Small effective population size in microrefugia?
Small effective population size in microrefugia?
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微型避难所的有效种群规模较小？
DOI：
10.1111/jse.12128
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发表时间：
2015
影响因子：
3.7
通讯作者：
Zhang Da-Yong
中科院分区：
文献类型：
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作者：
Bai Wei-Ning;Zhang Da-Yong
长期以来，人们认识到，在北半球的温带，更新世冰川使温带森林迁移到较低的纬度或海拔，那里的森林物种持续存在，直到气候变暖允许它们在间冰期再次扩张(Hewitt，1996,2000)。在这种模式下，温带树种只在远离大陆冰盖的地区存活，如欧洲南部半岛和北美东南部地区。东亚在整个更新世没有被广泛和统一的冰盖覆盖(休伊特，2000年)，但气候振荡也对植被产生了强烈的影响，产生了类似的收缩-扩张周期(哈里森等人，2001年)。然而，温带树木的现存分布不能仅用向北的重新殖民化来解释，因为仅来自南部避难所所需的重新殖民率将是不切实际的高。这种明显的矛盾被称为里德悖论(Clark等人，1998)，一种可能的解释需要额外的未知的隐蔽避难或微避难，其纬度比之前认为的要高得多(Stewart&Lister，2001)。来自古生态记录、遗传调查以及对过去气候和物种分布的模拟的大量数据有力地支持了这种北方避难所在塑造北半球温带森林树木分布方面的作用。事实上，除了传统的南方避难所(大避难所)之外，存在微避难所的证据似乎如此令人信服，以至于Mee&Moore(2014)呼吁加快行动，从记录微避难所的存在转向测试关于微避难所的生态和进化后果的具体假设。Mee&Moore(2014)确定了区分微型避难所和大型避难所的两个特征，即微型避难所支持较小的避难所人口，以及与大避难所相比，生物群落的多样性较少，两者都是由于地理面积较小。我们有些惊讶地发现，他们的讨论中没有种群结构或细分，因为，无论是否明确，强烈的孤立被广泛认为是微型避难所的一个明显特征。例如，Mosblech等人(2011年)将微型避难所明确定义为“相对于更广泛的景观，在不寻常的小气候中生存的孤立种群”(第419页)。同样，Hampe&Jump(2011，p.324)指出，“根据定义，气候遗迹(即微型避难所)仅限于较小的飞地，很少有机会在来自不同避难所的种群之间进行交流。”人们普遍认为，微型避难所内的种群与迁徙严重隔离，尽管大型避难所种群也被细分(Gomez&Lant，2007)，想必程度较小。Mee&Moore(2014)把重点放在微小避难所相对于大型避难所的小地理区域，但忽略了微小避难所种群的更强的隔离性。这可能具有误导性，因为人口隔离的总体影响是抵消小地理区域对有效人口数量的影响。最重要的是，假设有微型避难所隔离历史的现存种群一定比占据大避难所的种群具有更小的有效种群规模，从而具有更低的遗传多样性水平，这一假设不再安全。恰恰相反，由于…的原因，微型避难所种群在有效种群规模方面往往比大避难所种群更大，具有更高的遗传多样性
It has long been recognized that, in the temperate zone of the Northern Hemisphere, Pleistocene glaciations displaced temperate forests to lower latitudes or altitudes, where forest species persisted until the warming climate allowed them to expand again during interglacial periods (Hewitt, 1996, 2000). Under this model, temperate tree species survived during cold periods only in areas far from the continental ice sheets, such as the southern peninsulas of Europe and the southeastern regions of North America. East Asia was not covered by extensive and unified ice sheets throughout the Pleistocene (Hewitt, 2000), but climate oscillations also strongly impacted the vegetation, producing similar contraction–expansion cycles (Harrison et al., 2001). However, the extant distribution of temperate trees could not be explained by this northward recolonization alone because the required recolonization rates exclusively from southern refugia would be unrealistically high. This apparent contradiction became known as Reid’s paradox (Clark et al., 1998), and a possible explanation demanded additional unknown cryptic refugia or microrefugia at much higher latitudes than previously thought (Stewart & Lister, 2001). A considerable amount of data from paleo‐ecological records, genetic surveys, and the modeling of past climates and species distributions have provided strong support for the role of such northern refugia in shaping the observed distributions of temperate forest trees in the Northern Hemisphere. Indeed, the evidence for the existence of microrefugia beyond the traditional southern refugia (macrorefugia) appears so compelling that Mee & Moore (2014) called for an accelerated move from documenting the presence of microrefugia towards testing specific hypotheses about the ecological and evolutionary consequences of microrefugia. Mee & Moore (2014) identified two characteristics that distinguish microrefugia from macrorefugia, namely microrefugia supported smaller refugial populations and harbored less diverse biotic communities than macrorefugia, both being a result of small geographical area. We are somewhat surprised to find that population structure or subdivision is absent from their discussion, because, explicitly or not, strong isolation is widely recognized as a distinct feature of microrefugia. For example, Mosblech et al.(2011) defined microrefugia explicitly as “isolated populations surviving in unusual microclimates relative to the broader landscape”(p. 419). In a similar vein, Hampe & Jump (2011, p. 324) pointed out that “climate relicts (ie, microrefugia) are, by definition, confined to small enclaves with very few opportunities for interchange between populations from different refugia.” There is general agreement that populations inside the microrefugia are strongly isolated from migration, although macrorefugial populations are also subdivided (Gomez & Lunt, 2007), presumably to a lesser extent. Mee & Moore (2014) focused on small geographical areas of microrefugia relative to macrorefugia but ignored much stronger isolation of microrefugial populations. This can be misleading because the general effect of population isolation is to counteract the effects of small geographical area on the effective population size. Most significantly, it is no longer safe to assume that extant populations with a history of isolation in microrefugia must have a smaller effective population size and hence lower levels of genetic diversity than the populations occupying macrorefugia. Quite the contrary, microrefugial populations may often be larger in terms of effective population size and have higher genetic diversity than macrorefugial populations, for reasons …