ECOLOGY AND EVOLUTION OF THE SEXUAL AND ASEXUAL TIMEMA STICK INSECTS

‘Reproduction’ is one of the key characteristic of life. Despite this, our knowledge of the evolution of reproductive systems is still incomplete. In particular, the reasons for why the vast majority of eukaryotes use sex, and thus take a complicated and costly detour to reproduction, when straightforward routes, such asexuality, are available, remains a central and largely unanswered question in evolutionary biology. The aim of my thesis is to contribute to the understanding of this evolutionary mystery, and for that I use stick insects of the genus Timema as a study system. This small group of herbivorous insects, endemic to Western United States is ideal for studying and comparing sexual and asexual reproduction as seven asexual lineages have been identified in this group, each with a sexual sister species, allowing us to make multiple independent comparisons between sexual and asexual lineages. The perhaps most broadly accepted theoretical argument is that sex allows selection to work efficiently, which would ultimately favor the adaptive potential of populations. My objective during this thesis was to test two theories directly related to this, but working each time in two successive steps: i) I started by clarifying the ecological and evolutionary aspects and mecanisms concerned by these theories in Timema focusing only on sexual species and thus independently of the reproductive mode, ii) and I then empirically tested these theories. Specifically, I first investigated whether sexuals are able to exploit more ecological niches than asexuals, which would give them an advantage in fluctuating or heterogeneous environments. From this first investigation, I overall found that sexual species are systematically using a larger portion of their environment than their asexual relatives, but I did not find this pattern regarding their intrinsic and physiologic abilities to use their environment. The reduced portion used by asexuals is thus likely a consequence of external and biotic interactions that affect asexuals more strongly than sexuals. I secondly aimed to empirically test if sex confer an advantage when the allele combinations that are favored by selection vary over time, as it is the case in context of coevolution with parasites. My work suggests that parasites are indeed contributing to the maintenance of sex in Timema. In the last part of the thesis, I finally present some preliminary results regarding new Timema populations that I discovered by chance, that feature unusual reproductive strategies with a mixture of sexual, asexual ad facultatively asexual individuals. These populations will be very profitable for future research concerning the evolution of reproduction in Timema. Overall this thesis work contributes to a better understanding of several aspects of the ecology and evolution of Timema stick insects in partiular, and more generally contribute to give novel insights in the understanding of the maintenance of sex in the living world. -- L’une des caractéristiques essentielles d’un être vivant est sa capacité à se reproduire. Malgré cela, notre connaissance et compréhension de l'évolution de la reproduction est encore très partielle. En particulier, les raisons pour lesquelles la grande majorité des eucaryotes utilise un mode de reproduction aussi compliqué et raffiné que le sexe, alors que des manières beaucoup plus simples de se reproduire existent reste une véritable enigme de la biologie évolutive. Le but de ma thèse est de contribuer à la résolution de ce mystère évolutif. Pour cela j’étudie les phasmes du genre Timema, un petit groupe d'insectes herbivores endémique de l'ouest des États-Unis. C’est un système d’étude idéal pour comparer les coûts et bénéfices de la reproduction sexuée et de la reproduction asexuée car sept lignées asexuées ont été identifiées au sein de ce groupe, chacune avec une espèce ancestrale soeur sexuée. Cela nous permet de faire des comparaisons indépendantes entre lignées sexuées et asexuées. L’un des arguments théoriques le plus largement proposé pour expliquer la prédominance du sexe, est qu’il permet à la sélection naturelle de fonctionner plus efficacement, ce qui favoriserait le potentiel adaptatif des populations. Au cours de cette thèse, j’avais pour objectif de tester deux théories s’incrivant dans ce contexte. J’ai travaillé en deux étapes successives : J’ai tout d'abord étudié et clarifié les aspects et processus écologiques et évolutifs concernés par ces théories chez les Timema en se concentrant exclusivement sur les expèces sexuées, et donc indépendemment du mode de reproduction, puis, dans un second temps, j’ai testé empiriquement ces théories. Premièrement, j’ai verifié si les sexués sont capables d'exploiter plus de niches écologiques que les asexués, ce qui leur confererait un avantage au sein des environnements fluctuants ou hétérogènes. J'ai trouvé que les espèces sexuées utilisent systématiquement une plus large portion de leur environnement que les espèces asexuées, mais je n’ai pas retrouvé un tel pattern en ce qui concerne leurs capacités intrinsèques et physiologiques à utiliser cet environnement. Cette utilisation de l’environnement réduite des asexués comparé aux sexués indique que les pressions externes et biotiques affectent plus fortement la capacité des asexués à exploiter leur environnement que celle des sexués. Deuxiemement, j'ai verifié empiriquement si le sexe confère un avantage lorsque les combinaisons d'allèles favorisées par la sélection varient au cours du temps, comme c’est le cas lors d’une coevolution hotes-parasites. Mon travail suggère que les pressions parasitaires contribuent effectivement au maintien du sexe chez leurs hotes Timema. Dans la dernière partie de cette thèse, je présente des résultats préliminaires concernant de nouvelles populations de Timema que j’ai découvert par chance au cours du doctorat. Ces populations ont des stratégies reproductives inhabituelles comprenant une mixture d’individus sexués et asexués, et seront très utiles lors des futures recherches concernant l'évolution de la reproduction. Dans l'ensemble, ma thèse contribue à une meilleure connaissance de l'écologie et de l'évolution des phasmes Timema, et contribue plus généralement à comprendre pourquoi le sexe est le mode de reproduction prédominant au sein du monde vivant

Data from: Evolutionary dynamics of specialisation in herbivorous stick insects

Understanding the evolutionary dynamics underlying herbivorous insect mega-diversity requires investigating the ability of insects to shift and adapt to different host plants. Feeding experiments with nine related stick insect species revealed that insects retain the ability to use ancestral host plants after shifting to novel hosts, with host plant shifts generating fundamental feeding niche expansions. These expansions were however not accompanied by expansions of the realized feeding niches, as species on novel hosts are generally ecologically specialized. For shifts from angiosperm to chemically challenging conifer hosts, generalist fundamental feeding niches even evolved jointly with strong host plant specialization, indicating that host plant specialization is not driven by constraints imposed by plant chemistry. By coupling analyses of plant chemical compounds, fundamental and ecological feeding niches in multiple insect species, we provide novel insights into the evolutionary dynamics of host range expansion and contraction in herbivorous insects

Secondary feeding experiment: Survival data for 3 Timema population fed with 3 novel plants

We performed a feeding experiment using 3 Timema populations from 3 different Timema species. We measured survival of multiple individuals from each of these populations, after feeding them during ten days with 3 plants (i.e., 3 feeding treatments: Rhus ovata (sumac), Baccharis pilularis (coyote), Artemisia californica (sage)) currently not used, to our knowledge, by stick insects of the Timema genus under natural conditions

Parathyroid hormone is associated with the LV mass after aortic valve replacement

Aims : LV hypertrophy (LVH) is frequent after aortic valve replacement (AVR) and is often associated with comorbidities, including hypertension, obesity, renal failure and prosthesis-patient mismatch (PPM). However, whether other biological mechanism(s) may participate to LVH after AVR is still unknown. Parathyroid hormone (PTH) may play a role in LVH. However, it is presently unknown whether PTH is associated with LVH in patients that have undergone an AVR. Methods : In this cross-sectional study, 195 patients have been investigated at a mean of 8±3.5 years following AVR. LV function and mass were evaluated by Doppler echocardiography. The plasma levels of PTH, 25-hydroxyvitamin D (25-OHD), calcium and phosphate were measured. Results : There were 102 (52%) patients with LVH after AVR. In univariate analyses, PTH blood level was associated with LV mass (LVMi) and LVH. After adjustment for other risk factors, elevated PTH remained associated with LVMi (p=0.003) and LVH (p=0.02). In turn, the blood levels of 25-OHD and the renal function (GFR) were independently and inversely related to the blood level of PTH. Conclusions : After AVR, the level of PTH is independently associated with LVH. In turn, the level of PTH is related with the renal function and the level of 25-OHD

Breaking down carnivores mixed diets using noninvasive sampling: exploitation of anthropogenic foods and preys by rural free-ranging domestic cats (<em>Felis silvestris catus</em>) revealed by DNA-based methods

International audienc

Circulating Lp-PLA2 is associated with high valvuloarterial impedance and low arterial compliance in patients with aortic valve bioprostheses

Background: We previously reported that plasma Lp-PLA2 was associated with aortic valve disease progression and degeneration of bioprostheses. Low systemic arterial compliance and high valvuloarterial impedance (Zva) are predictors of poor survival in patients with aortic valve disease. However, the prevalence of high Zva after AVR is largely unknown and whether Lp-PLA2 could predict Zva has not been documented. We investigated the relationships between plasma lipoprotein-associated phospholipase A2 (Lp-PLA2) mass and activity and valvuloarterial impedance (Zva), an index of global LV hemodynamic load, in patients that underwent aortic valve replacement (AVR). Methods: A total of 195 patients with aortic bioprostheses underwent echocardiographic assessment of the prosthetic aortic valve function 8 ± 3.4 years after AVR. Lp-PLA2 mass and activity were measured. Results: In this group of patients, the mean Zvawas elevated (5.73±1.21mmHg·ml-1·m2). In univariate analyses, Lp-PLA2 mass (p=0.003) and Lp-PLA2 activity (p=0.046) were associated with Zva. After adjustment for covariates including age, gender, clinical risk factors, anti-hypertensive medications, body mass index and prosthesis size, Lp-PLA2 mass was associatedwith high Zva (=4.5mmHg·ml-1·m2) (OR: 1.29, 95%CI: 1.10–1.53; p= 0.005) and was inversely related with the systemic arterial compliance (ß =-0.01, SEM=0.003; p=0.003). Conclusions: An increased Zva, an index of excessive hemodynamic load, was highly prevalent 8-year post-AVR and was independently related to circulating Lp-PLA2

Association between plasma lipoprotein levels and bioprosthetic valve structural degeneration

Introduction: Structural valve degeneration (SVD) leads to the failure of aortic valve bioprostheses. It is suspected that lipid-derived factors could play a role in SVD. We hypothesised that oxidised low-density lipoprotein (OxLDL), OxLDL/LDL, OxLDL/high-density lipoprotein (OxLDL/HDL) and proprotein convertase subtilisin/kexin 9 (PCSK9) may be associated with SVD. Methods: We included 199 patients who underwent an aortic valve replacement with a bioprosthesis and had an echocardiography follow-up to evaluate the function of the prosthesis. SVD was defined as an increase in mean transprosthetic gradient (=10 mm Hg) or a worsening of transprosthetic regurgitation (=1/3) during the follow-up. Results: After a mean follow-up of 8±3.5 years, 41(21%) patients developed SVD. The univariate predictors of SVD were LDL (p=0.03), apolipoprotein B (p=0.01), OxLDL (p=0.02), OxLDL/HDL (p=0.009) and LDL associated with small, dense particles (LDL-C<255Å) (p=0.02). In a model adjusted for covariates, only OxLDL/HDL (OR 1.49, 95%CI 1.08 to 2.07 per 10 units, p=0.01) remained associated with SVD. There was a significant interaction between OxLDL/HDL and PCSK9 on SVD (p=0.05). After adjustment, compared with patients with low OxLDL/HDL (median, <25.4) and low PCSK9 (median, <298 ng/mL) (referent), patients with both an elevated OxLDL/HDL ratio and PCSK9 had a higher risk of SVD (OR 2.93, 95% CI 1.02 to 9.29, p=0.04). Conclusions: OxLDL/HDL ratio is independently associated with SVD