The Manila clam (Ruditapes philippinarum) was introduced in Europe in the 1970's and in the following years it became naturalized. Interactions with the native species include hybridization with the grooved carpet-shell (GCS) clam (R. decussatus), which may have both useful and undesirable consequences. Here we report an attempt to produce hybrids in captivity by crossing 3 females and 4–5 males of each species in a two-step protocol that favored hybrid fertilizations. One-hundred animals were sampled at 15 months after fertilization, and scored for one morphological diagnostic trait (siphon fusion) and two diagnostic genetic DNA markers (ITS-2 and Fas-i1). No hybrids were detected, although the 0% hybridization rate has an associated 95% confidence interval of 3.3%. This result suggests that successful hybrid fertilization may be infrequent and/or the hybrid offspring may have very low survival rate. Abundant offspring of the two parental species were obtained and provided an unprecedented opportunity to study the innate differences in biological traits between the two species without the confounding influence of environmental variability. Individuals with ripe gonads were significantly less frequent in the Manila clam, suggesting an innate trend to earlier summer spawning in this species. Manila clam grew 20% faster than GCS clam and showed 80% heavier shells. However GCS clam showed almost twice as much variability in size as Manila clam, and some individuals of this species were as large as the largest Manila clams. The observed difference in growth variability may reflect a general loss of genetic variability in Manila clam during the introduction in Europe, although a random effect from using a small number of parents in the mixed cross cannot be discarded. Discrimination between these explanations, as well as determining more precisely the occurrence of hybridization in hatcheries by studying larger numbers of parents and offspring, may help improving clam aquaculture in Europe while preserving the genetic resources of the GCS clam.

马尼拉蛤（（Ruditapes philippinarum）于1970年代在欧洲引入，并在随后的几年里被归化。与本地物种的相互作用包括与开沟的地毯壳（GCS）蛤（R. decussatus）杂交。），可能会同时产生有益和不利的后果。在这里，我们报告了通过有利于杂交受精的两步操作方法，通过杂交每个物种的3头雌性和4-5雄性来繁殖人工繁殖的尝试。受精后15个月对一百只动物进行采样，并对一种形态学诊断性状（虹吸融合）和两种诊断性遗传DNA标记（ITS-2和Fas-i1）进行评分。尽管杂交率为0％，但关联的95％置信区间为3.3％，但未检测到杂种。该结果表明成功的杂交受精可能很少，和/或杂交后代的存活率可能非常低。获得了两个亲本物种的丰富后代，并提供了前所未有的机会来研究两个物种之间生物学特性的先天差异，而不会受到环境可变性的混杂影响。成熟的性腺个体在马尼拉蛤中的发生频率明显降低，表明该物种早夏产卵的先天趋势。马尼拉蛤的生长速度比GCS蛤快20％，壳重达80％。然而，GCS蛤的大小变异性几乎是马尼拉蛤的两倍，并且该物种的某些个体与最大的马尼拉蛤一样大。在欧洲引进马尼拉蛤时，观察到的生长变异性差异可能反映了马尼拉蛤的遗传变异性普遍丧失，尽管在混合杂交中使用少量父母产生的随机效应不能被丢弃。这些解释之间的区别以及通过研究大量父母和后代来更精确地确定孵化场中杂交的发生，可能有助于改善欧洲的蛤类水产养殖，同时保留GCS蛤类的遗传资源。