pollination, recent advances in pollen-tracking methods and statistical approaches to linking plant phenotype, pollination performance, and reproductive fitness yield a steady flow of exciting new insights. In this introduction to the Special Issue “Pollen as the Link Between Phenotype and Fitness,” we start by describing a general conceptual model linking functional classes of floral phenotypic traits to pollination-related performance metrics and reproductive fitness. We use this model as a framework for synthesizing the relevant literature, highlighting the studies included in the Special Issue, and identifying gaps in our understanding and opportunities for further development of the field. The papers that follow in this Special Issue provide new insights into the relationships between pollen production, presentation, flower morphology, and pollination performance (e.g., pollen deposition onto stigmas), the role of pollinators in pollen transfer, and the consequences of heterospecific pollen deposition. Several of the studies demonstrate exciting experimental and analytical approaches that should pave the way for continued work addressing the intriguing role of pollen in linking plant phenotypes to reproductive fitness