Data from: Facultative parthenogenesis in a critically endangered wild vertebrate

Facultative parthenogenesis — the ability of sexually reproducing species to sometimes produce offspring asexually — is known from a wide range of ordinarily sexually reproducing vertebrates in captivity, including some birds, reptiles and sharks 1, 2 and 3. Despite this, free-living parthenogens have never been observed in any of these taxa in the wild, although two free-living snakes were recently discovered each gestating a single parthenogen — one copperhead (Agkistrodon contortrix) and one cottonmouth (Agkistrodon piscivorus). Vertebrate parthenogens are characterized as being of the homogametic sex (e.g., females in sharks, males in birds) and by having elevated homozygosity compared to their mother 1, 2 and 3, which may reduce their viability. Although it is unknown if either of the parthenogenetic snakes would have been carried to term or survived in the wild, facultative parthenogenesis might have adaptive significance. If this is true, it is reasonable to hypothesize that parthenogenesis would be found most often at low population density, when females risk reproductive failure because finding mates is difficult. Here, we document the first examples of viable parthenogens living in a normally sexually reproducing wild vertebrate, the smalltooth sawfish (Pristis pectinata). We also provide a simple approach to screen any microsatellite DNA database for parthenogens, which will enable hypothesis-driven research on the significance of vertebrate parthenogenesis in the wild.

兼性孤雌生殖（facultative parthenogenesis），即有性生殖物种偶尔可通过无性方式产生后代的能力，目前已在多种圈养的常规有性繁殖脊椎动物中被发现，包括部分鸟类、爬行类及鲨类[1,2,3]。尽管如此，此前从未在野外的上述类群中观测到自由生活的孤雌个体；不过近期有研究发现两条野生蛇类各自怀有一枚孤雌生殖后代——分别为铜头蝮（Agkistrodon contortrix）与棉口蝮（Agkistrodon piscivorus）。脊椎动物的孤雌个体具有两类典型特征：一是为同型配子性别（例如鲨类为雌性，鸟类为雄性）；二是相较于母体，其纯合性显著升高[1,2,3]，这一特征可能会降低个体的生存活力。目前尚不清楚这两条孤雌生殖的蛇类能否顺利足月分娩并在野外存活，但兼性孤雌生殖或许具有适应性意义。若这一推论成立，则可合理提出假说：当种群密度较低、雌性因难以寻觅配偶而面临繁殖失败风险时，孤雌生殖现象会更为常见。本研究首次记录了在常规有性繁殖的野生脊椎动物——栉齿锯鳐（Pristis pectinata）中存活的孤雌个体实例。此外，本研究还提供了一种简便方法，可从任意微卫星DNA数据库中筛选孤雌个体，这将推动针对野外脊椎动物孤雌生殖意义的假说驱动型研究。