100 Million Year Old Fairy Shrimp Reproduced Without Sex, Rare Fossils Reveal

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The ancient female fairy shrimp may have gotten along just fine without the males. Researchers studying freshwater fossils from the Cretaceous Period at the Koonwarra Fossil Bed in southern Australia have described a new species of now-extinct freshwater shrimp (Koonwarrella peterorum) whose females probably reproduced without sex – a phenomenon known as parthenogenesis, which is a type of asexual reproduction.

Parthenogenesis is the spontaneous development of an embryo from an unfertilized egg. It is known from occur in both plants and animals, although it is thought to be extremely rare. Some species, like whiptail lizardsreproduce exclusively by parthenogenesis, but some sexually reproducing species are known to reproduce parthenogenesis, as in the case of two fatherless Californian condors reported in the Journal of Heredity in 2021.

“As far as we can tell, [parthenogenesis] is unknown in the fairy shrimp fossil record,” co-investigator Thomas Hegna, assistant professor of paleontology at the State University of New York (SUNY) in Fredonia, told Live Science. this is the first time it has been recognized in freshwater varieties.

This new species was identified from 40 individual fossils across the Koonwarra Fossil Bed, a paleontological site dating to the Aptian Age (125-113 million years ago) rich in fossils, including feathers of the avian line. dinosaurs, as well as bony fish and invertebrates like these fairy shrimp. The fossils themselves are held in the Paleontological Collections of the Melbourne Museum in Victoria, Australia.

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The shrimp fossils unearthed from the Koonwarra Fossil Bed don’t look much like the shrimp found in the langoustines on your plate. Instead, they are much more closely tied to modernity sea ​​monkeys (Artemia saline), which are a variety of brine shrimp. K peterorum left their mark as 0.4-inch-long (1 centimeter) dark imprints in sedimentary rock that suggest they sported elongated bodies with multiple pairs of legs, making the fossils look slightly like the shadow of a small fern or the head of a toilet brush.

The study’s first author, Emma Van Houte, an undergraduate student at SUNY Fredonia, analyzed the fossils to determine their potential place on the evolutionary tree. However, there was a problem: most invertebrate species are classified by male morphology. Indeed, the males of most of these species have very distinct characteristics that are useful in distinguishing them from other species.

“Males have these large, grasping antennae used for sexual reproduction, as well as male genitals,” Van Houte told Live Science. None of the 40 specimens examined by Van Houte exhibited any of these characteristics.

Instead, Van Houte could clearly spot the egg pouches, implying that it was an all-female group of shrimp that likely reproduced asexually. After ruling out other explanations, such as hermaphroditism—when an individual possesses both male and female reproductive organs—or the premature breakdown of typically male characteristics, the only remaining explanation was that shrimp were parthenogenetic.

According to Hegna, one of the reasons why asexual production is rare is that the species that do so always pass on their Genoa, whether good or bad, whereas sexual reproduction allows animals to separate good genes from potentially harmful ones. However, parthenogenesis, he suggests, could be advantageous when it comes to dispersing to new places, like small, isolated ponds.

While fossil fairy shrimp in the Koonwarra Fossil Bed may be completely parthenogenic, there is evidence from modern fairy shrimp that asexual reproduction in these animals could exist on a gradient, Hegna noted.

“There is a population of fairy prawns in Australia that may be parthenogenetic,” Hegna said. But the species is not completely asexual either. “Males [in this species] are really, really rare. And so there can be this gradient that’s related to the dispersal strategy, which is pretty neat.”

This research was published on March 28 in Alcheringa: An Australasian Journal of Paleontology.

Originally posted on Live Science.

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