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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…

Advisors/Committee Members: David, Patrice (thesis director), Jarne, Philippe (thesis director).

▼ Current insights into general animal biology, including immune function, are derived mostly from a few model organisms, a necessity imposed by effort required for in-depth studies. Modern next-generation sequencing (NGS) enables genomics-level investigations to test whether specific aspects of biology are general or unique across animal phylogeny. Meaningful comparisons require thorough identification of phylogenetically-relevant species. To provide a touchstone for Biomphalaria glabrata, a freshwater snail that is a major study model for invertebrate immunity, physid snails (Physidae; Hygrophila; Panpulmonata; Gastropoda; Mollusca) will be developed as a model for comparative immunogenomics. Chapter 1 introduces current research capabilities and details the rationale behind developing a physid as a comparative model for B. glabrata. Chapter 2, submitted as a manuscript to the Journal of Molluscan Studies, describes the molecular characterization that was performed for species identification and confirms taxonomic placement of physid snails relative to B. glabrata. Comparative mitogenomics revealed high levels of intraspecific sequence divergence between the entire mitochondrial genomes of the two P. acuta isolates, identified a unique gene order, and compared substitutions rates of gene sequences from the mitochondrial genomes of other gastropods. Additional materials are provided in the Appendices; Appendix A provides supplemental information for Chapter 2 and Appendix B provides a report of preliminary results from NGS-based gene discovery for initial characterization of the immune response of P. acuta to bacterial exposure toward comparative immunogenomics. Results from this thesis support continuing efforts to develop P. acuta as a comparative immunogenomic model to B. glabrata. Advisors/Committee Members: Adema, Dr. Coenraad M., Stricker, Dr. Stephen, Takacs-Vesbach, Dr. Cristina.

▼ In urban areas, features such as high percentages of impervious ground cover, patchiness, and storm water runoff can lead to increases in temperature and external nutrient input into aquatic systems. Such factors can lead to changes in primary productivity, and thus the growth rates of primary consumers, as well as the vulnerability of primary consumers to predation. Additionally, isolated populations due to patchiness of natural areas in urban environments can lead to inbred populations, which can also influence growth rates and vulnerability of primary consumers. To assess how such factors can influence interspecific interactions, we test how temperature, resource availability, and standing genetic variation of the freshwater snail Physa acuta affects the snail's anti-predator responses and life history characteristics. We conducted an experiment in which we reared snails from inbred or wild-caught lineages at high or low temperatures, with high and low resource inputs, and with or without chemical cues of crayfish (Procambarus clarkii) predation. We assessed how these treatments affected predator avoidance behavior, anti-predator morphological responses, reproductive output, and survival. We found that snails reared in high temperatures, and with low resource availability were unable to exhibit typical morphological responses to predators. We also found that snails were more likely to exhibit anti-predator behaviors when resource availability was low and when temperatures were high, and that behavioral responses to predators were higher for inbred snails than wild-caught snails. Snail survival was significantly affected by temperature, resource availability, and standing genetic variation. Reproductive output of snails was also affected by temperature, resource availability, predator cue presence, and standing genetic variation. These results indicate that features common in urban systems can influence not only individuals' ability to persist in these environments, but also can have effects on species interactions in ways that can cascade through food webs and potentially change ecosystem functions. Advisors/Committee Members: McCoy, Michael W. (advisor).

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Monthly and forthnightly samplings were taken between April 1989 and November 1991 for the study of biology and population dynamics of freshwater pulmonate gastropods in lake Kerkini. The study was carried out in the old river bed of Strymonas river, in the northern part of the lake, where three different pulmonate species coexisted, P. acuta, L. stagnalis and L. auricularia. The seasonal variation of the water temperature in the lake was the same throughout the three years of the study. Dissolved oxygen in the water, during 1991 ranged between 2 and 8 mg/ l reaching the lowest values in the summer and the highest in autumn. pH values ranged between 7.25 and 9.5 and conductivity between 250 and 480 μs/cm. . Total hardness values ranged between 80 and 250 mg CaCO3/ l , therefore water can be characterized as medium hard to hard. Variation was noted in the concentration of orthophosphate (from 0.01 to 0.10 mg/ l) and chloride (from 3 to 17.9 mg/ l) in the water during 1991, while the highest values in both cases appeared in summer and autumn. In the present study a quantitative sampler was used for plant and pulmonate samples from different depths. The abudance of the three pulmonate species was estimated in relation to the water volume at different water depths, as well as their horizontal and vertical distribution. Seasonal variation of the relative distribution by λ2 index showed that spatial distribution of all three species appeared contagious on water surface with the exception of early spring for L. stagnalis. For the later species more samples appeared with a random distribution in relation to water depth. The distribution of L. stagnalis and L. auricularia was contagious on the water surface but random in the deeper layers.

Στο χρονικό διάστημα Aπρίλιος 1989 - Nοέμβριος 1991 πραγματοποιήθηκαν δεκαπενθήμερες και μηνιαίες δειγματοληψίες για τη μελέτη της βιολογίας και της δυναμικής των πληθυσμών των πνευμονοφόρων γαστεροπόδων της λίμνης Kερκίνης. H έρευνα έγινε στην παλιά κοίτη του ποταμού Στρυμώνα στο βόρειο τμήμα της λίμνης όπου συνυπήρχαν τρία είδη πνευμονοφόρων : η P. acuta η L. stagnalis και η L. auricularia. H εποχική διακύμανση της θερμοκρασίας του νερού της λίμνης ήταν όμοια και τα 3 χρόνια της μελέτης. Tο διαλυμένο στο νερό O2 στη διάρκεια του 1991 κυμάνθηκε από 2 έως 8 mg/ l με τις χαμηλότερες τιμές να εμφανίζονται το καλοκαίρι και τις υψηλότερες την άνοιξη και το φθινόπωρο. Tο pH κυμάνθηκε από 7.25 έως 9.5 και η αγωγιμότητα του νερού από 250 έως 480 μs/cm. Oι τιμές της ολικής σκληρότητας του νερού κυμάνθηκαν από 80 έως 250 mg CaCO3/ l και έτσι τα νερά χαρακτηρίστηκαν απο μετρίως σκληρά έως σκληρά. Στη διάρκεια του 1991 καταγράφηκε έντονη μεταβολή της περιεκτικότητας του νερού σε ορθοφωσφορικά (από 0.01 έως 0.10 mg/ l) και σε ιόντα χλωρίου (από 3 έως 17.9 mg/ l), ενώ οι υψηλότερες τιμές και στις δυο περιπτώσεις εμφανίστηκαν το καλοκαίρι. Στην παρούσα μελέτη χρησιμοποιήθηκε ποσοτικός δειγματολήπτης για λήψη δειγμάτων υδρόβιων φυτών και πνευμονοφόρων γαστεροπόδων παρέχοντας τη δυνατότητα για…