The Evolution of Placentas in the Fish Family Poeciliidae: an empirical study of macroevolution

新物种是如何以及为什么进化的？像眼睛这样的复杂器官是如何以及为什么进化的？这些现象发生的时间比我们的生命要长得多，这使得我们很难理解它们是如何发生的。物种的定义是不同的，而不是相互繁殖。不进行异种交配可能只是一个简单的问题，你选择在何时、何地或与谁交配。它也可能是由于无法产生能够生存和繁殖的后代造成的。今天的物种往往是通过多种机制相互隔离的，所以我们不知道它们最初是如何进化的。同样，复杂的器官就像有许多部件的机器，如果机器要工作，这些部件必须全部存在并很好地集成在一起，但是这种复杂性是如何产生的呢？在每一种情况下，大自然最经常呈现给我们的最终产品都没有任何关于它们是如何产生的线索；然而，有时大自然会提供一些物种，它们保留了这些过程的足够线索，使人们能够研究它们是如何发生的，就像这个研究项目的情况一样。这项工作的一个影响与所研究的复杂器官有关。这些研究人员正在研究胎盘的进化，并在这样一个背景下进行研究，他们可以将胎盘与近亲缺乏胎盘或胎盘不太复杂的物种进行比较。这种多样性使他们能够解决拥有胎盘的后果，包括它如何影响生育能力。这项研究将加强对学生在多个层次（高中、大学和研究生）的培训，并向公众提供宣传。拟议的研究结合了在两个分辨率水平上完成的工作。首先，研究人员将研究水蛭科鱼类的所有物种，使他们能够确定进化变化的时间和顺序。其次，他们将对科内的单个物种进行实验，以确定导致进化的机制。他们将对整个基因组进行测序，然后利用DNA序列重建家谱。他们将描述树上每个物种的生物学特征，包括雌性如何哺育后代，雄性和雌性如何选择配偶。这些鱼都能产活卵，但有些鱼在受精前就已经产卵了，而有些鱼在受精后继续产卵。后一组具有与哺乳动物胎盘相同的功能，但不同物种的胎盘发育程度不同，在发育过程中它们为幼崽提供了多少营养。物种在选择配偶的方式上也存在差异，一些物种的雄性身上有精致的装饰和求爱的表现，而另一些物种在颜色上没有性别差异，也没有求爱。生物学与家谱的整合将使研究人员能够推断出女性供应和配偶选择方面的进化时间和顺序。也有可能测试某些特征的进化是否与新物种形成速度的加速或减速有关。这样就有可能检验从进化理论中得出的预测，这些特征的进化是如何相互关联的。家谱还使研究人员能够识别近亲物种，这些物种在存在或不存在胎盘方面存在差异。这些物种对成为实验的对象，他们将对生殖隔离的生物学进行更详细的研究，包括评估多次交配和生殖隔离的进化速度。在这两个层面上所做的工作的整合将使研究人员能够详细了解交配系统和繁殖模式如何影响生殖隔离的进化，这些不同的物种形成方面如何相互作用来塑造科中物种的进化，以及它们如何影响物种形成的速度。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

How and why do new species evolve? How and why do complex organs, like eyes, evolve? These phenomena happen on time scales much longer than our lives, making it difficult for us to understand how they happened. Species are defined by being distinct from and not breeding with each other. Not interbreeding could be a simple matter of when, where or who you choose to mate with. It could also be caused by a failure to produce offspring that can survive and reproduce. Species today are often kept separate from one another by multiple mechanisms, so we do not know how they evolved in the first place. Likewise, complex organs are like machines with many parts that must all be present and well integrated if the machine is to work, but how did this complexity arise? In each case, nature most often presents us with end products without any clues about how they came about; however, sometimes nature provides groups of species that retain enough clues to these processes for one to be able to study how they occur, as in the case of this research program. One impact of this work pertains to the complex organ that is studied. These investigators are studying the evolution of placentas and are doing so in a context in which they can compare species with placentas with close relatives who lack placentas or have less complex placentas. This diversity enables them to address the consequences of having a placenta, including how it affects fertility. The research will enhance the training of students at multiple levels (high school, college, and post-graduate) as well as provide outreach to the public.The proposed research combines work done at two levels of resolution. First, the investigators will work on all species in the fish family Poeciliidae, enabling them to define the timing and order of evolutionary changes. Second, they will perform experiments on individual species within the family to characterize the mechanisms that cause evolution. They will sequence whole genomes then use the DNA sequences to reconstruct the family tree. They will characterize the biology of every species on the tree, including how females provision their young and how males and females choose who to mate with. These fish all bear live young, but some fully provision eggs before they are fertilized while others continue to provision eggs after fertilization. The latter group has the functional equivalent of a mammalian placenta, but species vary in how well the placenta is developed and how much they provision young during development. Species also differ in how they choose mates, with some having males with elaborate ornamentation and courtship displays and others with no sex differences in coloration and no courtship. The integration of biology with the family tree is what will enable the investigators to infer when and in what order female provisioning and aspects of mate choice evolved. It is also possible to test whether the evolution of certain traits is associated with an acceleration or deceleration of how fast new species are formed. It will then be possible to test predictions derived from evolutionary theory for how the evolution of these traits are inter-related with one another. The family tree also enables the investigators to identify closely related species that differ in the presence or absence of placentas. These species pairs become the subjects of experiments in which they will perform more detailed studies of the biology of reproductive isolation, including assessments of multiple mating and the rate of evolution of reproductive isolation. The integration of work done at both levels will enable the investigators to detail how mating systems and mode of reproduction affect the evolution of reproductive isolation, how these different facets of speciation have interacted to shape the evolution of species in the family and how they affect the rate of speciation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.