Matting in Springtails, an arthropod group close to insects, existed 105 million years ago

A team of experts from the University of Barcelona and the Geological and Mining Institute of Spain have found the first evidence of courtship display in the fossil records of Springtails.
A team of experts from the University of Barcelona and the Geological and Mining Institute of Spain have found the first evidence of courtship display in the fossil records of Springtails.
Research
(27/03/2018)

A scientific team found out the first evidence of courtship in Springtail fossil records ─these are small hexapod arthropods without wings, close to insects─ from 105 million years ago. The study, published in the scientific journal PLOS ONE, provides information on the oldest evidence of aggregative behaviours of these hexapods, which are present in most of the terrestrial ecosystems.

A team of experts from the University of Barcelona and the Geological and Mining Institute of Spain have found the first evidence of courtship display in the fossil records of Springtails.
A team of experts from the University of Barcelona and the Geological and Mining Institute of Spain have found the first evidence of courtship display in the fossil records of Springtails.
Research
27/03/2018

A scientific team found out the first evidence of courtship in Springtail fossil records ─these are small hexapod arthropods without wings, close to insects─ from 105 million years ago. The study, published in the scientific journal PLOS ONE, provides information on the oldest evidence of aggregative behaviours of these hexapods, which are present in most of the terrestrial ecosystems.

 

The authors of this study are the experts Alba Sánchez and Xavier Delclòs, from the Faculty of Earth Sciences and the Biodiversity Research Institute (IRBio) of the University of Barcelona; Enrique Peñalver, from the Geological and Mining Institute of Spain (IGME), and Michael S. Engel, from the University of Kansas (United States).

Hexapods ─a subphylum from arthropods which also includes insects─ are the organisms that display a higher diversity of matting and social behaviours. However, there is not much direct or indirect evidence of these behaviours in fossil records.

In the new study, the scientific team noted two of the behaviours which are also seen in current types of two extinct Springtail species. These new findings are based on the analysis of several pieces from the Cretaceous amber site in Peñacerrada (Spain), which is known worldwide regarding the study of fossils from the Mesozoic era.

Males with prehensile antennae

In the study, the authors analysed a male Springtail ─a preserved model in amber, from the Pseudosminthurides stoechus species─ which has modified antennae so as to hold the female Springtail during fertilization. These species belong to the family of Sminthurididae, a lineage which is currently represented by dozens of genres of cosmopolitan distribution which are usually found in water surface.

According to the lecturer Xavier Delclòs, from the Department of Earth and Ocean Dyanmics of the UB and IRBio, “despite most Springtail families do not show striking differences between males and females, in the Sminthurididae family -as well as in the fossil species we descrived- males have prehensile antennae to hold the females”.

Courtship challenge in the water

Springtails live in a wide range of terrestrial areas and can be found in many aquatic environments. The sperm transfer from the male to the female in Springtails is a complex process when it occurs in the surface of the water. Therefore, it is common to find morphological alterations and behaviours prone to matting in aquatic species.

According to the researcher Alba Sánchez (UB-IRBio), first author of the article, “the studied model in this research shows a series of morphological adaptations that suggest it lived in the surface of the water”. “Therefore -she adds-, holding the female with the antennae would be essential to guarantee fertilization. Also, it is possible that the male would dance or carry some complex ritual out using the modified antennae, just like it happens with its current relatives”.

The researcher stresses that “these findings are very significant because they are the first evidence of courtship behaviour in the whole fossil records of Springtails, which would have been taking place from 105 million years ago”.

The oldest evidence of aggregative behaviour

In some Springtail species, individuals tend to aggregate and can even build masses with millions of individuals that migrate long distances across the surface (swarming).

As part of the research study, the scientific team discovered in another amber piece, an aggregation of 45 Springtails of the fossil species Proisotoma communis. These findings are the oldest evidence of aggregative behaviour in the order of Springtails, since the only known record so far is a Springtail aggregation in amber in the Dominican Republic from 18 million years ago. 

According to the expert Enrique Peñalver (IGME), “we found, in a part of the amber which is smaller than a squared centimetre, a glimpse of what happened in the rain forest canopies: next to small sediment, fungi hypha, and plant remains, Springtails are stuck in groups, just like they were 105 million years ago”.  

“The findings the new article in PLOS ONE presents, show how old some breeding behaviours are in hexapods, as well as pre-social behaviours and some morphological modifications to ease the contact between males and females. Since these behaviours have spread up to now, researchers can deduce that pressures of natural selection have not changed a lot over these years for these small organisms”, conclude the authors.

The article, funded by national and autonomous governmental funds and the collaboration of the Natural Science Museum of Álaba (Vitoria-Gasteiz), is framed within the research studies of the Amberia group and the Consolidated Research Group on Sedimentary Geology of the University of Barcelona.

 

Images: J.A. Peñas and K. Beck