Latest recommendations
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29 Nov 2023
Individual differences in developmental trajectory leave a male polyphenic signature in bulb mite populationsJacques A. Deere & Isabel M. Smallegange https://doi.org/10.1101/2023.02.06.527265What determines whether to scramble or fight in male bulb mitesRecommended by Ulrich Karl Steiner based on reviews by 2 anonymous reviewersA classic textbook example in evolutionary ecology for phenotypic plasticity—the expression of different phenotypes by a genotype under different environmental conditions—is on Daphnia (Dodson 1989). If various species of this small crustacean are exposed to predation risk or cues thereof, their offspring show induced defense phenotypes including helmets, neck teeth, or head- and tail-spines. These induced morphological changes lower the risk of being eaten by a predator. As in Daphnia, induction can span over generations, while other induced phenotypic plastic changes are almost instantaneous, including many responses in physiology and behaviour (Gabriel et al. 2005). Larvae male bulb mites also show plasticity in morphologies throughout development. They can develop into a costly adult fighter morphology or a less costly, but vulnerable, scrambler type. The question Deere and Smallegange (Deere & Smallegange 2023) address is whether male bulb mite larvae can anticipate which type will likely be adaptive once they become adult, or alternatively, whether the resource availability or population density they experience during their larvae phase determines frequencies of adult scrambler and fighter types. They explore this question through experimental evolution, by removing different fractions of developing intermediate larva types. They thereby manipulate the stage structure of populations and alter selective forces on these stages. The potential shift of fixed genetics, imposed by the experimental selection regimes, is evaluated by fitness assays in green garden experiments. The exciting extension to classical experiments on phenotypic plasticity is that the authors aim at exploring eco-evolutionary feedbacks experimentally in a system that is a little more complex than basic host-parasite or predator-prey systems. The latter involve, for instance, rotifer-algae dynamics (Yoshida et al. 2003; Becks et al. 2012) or similar simple lab systems for which eco-evolutionary feedbacks have been demonstrated. The challenge for the exploration of more complex systems is revealed in the study by Deere and Smallegange. Their findings suggest that the frequencies of adult male morphotype is triggered by the environmental condition (nutrient availability) during the larval phase, i.e. a simple environmental induced plastic response. No fixed genetic shift in determining adult morphotype frequencies occurs. The trigger at the larva phase remains also not perfectly determined in their experiments, as population density and resource (food) availability are partly confounded. Additional complexity and selective aspects come into play in this system, as the targeted developmental stages that develop into fighter male morphs are also dispersal morphs. If selection on dispersal to avoid residing in food-limited environments is strong, triggering genetic shifts in fighter morphs by local population structure might be hard to experimentally achieve. Small sample sizes limit conclusions on complex interactions among duration of the experiment, population size, developmental stage types, and adult fighter frequencies. The presented study (Deere & Smallegange 2023) helps to bridge theoretical predictions and empirical evidence for eco-evolutionary feedbacks that goes beyond simple ecological-driven changes in population dynamics (Govaert et al. 2019).
References
Becks, L., Ellner, S.P., Jones, L.E. & Hairston, N.G. (2012). The functional genomics of an eco-evolutionary feedback loop: linking gene expression, trait evolution, and community dynamics. Ecol. Lett., 15, 492-501. | Individual differences in developmental trajectory leave a male polyphenic signature in bulb mite populations | Jacques A. Deere & Isabel M. Smallegange | <p style="text-align: justify;">Developmental plasticity alters phenotypes and can in that way change the response to selection. When alternative phenotypes show different life history trajectories, developmental plasticity can also affect, and be... | Evolutionary Ecology, Life History, Phenotypic Plasticity, Sexual Selection | Ulrich Karl Steiner | 2023-02-07 12:14:33 | View | ||
17 Jun 2022
Spontaneous parthenogenesis in the parasitoid wasp Cotesia typhae: low frequency anomaly or evolving process?Claire Capdevielle Dulac, Romain Benoist, Sarah Paquet, Paul-André Calatayud, Julius Obonyo, Laure Kaiser, Florence Mougel https://doi.org/10.1101/2021.12.13.472356The potential evolutionary importance of low-frequency flexibility in reproductive modesRecommended by Christoph Haag based on reviews by Michael Lattorff and Jens BastOccasional events of asexual reproduction in otherwise sexual taxa have been documented since a long time. Accounts range from observations of offspring development from unfertilized eggs in Drosophila to rare offspring production by isolated females in lizards and birds (e.g., Stalker 1954, Watts et al 2006, Ryder et al. 2021). Many more such cases likely await documentation, as rare events are inherently difficult to observe. These rare events of asexual reproduction are often associated with low offspring fitness (“tychoparthenogenesis”), and have mostly been discarded in the evolutionary literature as reproductive accidents without evolutionary significance. Recently, however, there has been an increased interest in the details of evolutionary transitions from sexual to asexual reproduction (e.g., Archetti 2010, Neiman et al.2014, Lenormand et al. 2016), because these details may be key to understanding why successful transitions are rare, why they occur more frequently in some groups than in others, and why certain genetic mechanisms of ploidy maintenance or ploidy restoration are more often observed than others. In this context, the hypothesis has been formulated that regular or even obligate asexual reproduction may evolve from these rare events of asexual reproduction (e.g., Schwander et al. 2010). A new study by Capdevielle Dulac et al. (2022) now investigates this question in a parasitoid wasp, highlighting also the fact that what is considered rare or occasional may differ from one system to the next. The results show “rare” parthenogenetic production of diploid daughters occurring at variable frequencies (from zero to 2 %) in different laboratory strains, as well as in a natural population. They also demonstrate parthenogenetic production of female offspring in both virgin females and mated ones, as well as no reduced fecundity of parthenogenetically produced offspring. These findings suggest that parthenogenetic production of daughters, while still being rare, may be a more regular and less deleterious reproductive feature in this species than in other cases of occasional asexuality. Indeed, haplodiploid organisms, such as this parasitoid wasp have been hypothesized to facilitate evolutionary transitions to asexuality (Neimann et al. 2014, Van Der Kooi et al. 2017). First, in haploidiploid organisms, females are diploid and develop from normal, fertilized eggs, but males are haploid as they develop parthenogenetically from unfertilized eggs. This means that, in these species, fertilization is not necessarily needed to trigger development, thus removing one of the constraints for transitions to obligate asexuality (Engelstädter 2008, Vorburger 2014). Second, spermatogenesis in males occurs by a modified meiosis that skips the first meiotic division (e.g., Ferree et al. 2019). Haploidiploid organisms may thus have a potential route for an evolutionary transition to obligate parthenogenesis that is not available to organisms: The pathways for the modified meiosis may be re-used for oogenesis, which might result in unreduced, diploid eggs. Third, the particular species studied here regularly undergoes inbreeding by brother-sister mating within their hosts. Homozygosity, including at the sex determination locus (Engelstädter 2008), is therefore expected to have less negative effects in this species compared to many other, non-inbreeding haplodipoids (see also Little et al. 2017). This particular species may therefore be less affected by loss of heterozygosity, which occurs in a fashion similar to self-fertilization under many forms of non-clonal parthenogenesis. Indeed, the study also addresses the mechanisms underlying parthenogenesis in the species. Surprisingly, the authors find that parthenogenetically produced females are likely produced by two distinct genetic mechanisms. The first results in clonality (maintenance of the maternal genotype), whereas the second one results in a loss of heterozygosity towards the telomeres, likely due to crossovers occurring between the centromeres and the telomeres. Moreover, bacterial infections appear to affect the propensity of parthenogenesis but are unlikely the primary cause. Together, the finding suggests that parthenogenesis is a variable trait in the species, both in terms of frequency and mechanisms. It is not entirely clear to what degree this variation is heritable, but if it is, then these results constitute evidence for low-frequency existence of variable and heritable parthenogenesis phenotypes, that is, the raw material from which evolutionary transitions to more regular forms of parthenogenesis may occur.
References Archetti M (2010) Complementation, Genetic Conflict, and the Evolution of Sex and Recombination. Journal of Heredity, 101, S21–S33. https://doi.org/10.1093/jhered/esq009 Capdevielle Dulac C, Benoist R, Paquet S, Calatayud P-A, Obonyo J, Kaiser L, Mougel F (2022) Spontaneous parthenogenesis in the parasitoid wasp Cotesia typhae: low frequency anomaly or evolving process? bioRxiv, 2021.12.13.472356, ver. 6 peer-reviewed and recommended by Peer Community in Evolutionary Biology. https://doi.org/10.1101/2021.12.13.472356 Engelstädter J (2008) Constraints on the evolution of asexual reproduction. BioEssays, 30, 1138–1150. https://doi.org/10.1002/bies.20833 Ferree PM, Aldrich JC, Jing XA, Norwood CT, Van Schaick MR, Cheema MS, Ausió J, Gowen BE (2019) Spermatogenesis in haploid males of the jewel wasp Nasonia vitripennis. Scientific Reports, 9, 12194. https://doi.org/10.1038/s41598-019-48332-9 van der Kooi CJ, Matthey-Doret C, Schwander T (2017) Evolution and comparative ecology of parthenogenesis in haplodiploid arthropods. Evolution Letters, 1, 304–316. https://doi.org/10.1002/evl3.30 Lenormand T, Engelstädter J, Johnston SE, Wijnker E, Haag CR (2016) Evolutionary mysteries in meiosis. Philosophical Transactions of the Royal Society B: Biological Sciences, 371, 20160001. https://doi.org/10.1098/rstb.2016.0001 Little CJ, Chapuis M-P, Blondin L, Chapuis E, Jourdan-Pineau H (2017) Exploring the relationship between tychoparthenogenesis and inbreeding depression in the Desert Locust, Schistocerca gregaria. Ecology and Evolution, 7, 6003–6011. https://doi.org/10.1002/ece3.3103 Neiman M, Sharbel TF, Schwander T (2014) Genetic causes of transitions from sexual reproduction to asexuality in plants and animals. Journal of Evolutionary Biology, 27, 1346–1359. https://doi.org/10.1111/jeb.12357 Ryder OA, Thomas S, Judson JM, Romanov MN, Dandekar S, Papp JC, Sidak-Loftis LC, Walker K, Stalis IH, Mace M, Steiner CC, Chemnick LG (2021) Facultative Parthenogenesis in California Condors. Journal of Heredity, 112, 569–574. https://doi.org/10.1093/jhered/esab052 Schwander T, Vuilleumier S, Dubman J, Crespi BJ (2010) Positive feedback in the transition from sexual reproduction to parthenogenesis. Proceedings of the Royal Society B: Biological Sciences, 277, 1435–1442. https://doi.org/10.1098/rspb.2009.2113 Stalker HD (1954) Parthenogenesis in Drosophila. Genetics, 39, 4–34. https://doi.org/10.1093/genetics/39.1.4 Vorburger C (2014) Thelytoky and Sex Determination in the Hymenoptera: Mutual Constraints. Sexual Development, 8, 50–58. https://doi.org/10.1159/000356508 Watts PC, Buley KR, Sanderson S, Boardman W, Ciofi C, Gibson R (2006) Parthenogenesis in Komodo dragons. Nature, 444, 1021–1022. https://doi.org/10.1038/4441021a | Spontaneous parthenogenesis in the parasitoid wasp Cotesia typhae: low frequency anomaly or evolving process? | Claire Capdevielle Dulac, Romain Benoist, Sarah Paquet, Paul-André Calatayud, Julius Obonyo, Laure Kaiser, Florence Mougel | <p style="text-align: justify;">Hymenopterans are haplodiploids and unlike most other Arthropods they do not possess sexual chromosomes. Sex determination typically happens via the ploidy of individuals: haploids become males and diploids become f... | Evolutionary Ecology, Life History, Reproduction and Sex | Christoph Haag | 2021-12-16 15:25:16 | View | ||
01 Mar 2024
Rapid life-history evolution reinforces competitive asymmetry between invasive and resident speciesElodie Chapuis, Philippe Jarne, Patrice David https://doi.org/10.1101/2023.10.25.563987The evolution of a hobo snailRecommended by Ben Phillips based on reviews by David Reznick and 2 anonymous reviewersAt the very end of a paper entitled "Copepodology for the ornithologist" Hutchinson (1951) pointed out the possibility of 'fugitive species'. A fugitive species, said Hutchinson, is one that we would typically think of as competitively inferior. Wherever it happens to live it will eventually be overwhelmed by competition from another species. We would expect it to rapidly go extinct but for one reason: it happens to be a much better coloniser than the other species. Now all we need to explain its persistence is a dose of space and a little disturbance: a world in which there are occasional disturbances that cause local extinction of the dominant species. Now, argued Hutchinson, we have a recipe for persistence, albeit of a harried kind. As Hutchinson put it, fugitive species "are forever on the move, always becoming extinct in one locality as they succumb to competition, and always surviving as they reestablish themselves in some other locality." It is a fascinating idea, not just because it points to an interesting strategy, but also because it enriches our idea of competition: competition for space can be just as important as competition for time. Hutchinson's idea was independently discovered with the advent of metapopulation theory (Levins 1971; Slatkin 1974) and since then, of course, ecologists have gone looking, and they have unearthed many examples of species that could be said to have a fugitive lifestyle. These fugitive species are out there, but we don't often get to see them evolve. In their recent paper, Chapuis et al. (2024) make a convincing case that they have seen the evolution of a fugitive species. They catalog the arrival of an invasive freshwater snail on Guadeloupe in the Lesser Antilles, and they wonder what impact this snail's arrival might have on a native freshwater snail. This is a snail invasion, so it has been proceeding at a majestic pace, allowing the researchers to compare populations of the native snail that are completely naive to the invader with those that have been exposed to the invader for either a relatively short period (<20 generations) or longer periods (>20 generations). They undertook an extensive set of competition assays on these snails to find out which species were competitively superior and how the native species' competitive ability has evolved over time. Against naive populations of the native, the invasive snail turns out to be unequivocally the stronger competitor. (This makes sense; it probably wouldn't have been able to invade if it wasn't.) So what about populations of the native snail that have been exposed for longer, that have had time to adapt? Surprisingly these populations appear to have evolved to become even weaker competitors than they already were. So why is it that the native species has not simply been driven extinct? Drawing on their previous work on this system, the authors can explain this situation. The native species appears to be the better coloniser of new habitats. Thus, it appears that the arrival of the invasive species has pushed the native species into a different place along the competition-colonisation axis. It has sacrificed competitive ability in favour of becoming a better coloniser; it has become a fugitive species in its own backyard. This is a really nice empirical study. It is a large lab study, but one that makes careful sampling around a dynamic field situation. Thus, it is a lab study that informs an earlier body of fieldwork and so reveals a fascinating story about what is happening in the field. We are left not only with a particularly compelling example of character displacement towards a colonising phenotype but also with something a little less scientific: the image of a hobo snail, forever on the run, surviving in the spaces in between. References Chapuis E, Jarne P, David P (2024) Rapid life-history evolution reinforces competitive asymmetry between invasive and resident species. bioRxiv, 2023.10.25.563987, ver. 2 peer-reviewed and recommended by Peer Community in Evolutionary Biology. https://doi.org/10.1101/2023.10.25.563987 Hutchinson, G.E. (1951) Copepodology for the Ornithologist. Ecology 32: 571–77. https://doi.org/10.2307/1931746 Levins, R., and D. Culver. (1971) Regional Coexistence of Species and Competition between Rare Species. Proceedings of the National Academy of Sciences 68, no. 6: 1246–48. https://doi.org/10.1073/pnas.68.6.1246. Slatkin, Montgomery. (1974) Competition and Regional Coexistence. Ecology 55, no. 1: 128–34. https://doi.org/10.2307/1934625. | Rapid life-history evolution reinforces competitive asymmetry between invasive and resident species | Elodie Chapuis, Philippe Jarne, Patrice David | <p style="text-align: justify;">Biological invasions by phylogenetically and ecologically similar competitors pose an evolutionary challenge to native species. Cases of character displacement following invasions suggest that they can respond to th... | Evolutionary Ecology, Life History, Species interactions | Ben Phillips | 2023-10-26 15:49:33 | View | ||
20 Nov 2019
Distribution of iridescent colours in hummingbird communities results from the interplay between selection for camouflage and communicationHugo Gruson, Marianne Elias, Juan L. Parra, Christine Andraud, Serge Berthier, Claire Doutrelant, Doris Gomez https://doi.org/10.1101/586362Feathers iridescence sheds light on the assembly rules of humingbirds communitiesRecommended by Sébastien Lavergne based on reviews by 2 anonymous reviewersEcology needs rules stipulating how species distributions and ecological communities should be assembled along environmental gradients, but few rules have yet emerged in the ecological literature. The search of ecogeographical rules governing the spatial variation of birds colours has recently known an upsurge of interest in the litterature [1]. Most studies have, however, looked at pigmentary colours and not structural colours (e.g. iridescence), although it is know that color perception by animals (both birds and their predators) can be strongly influenced by light diffraction causing iridescence patterns on feathers. References [1] Delhey, K. (2019). A review of Gloger’s rule, an ecogeographical rule of colour: definitions, interpretations and evidence. Biological Reviews, 94(4), 1294–1316. doi: 10.1111/brv.12503 | Distribution of iridescent colours in hummingbird communities results from the interplay between selection for camouflage and communication | Hugo Gruson, Marianne Elias, Juan L. Parra, Christine Andraud, Serge Berthier, Claire Doutrelant, Doris Gomez | <p>Identification errors between closely related, co-occurring, species may lead to misdirected social interactions such as costly interbreeding or misdirected aggression. This selects for divergence in traits involved in species identification am... | Evolutionary Ecology, Macroevolution, Phylogeography & Biogeography, Sexual Selection, Species interactions | Sébastien Lavergne | 2019-03-29 17:23:20 | View | ||
13 Nov 2023
Color polymorphism and conspicuousness do not increase speciation rates in LacertidsThomas de Solan, Barry Sinervo, Philippe Geniez, Patrice David, Pierre-André Crochet https://doi.org/10.1101/2023.02.15.528678Colour polymorphism does not increase diversification rates in lizardsRecommended by Alejandro Gonzalez Voyer based on reviews by 2 anonymous reviewersThe striking differences in species richness among lineages in the Tree of Life have long attracted much research interest. In particular, researchers have asked whether certain traits are associated with greater diversification, with a particular focus on traits under sexual selection given their direct link to mating isolation. Polymorphism, defined as the presence of co-occurring, heritable morphs within a population, has been proposed to influence diversification rates although the effect has been proposed as both promoting or alternatively impeding speciation. The effect of polymorphism may be positive, that is facilitating speciation if polymorphism allows to broaden the ecological niche, thus enabling range expansion, or enabling maintenance of populations in variable environments. Specialized ectomorphs have been observed in several species (e.g. Kusche et al. 2015, Lattanzio and Miles 2016, Whitney et al. 2018, Scali et al. 2016). Polymorphism may also facilitate speciation if a morph is lost during the colonization of a novel area or niche, resulting in rapid divergence of the remaining morphs and reproductive isolation from the ancestral population, known as the morph speciation hypothesis (West-Eberhard 1986, Corl et al. 2010). On the other hand, polymorphism may hamper speciation through disassortative maintaining by morph, which may maintain the polymorphism through the speciation process (Jamie and Meier 2020). An example of such a process is Heliconius numata where disassortative mate preferences based on color hampers ecological speciation (Chouteau et al. 2017). Previous evidence in birds and lizards suggests polymorphism favors diversification (Corl et al. 2010b, 2012, Hugall and Stuart-Fox 2012, Brock et al. 2021). Here, de Solan et al. (2023) test the effect of polymorphism on diversification in Lacertidae, a family of lizards containing more than 300 species distributed across Europe, Africa and Asia. The group offers a good model system to test the effect of polymorphism on speciation as it contains several species with colour polymorphism, sometimes present in both sexes but restricted to males when present in the flank. Using coloration data from the literature as well as photographs of live specimens for 295 species the authors tested whether the presence of polymorphism is associated with higher diversification rates. While undertaking their project, another group independently tackled the same question (Brock et al. 2021), using the same model system but coming to very different conclusions. Therefore, de Solan et al. (2023) decided to also contrast their results with those of Brock et al. (2021) to determine the factors responsible for the contrasting results of both studies. The latter I consider one of the strengths of the work, given the careful re-analyses to determine the causes of the discrepancies between both studies. De Solan et al. (2023) found no association between the presence of polymorphism and diversification rates, even though they used different analytical approaches. Thus, this study is interesting as it provides results that do not support a positive effect of polymorphism on species richness. The use of a phylogeny with more limited species sampling (García-Porta et al. 2019) implied that the authors had to manually add 75 species, of which 17 were added to the tree based on information from previously published trees and 68 were added at random locations within the genus. To control for potential biases the authors repeated the analyses using a sample of trees with the imputed taxa, results were broadly concordant across the set of trees. The careful re-analysis contrasting Brock et al. (2021) and de Solan et al. (2023) results suggests the difference is mainly due to a difference in how species were coded as presenting polymorphism, which differed between the two studies, as well as a difference in the package version used to run the state-dependent diversification models. Interestingly non-parametric analyses yielded similar results across both datasets. Garcia-Porta, J., Irisarri, I., Kirchner, M. et al. 2019. Environmental temperatures shape thermal physiology as well as diversification and genome-wide substitution rates in lizards. Nature Communications. 10: 4077. https://doi.org/10.1038/s41467-019-11943-x de Solan T, Sinervo B, Geniez P, David P, Crochet P-A (2023) Colour polymorphism and conspicuousness do not increase speciation rates in Lacertids. bioRxiv, 2023.02.15.528678, ver. 2 peer-reviewed and recommended by Peer Community in Evolutionary Biology. https://doi.org/10.1101/2023.02.15.528678 West-Eberhard, M.J. 1986. Alternative adaptations, speciation, and phylogeny (A review). Proceedings of the National Academy of Sciences. 83: 1388-1392. https://doi.org/10.1073/pnas.83.5.1388 | Color polymorphism and conspicuousness do not increase speciation rates in Lacertids | Thomas de Solan, Barry Sinervo, Philippe Geniez, Patrice David, Pierre-André Crochet | <p style="text-align: justify;">Conspicuous body colors and color polymorphism have been hypothesized to increase rates of speciation. Conspicuous colors are evolutionary labile, and often involved in intraspecific sexual signaling and thus may pr... | Evolutionary Ecology, Macroevolution, Speciation | Alejandro Gonzalez Voyer | 2023-02-22 10:05:03 | View | ||
15 Feb 2019
Architectural traits constrain the evolution of unisexual flowers and sexual segregation within inflorescences: an interspecific approachRubén Torices, Ana Afonso, Arne A. Anderberg, José M. Gómez and Marcos Méndez https://doi.org/10.1101/356147Sometimes, sex is in the headRecommended by Juan Arroyo based on reviews by 3 anonymous reviewersPlants display an amazing diversity of reproductive strategies with and without sex. This diversity is particularly remarkable in flowering plants, as highlighted by Charles Darwin, who wrote several botanical books scrutinizing plant reproduction. One particularly influential work concerned floral variation [1]. Darwin recognized that flowers may present different forms within a single population, with or without sex specialization. The number of species concerned is small, but they display recurrent patterns, which made it possible for Darwin to invoke natural and sexual selection to explain them. Most of early evolutionary theory on the evolution of reproductive strategies was developed in the first half of the 20th century and was based on animals. However, the pioneering work by David Lloyd from the 1970s onwards excited interest in the diversity of plant sexual strategies as models for testing adaptive hypotheses and predicting reproductive outcomes [2]. The sex specialization of individual flowers and plants has since become one of the favorite topics of evolutionary biologists. However, attention has focused mostly on cases related to sex differentiation (dioecy and associated conditions [3]). Separate unisexual flower types on the same plant (monoecy and related cases, rendering the plant functionally hermaphroditic) have been much less studied, apart from their possible role in the evolution of dioecy [4] or their association with particular modes of pollination [5]. References [1] Darwin, C. (1877). The different forms of flowers on plants of the same species. John Murray. | Architectural traits constrain the evolution of unisexual flowers and sexual segregation within inflorescences: an interspecific approach | Rubén Torices, Ana Afonso, Arne A. Anderberg, José M. Gómez and Marcos Méndez | <p>Male and female unisexual flowers have repeatedly evolved from the ancestral bisexual flowers in different lineages of flowering plants. This sex specialization in different flowers often occurs within inflorescences. We hypothesize that inflor... | Evolutionary Ecology, Morphological Evolution, Phenotypic Plasticity, Reproduction and Sex, Sexual Selection | Juan Arroyo | Jana Vamosi, Marcial Escudero, Anonymous | 2018-06-27 10:49:52 | View | |
06 Oct 2022
Evolution of sperm morphology in a crustacean genus with fertilization inside an open brood pouch.Duneau, David; Moest, Markus; Ebert, Dieter https://doi.org/10.1101/2020.01.31.929414Evolution of sperm morphology in Daphnia within a phyologenetic contextRecommended by Ellen Decaestecker based on reviews by Renate Matzke-Karasz and 1 anonymous reviewerIn this study sperm morphology is studied in 15 Daphnia species and the morphological data are mapped on a Daphnia phylogeny. The authors found that despite the internal fertilization mode, Daphnia have among the smallest sperm recorded, as would be expected with external fertilization. The authors also conclude that increase in sperm length has evolved twice, that sperm encapsulation has been lost in a clade, and that this clade has very polymorphic sperm with long, and often numerous, filopodia. Daphnia is an interesting model to study sperm morphology because the biology of sexual reproduction is often ignored in (cyclical) parthenogenetic species. Daphnia is part of the very diverse and successful group of cladocerans with cyclical parthenogenetic reproduction. The success of this reproduction mode is reflected in the known 620 species that radiated within this order, this is more than half of the known Branchiopod species diversity and the estimated number of cladoceran species is even two to four times higher (Forró et al. 2008). Looking at this particular model with a good phylogeny and some particularity in the mode of fertilization/reproduction, has thus a large value. Most Daphnia species are cyclical parthenogenetic and switch between sexual and asexual reproduction depending on the environmental conditions. Within the genus Daphnia, evolution to obligate asexuality has evolved in at least four independent occasions by three different mechanisms: (i) obligate parthenogenesis through hybridisation with or without polyploidy, (ii) asexuality has been acquired de novo in some populations and (iii) in certain lineages females reproduce by obligate parthenogenesis, whereas the clonally propagated males produce functional haploid sperm that allows them to breed with sexual females of normal cyclically parthenogenetic lineages (more on this in Decaestecker et al. 2009). This study is made in the context of a body of research on the evolution of one of the most fundamental and taxonomically diverse cell types. There is surprisingly little known about the adaptive value underlying their morphology because it is very difficult to test this experimentally. Studying sperm morphology across species is interesting to study evolution itself because it is a "simple trait". As the authors state: The understanding of the adaptive value of sperm morphology, such as length and shape, remains largely incomplete (Lüpold & Pitnick, 2018). Based on phylogenetic analyses across the animal kingdom, the general rule seems to be that fertilization mode (i.e. whether eggs are fertilized within or outside the female) is a key predictor of sperm length (Kahrl et al., 2021). There is a trade-off between sperm number and length (Immler et al., 2011). This study reports on one of the smallest sperm recorded despite the fertilization being internal. The brood pouch in Daphnia is an interesting particularity as fertilisation occurs internally, but it is not disconnected from the environment. It is also remarkable that there are two independent evolution lines of sperm size in this group. It suggests that those traits have an adaptive value. References Decaestecker E, De Meester L, Mergeay J (2009) Cyclical Parthenogenesis in Daphnia: Sexual Versus Asexual Reproduction. In: Lost Sex: The Evolutionary Biology of Parthenogenesis (eds Schön I, Martens K, Dijk P), pp. 295–316. Springer Netherlands, Dordrecht. https://doi.org/10.1007/978-90-481-2770-2_15 Duneau David, Möst M, Ebert D (2022) Evolution of sperm morphology in a crustacean genus with fertilization inside an open brood pouch. bioRxiv, 2020.01.31.929414, ver. 4 peer-reviewed and recommended by Peer Community in Evolutionary Biology. https://doi.org/10.1101/2020.01.31.929414 Forró L, Korovchinsky NM, Kotov AA, Petrusek A (2008) Global diversity of cladocerans (Cladocera; Crustacea) in freshwater. Hydrobiologia, 595, 177–184. https://doi.org/10.1007/s10750-007-9013-5 Immler S, Pitnick S, Parker GA, Durrant KL, Lüpold S, Calhim S, Birkhead TR (2011) Resolving variation in the reproductive tradeoff between sperm size and number. Proceedings of the National Academy of Sciences, 108, 5325–5330. https://doi.org/10.1073/pnas.1009059108 Kahrl AF, Snook RR, Fitzpatrick JL (2021) Fertilization mode drives sperm length evolution across the animal tree of life. Nature Ecology & Evolution, 5, 1153–1164. https://doi.org/10.1038/s41559-021-01488-y Lüpold S, Pitnick S (2018) Sperm form and function: what do we know about the role of sexual selection? Reproduction, 155, R229–R243. https://doi.org/10.1530/REP-17-0536 | Evolution of sperm morphology in a crustacean genus with fertilization inside an open brood pouch. | Duneau, David; Moest, Markus; Ebert, Dieter | <p style="text-align: justify;">Sperm is the most fundamental male reproductive feature. It serves the fertilization of eggs and evolves under sexual selection. Two components of sperm are of particular interest, their number and their morphology.... | Evolutionary Ecology, Morphological Evolution, Reproduction and Sex, Sexual Selection | Ellen Decaestecker | 2020-05-30 22:54:15 | View | ||
13 Sep 2019
Deceptive combined effects of short allele dominance and stuttering: an example with Ixodes scapularis, the main vector of Lyme disease in the U.S.A.Thierry De Meeûs, Cynthia T. Chan, John M. Ludwig, Jean I. Tsao, Jaymin Patel, Jigar Bhagatwala, and Lorenza Beati https://doi.org/10.1101/622373New curation method for microsatellite markers improves population genetics analysesRecommended by Aurelien Tellier based on reviews by Eric Petit, Martin Husemann and 2 anonymous reviewersGenetic markers are used for in modern population genetics/genomics to uncover the past neutral and selective history of population and species. Besides Single Nucleotide Polymorphisms (SNPs) obtained from whole genome data, microsatellites (or Short Tandem Repeats, SSR) have been common markers of choice in numerous population genetics studies of non-model species with large sample sizes [1]. Microsatellites can be used to uncover and draw inference of the past population demography (e.g. expansion, decline, bottlenecks…), population split, population structure and gene flow, but also life history traits and modes of reproduction (e.g. [2,3]). These markers are widely used in conservation genetics [4] or to study parasites or disease vectors [5]. Microsatellites do show higher mutation rate than SNPs increasing, on the one hand, the statistical power to infer recent events (for example crop domestication, [2,3]), while, on the other hand, decreasing their statistical power over longer time scales due to homoplasy [6]. References [1] Jarne, P., and Lagoda, P. J. (1996). Microsatellites, from molecules to populations and back. Trends in ecology & evolution, 11(10), 424-429. doi: 10.1016/0169-5347(96)10049-5 | Deceptive combined effects of short allele dominance and stuttering: an example with Ixodes scapularis, the main vector of Lyme disease in the U.S.A. | Thierry De Meeûs, Cynthia T. Chan, John M. Ludwig, Jean I. Tsao, Jaymin Patel, Jigar Bhagatwala, and Lorenza Beati | <p>Null alleles, short allele dominance (SAD), and stuttering increase the perceived relative inbreeding of individuals and subpopulations as measured by Wright’s FIS and FST. Ascertainment bias, due to such amplifying problems are usually caused ... | Evolutionary Ecology, Other, Population Genetics / Genomics | Aurelien Tellier | 2019-05-02 20:52:08 | View | ||
12 Nov 2021
How ancient forest fragmentation and riparian connectivity generate high levels of genetic diversity in a micro-endemic Malagasy treeJordi Salmona, Axel Dresen, Anicet E. Ranaivoson, Sophie Manzi, Barbara Le Pors, Cynthia Hong-Wa, Jacqueline Razanatsoa, Nicole V. Andriaholinirina, Solofonirina Rasoloharijaona, Marie-Elodie Vavitsara, Guillaume Besnard https://doi.org/10.1101/2020.11.25.394544An ancient age of open-canopy landscapes in northern Madagascar? Evidence from the population genetic structure of a forest treeRecommended by Miguel de Navascués based on reviews by Katharina Budde and Yurena ArjonaWe currently live in the Anthropocene, the geological age characterized by a profound impact of human populations in the ecosystems and the environment. While there is little doubt about the action of humans in the shaping of present landscapes, it can be difficult to determine what the state of those landscapes was before humans started to modify them. This is the case of the Madagascar grasslands, whose origins have been debated with arguments proposing them either as anthropogenic, created with the arrival of humans around 2000BP, or as ancient features of the natural landscape with a forest fragmentation process due to environmental changes pre-dating human arrival [e.g. 1,2]. One way to clarify this question is through the genetic study of native species. Population continuity and fragmentation along time shape the structure of the genetic diversity in space. Species living in a uniform continuous habitat are expected to show genetic structuring determined only by geographical distance. Recent changes of the habitat can take many generations to reshape that genetic structure [3]. Thus, we expect genetic structure to reflect ancient features of the landscape. The work by Jordi Salmona and collaborators [4] studies the factors determining the population genetic structure of the Malagasy spiny olive (Noronhia spinifolia). This narrow endemic species is distributed in the discontinuous forest patches of the Loky-Manambato region (northern Madagascar). Jordi Salmona and collaborators genotyped 72 individuals distributed across the species distribution with restriction associated DNA sequencing and organelle microsatellite markers. Then, they studied the population genetic structure of the species. Using isolation-by-resistance models [5], they tested the influence of several landscape features (forest cover, roads, rivers, slope, etc.) on the connectivity between populations. Maternally inherited loci (chloroplast and mitochondria) and bi-parentally inherited loci (nuclear), were analysed separately in an attempt to identify the role of pollen and seed dispersal in the connectivity of populations. Despite the small distribution of the species, Jordi Salmona and collaborators [4] found remarkable levels of genetic diversity. The spatial structure of this diversity was found to be mainly explained by the forest cover of the landscape, suggesting that the landscape has been composed by patches of forests and grasslands for a long time. The main role of forest cover for the connectivity among populations also highlights the importance of riparian forest as dispersal corridors. Finally, differences between organelle and nuclear markers were not enough to establish any strong conclusion about the differences between pollen and seed dispersal. The results presented by Jordi Salmona and collaborators [4] contribute to the understanding of the history and ecology of understudied Madagascar ecosystems. Previous population genetic studies in some forest-dwelling mammals have been interpreted as supporting an old age for the fragmented landscapes in northern Madagascar [e.g. 1,6]. To my knowledge, this is the first study on a tree species. While this work might not completely settle the debate, it emphasizes the importance of studying a diversity of species to understand the biogeographic dynamics of a region. References 1. Quéméré, E., X. Amelot, J. Pierson, B. Crouau-Roy, L. Chikhi (2012) Genetic data suggest a natural prehuman origin of open habitats in northern Madagascar and question the deforestation narrative in this region. Proceedings of the National Academy of Sciences of the United States of | How ancient forest fragmentation and riparian connectivity generate high levels of genetic diversity in a micro-endemic Malagasy tree | Jordi Salmona, Axel Dresen, Anicet E. Ranaivoson, Sophie Manzi, Barbara Le Pors, Cynthia Hong-Wa, Jacqueline Razanatsoa, Nicole V. Andriaholinirina, Solofonirina Rasoloharijaona, Marie-Elodie Vavitsara, Guillaume Besnard | <p>Understanding landscape changes is central to predicting evolutionary trajectories and defining conservation practices. While human-driven deforestation is intense throughout Madagascar, exception in areas like the Loky-Manambato region (North)... | Evolutionary Ecology, Phylogeography & Biogeography, Population Genetics / Genomics | Miguel de Navascués | 2020-11-27 09:07:21 | View | ||
07 Nov 2019
New insights into the population genetics of partially clonal organisms: when seagrass data meet theoretical expectationsArnaud-Haond, Sophie, Stoeckel, Solenn, and Bailleul, Diane https://arxiv.org/abs/1902.10240v6Inferring rates of clonal versus sexual reproduction from population genetics dataRecommended by Olivier J Hardy based on reviews by Ludwig TRIEST, Stacy Krueger-Hadfield and 1 anonymous reviewerIn partially clonal organisms, genetic markers are often used to characterize the genotypic diversity of populations and infer thereof the relative importance of clonal versus sexual reproduction. Most studies report a measure of genotypic diversity based on a ratio, R, of the number of distinct multilocus genotypes over the sample size, and qualitatively interpret high / low R as indicating the prevalence of sexual / clonal reproduction. However, a theoretical framework allowing to quantify the relative rates of clonal versus sexual reproduction from genotypic diversity is still lacking, except using temporal sampling. Moreover, R is intrinsically highly dependent on sample size and sample design, while alternative measures of genotypic diversity are more robust to sample size, like D*, which is equivalent to the Gini-Simpson diversity index applied to multilocus genotypes. Another potential indicator of reproductive strategies is the inbreeding coefficient, Fis, because population genetics theory predicts that clonal reproduction should lead to negative Fis, at least when the sexual reproduction component occurs through random mating. Taking advantage of this prediction, Arnaud-Haond et al. [1] reanalysed genetic data from 165 populations of four partially clonal seagrass species sampled in a standardized way. They found positive correlations between Fis and both R and D* within each species, reflecting variation in the relative rates of sexual versus clonal reproduction among populations. Moreover, the differences of mean genotypic diversity and Fis values among species were also consistent with their known differences in reproductive strategies. Arnaud-Haond et al. [1] also conclude that previous works based on the interpretation of R generally lead to underestimate the prevalence of clonality in seagrasses. Arnaud-Haond et al. [1] confirm experimentally that Fis merits to be interpreted more properly than usually done when inferring rates of clonal reproduction from population genetics data of species reproducing both sexually and clonally. An advantage of Fis is that it is much less affected by sample size than R, and thus should be more reliable when comparing studies differing in sample design. Hence, when the rate of clonal reproduction becomes significant, we expect Fis < 0 and D* < 1. I expect these two indicators of clonality to be complementary because they rely on different consequences of clonality on pattern of genetic variation. Nevertheless, both measures can be affected by other factors. For example, null alleles, selfing or biparental inbreeding can pull Fis upwards, potentially eliminating the signature of clonal reproduction. Similarly, D* (and other measures of genotypic diversity) can be low because the polymorphism of the genetic markers used is too limited or because sexual reproduction often occurs through selfing, eventually resulting in highly similar homozygous genotypes. References [1] Arnaud-Haond, S., Stoeckel, S., and Bailleul, D. (2019). New insights into the population genetics of partially clonal organisms: when seagrass data meet theoretical expectations. ArXiv:1902.10240 [q-Bio], v6 peer-reviewed and recommended by Peer Community in Evolutionary Biology. Retrieved from http://arxiv.org/abs/1902.10240 | New insights into the population genetics of partially clonal organisms: when seagrass data meet theoretical expectations | Arnaud-Haond, Sophie, Stoeckel, Solenn, and Bailleul, Diane | <p>Seagrass meadows are among the most important coastal ecosystems, in terms of both spatial extent and ecosystem services, but they are also declining worldwide. Understanding the drivers of seagrass meadow dynamics is essential for designing so... | Evolutionary Ecology, Population Genetics / Genomics, Reproduction and Sex | Olivier J Hardy | 2019-03-01 21:57:34 | View |
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