Out of the tropics: Macroevolutionary size trends in an old insect order are shaped by temperature and predators

Global body size distributions are shaped by selection pressures arising from biotic and abiotic factors such as temperature, predation and parasitism. Here, we investigated the ecological and evolutionary drivers of global latitudinal size gradients in an old insect order (Odonata; dragonflies and damselflies). Phylogenetic comparative analyses revealed that global size variation of extant taxa is negatively influenced by both regional avian diversity and temperature. Interestingly, fossil data show that the relationship between wing size and latitude has shifted: latitudinal size trends had initially negative slopes but became shallower or positive following the emergence of birds 150 MYA. These changing size-latitude trends over geological time were likely driven by bird predation and high dispersal ability of large dragonflies. Our results therefore suggest that latitudinal size gradients were shaped by temperature but also by predators driving the dispersal of large-sized clades ou..., The phylogenetic tree that we use in this study was constructed from odonate DNA-sequences downloaded from GenBank, using a traditional morphological taxonomy as our backbone (Waller and Svensson 2017). Our phylogeny comprised 1322 taxa, about a fifth of all known extant odonate species (about 6400 in total) (Schorr and Paulson 2015; Waller et al. 2019). Further and more detailed information about phenotypic data collection and phylogeny reconstruction is provided elsewhere (Waller and Svensson 2017; Waller et al. 2019) and  from our open online resource “The Odonate Phenotypic Database”: http://www.odonatephenotypicdatabase.org/shiny/odonates/.
Size data (wing lengths) from extinct odonate fossil taxa were obtained from Clapham and Karr (2012). Although we use our previously published Odonata phylogeny in the present study (Waller and Svensson 2017) and we have published data on interspecific body size variation from the Odonate Phenotypic Database (Waller et al. 2019), all of the anal..., All our statistical analysis have been carried out in the R statistical environment. We enclose a README-file in text-format, CSV-files with data and two R-files with code and functions to replicate all the analyses in the current paper.

全球体型分布格局由生物与非生物因素引发的选择压力塑造，此类因素包括温度、捕食与寄生作用。本研究针对古老昆虫纲蜻蜓目（Odonata，涵盖蜻蜓与豆娘）的全球纬度体型梯度，探究其生态与进化驱动因子。系统发育比较分析结果显示，现存类群的全球体型变异同时受到区域鸟类多样性与温度的负向调控。值得注意的是，化石数据表明翅长与纬度的关联已发生演变：在1.5亿年前鸟类起源之前，纬度体型梯度的初始斜率为负值，而在此之后斜率逐渐趋缓甚至转为正值。这种地质时间尺度下体型-纬度趋势的转变，大概率由鸟类捕食作用以及大型蜻蜓较强的扩散能力所驱动。因此本研究结果表明，纬度体型梯度不仅受温度塑造，同时也受到驱动大型演化支扩散的捕食者的影响……

本研究使用的系统发育树以传统形态分类学为框架，基于从GenBank下载的蜻蜓目DNA序列构建而成（Waller与Svensson，2017）。该系统发育树涵盖1322个类群，约占已知现存蜻蜓目物种总数（约6400种）的五分之一（Schorr与Paulson，2015；Waller等，2019）。有关表型数据采集与系统发育重建的更多细节，可参阅已发表文献（Waller及Svensson，2017；Waller等，2019）以及本研究开放的在线资源"蜻蜓目表型数据库（The Odonate Phenotypic Database）"：http://www.odonatephenotypicdatabase.org/shiny/odonates/。

已灭绝蜻蜓目化石类群的体型数据（翅长）取自Clapham与Karr（2012）的研究。尽管本研究使用了此前发表的蜻蜓目系统发育树（Waller及Svensson，2017），并已公开了来自蜻蜓目表型数据库的种间体型变异数据（Waller等，2019），但所有的……

本研究所有统计分析均在R统计编程环境中完成。我们随研究附带了文本格式的README文件、包含数据集的CSV文件，以及两段用于复现本文所有分析的R脚本与函数代码。