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THE FUNCTION OF FINE-SCALE SIGNAL TIMING STRATEGIES: SYNCHRONIZED CALLING IN STREAM BREEDING TREE FROGSHenry D Legett (8803115) 06 May 2020 (has links)
In dense mating
aggregations, such as insect and anuran choruses, signals produced at the same
time can overlap and interfere with one another, reducing the ability of
receivers to discriminate between individual signals. Thus, evolution by sexual
selection is expected to result in mating signal timing strategies that avoid
overlap. Patterns of signal alternation between competing males are commonly
observed in leks and choruses across taxa. In some species, however, signalers
instead deliberately overlap, or ‘synchronize’, their mating signals with
neighboring conspecifics. Given the assumed high cost of reduced mate
attraction when signals overlap, mating signal synchronization has remained an
evolutionary puzzle. Synchronization may be beneficial, however, if overlapping
signals reduce the attraction of nontarget receivers (predator avoidance
hypothesis). Synchronized signals could also constructively interfere,
increasing female attraction to the mating aggregation (the beacon effect
hypothesis). I investigate these functions of synchronized signaling in two
species of tree frogs that synchronize their mating calls: the pug-nosed tree
frog (<i>Smilisca sila</i>) and the Ryukyu Kajika frog (<i>Buergeria japonica</i>).
To examine the trade-offs imposed by call synchronization in each species, I
conduct a series of field and laboratory playback experiments on target (female
frogs) and nontarget (eavesdropping predators) receivers of frog calls. Results
from these experiments support both hypotheses, suggesting that synchronized
frog calls can reduce the attraction of predators and attract mates to the
chorus. In addition, I found reduced preferences for fine-scale call timings in
female <i>S. sila</i> and <i>B. japonica</i>, deviating from the expected
preferences observed in many other anuran and non-anuran species. Thus, while
males may enjoy multiple benefits from synchronized mating signals, relaxed
sexual selection for non-synchronous signals may be key to the evolution and
maintenance of mating signal synchrony.
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<strong>EVALUATING EFFECTS OF PERFLUORINATED ALKYL SUBSTANCES (PFAS) ON ANURAN LIPID HOMEOSTASIS THROUGH </strong><em><strong>XENOPUS LAEVIS </strong></em><strong>BODY & HEPATIC CONDITION</strong>Anna Grace Bushong (16612647) 18 July 2023 (has links)
<p> Per- and polyfluoroalkyl substances (PFAS) are a class of persistent environmental contaminants that have become ubiquitous, resulting in widespread exposure among humans and wildlife. Amphibians are regularly exposed in the field, making them susceptible to sublethal effects of PFAS exposure. In amphibians exposed to PFAS, deleterious effects have been observed, including reduction in body condition measured using the scaled mass index (SMI) and degraded hepatic condition, among others. PFAS may dysregulate lipid metabolism by altering signaling cascades regulated by peroxisome proliferator activated receptors (PPAR), but whether changes in energy stores can explain changes in amphibian SMI and/or hepatic condition remain underexplored. Since lipids are a critical energy reserve for anurans, understanding whether lipid metabolism is being perturbed is critical. The central objective of this thesis was to investigate the effect of PFAS on lipid homeostasis in <em>Xenopus laevis </em>tadpoles within the context of a PPAR mechanism of action (MOA), considering apical, molecular, and lipidomic endpoints. I conducted three studies: (a) a study to characterize SMI and the relative expression of the hepatic xPPARα/β/γ during metamorphosis, (b) a pharmaceutical exposure to assess the <em>in vivo</em> effects of xPPARα/β/γ agonism on hepatic gene expression for select downstream targets (<em>apoa5, fabp1, acox1, pck1</em>), and (c) a chronic PFAS exposure to investigate the effects of environmentally relevant concentrations (PFOS, PFHxS, PFOA, PFHxA at 0.5 ppb; binary mixture of PFOS:PFHxS at 1 ppb) on lipid homeostasis through apical endpoints (mass, snout vent length, SMI, hepatic condition), relative hepatic gene expression, and Multiple Reaction Monitoring (MRM) profiling of the hepatic lipidome for changes in relative class abundance. In study (a), I identified SMI and hepatic expression of <em>xPPARα/β/γ</em> is dynamic during late metamorphosis, indicating the potential for heightened susceptibility. However, in study (b), pharmaceutical agonists had no effect on <em>X. laevis</em> at high doses. For study (c), I did not observe effects on a majority of apical endpoints, including SMI, but detected a significant sex-specific reduction in hepatic condition for male<em> X. laevis</em> tadpoles exposed to single-chemical perfluorosulfonic acid (PFSA) treatments. For gene expression, I observed a transient downregulation for apolipoprotein-V (<em>apoa5</em>) at Nieuwkoop and Faber (NF) stage 62 for <em>X. laevis</em> tadpoles exposed to single-chemical perfluorocarboxylic acid (PFCA) treatments. Lipid profiling detected transient dysregulation of predominantly membrane lipids in-response to short-chain PFAS treatments at NF 58. Overall, our findings indicate PFAS may exert toxicity during anuran metamorphosis through multiple mechanisms of action (MOA) with sex-specific and developmental-stage specific outcomes.</p>
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