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Earliest evidence of parental care found in scavenger beetles

2014-09-16 09:47 Xinhua Web Editor: Mo Hong'e
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World's earliest evidence of parental care such as storing food for young offspring has been found in 125-million-year-old fossils of carrion beetles known as scavengers in northeast China, a new study led by Chinese researchers said Monday.

Parental care represents a significant behavioral adaptation in life history but fossil evidence that elucidates the origin and evolutionary history of this phenomenon is lacking, according to the study published in the US journal Proceedings of the National Academy of the Sciences.

Previously, the earliest fossil of carrion beetles found in Florissant, Colorado, only dated back to 35 million years ago.

In the past five years, however, new specimens of carrion beetles have been found in the 165-million-year-old Middle Jurassic Daohugou biota at Ningcheng county, Inner Mongolia of China, the 125-million-year-old Early Cretaceous Jehol biota at Beipiao City, Liaoning Province of China and the 99-million-year- old mid-Cretaceous Burmese amber, said Professor Huang Diying from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences, who led the study.

Huang told Xinhua they collected 37 well-preserved specimens from the Daohugou biota, five specimens from the Jehol biota, and six individuals preserved in Burmese amber, providing new insights into the origin and early evolution of parental care in carrion beetles, also known as Silphidae.

The specimens "extend the earliest records of the (Silphidae) family by about 130 million years, while they are close to modern forms as evidenced by their clubbed antennae, large mesoscutellum and truncate elytra," Huang said.

Further study using the scanning electron micrographs technology showed that two types of sensory organs are recognizable on the antennal club of the 165-million-year-old Jurassic silphids, perfectly corresponding to those in modern Silphidae, the researchers said.

The identical olfactory structures indicated that silphids in the Jurassic were already adapted to detecting sulfur-containing volatile organic compounds over long ranges, just as in modern Silphidae, they said.

"Mesozoic silphids may have been significant scavengers 165 million years ago," important to the breakdown and recycling of carcasses in ancient ecosystems, Huang said.

The 165-million-year-old Jurassic silphids, however, lack stridulatory files on the abdomen, which are significant for parent-offspring communication and defense, the researchers said, suggesting that "these scavengers did not care for their young, as in modern Silphinae."

The 125-million-year-old Cretaceous silphids are very similar to the Jurassic ones but they possess a pair of stridulatory files, indicating that a simple form of parental care had evolved by this early date, they said.

That meant "adults guarded small carcasses, alerting their brood to the presence of predators and defending them as necessary, " they wrote in the paper.

The 99-million-year-old silphids from Burmese amber have lamellate antennae that are very morphologically close to modern burying beetles, Huang said, suggesting these mid-Cretaceous burying beetles may have exploited and buried small rodents or birds as a source of nutrition for their larvae.

"This finding demonstrates that such significant adaptations, behavioral and morphological, associated with considerable parental investment, were already well established in the Cretaceous," said the researchers said.

"Although parental care is widespread across the hyperdiverse Coleoptera and has evolved independently multiple times, this is the earliest documentation of such behavioral adaptations within the clade."

Competition for resources and predation have been hypothesized as ecological factors important to the evolution of parental care and similar competitive pressures may have triggered the origin of parental care among ancient carrion beetles, the researchers added.

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