20 research outputs found
ECOLOGY AND EVOLUTION OF THE SEXUAL AND ASEXUAL TIMEMA STICK INSECTS
âReproductionâ 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.
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Lâune des caractĂ©ristiques essentielles dâun ĂȘtre vivant est sa capacitĂ© Ă se reproduire. MalgrĂ© cela, notre connaissance et comprĂ©hension de l'Ă©volution de la reproduction est encore trĂšs partielle. En particulier, les raisons pour lesquelles la grande majoritĂ© des eucaryotes utilise un mode de reproduction aussi compliquĂ© et raffinĂ© que le sexe, alors que des maniĂšres beaucoup plus simples de se reproduire existent reste une vĂ©ritable enigme de la biologie Ă©volutive. Le but de ma thĂšse est de contribuer Ă la rĂ©solution de ce mystĂšre Ă©volutif. Pour cela jâĂ©tudie les phasmes du genre Timema, un petit groupe d'insectes herbivores endĂ©mique de l'ouest des Ătats-Unis. Câest un systĂšme dâĂ©tude idĂ©al pour comparer les coĂ»ts et bĂ©nĂ©fices de la reproduction sexuĂ©e et de la reproduction asexuĂ©e car sept lignĂ©es asexuĂ©es ont Ă©tĂ© identifiĂ©es au sein de ce groupe, chacune avec une espĂšce ancestrale soeur sexuĂ©e. Cela nous permet de faire des comparaisons indĂ©pendantes entre lignĂ©es sexuĂ©es et asexuĂ©es.
Lâun des arguments thĂ©oriques le plus largement proposĂ© pour expliquer la prĂ©dominance du sexe, est quâil permet Ă la sĂ©lection naturelle de fonctionner plus efficacement, ce qui favoriserait le potentiel adaptatif des populations. Au cours de cette thĂšse, jâavais pour objectif de tester deux thĂ©ories sâincrivant dans ce contexte. Jâai travaillĂ© en deux Ă©tapes successives : Jâai tout d'abord Ă©tudiĂ© et clarifiĂ© les aspects et processus Ă©cologiques et Ă©volutifs concernĂ©s par ces thĂ©ories chez les Timema en se concentrant exclusivement sur les expĂšces sexuĂ©es, et donc indĂ©pendemment du mode de reproduction, puis, dans un second temps, jâai testĂ© empiriquement ces thĂ©ories. PremiĂšrement, jâai verifiĂ© si les sexuĂ©s sont capables d'exploiter plus de niches Ă©cologiques que les asexuĂ©s, ce qui leur confererait un avantage au sein des environnements fluctuants ou hĂ©tĂ©rogĂšnes. J'ai trouvĂ© que les espĂšces sexuĂ©es utilisent systĂ©matiquement une plus large portion de leur environnement que les espĂšces asexuĂ©es, mais je nâai pas retrouvĂ© un tel pattern en ce qui concerne leurs capacitĂ©s intrinsĂšques et physiologiques Ă utiliser cet environnement. Cette utilisation de lâenvironnement rĂ©duite des asexuĂ©s comparĂ© aux sexuĂ©s indique que les pressions externes et biotiques affectent plus fortement la capacitĂ© des asexuĂ©s Ă exploiter leur environnement que celle des sexuĂ©s. Deuxiemement, j'ai verifiĂ© empiriquement si le sexe confĂšre un avantage lorsque les combinaisons d'allĂšles favorisĂ©es par la sĂ©lection varient au cours du temps, comme câest le cas lors dâune coevolution hotes-parasites. Mon travail suggĂšre que les pressions parasitaires contribuent effectivement au maintien du sexe chez leurs hotes Timema. Dans la derniĂšre partie de cette thĂšse, je prĂ©sente des rĂ©sultats prĂ©liminaires concernant de nouvelles populations de Timema que jâai dĂ©couvert par chance au cours du doctorat. Ces populations ont des stratĂ©gies reproductives inhabituelles comprenant une mixture dâindividus sexuĂ©s et asexuĂ©s, et seront trĂšs utiles lors des futures recherches concernant l'Ă©volution de la reproduction. Dans l'ensemble, ma thĂšse contribue Ă une meilleure connaissance de l'Ă©cologie et de l'Ă©volution des phasmes Timema, et contribue plus gĂ©nĂ©ralement Ă comprendre pourquoi le sexe est le mode de reproduction prĂ©dominant au sein du monde vivant
Facultative parthenogenesis: a transient state in transitions between sex and obligate asexuality in stick insects?
Facultative parthenogenesis: a transient state in transitions between sex and obligate asexuality in stick insects?
Facultative parthenogenesis: a transient state in transitions between sex and obligate asexuality in stick insects?
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: 1.10â1.53; p=
0.005) and was inversely related with the systemic arterial compliance (Ă =-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<255Ă
) (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