A Cretaceous balloon lifts the veil on the antiquity and evolution of nuptial gifts

Abstract

Nuptial gift-giving is one of the most remarkable traits to have evolved among animal mating systems, and has brought about numerous hypotheses regarding their evolution and influence. Yet, their study has been confined to the modern fauna owing to their ephemeral nature and lack of traces on the environment suitable for preservation. Here we report the first paleontological and earliest evidence of nuptial gift-giving behavior from a male fly of Alavesia (Diptera: Empidoidea) that is an obligate flower visitor in Cretaceous amber carrying his gift, an empty frothy balloon. The fossil demonstrates the antiquity of this behavior, its occurrence in early diverging lineages of Empidoidea, and its maintenance over 99 million years. The nature of the fossil gift provides clues into the function of swarming and the diversity of gifts employed. Based on the phylogenetic pattern of feeding and mating traits, it is inferred that the gift initially alleviated nutrient pressure on females and may have been empty and secreted from male salivary glands in the first place, those with prey items inside were derived later. The evolution of these mating systems may have been a response to maximizing the usage of exogenous nutrients and for signal transmission.