Data_Sheet_5_The Waiting and Mating Game: Condition Dependent Mate Sampling in Female Gray Treefrogs (Hyla versicolor).PDF

Strong sexual selection by receivers can lead to the evolution of elaborate courtship behaviors in signalers. However the process by which receivers sample signalers and execute mate choice under complex signaling conditions—and thus the realized strength of sexual section—is poorly understood. Moreover, receivers can vary in condition, which can further influence mate sampling strategies. Using wild female frogs we tested two hypotheses at the intersection of these important problems: that some of the individual variation in mate sampling is explained by (1) the reproductive urgency hypothesis, which predicts that receivers in a more urgent reproductive state will sample mates less and/or (2) the reproductive investment hypothesis, which predicts that receivers that have invested less in the current reproductive effort will sample mates less. Eastern gray treefrogs, Hyla versicolor, were collected in amplexus and repeatedly tested for phonotaxis behavior using a dynamic playback assay. To evaluate if hormonal mechanisms explained variation in the mate sampling, three steroid hormones, estradiol, progesterone, and corticosterone, were collected using a noninvasive water-borne hormone assay, validated for this species in the present study. Finally, we measured clutch size (investment) and the duration of time required for each female to oviposit after being reunited with their male mate (urgency). We found repeatability in many of the behaviors, including mate sampling. We found that females with higher concentrations estradiol and corticosterone made quicker choices, and that females with higher progesterone sampled mates more. We also found that female frogs in a more urgent reproductive state had lower concentrations of progesterone and estradiol, thereby providing the first evidence of a relationship between gonadal hormones and reproductive urgency. Collectively we found some support for the reproductive urgency but not the investment hypothesis. Thus, even though a female frog's reproductive readiness is a highly transient life history stage, fine scale variation in her reproductive timeline could mitigate the strength of directional selection.

接收者强烈的性选择可能导致信号者进化出复杂的求偶行为。然而，接收者在复杂信号条件下的信号者样本选择过程以及由此产生的性选择强度，目前理解尚浅。此外，接收者的状态可能存在差异，这可能会进一步影响配偶采样策略。我们利用野生雌性青蛙，针对这些重要问题的交汇处提出了两个假设进行测试：一是配偶采样中的个体差异部分可以由（1）生殖紧迫性假设解释，该假设预测处于更紧迫的生殖状态下的接收者将减少配偶采样，或（2）生殖投资假设解释，该假设预测在当前生殖努力中投入较少的接收者将减少配偶采样。通过对东部灰树蛙（Hyla versicolor）的交配行为进行收集，并使用动态播放测试法对其音向性行为进行重复测试。为了评估激素机制是否解释了配偶采样中的变异，本研究采用了一种非侵入性水生激素测定法收集了三种类固醇激素：雌二醇、孕酮和皮质酮，并验证了该方法适用于本物种。最后，我们测量了卵巢大小（投资）以及每只雌蛙与其雄性配偶团聚后产卵所需的时间长度（紧迫性）。我们发现许多行为，包括配偶采样，都具有可重复性。我们发现雌二醇和皮质酮浓度较高的雌蛙做出选择的速度更快，而孕酮浓度较高的雌蛙配偶采样更多。我们还发现处于更紧迫生殖状态的雌蛙孕酮和雌二醇的浓度较低，从而提供了首个关于性腺激素与生殖紧迫性之间关系的证据。总体而言，我们发现对生殖紧迫性假设有一定的支持，但并非投资假设。因此，尽管雌性青蛙的生殖准备状态是一个高度短暂的生命史阶段，但其生殖时间表上的细微变化可能减轻方向性选择的强度。