Archive for March, 2017

Pleistocene Terrapins (Malaclemys terrapin)

March 20, 2017

Until recently, there was little fossil evidence of diamond-backed terrapins. This species inhabits salt marshes and mangrove swamps from the Gulf of Mexico to Cape Cod, Connecticut.  For most of the past 2 million years, sea level has been much lower than it is today due to the larger ice caps of long-lasting Ice Ages.  This means many potential fossil sites where the remains of terrapins might be found are submerged deep underwater and difficult to access.  Sea level has been the same or higher than it is today probably for less than 20% of the last million years, and this reduced the chances easily accessible fossil sites developed in salt marsh zones.  However, the remains of terrapins dating to the Pleistocene have been excavated from  3 sites in Florida, 1 in Georgia, and 1 in South Carolina.  These specimens weren’t described in the scientific literature until 2012.

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The diamond-backed terrapin is adapted to living in salt marshes.

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Diamond-backed terrapin habitat–a salt marsh.

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Diamond-backed terrapin range map.

The 3 sites in Florida where Pleistocene-age terrapin remains were discovered are Page-Ladson, Aucilla River, and Wekiva River.  Terrapin material turned up at Edisto Beach, South Carolina, and fossil hunters found terrapin bones in spoil piles dumped on Andrews Island, Georgia.  (All of Andrews Island is manmade, consisting of spoil piles dredged from the South Brunswick River, aka Fancy Bluff Creek. The Army Corps of Engineers periodically dredges the river to keep it deep enough for safe shipping. Plants have taken root there and it is an haven for wildlife.) The specimens are thought to be Pleistocene in age because they are associated with bones of other species that lived then.  The 3 sites in Florida and the 1 at Edisto Beach commonly yield bones of extinct Pleistocene mammals.  The spoil piles on Andrews Island contained the remains of snapping turtles (Chelydra serpentina), yellow-bellied cooters (Trachemys scripta), and the extinct giant tortoise (Hesperotestudo crassicutata).  These species all lived during the late Pleistocene.  The presence of these 3 species along with the terrapin indicates the local environment at the time of deposition was a brackish marsh bordering an open grassy savannah. Snapping turtles and yellow-bellied cooters are fresh water species that can tolerate brackish conditions, and giant tortoises preferred dry land environments.

Terrapins are not closely related to sea turtles.  Morphological and genetic evidence suggests they are most closely related to freshwater turtles in the Graptemys genus.  In North America this genus includes 10 species of map turtles and saw backs. Terrapins are the only turtle species uniquely adapted to live in salt marshes.  They have lachrymal salt glands that help them get rid of excess salt.  These are absent on all species of fresh water turtles.  Terrapins are also able to drink the layer of rain water that temporarily floats on top of salt water.  Terrapins feed upon shellfish–periwinkle snails are their favorite but they consume shrimp, crabs, and bivalves as well.

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The salt marsh periwinkle (Littorina irrorata) is the diamond-backed terrapin’s favorite food.

Terrapins were formerly so abundant they constituted the main source of protein for coastal slaves during the 18th and 19th century.  But a faddish craze for turtle soup circa 1900 greatly reduced their numbers.  All of the finest restaurants served turtle soup, and it was the most expensive item on the menu.  I’ve only had the opportunity to eat turtle meat once.  Turtle meat is very delicious, tasting like lobster.  Because terrapins feed on shellfish, their flesh likely reflects their diet.  Terrapins are presently a protected species but are still considered threatened.  Real estate development destroys their habitat, they drown in crab traps, cars run over them, and there are people who still eat them.  Egg-eating raccoons flourish as well, since most large predators that kept their population in check no longer exist on the east coast.  If I get the urge to eat turtle again, I’ll stick with the common snapping turtle which as their name suggests are still common.

Reference:

Ehret, Dana; and Benjamin Atkinson

“The Fossil Record of the Diamond-backed Terrapin, Malaclemys terrapin (Testudines: Emydidae)”

Journal of Herpetology 46 (3) September 2012

 

Pleistocene Oysters (Crassostrea virginica)

March 14, 2017

Before humans harvested them, oysters lived longer, grew larger, and produced denser quantities of offspring.  Scientists compared oyster shells from Pleistocene-age oyster reefs with those from Native-American archaeological sites and modern harvests.  Pre-human contact oysters lived as long as 30 years, while oysters since human colonization never live longer than 6 years.  Pleistocene oysters grew up to 10.2 inches, pre-historic oysters from Native-American middens grew to 7.4 inches, and modern oysters reach 6.1 inches.  Native-Americans harvested oysters in a sustainable way, but populations of oysters since European colonization have been reduced by over 99%, despite restoration efforts.  Pollution and overharvesting have destroyed oyster numbers.  This is unfortunate because oyster reefs are a productive natural community, providing habitat for at least 303 species that have co-evolved with oysters over the past 135 million years, ever since these bivalves first evolved. Scientists estimate the original oyster population of Chesapeake Bay was capable of filtering the entire contents of this estuary in just a few days, so they help clean the water as well.  Modern day estuaries are suffering without more abundant populations of oysters.

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Ancient oyster midden.

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Pelican in front of a Georgia oyster reef at low tide.

A representative of every species living in oyster reefs could fill a big city aquarium.  Barnacles, mussels, clams, and bryozoans attach themselves to the reefs and live out their lives filter feeding just like their hosts.  Mud crabs (Eurypanopeus depressus) graze on the algae and detritus that accumulates on the reefs and sometimes feed upon the smaller oysters.  Oyster pea crabs (Pinnotheres) depend upon reefs for their very survival. The seashore springtail (Anurida maratima), unusual salt water insects, prey on microorganisms living on the reefs.  Amphipods, worms (Polydora and Polychaetas), anemones, mites, and hydroids are commensal animals dependent upon the existence of oyster reefs.  Boring sponges (Cliona) and starfish directly prey on the oysters.

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The seashore springtail is a true insect that lives on oyster reefs.

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The depressed mud crab grazes on algae, detritus, and small oysters on oyster reefs.

Many small species of fish swim in and around oyster reefs during low tide because the structure affords protection from predators.  Species of fish commonly found in Georgia oyster reefs include in order of abundance naked goby (Gobiosoma bosci), feather blenny (Hypoblennius hentzi), skilletfish (Gobiosox strumosus), seaboard goby (Gobiosoma ginsbingi), striped blenny (Chasmodes bosguianus), oyster toad fish (Opsanus sp.), and the crested blenny (Hypleurochilus geminatus).  During high tide larger fish such as sheepshead, black drum, and croakers move in and feed upon the shellfish and smaller fish living on the reef.

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The naked goby is the most common fish living in Georgia oyster reefs.  They feed upon worms, crustaceans, and dead open oysters.

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The skillet fish clings to oysters with its sucking mouth.

Land vertebrates forage oyster reefs during low tide.  Raccoons and wading birds find many a meal on the reefs.  Oyster catchers (Haematopus palliatus) specialize on feeding upon the oysters and other bivalves growing here.  Even boat-tailed grackles exploit oyster reefs–they eat the amphipods and pea crabs crawling over the reef.

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The American oystercatcher thrives on oyster reefs.

Oysters have a complex life cycle.  They expel sperm and eggs into the ocean water, and when these sex cells meet by chance they form larva.  (Oysters change sexes, so that males become females and vice-versa.  Some individuals are hermaphroditic  and expel sperm and egg at the same time.)  The larva lives in the zooplankton until they develop a foot.  The oyster senses pheromones from other oysters on a reef and will attach its foot to the structure where it will remain for the rest of its life, filter feeding upon diatoms, dinoflagellates, inorganic particles, bacteria, and marsh plant detritus.

Oyster reefs also have life cycles.  When oysters begin colonizing an area it is known as the clustering phase.  Oysters attach to each other and on old dead oyster shells during the accretionary stage, building reefs.  Eventually, oysters reach a vertical limit and start building the reef horizontally during the senescent phase.  Large reefs block sediment and shell debris carried by tidal currents and this action can create islands.  Little Egg Island in the middle of the Altamaha River mouth is an example of an island created by an oyster reef.

References:

Bahr, Leonard, William Larsen

“The Ecology of Intertidal Oyster Reefs of the S. Atlantic Coast: A Community Profile”

U.S. Geological Survey 1981

Lockwood, R.; K. Kusperck, S. Bonanani, and Gratt, A.

“Reconstructing Population Demographics and Paleoenvironment of Pleistocene Oyster Assemblages: Establishing a Baseline for Chesapeake Bay Restoration”

North American Paleontological Convention 2014

Rick, Turbin; et. al.

“Millenial-scale Sustainablity of the Chesapeake Bay Native American Oyster Fishery”

PNAS 2016

Wharton, Charles

The Natural Environments of Georgia

Georgia Department of Natural Resources 1978

Shipwrecked on the Florida Coast in 1696

March 10, 2017

During September of 1696 an hurricane wrecked the Reformation on the shore near the present day town of Jupiter, Florida.  The Reformation was a small sailing vessel carrying Jonathan Dickinson and his household along with the crew of mariners.  Dickinson was a Quaker merchant in the process of moving from Jamaica to the new colony of Pennsylvania.  His household included his wife, infant son, 8 African-American slaves, and an Indian servant girl.  They were captured by the hostile Jobeses Indians shortly after salvaging their belongings on the beach.  Spain claimed Florida during this time period, and the Indians were subservient to the Spanish.  Although Spain had signed a peace treaty with England, the Indians never got the message, and they thought they were at war with the British or “Nickaleers” as they called them.  Dickinson’s party considered it wise to pose as Spanish, and this may have saved their lives.  The Indians were suspicious of Dickinson’s true identity but afraid to commit an atrocity against their Spanish masters.  Nevertheless, the Indians stole everything they had, literally stripping the clothes off their backs.  The Indians constantly threatened to kill them and offered little food, giving them 3 meals a week.  Eventually, Dickinson convinced a chief to let them walk north toward St. Augustine.  They traveled naked, exposed to hot days, cold nights and storms; while subsisting on a starvation diet.  After 2 months Spanish soldiers discovered the party and helped them make it the rest of the way to St. Augustine but not before  Dickinson’s cousin (probably weakened by malaria) and 2 of his servants died.  They were well treated by the Spanish who then assisted them to Charleston, South Carolina by providing boats, soldiers, Indian guides, and supplies.  Dickinson kept a journal of this ordeal and later published it.

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An hurricane wrecked the ship carrying Jonathan Dickinson and his family in 1696 near Jupiter, Florida.  The traveled on foot and in canoes from Jupiter to St. Augustine before they received real help.  The Indians they met provided little aid and threatened to kill them.

The Jobeses Indians did not practice agriculture.  Their diet consisted of fish, shellfish, and wild plant foods.  Dried palmetto berries were an important subsistence item, but members of Dickinson’s party had a hard time adjusting to them.  Dickinson described the taste as resembling “rotten blue cheese.”  Despite their starving condition, many in his party spit them out and just couldn’t keep them down.  They did find coco plums and sea grapes more palatable.  Coco plums are a tropical fruit native to south Florida and the West Indies.  The seed is also edible, reportedly tasting like almonds.  Sea grapes are another tropical fruit, though I have seen them as far north as Harbor Island, South Carolina (far outside their official range.)  They are not real grapes–the plant is a member of the buckwheat family.  Dickinson doesn’t mention prickly pears (Opuntia sp.), but this is a common species in the region exploited by the Indians as well.

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Coco plums (Chrisobalanus icaco).  This was 1 of the “berries” Jonathan Dickinson and family had to eat to survive.  They found these more palatable than Carolina palmetto berries.

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Palmetto berries were an important staple item in the Indian diet on the east coast of Florida.  The shipwrecked crew had a hard time tolerating them, even though they were starving.

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Sea grapes (Cocoloba uvifera).  This species is not closely related to real grapes but are in the buckwheat family.  These were also more palatable for the shipwrecked crew than palmetto berries.

The storm surge of the hurricane that wrecked the ship stranded fish for a mile on the beach.  Dickinson’s party gathered as many as they could before they spoiled.  After this, they depended upon the Indians for fish and clams.  Some of the Indians were excellent spear fishers in the surf, and others caught them from canoes at night, using torch lights that attracted the fish.  Dickinson doesn’t specify what kind of fish the Indians gave them with the exception of 1 entry which mentions drum, probably red drum (Scianops ocellatus).  This is the species nearly wiped out by the blackened redfish craze of the 1980s.

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Red drum.  Although they often ate fish on their journey, this is the only species specifically mentioned in Jonathan Dickinson’s journal.

Dickinson’s party didn’t come across cultivated fields until they almost reached St. Augustine.  Here, they found a field of “pompions.”  Pumpkins don’t grow well in Florida.  Instead, these were probably a variety of winter squash.  The Indians who lived north of St. Augustine on the Georgia and South Carolina coast did practice agriculture.  On Dickinson’s journey from St. Augustine to Charleston they were well supplied with corn, beans (which he mistakenly calls “peas”), squash, and unspecified herbs.  They were even able to procure garlic and hot pepper to season the corn and beans.

Dickinson barely mentions the wildlife they encountered.  He saw bear tracks “and the marks of other beasts” in the sand near an inlet.  When they traveled by sail between St. Augustine and Charleston, they often stopped for the night or a few days on the sea islands.  Deer and wild hogs abounded on these islands and their Indian guides hunted them and provided meat for everybody.  There were plenty of rabbits on 1 island but they didn’t stay long enough to hunt them.

Dickinson’s party had to traverse many natural communities between their shipwreck and Charleston such as beach, scrub pine, pine flatwoods and savannah, maritime forests, cypress swamps, mangroves, salt marshes, and ocean inlets.  Florida named a state park in honor of Jonathan Dickinson near the site of their shipwreck, and many of these natural communities are represented there.

Reference:

Dickinson, Jonathan

Jonathan Dickinson’s Journal or God’s Protecting Providence

Florida Classics Library 1985

The Amazing Fishing Spiders (Dolomedes sp.) are Greater than Jesus

March 6, 2017

Fishing spiders are more amazing than the so-called “amazing” Spider-Man. Fishing spiders really exist and have persevered for millions of years, while Spider-Man is a fictional character created by Steve Ditko in 1962.  Fishing spiders are greater than Jesus Christ because there is proof they can walk on water whereas there is little evidence the semi-fictional legend even existed.  The story of Jesus walking on water was invented by the unknown author of Mark, the oldest New Testament gospel, and it was plagiarized by the unknown authors of Matthew and John.  Their stories were so ridiculous they were too ashamed to attach their real names to them. Instead, they forged other people’s names to their scrolls, hoping to avoid ridicule.  Jesus could not walk on water.  The laws of physics as we understand them in the present day demonstrate he would sink.  But fishing spiders use hairs on their legs to stride on the surface tension of water, a feat I’m sure Jesus could not actually accomplish in real life.

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The striped fishing spider (Dolomedes scriptus) is large, growing up to 3 inches long.

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Fishing spider with dinner.

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Fishing spiders walk on water…like Jesus Christ allegedly could do.

Fishing spiders mostly hunt aquatic insects on top of the water, but they can also dive underwater to seize minnows, tadpoles, frogs, and crayfish.  They carry an air bubble with them attached to the hairs on their body when they dive underwater.  Their venomous fangs quickly deliver a mortal bite to their prey and the buoyant air bubble carries them back to the surface.  Fishing spiders are able to sense their prey the same way web-spinning spiders do.  Spiders detect vibrations made by insects captured in their web; fishing spiders feel vibrations made by prey moving through water.  Fishing spiders don’t need webbing to sense prey because water serves as their web.

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An Okefenokee fishing spider (D. okeefenokensis) with a crayfish.  I wonder how they get past the claws. They also prey on small frogs.

There are 9 species of fishing spiders native to North America in the Dolomedes genus.  8 of them are aquatic–the lone exception lives in trees.  The Okefenokee fishing spider lives in south Georgia and Florida but there are several species that occur as far north as southern Canada.  Striped fishing spiders were able to expand their range north following the end of the last Ice Age.  It would be interesting to know how long it took for this dispersal to take place.  It would also be interesting to know the evolutionary relationship between the 9 species and other closely related spiders.  It’s likely they evolved from terrestrial ancestors.  Alas, as far as I can determine, scientists have not yet studied Dolomedes genetics.

 

Coyote (Canis latrans) Evolution

March 2, 2017

The coyote is a remarkably adaptable and intelligent animal. The evolutionary history of this species began about 43 million years ago when its ancestors, the caniforms (dogs, bears, weasels, skunks, and raccoons) diverged from the feliforms (cats, hyenas, mongoose, and civets).  The canis genus likely originated in North America over 5 million years ago, having evolved from a primitive wolf-like animal known as eucyon.  Johnston’s coyote (Canis lepophagus) was an early member of the canis genus that lived in North America during the Pliocene from ~5 million years BP-~2 million years BP.  Most paleontologists who study the anatomy of canids believe C. lepophagus was ancestral  to wolves, coyotes, and dogs. Wolves crossed the Bering land bridge and colonized Eurasia, while coyotes stayed in North America.

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Canis lepophagus attempting to scavenge a carcass of a llama defended by a Borophagus, the bone-eating dog.  This illustration depicts a scene that may have occurred during the early Pliocene or late Miocene over 3 million years ago.  Canis lepophagus is thought to be the common ancestor of wolf, dog, and coyote.

At the Rancho La Brea Tar Pits in California coyote bones are the 3rd most common specimens to be excavated here behind dire wolves (Canis dirus) and saber-toothed cats (Smilodon fatalis).  Timber wolf (Canis lupus) skeletal material is present but uncommon.  The abundance of carnivore specimens from this site allows scientists to study changes over time in the anatomy of these species.  Ice Age coyotes from this locality were larger and more powerful than present day coyotes, and they had larger jaws and teeth.  There are probably a couple of reasons for this size disparity.  Pleistocene coyotes hunted larger prey and had a better diet.  They may have hunted juvenile individuals of megafauna species such as horse, bison, camel, and llama; and there was more meat to scavenge.  Moreover, they had to compete with larger carnivores and likely lived in bigger packs.  Dire wolves competitively excluded timber wolves from coyote range.  This benefitted coyotes as well because there was less of an ecological niche overlap between dire wolves and coyotes than there is between timber wolves and coyotes.  Less than 1000 years after the extinction of the Pleistocene megafauna, coyotes evolved to their present day size and stature.

Dire wolves are long gone and timber wolves have been extirpated from most of their former range, but coyote populations are increasing, and they have re-colonized eastern North America within the past century.  Coyotes are 1 of the few carnivores smart enough to avoid poison bait and traps.  Studies show they produce larger litter sizes in response to human hunting pressure.  Though human hunting of coyotes may cause a temporary decrease in their populations, in the long term their populations increase because they begin producing larger litters.  This explains why their populations increase despite being considered a pest that can be hunted year round with no bag limit.

Coyotes in northeastern North America interbred with the last timber wolves in eastern Canada and dogs, and these coyote-wolf-dog hybrids live in large cities and suburbs.  Genetic studies suggest these hybrids are 65% coyote, 25% wolf, and 10% dog.  Characteristics inherited from dogs help them tolerate urban noise, and some have even learned to look both ways before they cross roads.   They’ve adapted well to living on golf courses, city parks, abandoned farmland, vacant lots, cemeteries, and roadside ditches where they have frequent access to roadkill.  I think coyote-wolf-dog hybrids have colonized southeastern North America as well.  I’ve seen some that look like western coyotes, and others that resemble wolves.  More genetic studies of southeastern coyotes may confirm my hypothesis.

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Coyote-wolf hybrids have colonized northeastern North America.  I hypothesize some coyotes in southeastern North America have also bred with wolves and dogs.

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These photos help distinguish between coyote-wolf hybrids and pure bred coyotes.  I’ve seen canids in Georgia that resemble both.

Reference:

Meachen, Julie; and Joshua Samuels

“Evolution in Coyote (Canis latrans) in Response to Megafaunal Extinctions”

PNAS 2012