Institute for Applied Ecology, University of Canberra, Bruce, Australian Capital Territory, Australia.
Desert Ecology Research Group, School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales, Australia.
Mol Ecol. 2023 Dec;32(24):6766-6776. doi: 10.1111/mec.17174. Epub 2023 Oct 24.
In episodic environments like deserts, populations of some animal species exhibit irregular fluctuations such that populations are alternately large and connected or small and isolated. Such dynamics are typically driven by periodic resource pulses due, for example, to large but infrequent rainfall events. The repeated population bottlenecks resulting from fragmentation should lower genetic diversity over time, yet species undergoing these fluctuations appear to maintain high levels of genetic diversity. To resolve this apparent paradox, we simulated a metapopulation of constant size undergoing repeat episodes of fragmentation and change in gene flow to mimic outcomes experienced by mammals in an Australian desert. We show that episodic fragmentation and gene flow have contrasting effects on two measures of genetic diversity: heterozygosity and allelic richness. Specifically, fragmentation into many, small subpopulations, coupled with periods of infrequent gene flow, preserves allelic richness at the expense of heterozygosity. In contrast, fragmentation into a few, large subpopulations maintains heterozygosity at the expense of allelic richness. The strength of the trade-off between heterozygosity and allelic richness depends on the amount of gene flow and the frequency of gene flow events. Our results imply that the type of genetic diversity maintained among species living in strongly fluctuating environments will depend on the way populations fragment, with our results highlighting different mechanisms for maintaining allelic richness and heterozygosity in small, fragmented populations.
在诸如沙漠等间歇性环境中，一些动物物种的种群表现出不规则的波动，使得种群交替地大而连接或小而隔离。这种动态通常是由周期性的资源脉冲驱动的，例如，由于大而罕见的降雨事件。由于碎片化而导致的反复种群瓶颈应该会随着时间的推移降低遗传多样性，但经历这些波动的物种似乎保持着高水平的遗传多样性。为了解决这个明显的悖论，我们模拟了一个大小恒定的集合种群，经历了多次碎片化和基因流动变化的重复事件，以模拟澳大利亚沙漠中哺乳动物所经历的结果。我们表明，间歇性的碎片化和基因流动对两种遗传多样性衡量标准有相反的影响：杂合度和等位基因丰富度。具体来说，碎片化成许多小的亚种群，加上基因流动的不频繁时期，以牺牲杂合度为代价来保留等位基因丰富度。相比之下，碎片化成少数大的亚种群以牺牲等位基因丰富度来维持杂合度。杂合度和等位基因丰富度之间的权衡强度取决于基因流动的数量和基因流动事件的频率。我们的结果表明，生活在强波动环境中的物种所维持的遗传多样性类型将取决于种群碎片化的方式，我们的结果强调了在小的碎片化种群中维持等位基因丰富度和杂合度的不同机制。
