Social selection is density dependent but makes little contribution to total selection in New Zealand giraffe weevils

The methods are described in full in the associated paper and in “Directional selection on body size but no apparent survival cost to being large in wild New Zealand giraffe weevils” Rebecca J. Le Grice et al. 2019, Evolution, doi:10.1111/evo.13698 In brief aggregations of weevils were located on the trunks of karaka trees (Corynocarpus laevigatus), each weevil in the aggregation was measured and individually marked, and then the mating success of each weevil in a one hour period was recorded. This was repeated over several days, giving repeated measures of the composition of the aggregation of weevils on the tree and their mating success. We then used these records to determine the mean body size of same sex rivals in for each weevil in each day, as well as the density and sex ratio of the aggregation on each day. Using these values and the measures of individual body size, we were able to estimate direct and social selection, phenotypic assortment, and how these things varied with density and other factors.

所有方法的详细说明可见于相关论文，即Rebecca J. Le Grice等人2019年发表于《Evolution》的《Directional selection on body size but no apparent survival cost to being large in wild New Zealand giraffe weevils》（新西兰野生长颈鹿象鼻虫的体型定向选择与大型个体无明显生存代价），DOI:10.1111/evo.13698。简言之，研究人员在卡卡树（Corynocarpus laevigatus）的树干上定位到长颈鹿象鼻虫（giraffe weevils）聚群，对聚群内的每头象鼻虫进行体长测量并完成个体标记，随后记录每头象鼻虫在1小时观测时段内的交配成功率。该实验流程重复开展多日，由此获得该树干上象鼻虫聚群组成及其交配成功率的多组重复观测数据。研究人员利用这些记录，计算得到每日每头象鼻虫对应的同性竞争者平均体型，以及当日该聚群的种群密度与性比。结合上述参数与个体体长测量数据，本研究得以估算直接选择与社会选择强度、表型聚类（phenotypic assortment）效应，以及这些指标随种群密度与其他因素的变化规律。