Archive for October, 2017

Spider Romance or How to Eat your Mate

October 25, 2017

Halloween decorations often include mock spider webs  because many people think of spiders as creepy.  I don’t.  I think they are fascinating.  There are over 44,000 known species of spiders in the world with about 400 new species named every year.  Most spiders trap their prey in the sticky substance produced in their abdomen, then they quickly pounce on the struggling insect and inject a paralyzing venom that liquefies the insides.  After their prey is subdued the spider sucks the juices from the helpless victim.  I suppose that is an horrifying fate for insects, but people have nothing to fear from such a small organism so vulnerable to a rolled up newspaper.  (I never kill spiders.  Instead, I catch and release them, if they invade my house.)  The spider’s strategy of trapping prey in a web poses a dilemma for males seeking a mate.  It is difficult for a female spider to discern the difference between food and potential sex.  Male spiders must tap on the web in a certain way, communicating to the female they are a sperm donor, not a trapped fly. Mistakes are occasionally made.

Female spiders are larger than male spiders, but in some genera sexual dimorphism is extreme.  Evolution has led to female gigantism among orb-weaving spiders.  Nature has selected for large females and small males in orb-weavers for 4 reasons: a) large females are more fertile and produce more eggs, b) larger females are less likely to fall prey to predators, c) small males reach sexual maturity at an earlier age, and d) small males are better climbers and can reach females faster than others when journeying up the web.  If after sex, a female spider eats a male, there is no great loss.  The female has already been fertilized, and the male is more useful as extra nutrition.  This reproductive strategy is not satisfactory for lampshade spiders.  Female lampshade spiders have larger bodies than males, but the males do have longer legs.  This gives male lampshade spiders the ability to escape after mating, so they can impregnate other females.

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Female and male banana spiders (Nephilia clavipes).  Evolution has selected for large females and small males in spiders.  

Lampshade spiders construct webs in the shape of a lampshade, hence the name.  Females are larger than males in this species as well, but the males have longer legs, so they can escape after mating.

Humans are not as different from spiders as one might think, especially considering risky sex.  People aware of sexually transmitted diseases, including deadly AIDS, are still often willing to have unprotected sex with strangers.  Men and women cheat on their significant others, even though they realize their jealous partner might shoot or stab them, if their indiscretion is discovered.  And some people, mostly men, pay dominatrixes to bind them, putting them in a situation not dissimilar from male orb-weaver spiders.

Many men are attracted to woman who are larger than they are.  My personal preference is for women with really large breasts and buttocks, and I don’t mind if a woman is heavier than I am.  But some men have a fetish for extremely large women…in fact unrealistically giant women, known as giantesses.  They fantasize about a woman who can hold them in the palm of their hand.  The desire male spiders have for gigantic female spiders evidently exists in some human males as well.  Though psychological triggers in the environment probably influence this fetish, there must be something deep inside the mating urge, providing the platform for it to develop in people.  This template is something we share with spiders and likely goes back to a common ancestor over 500 million years ago.

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Many men are turned on by women who are much larger than they are.  Some even fantasize about giantesses.

The association of sexual excitement with fear of being eaten is another characteristic some humans share with spiders and other creatures.  I’m 55 years old, and I thought I was aware of every sexual fetish, but I first learned about the vore fetish within the last year.  Vore is short for devour–some people are sexually excited by the thought of being eaten by their sexual partner.  I don’t really understand this fantasy.  How, for example, does one reach sexual satisfaction after they’ve been eaten?  I think maybe this fantasy has something to do with being in the warm amniotic sac of a woman’s tummy.  Or maybe some are really thrilled with the thought sex might lead to their consumption.  Nevertheless, deep down inside, humans are like spiders in more ways than we would like to admit.

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People are not as different from spiders as one might think.  Some people get sexually excited at the thought of being eaten by their mate.  It’s known as a vore fetish.

Reference:

Kuntac, Matjaz; Jonathan Coddington

“Discovery of the Largest Orb-Weaving Spider Species: The Evolution of Gigantism in Nephilia”

Plos 1  October 2009

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The Oak Colonization of North America

October 19, 2017

Oaks are such an important part of the temperate forest ecosystem that it’s hard to imagine they originally evolved near the arctic circle.  During the Eocene about 45 million years ago the earth was mostly tropical and sea levels were much higher than they are today.  There were no ice caps, and climate at the poles was warm and temperate.  Nevertheless, for almost half the year the sun didn’t rise near the arctic circle, just as today night is nearly 6 months long in places like Alaska.  Seasonal darkness led to the evolution of deciduous trees that saved energy by dropping their leaves during winter when the sun didn’t rise.  This adaptation became a great advantage when worldwide climate cooled.  Deciduous trees pushed south because they were able to survive dormant cool seasons that began to occur during the start of the Oligocene ~33 million years ago.  Deciduous trees, especially oaks, replaced tropical species incapable of coping with winter frosts.  Deciduous trees didn’t waste energy with unnecessary growth during winter.

Evidence of the ancient forests where oaks originated exists near the arctic circle at a site known as Axel Heiberg Forest.  Today, this site is a polar desert, but wind erosion is gradually uncovering the forests that existed here 46 million years ago.  A series of floods, perhaps 1 every 10,000 years, covered these forests in sediment, so there are layers of tree stumps, roots, and fallen logs continuously being revealed, as winds strip the sediment away.  Sediment covered the forests rapidly during these catastrophic floods.  It is not a petrified forest because the geological conditions did not favor fossilization.  So once exposed to air, the ancient wood begins to decay, though the process is slow in cold arid conditions.  Scientists think the environment was a warm seasonal rain forest.  Tree composition consisted of dawn redwood, Chinese cypress, hemlock, pine, spruce, larch, gingko, and extinct species of birch, alder, sycamore, walnut, hickory, and oak.

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Location of Axel Heiberg forest–site of the oldest subfossil remains of oaks. Today, it is a polar desert, but during the Eocene it was a temperate seasonal rain forest.

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Subfossil wood from Axel Heiberg forest.

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Comparison between white oak leaves (top) and red oak leaves (bottom).  White oaks and red oaks ecologically complement each other and colonized North America at the same time.

Oaks are classified into 2 groups–red oaks and white oaks.  Genetic evidence suggests red oaks diverged from white oaks about 33 million years ago when they both began to colonize latitudes south of the arctic circle.  Red oaks produce crops of bitter acorns every other year, while white oaks produce more palatable acorns annually.  The strategic difference in acorn production is an ancient ecological balance, attracting squirrels and other seed distributors equally.  Genetic evidence also shows eastern red and white oaks are sister species to western red and white oaks.  Mexican oaks are sister species to eastern oaks, having diverged between 10-20 million years ago.  Oaks colonized eastern and western North America at the same time, then later eastern oaks invaded Mexico.

Mexico has more species of  oaks than any other region in the world (154 species).  If a region has more species of a genus, it usually is thought to be the region where that genus originated.  Instead, scientists believe Mexico has a greater number of oaks species because of differences in elevation in mountains closer to the equator.  Mexican mountains host many different ecological niches causing frequent speciation among oaks.  This explains why Mexico is home to more species of oaks than any other region in the world, though it is not where they originated.

Reference:

Hipp, Andrew; et. al.

“Sympatric Parallel Diversification of Major Oak Clades in the Americas and the Origin of Mexican Species Diversity”

New Phytologist September 2017

Alligators vs Sharks

October 15, 2017

Bloody battles between hundreds of alligators and sharks were an oddity of nature that occurred infrequently for millions of years.  Alligators are considered a freshwater species, but they do inhabit brackish lagoons and can even live in saltwater environments for weeks.  Alligators foraging near beaches normally prey on fish, shrimp, crabs, wading birds, raccoons, mink, and sea turtles.  Alligators take advantage of weather and tidal conditions that concentrate their prey in confined areas.  During the year 1877 near Jupiter, Florida a strong flood tide trapped a large number of fish in a bend of a tidal inlet, attracting an estimated 500 alligators.  The alligator feeding frenzy lasted for days, and the blood drew hundreds of sharks into the main channel of the inlet.  The current shifted and carried the alligators into the main channel where they fought sharks for hours.  Dead alligators and sharks washed ashore for days, following the battle.  It is unlikely such a spectacle could occur today.  Sharks have been overfished, greatly diminishing their population, and alligators, though on the increase, will never be as abundant as they were when Florida was mostly wilderness.  However, the primeval world was the scene of many alligator vs shark wars because they co-existed for millions of years, often competing for the same prey.  Alligators are a member of the crocodilian family.  The crocodilians evolved at least 83.5 million years ago, and the ancestors of the crocodilians, the Pseudosuchia, originated 250 million years ago.  The ancestors of the alligator’s ancestors undoubtedly came into conflict with sharks.  It’s an ancient rivalry.  Spectacular battles between large groups of alligators and sharks may no longer occur, but individual crocodilians and sharks still eat each other on occasion.

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Alligator preying on a nurse shark at the Ding Darling National Wildlife Refuge near Sanibel, Florida.  This photo is on the cover of this quarter’s Southeastern Naturalist.

An article published in this quarter’s Southeastern Naturalist collects all the known incidences of alligators preying on sharks and vice versa. On Wassaw Island, Georgia a scientist saw an alligator prey upon a bonnethead shark, and he also witnessed another alligator catch and eat a lemon shark.  A case of an alligator preying on a bonnethead took place at St. Mark, Florida as well.  Bonnetheads feed on crabs in shallow water, making them vulnerable to alligator attack.  The photo above shows an alligator preying on a nurse shark. Sharks have been recorded feeding upon bottom-dwelling southern and Atlantic stingrays, and stinging barbs are occasionally found embedded in alligators.

There are no recent incidents of known shark attacks on alligators, but there are 3 records from the late 19th century, including the account mentioned in the first paragraph.  In addition to that account a shark bit an alligator in 2 near Pilot Cove, Florida in 1884, and in 1888 5 or 6 alligators battled a similar number of sharks in the Indian River, resulting in some deaths of both.

Around the world there are numerous cases of crocodiles and sharks eating each other.  Bull sharks venture into fresh water and have been recorded falling victim to Australian salt water crocodiles.  Crocodile remains have been removed from the stomachs of tiger sharks near Australia, South Africa, and Indonesia.  Caimans filled the belly of at least 1 tiger shark off the coast of South America.

Who wins a fight between an alligator or crocodile and a shark?  It depends upon the size of the individual and who bites who first.  The larger individuals have the bigger bite and the advantage, but if they are close to the same size, the first to deliver a serious bite quickly gains the upper hand.

*Note the title of the reference below.  The dispassionate scientifically proper language amuses me to no end.  Translated into layman’s English it means alligators and sharks eating each other.

Reference:

Nifong, James; and Russel Lowers

“Reciprocal Intraguild Predation between Alligator mississippiensis (American alligator) and Elasmobranchiii in Southeastern United States”

Southeastern Naturalist 3 (16) 2017

The North Charleston Mastodon

October 8, 2017

Construction workers digging a foundation for a building in North Charleston, South Carolina 5 years ago uncovered the remains of a mastodon.  Bones including a partial tusk, femur, vertebrae, jaw, ribs, and feet were excavated.  One scientist also examined the surrounding sediment for pollen and plant remains. Apparently, the site was riverbank, and the mastodon likely was covered in flood-borne sediment.  I hope a paper is published detailing the information yielded by this site.  So far, all the information I can find comes from 2 abstracts that described poster presentations of the find at scientific meetings.  The authors didn’t even put the posters on the internet.

One presentation compared the pollen found here to that from other Pleistocene-aged sites located near the present day coast–St. Catherine’s Island, Reid’s and Bell’s Bluff, and a site along the Georgia-Florida border.  All of these sites were farther inland during Ice Ages.  Like these other sites, the North Charleston locality had a strange admixture of species presently found at higher latitudes with those still found in the region.  Water milfoil, an aquatic plant, occurred here.  This is not surprising because mastodons were semi-aquatic.  Hickory pollen was “unusually” abundant, indicating a moist temperate climate, but the pollen of red pine, a northern species, was found in association with sub-tropical Spanish moss.  Other Pleistocene sites in the region yield hemlock, basswood, and walnut–species no longer found this far south.  However, I’m skeptical about the identification of supposed red pine pollen.  This species currently occurs in New England, a region that was under glacial ice for much of the Ice Age when its range was forced south.  I doubt it occurred as far south as South Carolina though because there are no relic populations in the southeast.  Red pine pollen is distinguished from pollen of southern pines on the basis of size.  Pollen grains under 43 micrometers in size are classified as northern species of pine, while those over 43 micrometers are thought to be from southern pines.  Shortleaf pine is a common southern species of pine whose pollen grains overlap in size with red pine pollen grains.  Moreover, under the atmospheric conditions of low CO2 as occurred during Ice Ages, shortleaf pine pollen grains may have been slightly smaller than those of the present day.  In my opinion they look identical as the below photos show.  I believe pollen classified as red pine in the below reference and several other studies is from shortleaf pine which is still widespread in the region.

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Shortleaf pine pollen grains average a “maximum” 50-75 micrometers in size.

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Photos of northern species of pine pollen grains including red pine (Pinus resinosa), jack pine, and white pine.  Red pine and white pine pollen grains easily overlap in size with shortleaf pine.  Therefore, I’m not convinced of palynologists’ claim that red pine occurred in the southeast during Ice Ages.

Reference:

Rich, Fred

“The North Charleston Mastodon Site–New Insights Drawn from Paleoecological Synthesis”

The Geological Society of America: Southeastern Section–64th annual meeting

 

Inner Coastal Plain Deserts of the Ice Ages

October 4, 2017

A new study reinforces evidence, indicating some regions of southeastern North America were harsh environments during climatic phases when the ice sheets that covered Canada were expanding.  The scientists who wrote this paper took cores of sediment from 2 Carolina Bays (Jones and Singletary Lakes) located in Bladen County, North Carolina. Carolina Bays are elliptical depressions found on the Atlantic Coastal Plain that were formed during Ice Ages.  They were created by a combination of peat fires, and wind and water erosion.  The peat fires lowered the elevation, wind blew out the dried unconsolidated sediment, and wind-driven water shaped them into elliptical formations.  Jones and Singletary Lakes were also studied in the early 1950s in 1 of the first paleoecological studies of late Pleistocene environments of the south.  The new study analyzed pollen composition, charcoal abundance, and biomass; and the authors compared their results to the earlier study.  The data was dated using radio-carbon dating.

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Location of Bladen County, North Carolina.  This is the site of the study areas discussed in this blog entry.

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Photo of Singletary Lake, a Carolina Bay.  Scientists took a sediment core at the bottom of this lake and analyzed pollen, charcoal, and biomass abundance over the past 50,000 years.

Between ~60,000 years BP-~30,000 years BP climate fluctuated drastically between warm wet interstadials and cold arid stadials.  The glaciers covering Canada advanced then retreated then advanced again in fits and starts.  During glacial expansion more of earth’s atmospheric moisture became locked in glacial ice, causing prolonged droughts, but this moisture was released when glaciers were in a meltwater phase.  Oak and grass pollen increased during meltwater phases, and so did charcoal abundance.  An increase in vegetation meant there was more biomass to ignite and burn during electrical storms.  Oak and grass were fairly abundant from ~43,000 years BP-~32,000 years BP.  The environment mostly consisted of woodland and grassland during interstadials,  but about 30,000 years BP the situation deteriorated.

Ice sheets maintained a steady expansion from ~30,000 years BP-~21,000 years BP.  The initial drought that struck the region during this phase killed vegetation and caused a temporary spike of charcoal because the dead biomass was so flammable.  But after this initial spike, fire was rare to non-existent here.  Sand dunes rolled across the landscape because much of the region was sparsely vegetated.  I believe scrub oak thickets with thorny plants adapted to arid climates covered much of the landscape, but this type of environment doesn’t produce much pollen.  Thus, the amount of vegetation on the landscape then is understated in the pollen record.  For this reason I don’t believe the landscape was as bare as the authors of this study concluded when they wrote it was a “windswept sandy desert with riparian communities of pine and oak.”  Nevertheless, it was an harsh environment of thorny thickets interspersed with areas of bare soil and long distances between water and wetland environments where some trees and grass still grew.  Some tough species of mammals that could survive in this type of environment included horse, flat-headed peccary, helmeted musk-ox, and hog-nosed skunk.  Bison evolved into a smaller species more capable of living in a drier natural community. Overall, wildlife populations probably declined during this climatic phase.

About 21,000 years ago, the ice sheets began retreating and precipitation increased.  Oak and grass gradually increased in abundance, and eventually mesic species such as cypress, basswood, hemlock, and beech invaded the resulting wetter habitats.  ~12,000 years ago, man colonized the region and overhunted megafauna into extinction.  Human-set fires combined with an increase in biomass not being consumed by megaherbivores caused a great increase in fire frequency.

I’m skeptical of 1 claim made by this paper.  The authors estimated the average annual temperature and precipitation levels based on plant composition assumed from the pollen record.  During the Last Glacial Maximum they estimated the average January temperature at these sites was 20 degrees F, while the average July temperature was 68 degrees F.  However, they use 2 dubious assumptions.  They believe the pollen grains from northern species of pine can be distinguished from those of shortleaf pine, a southern species.  This is a doubtful assumption that I will examine more thoroughly in my next blog entry.  Moreover, the spruce pollen probably originated from an extinct species of temperate tree known as Critchfield’s spruce.  I don’t think they can estimate average annual temperatures based on pollen composition, unless the exact species are known with more certainty.

The outer coastal plain and the continental shelf, which was above sea level from ~80,000 years BP-~7,000 years BP, likely hosted richer environments than the inner coastal plain during stadials.  Sea breezes and weather fronts spawned in the Atlantic Ocean brought more moisture to the coast, allowing this region to maintain a mosaic of woodland, grassland, and wetland; while the inner coastal plain suffered greater aridity.  These fronts usually dissipated before they reached the inner coastal plain.  The coastal region likely served as a refuge for plants and animals that later re-colonized the inner coastal plain when climatic conditions improved.

Reference:

Spencer, Jessica; et. al.

“Late Quaternary Records of Vegetation and Fire in Southeastern North Carolina from Jones Lake and Singletary Lake”

Quaternary Science Review 174 October 2017