ISOLATING MECHANISM IN THREESPINE STICKLEBACKS (GASTEROSTEUS)
ISOLATING MECHANISM IN THREESPINE STICKLEBACKS (GASTEROSTEUS)
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DOI：
10.1139/f67-138
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发表时间：
1967-01-01
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影响因子：
--
通讯作者：
HAGEN, DW
中科院分区：
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作者：
HAGEN, DW
一个系统的检查隔离机制，所载的迈尔，这可能有助于保持生殖隔离之间的海洋（trachurus）和淡水（leiurus）threespine刺鱼。多年来，在小坎贝尔河这条不列颠哥伦比亚省的一条小型沿海河流中进行了实地工作，并辅以实验室实验。其他溪流也是在调查的后期才被纳入。Leiurus永远占据着溪流的上游; Trachurus是溯河产卵的，进入下游在淡水中繁殖。在这两个繁殖地之间，两者的数量都大大减少，杂交发生了。但仅限于一个狭窄的区域。这两个物种很容易区分。因此，形态分析提供了坚定的旁证，杂种是丰富的，回交发生，主要toleiurus。通过在实验室中在统一条件下饲养后代来证实杂交，所有组合都是杂交的。这样的后代也被用来证明leiurusandtrachurus. Behavioral实验表明，行为隔离和杂交表现正常的情况下，相当大的遗传分歧（其中大部分是多基因的）leiurusandtrachurus. Behavioral实验表明，没有行为隔离和杂交表现求爱和父母的照顾。也没有发现在饲养的杂交（F1的或回交）的遗传不相容性;所有的活力。季节性隔离只是部分发达的早期产卵移民的trachurus作出重大贡献的杂交（在小坎贝尔河）。由于行为和遗传块杂交不存在，有没有办法阻止杂交whenacriurus和trachurus走到一起。然而，这两个物种之间的共存率很低。田间观察和实验以及偏好性试验的证据表明，生态隔离是杂交的一个非常强大的障碍。这两个物种对它们经常出现的明显不同的栖息地表现出许多适应性，并且每个物种都对自己的栖息地表现出强烈的亲和力。在具有中间或邻近生境的地方，共存和杂交发生。杂交是环境的一种功能，在杂交区内（或在实验室饲养的杂交种中），不能检测到对杂交种的选择;然而，人们不得不假设它存在于杂交区外。发现的非常狭窄的区域以及反向渐变群表明存在针对杂交种的强烈选择。这些选择力是什么还有待发现。在对杂种劣性进行批判性分析之前，杂种区可能仍然知之甚少。留在杂种区的任何一个物种的基因型都处于强烈的选择劣势。因此，生态隔离的强化可能会发生，而摩尔关于这种强化基因型传播的批评并不适用于这种情况。迈尔区分了交配前和交配后的机制，指出自然选择的运作模式对两者来说是不同的。但在三松刺鱼中，一种交配前机制（生态隔离）和一种交配后机制（杂交劣势）无法区分。这是因为生态隔离是杂种劣性的原因。Leiurus和trachurus在生殖上是隔离的，具有发达的隔离机制，并表现出相当大的遗传差异。因此，这两个物种符合迈尔的物种定义。没有证据表明发生了基因渗入。事实上，一个反向的渐变群，表现出两个物种之间的形态分歧的逐步增加，作为混合区接近一起…
A systematic examination was made of isolating mechanisms, as set out by Mayr, that might serve to maintain reproductive isolation between the marine (trachurus) and the freshwater (leiurus) threespine sticklebacks. Field work was conducted in a small British Columbia coastal stream, the Little Campbell River, for years and complemented with laboratory experiments. Other streams were included late in the investigation.Leiuruspermanently occupies the upper reaches of the stream;trachurusis anadromous and enters the lower reaches to breed in freshwater. Between the breeding grounds of the two, where numbers of both are greatly reduced, hybridization occurs. But it is restricted to a narrow zone.The two species are easily distinguished. Thus, morphological analysis provided firm circumstantial evidence that hybrids are plentiful and that backcrossing occurs, predominately toleiurus. Hybridization was confirmed by rearing offspring under uniform conditions in the laboratory with crosses in all combinations. Such offspring were also used to demonstrate considerable genetic divergence (much of it polygenetic) betweenleiurusandtrachurus.Behavioural experiments demonstrated the absence of ethological isolation and hybrids performed courtship and parental care normally.Nor was genetic incompatibility found in the reared hybrids (F1's or backcrosses); all were vigourous. Seasonal isolation is only partially developed with early spawning migrants oftrachurusmaking a major contribution to hybridization (in the Little Campbell River).Since behavioural and genetic blocks to hybridization are not present, there is no means to prevent hybridization whereleiurusandtrachuruscome together. However, coexistence between the two species is very low. Evidence from observation and experiment in the field and from preference tests showed that ecological isolation is a very powerful barrier to hybridization. The two species show numerous adaptations to the distinctly different habitats they frequent, and each shows a strong affinity for its own habitat. In localities with intermediate or contiguous habitats, coexistence and interbreeding occur. Hybridization is a function of the environment.No selection against hybrids could be detected within the hybrid zone (or with laboratory reared hybrids); yet, one is forced to assume that it is present outside the zone. The very narrow zones as well as the reversed cline that were found indicate there is intense selection against hybrids. What these selective forces are remains to be found. Hybrid zones will probably continue to be poorly understood until a critical analysis of hybrid inferiority is made.Genotypes of either species that remain in the hybrid zone are at a strong selective disadvantage. Hence, reinforcement of ecological isolation probably occurs, and Moore's criticism concerning the spread of such reinforced genotypes would not apply to such cases. Mayr distinguishes between pre- and postmating mechanisms stating that the mode of operation of natural selection will be different for the two. But in threespine sticklebacks one premating mechanism (ecological isolation) and one postmating mechanism (hybrid inferiority) cannot be distinguished. This is so because ecological isolation is the cause of hybrid inferiority.Leiurusandtrachurusare reproductively isolated, have well developed isolating mechanisms, and exhibit considerable genetic divergence. The two, then, fulfill the species definition of Mayr. There is no evidence that introgression occurs. Indeed a reversed cline showing a progressive increase in morphological divergence between the two species as the hybrid zone is approached together with the …