School of Marine and Atmospheric Science, Institute for Ocean Conservation Science, Stony Brook University, Stony Brook, NY 11794, USA.
Biol Lett. 2013 May 1;9(3):20130003. doi: 10.1098/rsbl.2013.0003. Print 2013 Jun 23.
Sand tiger sharks (Carcharias taurus) have an unusual mode of reproduction, whereby the first embryos in each of the paired uteri to reach a certain size ('hatchlings') consume all of their smaller siblings during gestation ('embryonic cannibalism' or EC). If females commonly mate with multiple males ('behavioural polyandry') then litters could initially have multiple sires. It is possible, however, that EC could exclude of all but one of these sires from producing offspring thus influencing the species genetic mating system ('genetic monogamy'). Here, we use microsatellite DNA profiling of mothers and their litters (n = 15, from two to nine embryos per litter) to quantify the frequency of behavioural and genetic polyandry in this system. We conservatively estimate that nine of the females we examined (60%) were behaviourally polyandrous. The genetic mating system was characterized by assessing sibling relationships between hatchlings and revealed only 40 per cent genetic polyandry (i.e. hatchlings were full siblings in 60% of litters). The discrepancy stemmed from three females that were initially fertilized by multiple males but only produced hatchlings with one of them. This reveals that males can be excluded even after fertilizing ova and that some instances of genetic monogamy in this population arise from the reduction in litter size by EC. More research is needed on how cryptic post-copulatory and post-zygotic processes contribute to determining paternity and bridging the behavioural and genetic mating systems of viviparous species.
沙虎鲨（Carcharias taurus）具有一种不同寻常的繁殖方式，即位于成对子宫中的第一批胚胎（“幼仔”）在妊娠期内会消耗所有比其小的兄弟姐妹（“胚胎同类相食”或 EC）。如果雌性通常与多个雄性交配（“行为多配性”），那么产仔最初可能会有多个父亲。然而，EC 可能会排除除一个父亲之外的所有父亲，使其无法繁殖后代，从而影响物种的遗传交配系统（“遗传一夫一妻制”）。在这里，我们使用母亲及其产仔（n = 15，每个产仔 2 到 9 个胚胎）的微卫星 DNA 分析来量化该系统中行为和遗传多配性的频率。我们保守估计，我们检查的 9 只雌性（60%）是行为上的多配性。遗传交配系统的特征是评估幼仔之间的兄弟姐妹关系，仅揭示了 40%的遗传多配性（即 60%的产仔中幼仔是全同胞）。这种差异源于最初由多个雄性受精但仅与其中一个雄性产生幼仔的三只雌性。这表明，即使在受精卵子后，雄性也可以被排除在外，而该种群中一些遗传一夫一妻制的实例是由于 EC 导致产仔数量减少所致。需要更多的研究来了解隐式的交配后和配子后过程如何影响亲权，并弥合有胎生动物的行为和遗传交配系统之间的差距。
