Data from: Outbreeding effects in an inbreeding insect, Cimex lectularius

In some species, populations with few founding individuals can be resilient to extreme inbreeding. Inbreeding seems to be the norm in the common bed bug, Cimex lectularius, a flightless insect that, nevertheless, can reach large deme sizes and persist successfully. However, bed bugs can also be dispersed passively by humans, exposing inbred populations to gene flow from genetically distant populations. The introduction of genetic variation through this outbreeding could lead to increased fitness (heterosis) or be costly by causing a loss of local adaptation or exposing genetic incompatibility between populations (outbreeding depression). Here, we addressed how inbreeding within demes and outbreeding between distant populations impact fitness over two generations in this re-emerging public health pest. We compared fitness traits of families that were inbred (mimicking reproduction following a founder event) or outbred (mimicking reproduction following a gene flow event). We found that outbreeding led to increased starvation resistance compared to inbred families, but this benefit was lost after two generations of outbreeding. No other fitness benefits of outbreeding were observed in either generation, including no differences in fecundity between the two treatments. Resilience to inbreeding is likely to result from the history of small founder events in the bed bug. Outbreeding benefits may only be detectable under stress and when heterozygosity is maximized without disruption of coadaptation. We discuss the consequences of these results both in terms of inbreeding and outbreeding in populations with genetic and spatial structuring, as well as for the recent resurgence of bed bug populations.

在部分物种中，即便奠基个体（founding individuals）数量稀少的种群，仍可耐受极端近交（extreme inbreeding）。近交似乎是温带臭虫（Cimex lectularius）——一种无翅昆虫——种群中的常态，但该物种仍可形成大规模地方种群（deme）并成功存续。不过，温带臭虫可通过人类进行被动扩散，这会使近交种群接触到来自遗传距离较远种群的基因流（gene flow）。通过这种远交（outbreeding）引入的遗传变异，既可能提升适合度（fitness）并产生杂种优势（heterosis），也可能带来代价：比如导致本地适应性丧失，或是暴露种群间的遗传不相容性，进而引发远交衰退（outbreeding depression）。本研究针对这种重新出现的公共卫生害虫——温带臭虫，探究了地方种群内部的近交以及远缘种群间的远交，在两代内对其适合度的影响。我们比较了两种繁育方式下的家系适合度性状：一种为近交家系（模拟奠基事件后的繁殖过程），另一种为远交家系（模拟基因流事件后的繁殖过程）。研究发现，与近交家系相比，远交家系的抗饥饿能力显著提升，但该优势在远交繁殖两代后便会消失。在两代实验中均未观察到远交带来的其他适合度优势，包括两种繁育方式下的繁殖力（fecundity）无显著差异。温带臭虫对近交的耐受性，可能源于其种群历史中频繁发生的小型奠基事件。远交优势或许仅能在胁迫环境下，且当杂合性（heterozygosity）达到最大化且未破坏协同适应（coadaptation）时才能被检测到。我们还讨论了本研究结果对于存在遗传与空间结构的种群中近交与远交的意义，以及温带臭虫种群近期回升的相关启示。