Genetic and environmental influences on the size-fecundity relationship in Aedes albopictus (Diptera: Culicidae): Impacts on population growth estimates?

Population growth models are integral to ecological studies by providing estimates of population performance across space and time. Several models have been developed that estimate population growth through correlates of demographic traits, as measuring each parameter of the model can be prohibitive in experimental studies. Since differences in female size can accurately reflect changes in fecundity for many taxa, Livdahl and Sugihara developed a population growth index that incorporates size-fecundity relationships as a proxy for fecundity. To investigate the extent to which this model is robust to variation of this proxy, we tested if genetic (source population), temperature and resource treatments affect the size-fecundity relationship in Aedes albopictus (Skuse), the Asian tiger mosquito. We then determined if variation in the size-fecundity relationship alters the population growth estimates, lambda (λ’), when applied to Livdahl and Sugihara’s model. We performed 2 laboratory experiments in which we reared cohorts of four different geographic populations of A. albopictus across 5 temperature treatments (18, 21, 25, 18, 31°C) and three resource treatments (low, medium, high larval resources). We determined if the slope of the size-fecundity relationship varied by source population, temperature, or resource; and if variation in this relationship affects lambda (λ’) estimates in a competition study between A. albopictus and Culex pipiens (Linnaeus), the northern house mosquito. Temperature treatments significantly affected the size-fecundity relationship, resource level marginally affected the relationship, while source population had no effect. We found positive relationships between size and fecundity when mosquito larvae were reared at high temperatures and low resource levels but the relationship disappeared when mosquitoes were reared at a low temperature or with high levels of resources. The variation in the size-fecundity relationship produced from different temperatures resulted in statistically different lambda (λ’) estimates. However, these changes in lambda (λ’) did not alter the trends in the population performance across treatments or conclusions of the competition study. This study provides evidence that the population growth model is sensitive to variation in size-fecundity relationships and we recommend biologists apply the most compatible size-fecundity relationship to the models to obtain the most accurate estimates of population performance.

种群增长模型是生态学研究中不可或缺的工具，可用于估算种群在不同空间与时间维度上的种群表现。学界已开发出多种通过种群统计性状相关指标估算种群增长的模型，因为在实验研究中直接测量模型的每一项参数往往成本高昂、难以实现。鉴于在许多生物类群中，雌性个体体型差异可准确反映繁殖力的变化，Livdahl与Sugihara构建了一种种群增长指数，该指数将体型-繁殖力关系作为繁殖力的替代指标纳入模型。为探究该模型对该替代指标变异的稳健程度，我们以亚洲虎蚊（白纹伊蚊，*Aedes albopictus* (Skuse)）为研究对象，检验了遗传因素（源种群）、温度与资源处理是否会影响其体型-繁殖力关系。随后我们进一步验证，当将该模型应用于Livdahl与Sugihara的研究框架时，体型-繁殖力关系的变异是否会改变种群增长估算值λ（λ’）。我们开展了两项室内实验：将4个不同地理源种群的白纹伊蚊同龄群分别置于5个温度处理组（18、21、25、18、31℃）与3个资源处理组（低、中、高幼虫饵料水平）下饲养。我们首先检验了体型-繁殖力关系的斜率是否会因源种群、温度或资源水平而异；其次验证了该关系的变异是否会影响白纹伊蚊与北方家蚊（尖音库蚊，*Culex pipiens* (Linnaeus)）种间竞争实验中的λ（λ’）估算值。结果显示，温度处理对体型-繁殖力关系具有显著影响，资源水平仅存在边际效应，而源种群无显著影响。我们发现，当幼虫在高温与低资源水平下饲养时，雌性体型与繁殖力呈正相关关系；但在低温或高资源水平下饲养时，该相关关系不复存在。不同温度处理下产生的体型-繁殖力关系变异，导致λ（λ’）的估算值在统计学上存在显著差异。然而，λ（λ’）的这些变化并未改变不同处理下的种群表现趋势，也未影响该竞争实验的最终结论。本研究证实，种群增长模型对体型-繁殖力关系的变异具有敏感性，因此我们建议生态学家在模型中使用最适配的体型-繁殖力关系，以获得最为准确的种群表现估算值。