RT Journal Article SR Electronic T1 Evolutionary trade-off in reproduction of Cambrian arthropods JF Science Advances JO Sci Adv FD American Association for the Advancement of Science SP eaaz3376 DO 10.1126/sciadv.aaz3376 VO 6 IS 18 A1 Ou, Qiang A1 Vannier, Jean A1 Yang, Xianfeng A1 Chen, Ailin A1 Mai, Huijuan A1 Shu, Degan A1 Han, Jian A1 Fu, Dongjing A1 Wang, Rong A1 Mayer, Georg YR 2020 UL http://advances.sciencemag.org/content/6/18/eaaz3376.abstract AB Trade-offs play a crucial role in the evolution of life-history strategies of extant organisms by shaping traits such as growth pattern, reproductive investment, and lifespan. One important trade-off is between offspring number and energy (nutrition, parental care, etc.) allocated to individual offspring. Exceptional Cambrian fossils allowed us to trace the earliest evidence of trade-offs in arthropod reproduction. †Chuandianella ovata, from the early Cambrian Chengjiang biota of China, brooded numerous (≤100 per clutch), small (Ø, ~0.5 mm) eggs under carapace flaps. The closely related †Waptia fieldensis, from the middle Cambrian Burgess Shale of Canada, also brooded young, but carried fewer (≤ 26 per clutch), larger (Ø, ~2.0 mm) eggs. The notable differences in clutch/egg sizes between these two species suggest an evolutionary trade-off between quantity and quality of offspring. The shift toward fewer, larger eggs might be an adaptive response to marine ecosystem changes through the early-middle Cambrian. We hypothesize that reproductive trade-offs might have facilitated the evolutionary success of early arthropods.