Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) Observed Feeding on Chamaesaracha sp. in Eastern Colorado.

Egg, larval, and adult life stages of Colorado potato beetle, Leptinotarsa decemlineata (Say), were observed feeding on or attached to a previously undocumented host plant belonging to the genus Chamaesaracha in eastern Colorado on July 2017. At one site, L. decemlineata were more abundant on Chamaesaracha sp. than the accepted ancestral host plant, Solanum rostratum (Dunal). While future studies should confirm the ancestral status of the observed L. decemlineata and suitability of Chamaesaracha sp. for completion of development, our observations suggest a need for further characterization of the ancestral host range of L. decemlineata

Leptinotarsa decemlineata (Coleoptera: Chrysomelidae) Observed Feeding on Chamaesaracha sp. in Eastern Colorado.

Egg, larval, and adult life stages of Colorado potato beetle, Leptinotarsa decemlineata (Say), were observed feeding on or attached to a previously undocumented host plant belonging to the genus Chamaesaracha in eastern Colorado on July 2017. At one site, L. decemlineata were more abundant on Chamaesaracha sp. than the accepted ancestral host plant, Solanum rostratum (Dunal). While future studies should confirm the ancestral status of the observed L. decemlineata and suitability of Chamaesaracha sp. for completion of development, our observations suggest a need for further characterization of the ancestral host range of L. decemlineata

Sexual selection and hermaphroditism : quantitative empirical approach in the freshwater gastropod Physa acuta

La théorie de la sélection sexuelle a été largement élaborée à partir du constat de dimorphisme sexuel chez les espèces à sexes séparés. Une de ses caractéristiques générales est une sélection plus forte pour l'augmentation du nombre de partenaires sexuels chez les mâles que chez les femelles qui résulterait d'un investissement différentiel dans les descendants entre les deux sexes (anisogamie). Si hermaphrodisme et sélection sexuelle sont considérés comme compatibles depuis les travaux de Charnov (1979), les études sur le sujet restent rares que ce soit chez des animaux ou des plantes. Une raison importante est que la méthodologie disponible pour quantifier la sélection sexuelle ne prend pas en compte les particularités des hermaphrodites (par ex., corrélations ou effets croisés entre les deux fonctions sexuelles d'un même individu, autofécondation). Le premier objectif de cette thèse est de combler cette lacune méthodologique en proposant un cadre travail adapté aux hermaphrodites, que nous appliquons dans une étude empirique chez Physa acuta, un gastéropode hermaphrodite d'eau douce. Nous observons que la sélection sexuelle est plus intense sur la fonction mâle, comme généralement chez les espèces gonochoriques. Par ailleurs, nous ne détectons aucun effet des particularités des hermaphrodites dans cette expérience. Dans un deuxième temps, nous nous intéressons de manière plus détaillée aux composantes du succès reproducteur mâle (RSm). Nous montrons que chez P. acuta il existe une priorité spermatique au premier partenaire mâle lorsque plusieurs individus sont en compétition. Enfin, nous proposons une décomposition de la variance de RSm en ses composantes pré- et post-copulatoires, qui représentent respectivement 60 et 40% de la variance. Dans la troisième partie, nous intégrons la sélection sexuelle à l'étude de l'évolution de l'allocation sexuelle d'un hermaphrodite, via une approche d'évolution expérimentale chez P. acuta. Menée sur plus de 10 générations, elle vise à faire évoluer l'allocation sexuelle de manière disruptive (lignées mâle ou femelle) en sélectionnant les composantes mâle et femelle du succès reproducteur. Les résultats préliminaires suggèrent qu'il est possible de manipuler l'allocation sexuelle chez un hermaphrodite simultané en sélectionnant sur son régime d'appariement. Nous concluons que l'anisogamie suffit à justifier l'existence de la sélection sexuelle sans avoir à supposer un dimorphisme sexuel. Son étude chez les hermaphrodites simultanés ouvre des perspectives pour la compréhension du rôle de l'allocation sexuelle dans l'évolution des systèmes de reproduction.A cornerstone of the theory of sexual selection in gonochoric species is sexual dimorphism. A very general result is stronger selection on males than on females for increasing mating success, and this fundamentally relies on differential investment in offspring between the sexes (anisogamy). Although sexual selection does operate in hermaphroditic species as well, few empirical studies have been performed whether in animals or in plants. The main reason is that the current framework for studying sexual selection does not incorporate the particularities of hermaphrodites, including correlations or cross-sex effects between sex functions and self-fertilization. The first goal of this thesis is to fill this gap by proposing an appropriate framework for hermaphrodites (generalizing that available for gonochoric species). It was applied to approach sexual selection in the hermaphroditic freshwater gastropod Physa acuta. Sexual selection turns out to be stronger on the male than on the female function, as classically observed in gonochorists. Moreover, we do not detect any effect in relation to hermaphrodites' particularities. We then focus on the components of male reproductive success (RSm) in more details. We detect a pattern of sperm precedence in conditions of sperm competition. We develop a new method for decomposing the variance in RSm into pre- and post-copulatory components (representing 60 and 40% of the variance respectively). The third section aims at integrating sexual selection in studies of sex allocation and its evolution. It relies on a protocol of experimental evolution in P. acuta. Conducted over more than 10 generations. Its aim is to observe the evolution of sex allocation by disruptively selecting male and female components of reproductive success. Preliminary results indeed suggest that it is possible to manipulate sex allocation in a simultaneous hermaphrodite by manipulating its mating system. We conclude that anisogamy alone is a sufficient condition for sexual selection to proceed, and that sexual dimorphism is not required. Study sexual selection in simultaneous hermaphrodites gives insights for understanding the role of sex allocation in the evolution of mating systems

Data from: Disentangling precopulatory and postcopulatory sexual selection in polyandrous species

Sexual selection operates on a sequence of events, from mating to offspring production. Which stages in this sequence undergo stronger selection, especially the relative importance of pre- versus postcopulatory processes, are intensely debated issues. Unequal siring success among mates of polyandrous females is classically taken as evidence for a large contribution of postcopulatory processes to the variance in male reproductive success (var(RSm)). However paternity skews also depend on the timing and number of copulations, a source of variation that should be considered precopulatory rather than postcopulatory. We develop a method for decomposing var(RSm) accounting for copulatory activity and apply it to experimental mating groups of the snail Physa acuta. In our experiment, 40% of var(RSm) emerges at the precopulatory stage, only half of which depends on variation in mating success (number of partners). Ignoring copulation characteristics can therefore lead to severe underestimation of precopulatory sexual selection. Moreover, although only 36% of var(RSm) arises at the postcopulatory stage, this is when sexual selection on body weight mostly occurs. Finally, trade-offs were detected between different components of precopulatory success while pre- and postcopulatory success appear independent. Our study opens the way to a detailed quantitative understanding of sexual selection in polyandrous species

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Additive genetic variance for traits least related to fitness increases with environmental stress in the desert locust, Schistocerca gregaria

Under environmental stress, previously hidden additive genetic variation can be unmasked and exposed to selection. The amount of hidden variation is expected to be higher for life history traits, which strongly correlate to individual fitness, than for morphological traits, in which fitness effects are more ambiguous. However, no consensual pattern has been recovered yet, and this idea is still debated in the literature. Here, we hypothesize that the classical categorization of traits (i.e., life history and morphology) may fail to capture their proximity to fitness. In the desert locust, Schistocerca gregaria, a model organism for the study of insect polyphenism, we quantified changes in additive genetic variation elicited by lifetime thermal stress for ten traits, in which evolutionary significance is known. Irrespective of their category, traits under strong stabilizing selection showed genetic invariance with environmental stress, while traits more loosely associated with fitness showed a marked increase in additive genetic variation in the stressful environment. Furthermore, traits involved in adaptive phenotypic plasticity (growth compensation) showed either no change in additive genetic variance or a change of moderate magnitude across thermal environments. We interpret this mitigated response of plastic traits in the context of integrated evolution to adjust the entire phenotype in heterogeneous environments (i.e., adaptiveness of initial plasticity, compromise of phenotypic compensation with stress, and shared developmental pathway). Altogether, our results indicate, in agreement with theoretical expectations, that environmental stress can increase available additive genetic variance in some desert locust traits, but those closely linked to fitness are largely unaffected. Our study also highlights the importance of assessing the proximity to fitness of a trait on a case-by-case basis and in an ecologically relevant context, as well as considering the processes of canalization and plasticity, involved in the control of phenotypic variation

Data from: Extra molting and selection on nymphal growth in the desert locust

In insects, extra-molting has been viewed as a compensatory mechanism for nymphal growth that contributes to optimize body weight for successful reproduction. However, little is known on the capacity of extra-molting to evolve in natural populations, which limits our understanding of how selection acts on nymphal growth. We used a multi-generational pedigree, individual monitoring and quantitative genetics models to investigate the evolution of extra-molting and its impact on nymphal growth in a solitarious population of the desert locust, Schistocerca gregaria. Growth compensation via extra-molting was observed for 46% of the females, whose adult weight exceeded by 4% that of other females, at a cost of a 22% longer development time. We found a null heritability for body weight threshold only, and the highest and a strongly female-biased heritability for extra molting. Our genetic estimates show that (1) directional selection can act on growth rate, development time and extra-molting to optimize body weight threshold, the target of stabilizing selection, (2) extra-molting can evolve in natural populations, and (3) a genetic conflict, due to sexually antagonistic selection on extra-molting, might prevent its fixation. Finally, we discuss how antagonistic selection between solitarious and gregarious environments and/or genetic correlations between growth and phase traits might also impact the evolution of extra-molting in locusts

Data from: Reduced mate availability leads to evolution of self-fertilization and purging of inbreeding depression in a hermaphrodite

Basic models of mating-system evolution predict that hermaphroditic organisms should mostly either cross-fertilize, or self-fertilize, due to self-reinforcing coevolution of inbreeding depression and outcrossing rates. However transitions between mating systems occur. A plausible scenario for such transitions assumes that a decrease in pollinator or mate availability temporarily constrains outcrossing populations to self-fertilize as a reproductive assurance strategy. This should trigger a purge of inbreeding depression which in turn encourages individuals to self-fertilize more often and finally to reduce male allocation. We tested the predictions of this scenario using the freshwater snail Physa acuta, a self-compatible hermaphrodite that preferentially outcrosses and exhibits high inbreeding depression in natural populations. From an outbred population, we built two types of experimental evolution lines, controls (outcrossing every generation) and constrained lines (in which mates were often unavailable, forcing individuals to self-fertilize). After ca. twenty generations, individuals from constrained lines initiated self-fertilization earlier in life and had purged most of their inbreeding depression compared to controls. However, their male allocation remained unchanged. Our study suggests that the mating system can rapidly evolve as a response to reduced mating opportunities, supporting the reproductive assurance scenario of transitions from outcrossing to selfing