Mating and aggregative behaviors among basal hexapods in the Early Cretaceous.

Alba Sánchez-García,Enrique Peñalver,Xavier Delclòs,Michael S Engel

doi:10.1371/journal.pone.0191669

Abstract

Among the many challenges in paleobiology is the inference and reconstruction of behaviors that rarely, if ever, leave a physical trace on the environment that is suitable for fossilization. Of particular significance are those behaviors tied to mating and courtship, individual interactions critical for species integrity and continuance, as well as those for dispersal, permitting the taxon to expand its distribution as well as access new habitats in the face of local or long-term environmental change. In this context, two recently discovered fossils from the Early Cretaceous amber of Spain (ca. 105 mya) give a detailed view of otherwise fleeting ethologies in Collembola. These occurrences are phylogenetically spaced across the class, and from species representing the two major clades of springtails—Symphypleona and Entomobryomorpha. Specifically, we report unique evidence from a symphypleonan male (Pseudosminthurides stoechus Sánchez-García & Engel, 2016) with modified antennae that may have functioned as a clasping organ for securing females during mating on water’s surface, and from an aggregation of entomobryomorphan individuals (Proisotoma communis Sánchez-García & Engel, 2016) purportedly representing a swarming episode on the forest floor. We demonstrate that the mating behavioral repertoire in P. stoechus, which is associated with considerable morphological adaptations, likely implied elaborate courtship and maneuvering for guarantee sperm transfer in an epineustic species. These discoveries reveal significant behaviors consistent with modern counterparts and a generalized stasis for some ancient hexapod ethologies associated with complex mating and courtship and social or pre-social aggregations, so critical to specific constancy and dispersal.

Highlights

Aside from trace fossils, some of the most remarkable examples of fossilized behaviors have been discovered in amber
Courtship behavior In Collembola, fertilization is through the transfer of spermatophore, which occurs in a variety of fashions, and sometimes implies dimorphic structures correlated with a number of behavioral attributes [3]
Among the diversity of modified antennae observed in extant sminthuridid genera, they mainly vary in the number, position, and morphology of the elements in the second and third antennomeres, usually formed of distinct papillae and accompanied by several trichobothria and other setae [31]

Summary

Introduction

Aside from trace fossils, some of the most remarkable examples of fossilized behaviors have been discovered in amber. Amber holds a special significance in paleobiological studies due to its ability to capture ‘snapshots’ of biotic interactions and behaviors directly, as well as to preserve organisms with sufficient life-like fidelity as to permit fine examination of morphologies. Springtails exhibit a large suite of reproductive and developmental strategies [2,3,4]. They comprise a lineage of ubiquitous and ecologically varied hexapods, who together with the Protura and Diplura comprise the living sister group to the hyper-diverse insects [5]. Springtails are among the few arthropod groups that live successfully in polar regions, reflective of their considerable niche breadth

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Results

Conclusion