New Study of the Seda-DNA in Hall’s Cave, Texas

A new study of seda-DNA and bone DNA from Hall’s Cave documents the changes over time in the plant and animal communities on the Edward’s Plateau in Texas.  Previously, scientists had collected and identified thousands of bones in Hall’s Cave from 56 species of mammals, 30 species of birds, 9 species of amphibians, 3 species of reptiles, and 2 species of fish.  The bones date from the Last Glacial Maximum (~20,000 years BP) to the early Holocene (~9,000 years BP).  The new study extracted DNA from the bones but in addition took samples of DNA from the sediment. (Scientists call DNA from sediment samples, “seda-DNA.”)  Sampling DNA from the sediment has the added advantage of detecting the presence of plant remains that were otherwise unidentifiable, and the presence of animals that perchance left no skeletal remains at all in the cave.  For example 2/36 bone samples were from cat but 7/10 sediment samples detected cat.  Jaguars and bobcats urinated, defecated, and shed hair in the cave but left no skeletal remains.  The seda-DNA samples detected 36 of the 56 species of mammals known to have  occurred in the cave from fossil evidence but they found an additional 7 species of mammals as well as additional species of birds not collected as fossils here, including ducks and geese.  They also determined which species of woodrat lived in the cave, an identification not really possible by just looking at the bones.

Deer mouse, cottontail rabbit, and eastern woodrat were the most common species of small mammals found in the cave since the Last Glacial Maximum, and these species occurred throughout all climate phases.  White-tailed deer and bison were the most common large mammals found in the cave and they too were found throughout all climate phases, though they became less abundant over time.  Hackberry and oak were the most common plant species found in the cave, and they were found throughout all climate phases.  Hackberry still grows near the entrance of the cave.  According to local pollen studies, pine was the most common tree growing on the Edward’s Plateau during the Ice Age, but it is absent from the cave.  Pine simply didn’t grow near the cave.

Hall’s Cave.

Location of Edward’s Plateau.

Dendrogram of species found via DNA sampling in Hall’s Cave.  From the below referenced study.

The study sheds light on the changes that occurred on the Edward’s Plateau since the Last Glacial Maximum.  During the height of the last Ice Age weather patterns differed from those of today–more precipitation fell on southwestern North America whereas southeastern North America was more arid.  As a result, the Edward’s Plateau hosted a prairie environment with trees found at scattered locations.  Soils were much thicker because dense grass regularly decayed.  Deeper soils were good environments for prairie dogs, 13-lined ground squirrels, pocket gophers, and marmots.  Common large mammals included camel, pronghorn, and flat-headed peccary that were preyed upon by saber-tooths, dire wolves, and giant short-faced bears.  Birds that preferred treeless plains–prairie chickens, upland sandpipers, horned larks–abounded here then.

The environment changed here about 15,000 years ago during the Boling/Alerod Interstadial when temperatures and precipitation increased.  The prairie converted to open woodland and forest with widely spaced oak, ash, juniper, walnut, mulberry, and hackberry trees.  Plenty of grass still grew between the trees…enough to support a population of horses.  Many of the open plains animals disappeared from the record here including the pronghorn, camel, and flat-headed peccary.  Black-tailed jackrabbits, northern grasshopper mice, and prairie chickens all left the area as well.  However, turkey, bobwhite quail, and barking tree frogs moved onto the Plateau because they liked the newly expanded tree and thicket habitats.

12,900 years ago, during the Younger Dryas cold phase, the climate suddenly became much colder and dryer.  Vegetation decreased and the region became desert-like.  Small and large mammal and plant diversity decreased.  Following the end of this cold phase, temperatures and precipitation increased, though rainfall didn’t increase to the levels of the LGM and Boling/Alerod Interstadial.  Soils of the Edward’s Plateau were still thinner than they were during the LGM and today the region is dominated by a plant community of live oak, juniper, and hackberry.  Plant and small animal diversity rebounded but large mammal diversity did not.  The authors of this paper suggest man is likely responsible.  Plant and small mammal ranges adjusted to climate change, and they disappear and re-appear in the seda-DNA samples over time.  If not for overhunting by man, the same should hold true for large mammals.  14 species of large mammals that lived on the Edward’s Plateau during the late Pleistocene are either extinct or extirpated from the region.

Plant and animal composition does not stay constant, and the study found some non-analogue components living side by side.  Today, white-tailed jack rabbits and barking tree frogs have ranges that do not come close to overlapping, but both species lived on the Edward’s Plateau during the Boling/Alerod Interstadial.    Bog lemmings and least weasels ranged much farther south then and co-occurred with species of more southerly affinities.  Animal and plant communities are dynamic and always changing.

Range of barking tree frog.

Range of white-tailed jack rabbit.  White tailed jack rabbits and barking tree frogs both lived on the Edward’s Plateau during a warm interstadial of the last Ice Age, indicating the existence of non-analogue environments dissimilar to any that occur today.

Reference:

Seersholm, F.; et al

“Rapid Range Shifts and Megafaunal Extinctions Associated with Late Pleistocene Climate Changes”

Nature Communications 2020

https://www.nature.com/articles/s41467-020-16502-3#:~:text=Large%2Dscale%20changes%20in%20global,impacted%20ecosystems%20across%20North%20America.&text=Instead%2C%20five%20extant%20and%20nine,the%20end%20of%20the%20Pleistocene.

Tuna- The Superfish

Most people think of tuna as just some fish in a can that is an ingredient in tuna salad.  They don’t appreciate what a spectacular animal it is.  Biology books state that fish are cold-blooded, but tuna are an exception to this rule.  Tuna are actually a warm-blooded fish, and this physiology enables them to swim at ultra high speeds of up to 47 mph.  That is faster than most boats.  However, their warm-blooded physiology has a greater temperature range than those of mammals and birds.  Their blood temperatures do vary, while mammal and bird temperatures generally stay constant, unless they are sick.  The video below shows off the impressive speed of this animal.  They swim with dolphins for protection against sharks, explaining why dolphins can get caught in nets intended for tuna.

 

Tuna are large predatory fish that can swim up to 47 mph.

There are 15 species of tuna within 5 genera including the Allothonnus (thunder tunas), the Auxil (frigate tunas), Euthynnus (little tunas), Katsunnus (skipjacks), and Thunnus (true tunas).  Bonitos are considered a sister species to the tunas, and both are part of the mackerel sub-group.  4 species of tuna overwhelmingly make up the tuna found in supermarket cans and at fish markets and sushi restaurants.  These include bluefin, yellowfin, skipjack, and albacore.

Tuna did not become a popular food fish until well into the 20th century, but now every grocery store in the U.S. stocks tuna.  It doesn’t seem likely to me that this can go on forever.  Eventually, wild tuna populations will become too depleted to support this fishery.  The future of tuna remaining a staple in our diet is aquaculture, but tuna fish farming is in its infancy.  Some Japanese have had experimental tuna fish farms for decades, but the 1st tuna farm in America just opened business last year in San Diego.  Tuna fish farming, unlike tilapia, catfish, and salmon aquaculture, has a long way to go.

There is evidence from Indonesia that humans caught tuna as early as 42,000 years ago. (See: https://markgelbart.wordpress.com/2011/12/07/deep-sea-fishing-42000-bp/ ) It’s surprising some primitive people had deep sea fishing technology that early, though tuna swam closer to shore during the Pleistocene because land extended over the continental shelf and deep waters were located closer to the coast then.

The most common species of tuna found in a can–albacore.

500 pound tuna are worth over 3 million dollars to sushi chefs.

1 of my favorite summer dishes is tuna noodle salad and it is very easy to make. Mix a 12 oz package of tuna with the juice of a lemon.  Add a 16 oz box of cooked macaroni, mayo to taste, a can of peas, chopped celery, chopped Vidalia onion, and couple of chopped hard boiled eggs. Stir it up and serve it warm or cold from the refrigerator.

This is my tuna noodle salad.  It’s great warm or straight out of the refrigerator on a hot summer’s day.

North American Army Ants

Most people are familiar with the army ants of South America and the driver ants of Africa featured in many nature documentaries, but few are aware army ants also occur in North America.  There are 30 species of army ants from the Neivamyrmex genus and 1 species from the Novamyrmex genus living on this continent.  North American army ants differ from those of South America and Africa.  North American army ants cross the landscape in more narrow spear-headed swarms than those of their tropical cousins.  Nevertheless, they are just as predatory.

A species of North American army ant.  Notice how thick their antenna are. Years ago, I witnessed army ants tearing apart an earthworm in Columbia County, Georgia. This photo is by Alex Wild from the below link.

Army ants don’t live in permanent nests.  Instead, they alternate between foraging and stationary phases.  During foraging phases they roam across the land searching for food to feed their larva.  They mostly eat other ants and are built to subdue other species.  They have muscular bodies and thick antennas that other ants can’t bite through.  When the larva go into the pupa stage, army ants enter the stationary phase and live within a swarm of their own bodies.  Colonies produce new queens every 3 years, and the colony will split into 2 after the new queen is born.  Most army ant colonies perish when the queen dies, but some manage to track down a closely related queen and will merge with that colony.

There are over 200 species of army ants worldwide including 5 genera in the Americas and 2 genera in Africa and Asia.  A study of army ant genetics determined some genera of American army ants are closely related to African army ants.  They diverged 100 million years ago before Africa and South America drifted apart.  Other genera of army ants are not closely related to other army ants and are examples of convergent evolution.

Range map of army ants in North America.  Map is also from the below reference.

Cold climate apparently is a limiting factor for army ant distribution, but it might not be the temperatures.  I noticed in the map of their distribution that the northern limits of their range approximately corresponds to the southern limit of Ice Age glaciers.  Like many species of trees, they simply have been unable to colonize deglaciated territory even though they can survive the cold temperatures of Iowa and Nebraska.

Reference:

Most of the information for this blog entry comes from Alex Wild, a Texas entomologist.  This links to his website.

http://www.myrmecos.net/2008/12/14/army-ants-of-the-north/

Another Pleistocene Survivor–The Bird-Voiced Tree Frog (Hyla avivoca)

I discovered a new creature in my yard.  Green tree frogs (Hyla cinerea) are abundant here and often sneak into our house, but I was unaware that my yard is also home to the bird-voiced tree frog until I saw the below specimen in my cat’s water dish.  I saw another one a few weeks later.  Most of the time they stay in the tree tops and that is probably why I’d never seen one before, though maybe they had a good few years of reproduction and are on the increase at my locality.  Bird-voiced tree frogs can be green or gray, depending upon the temperature.

Bird-voiced tree frog.

Video of a bird-voiced tree frog call.

Bird-voiced tree frogs have an interesting range distribution.  They likely diverged from their closest living relatives in the Mississippi River Valley and dispersed across Alabama and Georgia.  Their preferred habitat is swampy bottomland forest, and during warm climate cycles this type of habitat is common in the southeast.  The habitat in my yard is a sandhill loblolly pine/sand laurel oak woodland, but McBean Creek bottomland is just about a mile away.  Bird-voiced tree frogs are absent from peninsular Florida.  They may have occurred in peninsular Florida in the past but were extirpated when most of the state was under ocean during marine high stands.

Bird-voiced tree frog range map.

I searched the paleobiology database and learned no fossils of this species have ever been found.  A small animal that lives in a forest has a lesser chance of becoming preserved as a fossil.  Leaves turn the soil acid, dissolving bones.  As far as I can determine, no genetic studies of bird-voiced tree frogs have ever been conducted.  It is an understudied species.

Permafrost as far South as Georgia during the Last Glacial Maximum

This is at least the 7th article I’ve written about Carolina Bays, but I keep coming across new and fascinating studies of these curious geological features. (See: https://markgelbart.wordpress.com/?s=Carolina+Bays ) These oval shaped depressions occur across the Carolinas and Georgia.  Their origins baffle scientists, but the commonly accepted explanation is they are topographical formations resulting from Ice Age wind and water erosion.  (Extraterrestrial explanations can be ruled out because Carolina Bays are of different ages, and there are 500,000 of them compared to just 250 known impact craters on the entire earth’s surface.)  I’ve long understood how wind and water erosion shaped the depressions, but I’ve never been satisfied with explanations for how the land initially subsided.  Some think wind simply blew unconsolidated sediment out of the pits, while I’ve suggested the land subsidence occurred due to peat fires (as occasionally occurs today).  In a new book Chris Swezey of the U.S. Geological Service proposed the initial subsidence of Carolina Bays was caused by discontinuous patches of permafrost that thawed during summers and collapsed.

Formerly, scientists thought permafrost (ground that stays frozen year round) extended as far south as northern Virginia during the Last Glacial Maximum, but Swezey believes there were patchy discontinuous areas of permafrost as far south as Georgia.  Carolina Bays resemble geological features found in southern Alaska today where permafrost is scattered and temporary.  The land swells and collapses and fills with water in oval depressions.  Northern Alaska hosts continuous permanent permafrost.

Discontinuous patches of permafrost create lakes in southern Alaska that resemble Carolina Bays located in the upper coastal plain of Georgia and the Carolinas.

Temperature graph showing average temperatures and sea level fall during the Last Glacial Maximum. Note the dips at about 27,000 and 24,500 years BP.  This is when discontinuous permafrost could have developed on some Georgia and Carolina soils.

I believe this map is misleading.  It shows the southern extent of the boreal forest zone, but zonal forest types as we know them today didn’t exist then.  From the below referenced paper.

Georgia must have been much colder during Ice Ages than I thought.  Most Carolina Bays formed between 35,000 years BP-15,000 years BP when glaciers expanded to cover Canada and New England.  Some date to earlier stadials of the Wisconsinian Ice Age.  Patchy permafrost in the Carolinas and Georgia likely occurred during especially cold phases of the Ice Age that probably lasted for decades rather than centuries.

Landscapes in Georgia during the LGM must have been varied and interesting.  Wetlands on Carolina Bays likely attracted summer populations of ducks, geese, and swans.  Sand dunes from dried out riverbeds rolled over the land, smothering mixed woodlands of pine, spruce, and oak.  Arid conditions favored grasslands that fed horse, bison, and llama; in turn pursued by giant lions and dire wolves.  Strange as it may seem, caribou and stag-moose ranged into this latitude.  Zonal vegetation as we know it didn’t exist then.  Instead, habitats were patchy and species compositions were dissimilar to those of any existing types of forest.  Local microclimates might favor oak thickets, open spruce woodlands, mature pine forests, grassy meadows, small marshy wetlands, or bare soil.  Less than 100 miles east of the inner coastal plain the climate was markedly warmer.  Land extending into what today is the Atlantic Ocean  hosted more warm weather species of plants and animals because it was closer to warmer ocean currents that moderated coastal climates.  Inland, the boundary between cold and warm climates frequently fluctuated, contributing to the patchy unstable environments unlike those of today.

Reference:

Swezey, Chris

“Quaternary Eolian Sand Dunes and Carolina Bays of the Atlantic Coastal Plain Province, USA”

in

Inland Dunes of North America

edited by Lancaster, Nicholas and Patrick Hesp

Springer Books 2020