Length measurements of sperms of 51 species of Cypridoidea ostracods were taken to supplement the paucity of ostracod sperm data in the published literature. The lengths of the posterior regions ...(carrying the mitochondria) and the thinner anterior regions were also measured when appropriate. Maximum lengths of sperms for individual species varied from 268 μm for Fabaeformiscandona velifera Smith and Janz, 2008 through to 11 787 μm for Australocypris robusta De Deckker, 1974; these lengths represent the shortest so far recorded for the superfamily and the longest ever recorded in ostracods, respectively. There appears to be only a loose relationship between taxonomy and sperm lengths. Species of the subfamily Candoninae generally have the shortest sperms compared with other subfamilies, but one Candoninae species, Candona altoides Petkovski, 1961, has sperms longer than some species of the families Cyprididae, Ilyocyprididae and Notodromadidae. The family Cyprididae showed the most variation, with sperms ranging from 1000 μm through to 11 787 μm in length. No hypothesis satisfactorily explains the origin of giant sperms in ostracods or the longevity of this trait through geological eras, and their existence remains enigmatic.
Spermatozoa of the ostracod superfamily Cypridoidea include some of the longest in the animal kingdom, but unlike other so-called giant spermatozoa, they are aflagellate, probably evolved only once, ...and represent an exceptionally old trait. Sperm length variations within cypridoidean species remain poorly known, a lack that hinders the development of hypotheses to explain their length and variation. For this study, the lengths of 500 spermatozoa from each of five species of freshwater cypridoidean ostracods,
Candonopsis tenuis
(Brady, 1886),
Fabaeformiscandona subacuta
(Yang, 1982),
Heterocypris rotundata
(Bronshtein, 1928),
Ilyocypris japonica
Okubo, 1990, and
Notodromas trulla
Smith and Kamiya, 2014, were measured, including the lengths of the posterior and anterior regions. No overall pattern in sperm variation was discernible. Length variations between species, between males of the same species, and within individual males varied from low (
Candonopsis tenuis
) to extraordinarily large (
Notodromas trulla
and
Fabaeformiscandona subacuta
). Sperm competition, cryptic female choice, sperm heteromorphism, and testis size are unlikely to explain all of the variations observed. Age structures of the populations sampled might play a role in explaining some intraspecific variation. The differing amounts of variation in sperm characters revealed in this study suggest that multiple evolutionary trends and pressures shape sperm lengths in this superfamily.
Ostracods are the most abundantly preserved arthropod group in the fossil record, but they are almost entirely represented only by their calcitic carapaces. In over two hundred years of fossil ...ostracod research, only about 33 occurrences of fossil ostracods that include preserved appendages, or soft parts, have been reported. These range from the Ordovician through to the Holocene, and are from a wide range of paleoenvironments, including the seas, brackish inlets, lakes, caves, and the edges of ancient forests. Preservation includes silica, phosphate, goethite, pyrite or calcite mineralization replacing or coating soft parts, or direct preservation of the chitinous body and appendages, such as with amber entombment and mummification. Although rare, they have provided information on the morphology of some of the earliest ostracods, given clues about phylogenetic relationships of extinct groups, and demonstrated remarkably long periods of evolutionary stasis. Preserved sexual organs, eggs, brooded juveniles and even spermatozoa have given valuable insights into the reproduction of the group. Technological advances, such as scanning electron microscopy and more recently micro- and nanotomography, have dramatically expanded our capabilities to study these specimens, even down to the sub-cellular level. This review presents these occurrences in a historical context, from the first to the most recently reported, and highlights how these discoveries have contributed to our understanding of ostracod evolution.
•Complete overview of publications on ostracods with soft part preservation from 1876 to 2020.•Review of soft part preservation in fossil ostracods in historical context.•Relevance of soft part preservation in improving our understanding of ostracod evolution.•Improved and new figures of exceptionally preserved ostracods.•Information on current depositories of the described specimens.
In her publication on a Holocene sedimentary succession of the Eastern Adriatic coast, here in the same volume, the author V. Hajek-Tadesse describes a new ostracod (Crustacea) species. She assigns ...it to the previously monospecific genus Juxilyocypris Kempf, 2011, which is now holding the two fossil species J. schwarzbachi (Kempf, 1967) and J. kempfi Hajek-Tadesse, 2018. These three taxa, and their taxonomic proximity give a perfect memento of three palaeontologists of the Cologne University, whose lives and achievements were similarly interwoven.
Cypridoidean ostracods are one of a number of animal taxa that reproduce with giant sperm, up to 10 000 µm in length, but they are the only group to have aflagellate, filamentous giant sperm. The ...evolution and function of this highly unusual feature of reproduction with giant sperm are currently unknown. The hypothesis of long-term evolutionary persistence of this kind of reproduction has never been tested. We here report giant sperm discovered by propagation phase contrast X-ray synchrotron micro- and nanotomography, preserved in five Miocene ostracod specimens from Queensland, Australia. The specimens belong to the species Heterocypris collaris Matzke-Karasz et al. 2013 (one male and three females) and Newnhamia mckenziana Matzke-Karasz et al. 2013 (one female). The sperm are not only the oldest petrified gametes on record, but include three-dimensional subcellular preservation. We provide direct evidence that giant sperm have been a feature of this taxon for at least 16 Myr and provide an additional criterion (i.e. longevity) to test hypotheses relating to origin and function of giant sperm in the animal kingdom. We further argue that the highly resistant, most probably chitinous coats of giant ostracod sperm may play a role in delaying decay processes, favouring early mineralization of soft tissue.
Ostracods of the superfamily Cypridoidea have giant spermatozoa. However, little data exist on the sperm-egg interaction in this group: only two publications have so far given the most ambiguous ...indication that the entire sperm enters the egg on fertilization. These assumptions have not yet been tested with modern techniques, nor has their putative value for developmental and evolutionary investigations been realized. The present paper gives the first, clear, light- and scanning electron microscopical evidence of the entire giant ostracod spermatozoon being incorporated into the egg. Coiling of the sperm underneath the egg shell is shown in the early zygotes of the species Mytilocypris praenuncia and Pseudocandona marchica. Additionally, data on the morphology of female and male reproductive tracts are given for M. praenuncia. Hypotheses on the evolution of giant filiform sperm in the Animal Kingdom are reviewed, and their applicability to ostracods is discussed. The demonstrated ingression of the entire sperm implies the entry of the two giant paternal mitochondrial derivates into the zygote in Cypridoidea and potentially casts doubt upon the dogma of strict maternal inheritance of mitochondrial DNA. Evidence of paternal inheritance of mtDNA in several organisms has recently given rise to a controversial debate on this issue; the possible significance of this phenomenon for molecular studies on ostracod phylogeny and evolution is discussed.
1. The adaptive significance of the observed variations in sex ratios in non-marine ostracods is unclear. This study quantified the fecundity of females taken from a presumed fully sexual Eucypris ...virens population that were experimentally combined with different proportions of males (male : female sex ratios: 1 : 1, 1 : 2, 1 : 4, 1 : 8 and 0 : 1). 2. The results yielded no indications that female fecundity is altered by short-term variations in the proportion of males, at least not within the range of sex ratios that are common in natural ostracod populations. Complete removal of males, however, did strongly reduce hatching success of dried eggs. This suggests the need for multiple mating events during the reproductive lifetime of the female. It also emphasizes the need for a minimum number of males, although this minimum number evidently may be rather low, as we found a high number of spermatozoa in the seminal receptacles after a single mating event. 3. The sex ratio in the source population was strongly female biased (1 : 3.4; n = 514), whereas in the hatchling assemblages reared in the laboratory, males and females were found in equal proportions (1 : 1.0; n = 1516), irrespective of the prevailing sex ratio. This clear discrepancy is intriguing, and points to the importance of epigenetic factors for the determination of field sex ratios.
During an ostracod sampling campaign in the city of Munich (Germany) samples were taken from containers in a greenhouse of the Munich Botanical Garden. Beside the ubiquitous species Cypridopsis vidua ...(O. F. Müller, 1776), the samples contained four alien species, i.e., Chlamydotheca arcuata (Sars, 1901), Strandesia bicuspis (Claus, 1892), Tanycypris centa Chang, Lee & Smith, 2012, and Tanycypris alfonsi Nagler, Geist & Matzke-Karasz, 2014. While sorting the living Tanycypris specimens, a yet undescribed usage of the caudal rami was observed. Freshwater ostracods usually move on or in the sediment by using their first and second antennae, walking legs and - if not reduced - their caudal rami. During (non-swimming) locomotion of most freshwater ostracods with well-developed caudal rami, they help pushing the body forward by being used as a lever. This movement can be fast, but has never been reported to include sudden jumps. In contrast, both investigated Tanycypris species show an extraordinarily fast movement, especially when disturbed. Recordings with a high-speed camera were made, shooting horizontally into a 1.5-mm-thick micro-aquarium. The fast movement could be identified as a powerful jump, much resembling the movement of a catapult, propelled by a very rapid repulsion of the caudal rami from the ground. Although sized only around 1 mm, the observed specimens reached top speeds of up to 0.75 ms−1. Anatomically, this speed is obtained by the exceptional length of the caudal rami in Tanycypris, combined with a well-developed musculature, which stretches from a broadened posterior end of soft body along the so-called 'caudal rami attachment'. The jump itself resembles that of springtails or fleas, where the jump is powered by the energy previously stored in an elastic proteinaceous material; however, in Tanycypris no such mechanism could be detected and thus the energy for the catapult-like jump must be considered muscular, possibly aided by tendon-like structures and/or a mechanism involving a muscular pre-tension by a click-joint as recorded for Squillids.
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