动物的物种起源常常与地理障碍有关，比如山水等地理分布隔开了物种，也造成了生殖隔离。日前，美国密苏里大学的研究人员研究发现仅染色体的数量就可以控制物种隔离，相关论文发表在Proceedings of the Royal Society B:Biological Sciences。
MU文学院生物科学系主任Carl Gerhardt教授和博士生Mitch Tucker研究了两种生活在密苏里关系紧密的灰色树蛙物种，东部灰树蛙和科普灰树蛙。
Gerhardt说不管对人类还是树蛙，用肉眼来看这两种树蛙长的很相似。唯一不同的就是染色体的数量，东部灰树蛙有两倍数量的染色体。
为了吸引伴侣，这两个物种在它们叫声表现方面有所区别。雄性青蛙都唱同样的“情歌”——只是一只树蛙唱的慢一点。
研究人员在早前的研究发现树蛙染色体数越多，细胞越大，这就降低了颤音的频率。雌性树蛙对雄性叫声的选择是否同样与染色体数有关尚不清楚。
为解决这个疑惑，Tucker通过模拟树蛙发育早期的春季温度，模拟了树蛙染色体复制的过程。雌性树蛙发育成熟后，向这些雌蛙播放电脑合成的不同颤音频率的雄性树蛙的叫声。研究人员发现雌蛙蹦向染色体相匹配的雄性树蛙，这也表明了雌性树蛙的偏好。
Gerhardt说这就表明了仅染色体的数量就可以控制物种隔离。随着染色体数量增加，细胞大小也改变了，而这可能是叫声和选择变化的直接原因。
据Gerhardt说，东部灰树蛙可能是因染色体复制、行为变化和生殖隔离而导致快速进化的罕见案例。（生物谷Bioon.com）
doi:10.1098/rspb.2011.1968
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PMID:
Parallel changes in mate-attracting calls and female preferences in autotriploid tree frogs
Tucker MA, Gerhardt HC.
For polyploid species to persist, they must be reproductively isolated from their diploid parental species, which coexist at the same time and place at least initially. In a complex of biparentally reproducing tetraploid and diploid tree frogs in North America, selective phonotaxis-mediated by differences in the pulse-repetition (pulse rate) of their mate-attracting vocalizations-ensures assortative mating. We show that artificially produced autotriploid females of the diploid species (Hyla chrysoscelis) show a shift in pulse-rate preference in the direction of the pulse rate produced by males of the tetraploid species (Hyla versicolor). The estimated preference function is centred near the mean pulse rate of the calls of artificially produced male autotriploids. Such a parallel shift, which is caused by polyploidy per se and whose magnitude is expected to be greater in autotetraploids, may have facilitated sympatric speciation by promoting reproductive isolation of the initially formed polyploids from their diploid parental forms. This process also helps to explain why tetraploid lineages with different origins have similar advertisement calls and freely interbreed.
