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 

Genetic diversity in temperate and boreal forests tree species has been strongly affected by late Pleistocene climate oscillations [2,3,5], but also by anthropogenic forces. Particularly in Europe, where a long history of human intervention has re-distributed species and populations, it can be difficult to know if a given forest arose through natural regeneration and gene flow or through some combination of natural and human-mediated processes. This uncertainty can confound inferences of the causes and consequences of standing genetic variation, which may impact our interpretation of demographic events that shaped species before humans became dominant on the landscape. In their paper entitled "Genomic data provides new insights on the demographic history and the extent of recent material transfers in Norway spruce", Chen et al. [1] used a genome-wide dataset of 400k SNPs to infer the demographic history of Picea abies (Norway spruce), the most widespread and abundant spruce species in Europe, and to understand its evolutionary relationship with two other spruces (Picea obovata [Siberian spruce] and P. omorika [Serbian spruce]). Three major Norway spruce clusters were identified, corresponding to central Europe, Russia and the Baltics, and Scandinavia, which agrees with previous studies. The density of the SNP data in the present paper enabled inference of previously uncharacterized admixture between these groups, which corresponds to the timing of postglacial recolonization following the last glacial maximum (LGM). This suggests that multiple migration routes gave rise to the extant distribution of the species, and may explain why Chen et al.'s estimates of divergence times among these major Norway spruce groups were older (15mya) than those of previous studies (5-6mya) – those previous studies may have unknowingly included admixed material [4]. Treemix analysis also revealed extensive admixture between Norway and Siberian spruce over the last ~100k years, while the geographically-restricted Serbian spruce was both isolated from introgression and had a dramatically smaller effective population size (Ne) than either of the other two species. This small Ne resulted from a bottleneck associated with the onset of the iron age ~3000 years ago, which suggests that anthropogenic depletion of forest resources has severely impacted this species. Finally, ancestry of Norway spruce samples collected in Sweden and Denmark suggest their recent transfer from more southern areas of the species range. This northward movement of genotypes likely occurred because the trees performed well relative to local provenances, which is a common observation when trees from the south are planted in more northern locations (although at the potential cost of frost damage due to inappropriate phenology). While not the reason for the transfer, the incorporation of southern seed sources into the Swedish breeding and reforestation program may lead to more resilient forests under climate change. Taken together, the data and analysis presented in this paper allowed inference of the intra- and interspecific demographic histories of a tree species group at a very high resolution, and suggest caveats regarding sampling and interpretation of data from areas with a long history of occupancy by humans.

References

[1] Chen, J., Milesi, P., Jansson, G., Berlin, M., Karlsson, B., Aleksić, J. M., Vendramin, G. G., Lascoux, M. (2018). Genomic data provides new insights on the demographic history and the extent of recent material transfers in Norway spruce. BioRxiv, 402016. ver. 3 peer-reviewed and recommended by PCI Evol Biol. doi: 10.1101/402016
[2] Holliday, J. A., Yuen, M., Ritland, K., & Aitken, S. N. (2010). Postglacial history of a widespread conifer produces inverse clines in selective neutrality tests. Molecular Ecology, 19(18), 3857–3864. doi: 10.1111/j.1365-294X.2010.04767.x
[3] Ingvarsson, P. K. (2008). Multilocus patterns of nucleotide polymorphism and the demographic history of Populus tremula. Genetics, 180, 329-340. doi: 10.1534/genetics.108.090431
[4] Lockwood, J. D., Aleksić, J. M., Zou, J., Wang, J., Liu, J., & Renner, S. S. (2013). A new phylogeny for the genus Picea from plastid, mitochondrial, and nuclear sequences. Molecular Phylogenetics and Evolution, 69(3), 717–727. doi: 10.1016/j.ympev.2013.07.004
[5] Pyhäjärvi, T., Garcia-Gil, M. R., Knürr, T., Mikkonen, M., Wachowiak, W., & Savolainen, O. (2007). Demographic history has influenced nucleotide diversity in European Pinus sylvestris populations. Genetics, 177(3), 1713–1724. doi: 10.1534/genetics.107.077099 "

Recent methodological developments and increased genome sequencing efforts have introduced the tantalizing possibility of inferring ancestral phenotypes using DNA from contemporary species. One intriguing application of this idea is to exploit the apparent correlation between substitution rates and body size to infer ancestral species' body sizes using the inferred patterns of substitution rate variation among species lineages based on genomes of extant species [1].
The recommended paper by Figuet et al. [2] examines the utility of such approaches by analyzing the Cetartiodactyla, a clade of large mammals that have mostly well resolved phylogenetic relationships and a reasonably good fossil record. This combination of genomic data and fossils allows a direct comparison between body size predictions obtained from the genomic data and empirical evidence from the fossil record. If predictions seem good in groups such as the Cetartiodactyla, where there is independent evidence from the fossil record, this would increase the credibility of predictions made for species with less abundant fossils.
Figuet et al. [2] analyze transcriptome data for 41 species and report a significant effect of body mass on overall substitution rate, synonymous vs. non-synonymous rates, and the dynamics of GC-content, thus allowing a prediction of small ancestral body size in this group despite the fact that the extant species that were analyzed are nearly all large.
A comparative method based solely on morphology and phylogenetic relationships would be very unlikely to make such a prediction. There are many sources of uncertainty in the variables and parameters associated with these types of approaches: phylogenetic uncertainty (topology and branch lengths), uncertainty about inferred substitution rates, and so on. Although the authors do not account for all these sources of uncertainty the fact that their predicted body sizes appear sensible is encouraging and undoubtedly the methods will become more statistically sophisticated over time.

References

[1] Romiguier J, Ranwez V, Douzery EJP and Galtier N. 2013. Genomic evidence for large, long-lived ancestors to placental mammals. Molecular Biology and Evolution 30: 5–13. doi: 10.1093/molbev/mss211

[2] Figuet E, Ballenghien M, Lartillot N and Galtier N. 2017. Reconstruction of body mass evolution in the Cetartiodactyla and mammals using phylogenomic data. bioRxiv, ver. 3 of 4th December 2017. 139147. doi: 10.1101/139147

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

Assessing population connectivity is central to understanding population dynamics, and is therefore of great importance in evolutionary biology and conservation biology. In the marine realm, the apparent absence of physical barriers, large population sizes and high dispersal capacities of most organisms often result in no detectable structure, thereby hindering inferences of population connectivity. In a review paper, Gagnaire et al. [1] propose several ideas to improve detection of population connectivity. Notably, using simulations they show that under certain circumstances introgression from one species into another may reveal cryptic population structure within that second species.
The isolated Kerguelen archipelago in the south of Indian Ocean represents a typical situation where the structure of coastal marine organisms is expected to be difficult to detect. In an elegant genomic study, Fraïsse et al. [2] take advantage of introgression from foreign lineages to infer fine-grained population structure in a population of mussels around the Kerguelen archipelago, and investigate its association with environmental variables. Using a large panel of genome-wide markers (GBS) and applying a range of methods that unravel patterns of divergence and gene flow among lineages, they first find that the Kerguelen population is highly admixed, with a major genetic background corresponding to the southern mussel lineage Mytilus platensis introgressed by three northern lineages. By selecting a panel of loci enriched in ancestry-informative SNPs (ie, SNPs highly differentiated among northern lineages) they then detect a fine-scale genetic structure around the Kerguelen archipelago, and identify a major connectivity break. They further show an associating between the genetic structure and environmental variables, particularly the presence of Macrocystis kelp, a marker of habitat exposure to waves (a feature repeatedly evidenced to be important for mussels). While such association pattern could lead to the interpretation that differentiated SNPs correspond to loci directly under selection or linked with such loci, and even be considered as support for adaptive introgression, Fraïsse et al. [2] convincingly show by performing simulations that the genetic-environment association detected can be entirely explained by dispersal barriers associated with environmental variables (habitat-associated connectivity). They also explain why the association is better detected by ancestry-informative SNPs as predicted by Gagnaire et al. [1]. In addition, intrinsic genetic incompatibilities, which reduce gene flow, tend to become trapped at ecotones due to ecological selection, even when loci causing genetic incompatibilities are unlinked with loci involved in adaption to local ecological conditions (Bierne et al. [3]’s coupling hypothesis), leading to correlations between environmental variables and loci not involved in local adaptation. Notably, in Fraïsse et al. [2]’s study, the association between the kelp and ancestry-informative alleles is not consistent throughout the archipelago, casting further doubt on the implication of these alleles in local adaptation.
The study of Fraïsse et al. [2] is therefore an important contribution to evolutionary biology because 1) it provides an empirical demonstration that alleles of foreign origin can be pivotal to detect fine-scale connectivity patterns and 2) it represents a test case of Bierne et al. [3]’s coupling hypothesis, whereby introgressed alleles also enhance patterns of genetic-environment associations. Since genomic scan or GWAS approaches fail to clearly reveal loci involved in local adaptation, how can we disentangle environment-driven selection from intrinsic reproductive barriers and habitat-associated connectivity? A related question is whether we can reliably identify cases of adaptive introgression, which have increasingly been put forward as a mechanism involved in adaptation [4]. Unfortunately, there is no easy answer, and the safest way to go is to rely – where possible – on independent information [5], in particular functional studies of the detected loci, as is for example the case in the mimetic butterfly Heliconius literature (e. g., [6]) where several loci controlling colour pattern variation are well characterized.

References

[1] Gagnaire, P.-A., Broquet, T., Aurelle, D., Viard, F., Souissi, A., Bonhomme, F., Arnaud-Haond, S., & Bierne, N. (2015). Using neutral, selected, and hitchhiker loci to assess connectivity of marine populations in the genomic era. Evolutionary Applications, 8, 769–786. doi: 10.1111/eva.12288
[2] Fraïsse, C., Haguenauer, A., Gerard, K., Weber, A. A.-T., Bierne, N., & Chenuil, A. (2018). Fine-grained habitat-associated genetic connectivity in an admixed population of mussels in the small isolated Kerguelen Islands. bioRxiv, 239244, ver. 4 peer-reviewed and recommended by PCI Evol Biol. doi: 10.1101/239244
[3] Bierne, N., Welch, J., Loire, E., Bonhomme, F., & David, P. (2011). The coupling hypothesis: why genome scans may fail to map local adaptation genes. Molecular Ecology, 20, 2044–2072. doi: 10.1111/j.1365-294X.2011.05080.x
[4] Hedrick, P. W. (2013). Adaptive introgression in animals: examples and comparison to new mutation and standing variation as sources of adaptive variation. Molecular Ecology, 22, 4606–4618. doi: 10.1111/mec.12415
[5] Ravinet, M., Faria, R., Butlin, R. K., Galindo, J., Bierne, N., Rafajlović, M., Noor, M. A. F., Mehlig, B., & Westram, A. M. (2017). Interpreting the genomic landscape of speciation: a road map for finding barriers to gene flow. Journal of Evolutionary Biology, 30, 1450–1477. doi: 10.1111/jeb.13047.
[6] Jay, P., Whibley, A., Frézal, L., Rodríguez de Cara, M. A., Nowell, R. W., Mallet, J., Dasmahapatra, K. K., & Joron, M. (2018). Supergene evolution triggered by the introgression of a chromosomal inversion. Current Biology, 28, 1839–1845.e3. doi: 10.1016/j.cub.2018.04.072