Archive for August, 2025

Some Selected Dragonfly Species Native to Georgia

August 27, 2025

There are 125 species of dragonflies that live in Georgia and 6000 species in the whole world. Dragonflies along with damselflies belong to the Odonata Order of insects. They are predatory insects during both their larval and adult stages. Dragonfly larvae are aquatic and crawl along the bottom of ponds and streams where they prey upon insects, snails, worms, tadpoles, and minnows. The larvae molt several times before emerging as adults. Adult dragonflies grab other flying insects such as butterflies and moths, flying ants, mosquitoes, flies, other dragonflies, bees, and even wasps. They use their spiny legs and mandibles to catch their prey. Some species of dragonflies, like some butterflies, migrate, but individuals don’t live long enough to reach the northern parts of their ranges. Instead, descending broods gradually expand their range north during spring and early summer, then during late summer and fall, the next generations migrate south.

Dragonfly lifecycle. They can fly like helicopters, hovering and flying backwards.

During the Paleozoic dragonflies reached astonishing size. Meganuera meganiseptera lived during the Permian Age about 300 million years ago and had a wingspan of 28 inches. This giant species of dragonfly perished during the end of Permian mass extinction when 96% of marine animals and 75% of land animals went extinct. Some scientists think insects can’t grow this large in modern atmospheric conditions because oxygen levels are much lower now than they were then. However, it’s more likely insects don’t grow that large today because they would be more vulnerable to bird predation.

Insects probably don’t grow this large today because they would be more vulnerable to bird predation.

Common species of dragonflies occurring in Georgia today include black saddle bags (Tramea lacerata), green darners (Anax junius), and eastern amber wings (Perithemis tenera). Black saddlebags grow up to 2 inches. I’ve seen these in my yard, far from water. Green darners, so named because they resemble darning needles, are even larger, reaching lengths of 3 inches. I see these nearly every time I walk along a marsh during the warmer months. Eastern amber wings are smaller, less than an inch, and they mimic wasps as a defense mechanism. They occur in swarms.

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Pleistocene Insects from the Yukon

August 20, 2025

Scientists can learn about past climates and environments by studying the insect species composition found in dated layers of sediment. This isn’t possible in most parts of the world because of poor preservation processes, but it is in the Yukon were rapid sedimentation combined with permafrost conditions have preserved insect remains for the past 250,000 years in some localities. This includes 2 full glacial and interglacial climate phases. Today, the Old Crow River valley consists of coniferous forest, wetlands, and wet tundra; but in the past the environment has fluctuated between dry desert grassland during Ice Ages, and open spruce parkland during Interglacial periods. (This region was north of the massive glaciers that covered most of Canada when Ice Ages occurred.) The present day Interglacial is different from previous Interglacial periods because forests are thicker. The extinction of megafauna likely explains why denser forests predominate today. During past Interglacial times herds of horses, camels, mastodons, mammoths, and ground sloths kept woodlands more open.

Location of study area from the below referenced paper.

Insect remains found in sedimentary cores from the Yukon.

A specimen of Dyschirius laevifasciatus was found in a Yukon sediment core. It no longer lives this far north.

A species of rove beetle (not the one in the above photo) that today is only known from the Pacific Coast formerly lived in the Yukon interior. It probably lived on a glacial lake shoreline, similar to the beach zones it occurs in today.

Some fossil insect remains suggests previous Interglacial periods were warmer than the present day Interglacial. Scientists found remains of Dyschirius laevifasciatus, a species of ground beetle that lives much farther south today in sediment layers dating to the Sangamonian Interglacial. Beetles in this genus prefer wet sand habitats, and these remains indicate a glacial lake beach occurred here. They also found remains of a species of rove beetle (Kallisus nitodus) that not only doesn’t live this far north but is today only known from the Pacific Coast. This species formerly was able to range into drier inland habitats. Why its range has contracted is a mystery. Perhaps, it never recolonized the region after a glacial lake dried up.

The insect species composition during previous Interglacial periods differs from present day species composition. There were some species that live in wooded areas–bark beetles, a species of weevil, and a few ant species–but much fewer than today. Even though the climate was warmer and probably wetter than today, forests weren’t as dense, and trees grew farther apart, like a parkland. Steppe grassland species still occurred.

The scientists who authored the below referenced study took sample cores from 4 sites in the Old Crow River Valley. They often encountered ice wedges marking areas when the permafrost melted during previous Interglacial periods. Then the water refroze. The insects were buried in sediment when rivers flooded and when glacial lake levels rose as temperatures increased. The scientists used wet screening to find the subfossil insect parts. Insect exoskeletons float to the surface when sediment is immersed in water. From dozens of sample cores they collected thousands of specimens from over 100 species. Radiocarbon dating can only be used for organic material that is younger than 50,000 years, but insect species composition can be used in conjunction with other methods to date sedimentary layers older than this. Layers with mostly steppe grassland species indicate Ice Ages, and layers with some woodland species indicate Interglacial periods.

Though climate changed in the Yukon, evidence from this study suggests it has changed less here than in other regions of the world. The Yukon is near the Arctic Circle and has remained cold for millions of years.

Kazima, S. et. al.

“Middle Pleistocene (MIS 5) to Holocene Fossil Insect Assemblages from the Old Crow Basin, Northern Yukon, Canada”

Quaternary International 341 August 2014

https://www.researchgate.net/publication/329626444_Middle_Pleistocene_MIS_7_to_Holocene_fossil_insect_assemblages_from_the_Old_Crow_basin_northern_Yukon_Canada

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Great White Sharks (Carcharadon carcharias) Almost Went Extinct During the Last Ice Age

August 13, 2025

Scientists attempting to solve a genetic mystery about great white sharks instead discovered a surprising detail about the history of this species. 20 years ago, scientists learned there were big genetic inconsistencies between great white shark mitochondrial DNA, mostly inherited from the female side, and nuclear DNA material inherited from both parents. This could be caused by genetic variation before speciation, hybridization before speciation, different dispersal patterns between sexes, or different environmental selection processes between sexes. Scientists collected genetic data from great white sharks for 13 years and put this data into different models to try and understand why. They assumed this dissonance was most likely caused by females staying in the same geographic area, while males migrated long distances and interbred with other populations. The models they used couldn’t solve the mystery. Even extreme models that assumed females didn’t migrate at all couldn’t explain why mitochondrial DNA was so different. However, the scientists who studied this did learn great white sharks almost became extinct during the last Ice Age.

Great white sharks almost went extinct during the last Ice Age because their shallow water habitat was replaced by dry land. There were no great white sharks in the Atlantic Ocean until about 7000 years ago, though they may have repopulated it during previous interglacials. Loss of shallow coastal habitat is probably the same reason megalodon went extinct 2 million years ago when Ice Ages became more severe.

Seals make up a good part of great white shark diet in some regions.

Frontal view of a great white shark.

10,000 years ago, great white sharks were on the decline and limited to 1 population between South Africa and Australia. Their favored habitat–shallow coastal waters–was nearly eliminated when sea levels fell, as so much of earth’s atmospheric moisture became locked into massive glaciers. Dry land extended into what was formerly and would become shallow coastal waters. This is also likely the reason megalodon became extinct at the beginning of the Pleistocene. 7,000 years ago, great white sharks began to increase in numbers and today there are 3 populations–the coasts of South Africa and Australia, North Atlantic coasts, and North Pacific coasts. Scientists estimate the great white shark population worldwide is only 20,000. They are still vulnerable to extinction.

Reference:

Lasa-Judart, R.; S. Corrigan, C. Yang

“A Genomic Test of Sex-Biased Dispersal in White Sharks”

PNAS 122 (32) July 2025

https://www.pnas.org/doi/10.1073/pnas.2507931122

See this article for an explanation about how scientists use the molecular clock to study the history of a species.

https://www.nature.com/scitable/topicpage/the-molecular-clock-and-estimating-species-divergence-41971/

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Pleistocene Doves

August 6, 2025

Mourning doves (Zenaida macrura) are the most common bird species in Georgia, but they aren’t nearly as abundant as the now extinct passenger pigeon (Ectopistes migratorius) used to be seasonally in state. Their cooing can be heard in fields and yards throughout the breeding season. It’s a peaceful sound, perhaps explaining why doves are considered a symbol of peace. Mourning doves are an ancient species known to have occurred in North America for at least 2 million years. They favor open habitat with trees for nesting. They feed upon grass seeds, berries, and buds. Meadows, fields, and pastures are where these sources of food abound. Mourning doves found plenty of favorable habitat when Pleistocene megafauna kept woodlands open with their foraging and trampling. Pleistocene-aged fossil and subfossil specimens of mourning doves have been found from California to Florida, and they likely had a continent-wide distribution for over a million years.

Mourning doves are the most common bird species in Georgia.

Non-native Eurasian collared doves occur in Georgia.

Common ground doves range into southern Georgia, but I have only seen them in Florida.

All doves and pigeons belong to the Columbidae family which includes 51 genera and 352 species. Some like the dodo and the passenger pigeon have gone extinct within the past few centuries. The Bermuda dove, an extinct subspecies of ground dove went extinct when rising sea levels at the end of the last Ice Age inundated their habitat. Scientists used to think pigeons and doves diverged from other birds during the Cretaceous when dinosaurs still roamed the earth, but more recent genetic studies suggest they diverged from other birds about 30 million years ago. Their closest living relatives are sand grouses and tropical turacos.

A genetic study places pigeons and doves between sand grouses and turacos. From the below referenced study by Stiller, et al.

Another genetic study determined pigeons and doves diverged from other bird species about 30 million years ago. From the below referenced study by Soares, et al.

3 species of pigeons and doves live in Augusta, Georgia where I reside. Mourning doves are common in my neighborhood, and recently I have been seeing non-native Eurasian collared doves, also known as ring-necked doves (Streptopelia decaocto). City pigeons, also known as rock doves (Columba livia) occur in more urban areas of the city where they nest on buildings. Common ground doves (Columbina passerina) range just south of Augusta. I did see some when I visited Bradenton, Florida a few years ago.

A new study surveyed 82 sites in the Pee Dee Region of the Carolinas, looking for Eurasian collared doves. They found 36 of the sites occupied by this species. 22 of the sites were urban and 14 were rural. The study indicates this species has been undercounted by traditional bird surveys. They are expanding into the piedmont from the coastal plain, a region that experiences more habitat loss.

References:

McNair, D

“Population Persistence and Landscape Use of Eurasian Collared Doves in North Pee Dee Region of the Carolinas”

Southeastern Naturalist 24 (1) 2025

Soares, A.; et. al.

“Complete Mitochodrial Genomes of Living and Extinct Pigeons Revises the Taxonomy of Columbiformes Radiation”

BMC Ecology and Evolution 12 (230) 2016

Stiller, J.; et. al.

“Complexity of Avian Evolution Revealed by Family-Level Genomes”

Nature 629 (8013) 2024

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