Phenotypic plasticity can lead to rapid and important changes of trait distributions depending on environmental conditions, with important consequences for population dynamics, species interactions and adaptation. To better understand the evolution and importance of plasticity, we need to improve our ability to quantify and compare phenotypic plasticity among organisms, and estimate the evolutionary potential of plastic capacity. Plasticity is classically quantified through regression slopes, with units of traits per environment that by definition vary across organisms, traits and studies, and makes complex the comparison of how does plasticity vary across biological units, especially when linear versus quadratic reaction norms are considered. A clear methodology to quantify phenotypic plasticity in a way that allow for comparison across traits, organisms and environments is lacking.

In this contribution, Pierre de Villemereuil and Luis-Miguel Chevin clarify key concepts about variability and evolutionary potential of plasticity, and propose an efficient method to partition phenotypic variance between genotype and environment. Expanding from the classical (too) simple regression slope approach, and directly integrating the genetic variability of plasticity, they provide a clear framework to quantify the part of phenotypic variance resulting from phenotypic plasticity, integrate the role of the shape of reaction norms, and estimate the heritable variation of trait plasticity. They integrate this method in a R package named Reacnorm, with step by step decision tree, that should greatly help the applicability of this framework.

The authors here propose a contribution that simultaneously clarify key concepts and challenges about plasticity and reaction norms, being very interesting on the theoretical side, and is directly and quite simply applicable to any trait and organism. This should help and stimulate comparative studies of how does plasticity vary across traits, organisms and environmental contexts, both using already published datasets and through new experiments.

References

Pierre de Villemereuil, Luis-Miguel Chevin (2025) Partitioning the phenotypic and genetic variances of reaction norms. EcoEvorxiv, ver.4 peer-reviewed and recommended by PCI Evol Biol https://doi.org/10.32942/X2NC8B

Most flowering plants (almost 90% of species) are pollinated by animals (Ollerton et al. 2011). In fact, many plants are completely dependent on pollinator visits for reproductive success, due to the complete inability of selfing if they are self-incompatible or have strong gender differentiation, as in dioecious plants. Others have diminished reproductive output in the absence of pollinators, even being self-compatible, if their flowers present strong herkogamy or dichogamy, making autonomous selfing more difficult. Ultimately, all animal-pollinated plant species rely on pollinators for outcrossing. Depending on the genetic structure of plant populations and the movement patterns of these animals, outcrossing patterns will shape the population genetic variation, which will determine its adaptive fate. Thus, understanding the mechanisms governing the pollination interaction is crucial for unraveling the uncertainties of a huge proportion of biodiversity on Earth. Being mutualistic by definition, the animal side of this interaction is less understood, despite most pollinator groups being likely dependent on it for their persistence and perhaps diversity (Ollerton 2017). The role of pollinators in plant diversification has generated much literature and controversy ever since Darwin and his “abominable mystery” about angiosperm diversification (Friedman 2009). However, the other way around, that of plant`s effect on pollinator diversification, is more debatable. A remarkable example of this effect is the possible case of co-speciation mediated by nursery (brood site) pollination, which also includes antagonistic insect herbivory (Wiens et al. 2015), as in some Silene species and their moth pollinators and herbivores (Hembry and Althoff 2016).
 
A properly functional pollination interaction relies on efficient pollinators being attracted to flowers (by visual and olfactory stimuli), rewarded or deceived by them (in feeding, nesting, basking, mating, etc. sites), fit the flower shape and contact the sex organs to enhance both male and female plant fitness. Whereas flower rewards, visually attractive stimuli, and flower architecture and shape greatly dominate pollination studies; there are much fewer studies of olfactory attractive stimuli through flower volatile organic compounds (VOC), due to inherent methodological difficulties (Raguso 2008). Most of the studies dealing with flower volatiles are correlative by nature, whereas manipulative experimental approaches are far less common. 
 
Albeit still plant-centered, the manuscript by Barbot et al. (2024) on Silene dioica and its varied pollinator arrays has great merit in including many of the issues mentioned above to solve long-standing questions in plant reproduction. It elegantly fills a gap with well-designed and performed experiments in a particular pollination mode, nursery pollination, which is now considered more frequent and diverse than formerly thought (Nunes et al. 2018, Haran et al. 2023, Suetsugu 2023). The authors demonstrate that Silene dioica has a truly mixed pollination system, including not only generalist diurnal pollinators as it was formerly considered but also nocturnal pollinators of similar proven efficiency. Although the specialized nursery pollination system of Silene-Hadena is widely reported and described in the literature (Kephart et al. 2006; Prieto-Benítez et al. 2017), it was not formerly considered important for Silene dioica, based on its floral syndrome. However, the experiments designed by Barbot et al. (2024) explore in detail the mechanisms of attraction of nocturnal pollinators and their consequences for plant reproductive success, fully confirming the proper functioning of nursery pollination in this plant species. All these prospects are robustly performed through classical sound phenotypic selection analyses and manipulative experiments, together with other approaches less frequent due to technical difficulties but critical when testing authors’ hypotheses. In particular, male fitness estimates using suitable microsatellite markers are especially appropriate in this dioecious species, although they are also very useful in hermaphroditic species when different pollinators and flower variants are interacting (Kulbaba and Worley 2013, Simón-Porcar et al. 2015). Finally, the manipulation of flower fragrance (in fact, of a single VOC) has proved also critical to getting insight into its effect on night pollinators and their joint role as ovipositors and thus predators. All these questions are addressed with a fully crossed experimental design that allows unveiling interactions between experimental factors, a challenge in experimental biology, especially under natural conditions. 
 
In evolutionary biology, most experiments are carried out in laboratories, where factors under scrutiny are carefully controlled and hence their effects are easy to reproduce. The cost of this approach is that the variables of interest are oversimplified and difficult to extrapolate to real ecological conditions. In evolutionary ecology, experiments under field conditions greatly solve this shortcoming, but the cost arises in the difficulties of dealing with several interacting and uncontrolled factors. The study by Barbot et al. (2024) nicely addresses real-world questions in a specialized pollination plus herbivory interaction. The results are robust and pave the road for further overarching pursuits, as mentioned by the reviewers. Thus, it would be interesting to assess actual, absolute values of pollen dispersal distance in natural populations, the selection exerted through the complete reproductive period of male and female plants, provided that they are different, or the effect of using more natural flower bouquets, in the next steps. However, as it stands, this outstanding study will be of high interest to scholars on any of the many topics dealt with there, but also to students willing to start research in the fascinating field of experimental pollination biology, given the wide array of questions addressed and the modern methodological approaches provided.
 
Acknowledgments

The authors of this recommendation benefitted from grants provided by grants PID2021-122715NB-I00 and TED2021-131037B-I00 funded by MCIN/AEI/ 10.13039/501100011033 and by the “European Union NextGeneration EU/PRTR”, and by MSCA-IF-2019-89789.
 
References

Barbot, E., Dufaÿ, M., Godé, C., & De Cauwer, I. (2024). Exploring the effect of scent emission and exposition to diurnal versus nocturnal pollinators on selection patterns on floral traits. Zenodo. https://doi.org/10.5281/zenodo.11490231

Friedman, W. E. (2009). The meaning of Darwin's “abominable mystery”. American Journal of Botany, 96(1), 5-21. https://doi.org/10.3732/ajb.0800150

Haran, J., Kergoat, G. J., & de Medeiros, B. A. (2023). Most diverse, most neglected: weevils (Coleoptera: Curculionoidea) are ubiquitous specialized brood-site pollinators of tropical flora. Peer Community Journal, 3. https://doi.org/10.24072/pcjournal.279 

Hembry, D.H. and Althoff, D.M. (2016), Diversification and coevolution in brood pollination mutualisms: Windows into the role of biotic interactions in generating biological diversity. American Journal of Botany, 103: 1783-1792. https://doi.org/10.3732/ajb.1600056

Kephart, S., Reynolds, R. J., Rutter, M. T., Fenster, C. B., & Dudash, M. R. (2006). Pollination and seed predation by moths on Silene and allied Caryophyllaceae: evaluating a model system to study the evolution of mutualisms. New Phytologist, 169(4), 667-680. https://doi.org/10.1111/j.1469-8137.2005.01619.x

Kulbaba, M. W., & Worley, A. C. (2013). Selection on Polemonium brandegeei (Polemoniaceae) flowers under hummingbird pollination: in opposition, parallel, or independent of selection by hawkmoths?. Evolution, 67(8), 2194-2206. https://doi.org/10.1111/evo.12102

Nunes, C. E. P., Maruyama, P. K., Azevedo-Silva, M., & Sazima, M. (2018). Parasitoids turn herbivores into mutualists in a nursery system involving active pollination. Current Biology, 28(6), 980-986. https://doi.org/10.1016/j.cub.2018.02.013

Ollerton, J. (2017). Pollinator diversity: distribution, ecological function, and conservation. Annual review of ecology, evolution, and systematics, 48(1), 353-376. https://doi.org/10.1146/annurev-ecolsys-110316-022919

Ollerton, J., Winfree, R., & Tarrant, S. (2011). How many flowering plants are pollinated by animals?. Oikos, 120(3), 321-326. https://doi.org/10.1111/j.1600-0706.2010.18644.x

Prieto-Benitez, S., Yela, J. L., & Gimenez-Benavides, L. (2017). Ten years of progress in the study of Hadena-Caryophyllaceae nursery pollination. A review in light of new Mediterranean data. Flora, 232, 63-72. https://doi.org/10.1016/j.flora.2017.02.004

Raguso, R. A. (2008). Wake up and smell the roses: the ecology and evolution of floral scent. Annual review of ecology, evolution, and systematics, 39(1), 549-569. https://doi.org/10.1146/annurev.ecolsys.38.091206.095601

Simón-Porcar, V. I., Meagher, T. R., & Arroyo, J. (2015). Disassortative mating prevails in style-dimorphic Narcissus papyraceus despite low reciprocity and compatibility of morphs. Evolution, 69(9), 2276-2288. https://doi.org/10.1111/evo.12731

Suetsugu, K. (2023). A novel nursery pollination system between a mycoheterotrophic orchid and mushroom-feeding flies. Ecology, 104(11), e4152. https://doi.org/10.1002/ecy.4152

Wiens, J. J., Lapoint, R. T., & Whiteman, N. K. (2015). Herbivory increases diversification across insect clades. Nature communications, 6(1), 8370. https://doi.org/10.1038/ncomms9370 

Insecticide resistance in mosquitoes represents a notable challenge to public health efforts aimed at controlling vector-borne diseases. Among mosquito species, Aedes aegypti is particularly significant due to its extensive geographic spread and its ability to transmit arboviruses causing diseases such as dengue, yellow fever, Zika, and chikungunya (Brown et al., 2014). Insecticide resistance typically develops through two main mechanisms: target-site mutations, which affect the insecticide's interaction with its target, and metabolic resistance, in which insecticide detoxification is enhanced in mosquitoes. While target-site mutations are well characterized, the mechanisms underlying metabolic resistance are understudied. 

The study by Bacot and colleagues (2024) contributes to our understanding of the genetic and evolutionary mechanisms driving insecticide resistance, focusing on a case of metabolic resistance in Aedes aegypti from French Guiana. Following the recent identification of a copy number variant region on chromosome 1, potentially linked to overexpression of detoxification enzymes (Cattel et al., 2020), this study explores the region’s genomic architecture, its likely origin and provides compelling evidence for its role in insecticide resistance.

Through RNA sequencing and whole-genome pool sequencing, the authors reveal that this 220 kilobase duplication increases the expression level of several clustered P450 genes. Cytochrome P450s are known to play a role in breaking down pyrethroids like deltamethrin, a commonly used insecticide. The role of P450 enzymes in detoxification was demonstrated by treating mosquitoes with piperonyl butoxide, a P450 enzyme inhibitor, and observing reduction in deltamethrin resistance, further confirmed by RNA interference experiments. Despite the clear advantages of this genomic duplication in conferring resistance, the study also uncovers a fitness cost associated with carrying the duplication. Through experimental evolution, the authors find that mosquitoes with the duplication experience reduced fitness in the absence of insecticide pressure. Given the regions structural complexity, the authors could not completely disassociate the effect of the duplicated region and that of a target-site mutation. However, they developed an assay that can accurately track the presence of this resistance allele in mosquito populations. 

Altogether, the study by Bacot et al. (2024) highlights the challenges of characterizing the phenotypic effect of copy number variant regions in complex genomes, such as that of Aedes aegypti. It emphasizes the need for further studies on the origin and spread of this duplication to better understand how similar resistance mechanisms might evolve and disseminate. Overall, the completeness and coherence of the narrative, the detailed and thorough analysis, and the insightful discussion, make this work not only a significant contribution to the field of insecticide resistance but an interesting read for the general evolutionary biology community.   

References

Brown, J. E., Evans, B. R., Zheng, W., Obas, V., Barrera-Martinez, L., Egizi, A., Zhao, H., Caccone, A., & Powell, J. R. (2014). Human impacts have shaped historical and recent evolution in Aedes aegypti, the dengue and yellow fever mosquito. Evolution, 68(2), 514–525. https://doi.org/10.1111/evo.12281

Cattel, J., Faucon, F., Le Péron, B., Sherpa, S., Monchal, M., Grillet, L., Gaude, T., Laporte, F., Dusfour, I., Reynaud, S., & David, J. P. (2019). Combining genetic crosses and pool targeted DNA-seq for untangling genomic variations associated with resistance to multiple insecticides in the mosquito Aedes aegypti. Evolutionary applications, 13(2), 303–317. https://doi.org/10.1111/eva.12867

Tiphaine Bacot, Chloe Haberkorn, Joseph Guilliet, Julien Cattel, Mary Kefi, Louis Nadalin, Jonathan Filee, Frederic Boyer, Thierry Gaude, Frederic Laporte, Jordan Tutagata, John Vontas, Isabelle Dusfour, Jean-Marc Bonneville, Jean-Philippe David (2024) A genomic duplication spanning multiple P450s contributes to insecticide resistance in the dengue mosquito Aedes aegypti. bioRxiv, ver.5 peer-reviewed and recommended by PCI Evol Biol https://doi.org/10.1101/2024.04.03.587871

A comprehensive study by Roux et al 2024 investigates the impact of eusociality on the efficacy of natural selection in termites, with and additional focus on whether higher levels of social complexity are associated with lower effective population size (Ne) and relaxed purifying selection.

Eusociality is characterized by a division of reproductive labor, cooperative care of offspring, and overlapping generations, and has evolved independently across various animal taxa with the most complex social systems found in Hymenoptera (bees, wasps, ants) and termites. Because reproduction is limited to a few individuals, this leads to a reduced effective population size (Ne), which impacts genome evolution. Smaller Ne increases the influence of genetic drift, weakening the efficiency of natural selection and allowing the accumulation of weakly deleterious mutations. This phenomenon, known as the "drift barrier," alters the mutation-selection balance in eusocial organisms.

Studies in a range of social arthropods including ants, termites, crustaceans and spiders have shown an elevated ratio of nonsynonymous to synonymous substitutions (dN/dS), indicating relaxed purifying selection due to small Ne. In termite species with complex social structures, such as those with large colonies and high caste specialization, there are reports of higher dN/dS ratios compared to simpler social species. This suggests that higher social complexity, reflected in traits like nesting strategies and developmental pathways, further reduces Ne and the effectiveness of natural selection. 

The authors address these hypotheses by exploring the genomic impact of eusociality in termites (Isoptera) taking two approaches: First, they analyze transcriptome data from 66 Blattodea species and calculate the ratio of non-synonymous to synonymous mutations (dN/dS) as an indicator of natural selection efficiency and effective population size. They analyses reveal an increased dN/dS ratio in termites compared to other Blattodea species, reinforcing the notion that convergent evolution toward eusociality significantly reduces effective population size and weakens natural selection efficiency across the genome. Additionally, a comparison of 68 termite transcriptomes shows that this effect is more pronounced in species with higher social complexity. This is exciting as it advances our understanding of how increasing complexity in social organization decreases Ne and the efficiency of natural selection. The study substantiates the notion that social transitions follow evolutionary trajectories where lower and Ne and increasing drift have negative consequences for genome evolution (Ma et al 2024).

References

Camille Roux, Alice Ha, Arthur Weyna, Morgan Lode, Jonathan Romiguier (2024) The impact of social complexity on the efficacy of natural selection in termites. bioRxiv, ver.2 peer-reviewed and recommended by PCI Evol Biol. https://doi.org/10.1101/2024.04.26.591327

Jilong Ma, Jesper Bechsgaard, Anne Aagaard, Palle Villesen, Trine Bilde, Mikkel Heide Schierup (2024) Sociality in spiders is an evolutionary dead-end. 
bioRxiv 2024.04.22.590577. https://doi.org/10.1101/2024.04.22.590577

The introduction of Ludwigia species as ornamental plants in both North America and Europe dates back almost two centuries, during which time they expanded as naturalized and later invasive species in these territories (Dandelot et al. 2005, Okada et al. 2009). Repeated deliberate or non-deliberate introductions over time of this species complex that can hybridize has given rise to an evolutionarily complex scenario, which is compounded by the difficulty in delimiting some of these species and by the diversity of their modes of reproduction.

Dandelot (2004) and Dandelot et al. (2005) determined the presence of two Ludwigia taxa in France, L. peploides subsp. montevidensis (Spreng.) P.H.Raven (here after Lpm), and L. grandiflora subsp. hexapetala (Hook. & Arn.) G.L.Nesom & Kartesz (here after Lgh), based on their cytotypes (2n = 16, and 2n = 80, respectively) and without evidence of hybridization between them. Furthermore, despite a predominantly vegetative reproduction observed for both species, they differed in their breeding systems. While Lpm is self-compatible and produce a high number of viable seeds in all populations, Lgh is self-incompatible and its populations may drastically differ in seed viability (Dandelot 2004). Several years later, Portillo-Lemus et al. (2021) determined that the differences in seed production between some populations of Lgh are due to the existence of a heteromorphic reproductive system in this taxon, involving a self-incompatible morph (long-style morph; hereafter L-morph), and a self-compatible morph (short-style morph: hereafter S-morph). Moreover, Portillo-Lemus et al. (2022) observed that self-pollen in the L-morph flowers stop growing lately (i.e., in the ovarian area) without fertilizing the ovules, concluding that a late-acting self-incompatible system (hereafter, LSI) is present in this morph.

At this point, it is relevant to understand the possible interactions between populations of different morphs in Lgh, and the implications that they may have on their expansive success in non-native areas in order to develop more effective management plans. To achieve this goal, Stoeckel et al. (2024) analyzed the population genetics in 53 Lgh populations in western Europe (without finding any Lpm population in the sampling area), 40 of which exclusively presented the L-morph and 13 the S-morph. This fact offered the opportunity to compare and interpret the differences between populations of different morphs in Lgh. Other previous works on genetic diversity of Lgh in peripatric or non-native areas pointed to a high clonality and an extremely low genetic diversity (Okada et al. 2009, Armitage et al. 2013), concluding in a monoclonal or few ancestral original clones for these invasive populations.

However, the investigations of Stoeckel et al. (2024) found a high genetic diversity in all populations of Lgh studied despite their predominant clonal reproduction. Interestingly, they found that sexual reproduction is also present, not only in the S-morph by selfing, but also in the L-morph, although limited and preferably by allogamy. They discuss the advantages and drawbacks of the different modes of reproduction observed in Lgh populations, the interactions among them, and the implications that both, the scarcely documented LSI (Gibbs 2014) and selfing, have in the reproductive success and in the maintenance of the high genetic diversity observed in Lgh in western Europe.

The contrasting results with the previous ones (Okada et al. 2009, Armitage et al. 2013) stress the relevance of using appropriate markers and analyses to assess the genetic diversity in autoployploid species, as well as the necessity of knowing the modes of reproduction in the populations studied for an optimal interpretation of the genetic metrics. The approach of the study by Stoeckel et al. (2024) had the challenge of having found suitable markers to deal with a taxon of complex origin such as Lgh, whose genome is compound by a set of autotetraploid chromosomes shared with Lpm and traces of ancient hybridizations of other diploid lineages (Barloy et al. 2024). Using RAD-Seq, Stoeckel et al. (2024) generated an original set of 36 polymorphic SNPs shared between Lgh and Lpm ensuring that these SNPs belong to the tetraploid part of the Lgh genome derived from Lpm. Another interesting contribution of this work is the exhaustive analysis of several genetic descriptors (indexes) and the interpretative guide they provide for each of them in relation to the different modes of reproduction of the study system. Finally, they propose a pair of very useful synthetic indices (i.e., clonality index and selfing index), since they allow to classify populations according to their levels of clonality and selfing.

Stoeckel et al. (2024) conclude the relevance that selfing and LSI populations, and the hybridization between them may have on the expansion and success of invasive plant species, and the necessity to know the modes of reproduction of these populations jointly with their genetic diversity in order to develop appropriate management plans. This study raises new questions such as the modes of reproduction and genetic diversity and structure have other Lgh populations, both invasive and native, and the dynamics of these populations under different future scenarios.

References

Armitage, J. D., Könyves, K., Bailey, J. P., David, J. C., & Culham, A. (2013). A molecular, morphological and cytological investigation of the identity of non-native Ludwigia (Onagraceae) populations in Britain. New Journal of Botany, 3(2), 88–95. https://doi.org/10.1179/2042349713Y.0000000023

Barloy, D., Lemus, L. P.-, Krueger-Hadfield, S. A., Huteau, V., & Coriton, O. (2024). Genomic relationships among diploid and polyploid species of the genus Ludwigia L. section Jussiaea using a combination of cytogenetic, morphological, and crossing investigations. ver. 4 peer-reviewed and recommended by Peer Community in Evolutionary Biology. https://doi.org/10.1101/2023.01.02.522458

Dandelot, S. (2004). Les Ludwigia spp. invasives du Sud de la France: Historique, Biosystématique, Biologie et Ecologie [PhD thesis, Aix-Marseille 3]. https://www.theses.fr/2004AIX30052

Dandelot, S., Verlaque, R., Dutartre, A., & Cazaubon, A. (2005). Ecological, dynamic and taxonomic problems due to Ludwigia (Onagraceae) in France. Hydrobiologia, 551(1), 131–136. https://doi.org/10.1007/s10750-005-4455-0

Gibbs, P. E. (2014). Late-acting self-incompatibility – the pariah breeding system in flowering plants. New Phytologist, 203(3), 717–734. https://doi.org/10.1111/nph.12874

Okada, M., Grewell, B. J., & Jasieniuk, M. (2009). Clonal spread of invasive Ludwigia hexapetala and L. grandiflora in freshwater wetlands of California. Aquatic Botany, 91(3), 123–129. https://doi.org/10.1016/j.aquabot.2009.03.006

Portillo Lemus, L. O., Bozec, M., Harang, M., Coudreuse, J., Haury, J., Stoeckel, S., & Barloy, D. (2021). Self-incompatibility limits sexual reproduction rather than environmental conditions in an invasive water primrose. Plant-Environment Interactions, 2(2), 74–86. https://doi.org/10.1002/pei3.10042

Portillo Lemus, L. O., Harang, M., Bozec, M., Haury, J., Stoeckel, S., & Barloy, D. (2022). Late-acting self-incompatible system, preferential allogamy and delayed selfing in the heteromorphic invasive populations of Ludwigia grandiflora subsp. hexapetala. Peer Community Journal, 2. https://doi.org/10.24072/pcjournal.108

Stoeckel, S., Becheler, R., Portillo-Lemus, L., Harang, M., Besnard, A.-L., Lassalle, G., Causse-Védrines, R., Michon-Coudouel, S., Park D. J., Pope, B. J., Petit, E. J. & Barloy, D. (2024) Reproductive modes in populations of late-acting self-incompatible and self-compatible polyploid Ludwigia grandiflora subsp. hexapetala in western Europe. biorxiv, ver.4 peer-reviewed and recommended by PCI Evol Biol https://doi.org/10.1101/2024.03.21.586104