Genetic evidence for multiple paternity in the critically endangered Cuban crocodile (Crocodylus rhombifer)

Conservation strategies can be most effective when factors influencing the persistence of populations are well-understood, including aspects of reproductive biology such as mating system. Crocodylians have been traditionally associated with a polygynous mating system, with genetic studies revealing multiple paternity of clutches in several species. The endemic Cuban crocodile, Crocodylus rhombifer, is currently listed as Critically Endangered, and is one of the least understood crocodylian species in terms of its mating behavior. Here, we tested a hypothesis of multiple paternity in the Cuban crocodile by collecting genotypic data at nine microsatellite loci for 102 hatchlings from five nests sampled at the Zapata Swamp captive breeding facility and analyzing them in relation to data previously collected for 137 putative parents. All five nests showed evidence of multiple paternity based on the numbers of alleles per locus, with sibship analyses reconstructing all nests as having four to six full-sib family groups. Accordingly, mean pairwise relatedness values per nest ranged from 0.21 to 0.39, largely intermediate between theoretical expected values for half-siblings (0.25) and full-siblings (0.50). It is not possible to differentiate whether the multiple paternity of a nest was due to multiple matings during the same breeding season, or a result of sperm storage. Our results reveal that the C. rhombifer mating system is likely best characterized as promiscuous and suggest that the standard practice of enforcing a 1:2 sex ratio at the captive breeding facility should be altered in order to better maintain a demographically and genetically healthy ex situ population.

保育策略之成效显著，往往取决于对影响种群持续存在的因素的深入理解，其中包括繁殖生物学方面的诸多方面，如交配系统。鳄鱼类传统上被认为与一夫多妻的交配系统相关联，遗传学研究揭示了多种物种巢穴中存在多个父系。本地的古巴鳄（Crocodylus rhombifer）目前被列为濒危物种，就其交配行为而言，是鳄鱼类中研究最为匮乏的物种之一。在本研究中，我们通过对来自五个巢穴、在Zapata沼泽养殖场采集的102只幼鳄在九个微卫星位点上的基因型数据进行收集和分析，并将这些数据与之前收集的137个疑似父系的资料进行关联，以检验古巴鳄存在多个父系的假设。结果显示，基于每个位点的等位基因数量，所有五个巢穴均显示出多个父系的证据，同胞分析重建了所有巢穴均包含四至六个同父同母的家庭群体。因此，每个巢穴的平均成对相关系数值介于半同胞的理论预期值（0.25）和全同胞的理论预期值（0.50）之间。无法区分一个巢穴的多个父系是由于同一繁殖季节内的多次交配，还是由于精子储存的结果。我们的研究结果表明，C. rhombifer的交配系统很可能被描述为滥交性的，并建议应当改变在养殖场强制执行1:2性别比例的常规做法，以便更好地维持一个在种群学和遗传学上均健康的离体种群。