Sexual Intercourse Involving Giant Sperm in Cretaceous Ostracode

Abstract

Reproduction with giant sperm occurs in distinct groups scattered over the animal kingdom. Although experiments in Drosophila assessed the influence of different selection pressures on this character, no information was available on its long-term stability. Sub-micrometer-resolution synchrotron quantitative phase tomography (holotomography) of exceptionally well-preserved three-dimensional Cretaceous ostracode fossils from the Brazilian Santana Formation indicates that ostracode reproduction with giant sperm persisted for at least over the past 100 million years. Remnants of the male sperm pumps as well as giant, inflated female sperm receptacles evidence that, despite high costs, reproduction with giant sperm can be an evolutionary successful strategy.

Early Cretaceous ostracod biostratigraphy of eastern Brazil and western Africa: An overview

“…This would mean that species of these genera would be able to recolonise the lake after an evaporative event as soon as aquatic conditions were re-established. Due to the excellent preservation of a number of specimens from the Araripe Basin, P. micropapillosa has been directly shown to display sexual dimorphism in internal characteristics (though not in the external features of the carapace) (Smith, 2000a) and giant sperm as seen in modern cypridoids (like Eucypris virens) (Matzke-Karasz et al, 2009), and potential ostracod eggs have also been recovered from the same formation (Smith, 1999).…”

Exceptionally well-preserved giant spermatozoa in male and female specimens of an ostracod Cypria ophtalmica (Crustacea: Ostracoda) from Late Glacial lacustrine sediments of Southern Carpathians, Romania

“…Species belonging to the suborder Cypridocopina, which are approximately 1-mm-long, can have 1-cm-long sperm, i.e., ten times of their body length (MatzkeKarasz 2005). It is probable that these giant sperm evolved only once in ostracods and have been present for at least the past 100 million years (Matzke-Karasz et al 2009). …”

What do isogamous organisms teach us about sex and the two sexes?

“…Another factor that makes a reversal to isogamy difficult is that anisogamous species have achieved tight linkage or sex-limitation of expression of sizedetermining loci, which can block the evolutionary path from anisogamy back to isogamy [67]. Despite these stabilizing factors, there are known cases where 'giant sperm' have evolved secondarily [87][88][89], approaching isogamy in terms of size; such special cases are, however, quite different from an actual evolutionary reversal to morphological similarity, because a clear sperm-egg dichotomy in morphological traits is maintained.…”