Dipartimento di Biologia Animale e dell'Uomo, Università di Torino, Via Accademia Albertina, 13, 10123 Torino, Italy.
Zoology (Jena). 2012 Dec;115(6):372-8. doi: 10.1016/j.zool.2012.04.006. Epub 2012 Sep 28.
In anurans, fecundity (clutch size) is the most important determinant of female reproductive success. We investigated three possible causes responsible for fecundity variation in female Italian treefrogs, Hyla intermedia, during four breeding seasons: (i) variation in morphological (body size and condition) and life-history (age) traits; (ii) variation in the tradeoff between the number and the size of eggs; (iii) seasonal effects and within-season differences in the timing of deposition. At the population level, we found no evidence for a tradeoff between the number and the size of eggs, because they both correlated positively with females' body size. Conversely, neither age nor post-spawning body condition showed any effect on female reproductive investment. Independent of body size, we found no evidence for variation in reproductive effort among different breeding seasons, but strong evidence for a decrease of clutch size and an increase of egg size with the advancing of a breeding season. To test for the functional significance of the observed temporal variation in allocation strategy, we carried out a rearing experiment in semi-natural conditions on a random sample of ten clutches. The experiment showed a negative effect of clutch size and a positive effect of egg size on both tadpole growth and developmental rates, suggesting that reproductive investment, although constrained by body size, can be adjusted by females to the time of deposition to increase the chances of offspring survival.
在有尾两栖类动物中，繁殖力（卵的数量）是决定雌性生殖成功的最重要因素。在四个繁殖季节中，我们研究了意大利树蛙（Hyla intermedia）的三个可能导致雌性繁殖力变化的原因：（i）形态（体型和状况）和生活史（年龄）特征的变化；（ii）卵的数量和大小之间权衡的变化；（iii）季节性效应以及产卵时间的年内差异。在种群水平上，我们没有发现卵的数量和大小之间存在权衡的证据，因为它们都与雌性的体型呈正相关。相反，年龄或产卵后身体状况都没有对雌性的生殖投资产生任何影响。独立于体型，我们没有发现不同繁殖季节之间生殖努力的变化，但有强烈的证据表明，随着繁殖季节的推进，卵的数量减少，卵的大小增加。为了检验所观察到的分配策略随时间变化的功能意义，我们在半自然条件下对随机抽取的十个卵进行了养殖实验。实验表明，卵的数量对幼体生长和发育速度有负面影响，而卵的大小则有积极影响，这表明生殖投资虽然受到体型的限制，但可以通过雌性根据产卵时间进行调整，以增加后代生存的机会。
