Eggs With Trilobite Larvae in a Cambrian Community. Modeling the Hydrodynamics

Background: Reproductive behaviors include mating, pregnancy, birth, and ulterior brood care. Fossil records (eggs, nests, etc.) provide a glimpse into the reproductive sequences of ancient animals. Here, we show putative trilobite egg clusters from the middle Cambrian (Miaolingian, Wuliuan Stage) that were found in the Kaili Formation, South China. The arrangement of these egg clusters would ensure efficient oxygen diffusion from the water into cells.Results: We applied a computational fluid mechanics simulation method to understand the behavior of Kaili trilobite eggs in Cambrian seawater under different flow patterns. The drag force and lift force load on the eggs increased rapidly when current speeds exceeded 0.2 m/s. Moreover, the drag coefficient of the single egg model was 1.8–2 times larger than that of each egg in the egg cluster model. The trilobite larva within the egg cluster (ca. 0.5 mm in size) are smaller than the eggs (ca. 0.6 mm), which indicates that they had recently hatched.Conclusions: We suggest that not all trilobites had an unmineralized preliminary stage in their ontogeny and that some protaspis shield may have been formed before hatching. Moreover, we hypothesize that aquatic animals can use egg clustering to effectively reduce the effects of drag and lift forces from the surrounding water.

Population studies of tree-defoliating insects in Canada: a century in review

Our review highlights research during the past century focussed on the population ecology of outbreak-prone insect defoliators in Canadian forests. Based on reports from national and provincial surveys that began in the 1930s, there have been at least 106 insect defoliators reported to outbreak, most of which are native Lepidoptera, Hymenoptera (sawflies), or Coleoptera (in order of frequency from most to least). Studies comparing life-history traits of outbreak versus non-outbreak species to better understand why certain species are more outbreak-prone indicate several traits especially common among outbreak species, including egg clustering and aggregative larval feeding. There have been at least 50 time-series studies examining the spatiotemporal population behaviour of 12 major defoliator species. These studies provide evidence for both regular periodicity and spatial synchrony of outbreaks for most major species. Life-table studies seeking to understand the agents causing populations to fluctuate have been carried out for at least seven outbreak species, with the majority identifying natural enemies (usually parasitoids) as the major driver of outbreak collapse. Our review concludes with several case studies highlighting the impact and historical underpinnings of population studies for major defoliator species and a discussion of potential avenues for future research.