Mesozoic insect fossils reveal the early evolution of twig mimicry

中生代的昆虫化石揭示了枝状拟态的早期演化

Twig mimicry among insects,whereby they imitate branches and twigs of plants to escape predation or enhance prey capture,is most common and diversified in Phasmatodea(stick and leaf insects),a group of iconic models for understanding the evolution of camouflage and mimicry.Extant stick and leaf insects exhibit a wide array of exaggerated morphologies mimicking twigs,bark,fresh or dried leaves,ferns,and even moss[1].However,the Mesozoic lineages Susumaniidae and Pterophasmatidae,considered as stem groups to Phasmatodea s.str.,lack obvious characters relating to the familiar twig mimicry of the latter clade.

许多竹节虫(?目)通过模拟树枝来隐藏保护自己,但由于缺乏化石材料,这种“枝状拟态”的早期形成过程尚不清楚.本文描述了来自中国内蒙古中侏罗统地层和缅甸北部白垩纪中期琥珀中的多件竹节虫化石标本,基于系统发育分析揭示了竹节虫枝状拟态特征可能的早期演化方式.结果表明,中侏罗时期的竹节虫已经开始形成细长的体型,在胸部和腹部占整个身体的长度比例不变的情况下,从侏罗纪中期到白垩纪中期近6000万年的进化过程中,竹节虫的中、后胸占整个胸部的比例逐渐增大,前胸则变短,说明中、后胸的延长在枝状拟态出现和进化过程中起了重要作用.此外,研究还发现竹节虫的后胸和第一腹节在中生代相继在腹面、背面发生了融合,明显变长的足部更加增强了枝状拟态的效果.竹节虫“枝状拟态”的出现很有可能和被子植物在白垩纪早期的繁盛有关.