Prather Robert B, Shuster Stephen M
Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona, United States of America.
PLoS One. 2015 Dec 23;10(12):e0145681. doi: 10.1371/journal.pone.0145681. eCollection 2015.
Pea crabs, Dissodactylus primitivus, inhabit multiple echinoid (heart urchin) hosts. Male and female crabs move among hosts in search for mates, and both sexes mate multiple times, creating opportunities for post-copulatory sexual selection. For such selection to occur, only a fraction of the males who succeed in mating can also succeed in siring progeny. Jossart et al. 2014 used 4 microsatellite loci to document parentage and mating frequencies of both sexes in D. primitivus. From these data we identified the mean and variance in female offspring numbers, as well as the proportions of the female population that were gravid and not bearing offspring. We next identified the proportions of the male population who had (1) mated and sired offspring, (2) mated but failed to sire offspring, and (3) failed to mate altogether. We used these results to estimate the opportunity for selection on males and females in terms of mate numbers and offspring numbers, and estimated the sex difference in the opportunity for selection (i.e., the opportunity for sexual selection) using both forms of data. We then partitioned the total variance in male fitness into pre- and post-copulatory components and identified the fraction of the total opportunity for selection occurring in each context. Our results show that the opportunity for selection on each sex was of similar magnitude (0.69-0.98), consistent with this polyandrogynous mating system. We also found that 37% of the total opportunity for sexual selection on males occurred within the context of post-copulatory sexual selection. However, the fraction of the total opportunity for selection that was due to sexual selection, estimated using both mate numbers and offspring numbers, was 9% and 23% respectively. Thus, we further reduced our estimate of the opportunity for post-copulatory sexual selection in D. primitivus to less than 10% of the total opportunity for selection (0.37 of 0.09 and 0.23 = 0.03 and 0.09). Our results provide the first estimate of the maximum possible strength of post-copulatory sexual selection in crustaceans using this approach.
豌豆蟹（Dissodactylus primitivus）寄居于多种海胆类（心形海胆）宿主中。雄蟹和雌蟹在宿主之间移动以寻找配偶，并且两性都会多次交配，这为交配后的性选择创造了机会。要发生这种选择，只有一部分成功交配的雄性能够成功使雌性受孕并繁衍后代。乔萨特等人在2014年使用4个微卫星位点记录了原始豌豆蟹两性的亲代关系和交配频率。根据这些数据，我们确定了雌性后代数量的均值和方差，以及怀孕但未生育后代的雌性群体比例。接下来，我们确定了雄性群体中（1）已交配并成功繁衍后代、（2）已交配但未能成功繁衍后代以及（3）完全未能交配的比例。我们利用这些结果，从配偶数量和后代数量方面估计了雄性和雌性的选择机会，并使用这两种数据形式估计了选择机会的性别差异（即性选择机会）。然后，我们将雄性适合度的总方差划分为交配前和交配后两个部分，并确定了在每种情况下发生的总选择机会的比例。我们的结果表明，两性的选择机会大小相似（0.69 - 0.98）），这与这种多雄多雌的交配系统一致。我们还发现，雄性性选择的总机会中有37%发生在交配后的性选择背景下。然而，分别使用配偶数量和后代数量估计的、归因于性选择的总选择机会比例分别为9%和23%。因此，我们将原始豌豆蟹交配后性选择机会的估计值进一步降低至总选择机会的不到10%（0.37乘以0.09和0.23分别得到0.03和0.09）。我们的结果首次使用这种方法估计了甲壳类动物交配后性选择的最大可能强度。
