Discovery of the oldest known brood care in insects

Discovery of the oldest known brood care in insects

Science

Jurassic insects carried clusters of eggs on their feet. Paleontologists recently discovered evidence of this parenting behavior in remarkably well-preserved fossils in China. This would be the first example of brood care in an insect species.

Brood care improves the chances of survival of the offspring by ensuring protection and/or access to food by the parents (usually the females). These behaviors evolved independently and multiple times in several groups of animals, including mammals, birds, and dinosaurs. Arthropods, in particular various lines of insects, are also concerned. However, few fossils have made it possible to directly document such ephemeral behavior until now, hence the interest of this study published in the Proceedings of the Royal Society B: Biological Sciences.

Eggs attached to a leg
A team of paleontologists announces that they have excavated more than 160 fossils of an ancient species of water bug named Karataviella popovi in ​​the Haifanggou Formation, a rock deposit in northeast China. These animals would have evolved during the Jurassic period, around 163.5 million years ago.

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These insects had three legs. The mesotibia was the middle one. Among these fossils, the team identified about 30 adult females with a group of eggs anchored to their left midtibia. The study authors speculate that the unoccupied right midtibia could have been used to maintain balance when swimming and feeding.

That being said, all of these eggs were arranged in five or six rows of six to seven specimens attached by a short stalk. Each egg measured approximately 1.14 to 1.20 mm. The latter were particularly large compared to the overall size of the females, which measured less than thirteen millimeters in length.

Promote oxygen supply?
According to paleontologists, the females first secreted a sticky mucus on their middle leg. They then probably laid their eggs directly on it by performing specific bending movements of the abdomen.

The authors also point out that laying large eggs always comes at a cost. The latter are indeed more difficult to aerate with oxygen than small eggs. It may be that by carrying eggs on their left midtibia, and allowing them to be cradled at the end of their stalk, these insects have maximized the flow of oxygen from the surrounding water to their developing offspring.

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If this hypothesis is to be believed, then this new discovery would represent the oldest direct evidence of brood care in insects, pushing the record back by more than 38 million years. If this is the case, the relevant adaptations associated with the maternal investment of insects would therefore date back at least to the Upper Middle Jurassic.