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Lab 10   Physiology of the Circulatory System

 

 

Introduction: The human circulatory system is a collection of structures thorough which oxygen and nutrient rich blood flows to all tissues of the body for metabolism and growth, and to remove metabolic wastes. The blood is pumped to these tissues by the heart through a circuit composed of arteries, arterioles, capillaries, venules, and veins. Oxygenated blood is pumped to the tissues from the left side of the heart, whereas deoxygenated blood is pumped to the lungs from the right side of the heart. This circuit where gas exchange takes place within the alveoli of the lung is very important and is known as the pulmonary circuit. When the body is exercised changes can take place in the circulatory system that allow more blood to pass to actively respiring muscle cells and less to nonmuscular tissue. Increased heart rate, arterial pressure, body temperature, and breathing rate also occur during exercise.

Arterial blood pressure is directly dependant on the amount of blood pumped by the heart per minute and the resistance to blood flow through the arterioles. This is an important measurable aspect of the circulatory system and it is measured using a sphygmomanometer. This device has an inflatable cuff that connects to a hand pump and a pressure gauge, graduated in millimeters of mercury, by rubber tubing. The cuff is wrapped around the upper arm and inflated, the person taking the pressure then listens for two sounds and observes the gauge to determine what the blood pressure is. The systolic number is determined by the first noise heard as the cuff is deflated, and the diastolic number is determined by the last distinct noise heard.

Hypothesis: From this experiment it is expected that a subject’s heart rate and blood pressure will change during rest and exercise based on how physically fit they are. If the subject is in good shape the heart rate will not increase significantly and the blood pressure will increase. The opposite is true of someone in poor shape.

Materials: The materials used in this experiment include a blood pressure kit, alcohol swabs, a stopwatch, two depression slides, a cotton ball, four rubber bands, a pipet, a petri dish, a Daphnia culture, a stereomicroscope, and some ice.

Methods:

A. Measuring Blood Pressure: To measure blood pressure, one member of the lab group sat down in a chair, rolled up his sleeve, and then the sphygmomanometer cuff was placed around his upper left arm at heart level. The cuff was then pumped to 200mm Hg, which is safely higher than the blood pressure of the subject. The stethoscope was then placed in the well of the subject’s elbow, where the brachial artery is located, and pressure was slowly released as the taker listened for a pulse. The pressure on the gauge was noted when first sound of Korotkoff was heard, which is the pressure that blood is first able to pass through the artery during systole, representing systolic pressure. The sounds of Korotkoff are heard between the systolic and diastolic blood pressures. The diastolic pressure is the reading of the gauge at the time the sounds of Korotkoff can no longer be heard. The subject’s blood pressure was taken two more times and an average was calculated and recorded in Table 1.

Average Blood Pressure

B. Physical Fitness Test: The first numbers recorded from this section of the experiment were those of standing vs. resting blood pressure. To do this a member of the lab group had to lie down on a table for five minutes. After five minutes the subject’s blood pressure was taken while he was still lying down and the numbers were recorded in Table 2. The subject remained lying down for another two minutes, stood up, and their blood pressure was taken again. The standing systolic pressure was subtracted from the resting systolic pressure and recorded in Table 2. A chart was used to determine the number of points received by the subject and recorded in Table 3.

The next part of this section is where the subject’s standing heart rate was determined. Taken by the subject was the radial artery pulse by counting the number of beats for 30 seconds. That number was multiplied by 2 to obtain the number of beats per minute. That number was recorded in Table 3. Another chart was used to determine the amount of points the subject received for this section and that number was also recorded in Table 3.

Next the resting heart rate was determined by having the subject lie down on a table for five minutes. After five minutes the subject’s pulse was taken and recorded in Table 3. Once again a chart was used to determine the number of points the subject received for this section of the experiment and the number was recorded in Table 3.

Next the Baroreceptor reflex test was given to the subject. The subject had to lie down for five minutes, stand up quickly, and record the pulse. From this number the resting heart rate was subtracted and recorded in Table 3. A chart was then used to determine the number of points the subject received for this section and recorded in Table 3.

The endurance test was the last leg of this section of the experiment. To do this the subject stepped up with one foot onto an 18 inch high surface and then brought up the other foot onto the surface. This was continued for 15 seconds, and then his pulse was taken at several intervals. First the pulse was taken right after the exercise for 15 seconds and multiplied by four. This was repeated one more time after that as well. Then the pulse was taken every 30 seconds for 120 seconds after that. The data was recorded in Table 4. The amount of time it took for the subject’s heart rate to return to normal was figured and a chart was used to award points. These heart rates were then compared to the standing heart rate. Next, the standing heart rate was subtracted from the rate taken right after exercise, and yet another chart was used to award points.

C. Investigating Heart Rate in Daphnia: Two depression slides were obtained and a small piece of cotton was placed in the center of one of the slides. Several Daphnia were placed on the slide with a pipet and the other slide was placed on top of this slide and wrapped together with a rubber band on each end. A petri dish was filled with room-temperature water, 1cm deep and the slides were placed into it. The heart of the largest Daphnia was then located under the stereomicroscope and the number of beats in 15 seconds was determined, multiplied by four, and the results placed in Table 5. Into the dish was then added ice water and the same Daphnia’s heart rate was determined and recorded in Table 5. Gradually warm water was added and the heart rate was taken at five minute intervals until the normal heart rate is noted. These results were put in Table 5.

Results:

Table 1

Table 2

Standing vs. Resting Blood Pressure

Table 3

Fitness Points

Table 4

Heart Rate After Exercise

Questions:

1. What changes occur in the circulatory system when a person stands up from a prone position? How do these changes affect the heart rate and blood pressure of the individual?

The circulatory system is not working very hard when a person is at rest so when that person stands up suddenly the blood pressure and heart rate of that person increase.

2. How does the circulatory system, and the heart in particular, of a conditioned athlete differ from that of a person in poor shape?

The heart of a conditioned athlete is stronger because it has been worked harder pumping more blood when that person exercises. The heart of a person in poor shape has not been worked as hard.

3. Why is high blood pressure dangerous? What health problems does it lead to?

High blood pressure is dangerous because the heart has to work to hard to push the blood through the various veins and arteries and a heart attack can occur.

4. What sort of behaviors encourage high blood pressure? Why?

Eating fatty foods and not exercising cause high blood pressure because the heart is not working hard to pump the blood, which makes it weak.

Table 5

Change in Metabolic Rate

Questions:

1. Why does the rate of activity of ectothermic organisms increase with a rise in the temperature of its environment? How is this different from an endothermic organism?

Ectothermic organisms’ body heat is determined by the environment, so their metabolic rates also change with this. Endotherms have a constant body temperature and do not change their metabolic rate strictly based on environmental conditions.

2. If this experiment were performed on a human subject, what results would you expect? Explain.

A human’s heart would also be affected by the temperature changes, but not to the extent that the Daphnia heart did.

Error Analysis: The only possible source of error in this lab would have been the slight misreading of the gauge on the sphygmomanometer.

Conclusions: Cardiovascular fitness is very important to living a healthy life. If one doesn’t exercise and eat healthy foods they run a risk of being in poor shape and having a heart attack or other serious things. Heart rate and blood pressure readings can give a person a good idea about how healthy they are or how healthy they need to be. Blood pressure is so important to a person’s health it is checked at every visit to the doctor or hospital.

BACK

Introduction to Biology Review

1. All living things are called _______________________.

2. The approximately 40 million types of living things on Earth are known as ______________________.  How many have been identified? __________________.

3. The land, water, and air on Earth that sustains life is known as the ___________________________.

4. A species is a group of organisms so similar to one another that they can _______________________ or _____________________________.

5. Evolution simply means ______________________________________.

6. When hereditary information from two parts of a single organism or from two organisms of the same species is combined it is called  _______________________.

7. An organism that must take in food is a(n) _________________________.

8. The encoded, genetic instructions for making many other molecules necessary for life is called  __________________. 

9.  Produces greatly magnified images of surface details ________________  _____________  __________________  or ______________.

10. Increase of an object’s apparent size is ________________________________.

11. The production of offspring is called __________________________________.

12. The formation of two cells from an existing cell is called ______________   _____________________________.

13. Produces a greatly magnified image of internal details ___________________  _______________   ______________ or _____________.

14. Ultimately, almost all living organisms get their energy from the _______________.

15. ______________________  reproduction involves no recombination of genetic material, or exact duplication of the parent.

16. ________________________ reproduction involves combining hereditary information from two  different species or from two organisms of the same species.

17. A short segment of DNA that contains instructions for a single trait is called a(n) __________________________.

18. What is the smallest unit of life capable of carrying out all life functions?

19. Sum of all chemical processes of an organism _______________________________.

20. Through the process of ____________________________________ plants capture the energy from the sun and change it into a form of energy that can be used by living things.

21. Capability of showing clear details refers to ________________________________.

22. The study of how organisms interact with each other and their environment is called ___________________________.

23. The process by which an adult organism arises is called _______________________.

24. When hereditary information from different organisms is not combined it is called __________________________ reproduction.

25. An organism that makes its own food is called a(n) __________________. Give an example.

26. To maintain their internal organization, all living things must have a constant supply of _____________________.

27. Reproduction involves the transfer of genetic information from _____________________  to ____________________.

28. The stable internal environment maintain by living things is called ________________.

29. The most important driving force in evolution is ____________________.

30. The scientific process that involves using the five senses is _______________________.

31. Data that are quantitative are always represented by __________________________.

32. A hypothesis is a statement that can be _______________________________.

33. A broad and comprehensive statement of what is believed to be true is a(n) ______________________________.

34. A small part used to represent an entire population is called a(n) __________________________________.

35. Organisms that are composed of only one cell are called _________________.

36. Organisms composed of more than one cell, such as a plant, are called ______________________.

37. What type of microscope has the greatest magnification?

38.  Cell division and cell enlargement together results in ____________________.

39. Cell division and cell differentiation results in ________________________.

40. How does a theory differ from a hypothesis?

41. List the six major characteristics of living things.

42.  Compare cell division in unicellular & multicellular organisms.

43. Why is it important for scientist to communicate about their work?

44. Why do scientists use SI rather than the system of measurement adopted for use in their own country?

45. How do autotrophs differ from heterotrophs in obtaining energy?

46.  Would a field biologist who studies the ecology of a bird species necessarily use the same scientific methods as a laboratory biologist who studies how a virus infects cells?  Why or Why Not?

47.  How does the growth of a nonliving thing differ from growth of a living thing?

48. Why are so many organisms yet to be discovered, identified, and described?

49. List the six major themes of biology.

SECTION 46-1,  THE HUMAN BODY PLAN

The human body begins to take shape during the earliest stages of embryonic development.  While the embryo is a tiny hallow ball of dividing cells, it begins forming the tissues and organs that compose the human body.  By the end of its third week, human embryo has bilateral symmetry (a body plan in which the left and right sides mirror each other) and is developing vertebrate characteristics that will support an upright body.

OBJECTIVES:  Define Anatomy and Physiology, and explain how they are related. List and describe the major characteristics of life. Define homeostasis, and explain its importance to survival. Describe a Homeostatic Mechanism.List and describe the four types of tissues that make up the human body.  Explain how tissues, organs, and organ systems are organized.  Summarize the functions of the primary organ systems in the human body. Name and locate four human body cavities, and describe the organs that each contain. Properly use terms that describe relative positions, body sections, and body regions.

1. The human body is a precisely structured container of Chemical Reactions.

2. Biology is the Study of Living Things including the Study of the Human Body.

3. The Study of BODY STRUCTURE, which includes Size, Shape, Composition, and perhaps even Coloration, is called ANATOMY.

4.  The Study of HOW the BODY FUNCTIONS is called PHYSIOLOGY.

5. The purpose of this course is to enable you to gain an understanding of Anatomy and Physiology with the emphasis on Normal Structure and Function.  You will examine the anatomy and physiology of the major body systems.

LEVELS OF STRUCTURAL ORGANIZATION

1. CHEMICAL LEVEL

A. The Chemicals that make up the body may be divided into TWO major categories:  INORGANIC AND ORGANIC.

B. INORGANIC CHEMICALS are usually simple molecules made of one or more elements other than CARBON.  Examples:  Water, Oxygen, Carbon Dioxide (an exception), and Minerals such as iron, calcium, and sodium.

C. ORGANIC CHEMICALS are often VERY Complex and ALWAYS CONTAIN THE ELEMENTS CARBON AND HYDROGEN.  Examples:  Carbohydrates, Fats, Proteins, and Nucleic Acids.

2. CELLULAR LEVEL

A. The SMALLEST LIVING UNITS OF STRUCTURE AND FUCTION ARE CELLS.

B. Cells are the smallest living subunits of a multicellular organism such as a human being.

C. There are many different types of cells; each is made of chemicals and carries out specific chemical reactions.

3. TISSUE LEVEL

A. A Tissue is a group of cells with similar structure and function.

B. There are FOUR Groups of Tissue.

C. EPITHELIAL TISSUE – Cover or line body surfaces; some are capable of producing secretions with specific functions.  The outer layer of the Skin and Sweat Glands are examples of Epithelial Tissue.

D. CONNECTIVE TISSUE – Connects and supports parts of the body; some transport or store materials.  Blood, Bone, and Adipose Tissue (Fat) are examples.

E. MUSCLE TISSUE – Specialized for CONTRACTION, which brings about movement.  Our Skeleton Muscles and the Heart are examples.

F. NERVE TISSUE – Specialized to generate and transmit Electrochemical Impulses that regulate body functions.  The Brain and Optic Nerves are examples.

4. ORGAN LEVEL

A. An Organ is a group of TWO or more different types of Tissues precisely arranged so as to accomplish Specific Functions and usually have recognizable shape.

B. Heart, Brain, Kidneys, Liver, Lungs are Examples.

5. ORGAN SYSTEMS (System Level)

A. An Organ System is a group of organs that all contribute to a Particular Function.

B. Examples are the Circulatory, Respiratory, and Digestive Systems.

C. Each organ system carries out its own specific function, but for the organism to survive the organ systems must work together- this is called INTEGRATION OF ORGAN SYSTEM.

6. ORGANISM LEVEL

A. The MOST Complex Level.

B. ALL the Organ Systems of the body functioning with one another constitute the TOTAL ORGANISM – ONE LIVING INDIVIDUAL.

LIFE PROCESSES or CHARACTERISTICS OF LIFE

1. All living organisms carry on certain processes that set them apart from nonliving things.

2. The Following are Several of the more important life processes of Humans:

A. METABOLISM is the sum of all the chemical reactions that occur in the body.  One phase of Metabolism called CATABOLISM provides the ENERGY needed to sustain life by BREAKING DOWN substances such as food molecules.  The other phase called ANABOLISM uses the energy from catabolism to MAKE various substances that form body structures and enable them to function.

B. ASSIMILATION is the changing of Absorbed substances into forms that are chemically different from those that entered body fluids.

C. REPONSIVNESS is the ability to Detect and Respond to changes Outside or Inside the Body. Seeking Water to quench thirst is a response to water loss from body tissue.

D. MOVEMENT includes motion of the whole body, individual organs, single cells, or even structures inside cells.

E. GROWTH refers to an Increase in Body Size.  It may be due to an increase in the size of existing cells, the number of cells, or the amount of substance surrounding cells. It occurs whenever an organism produces new body materials faster than old ones are worn out or replaced.

F. DIFFERENTIATION is the process whereby unspecialized cells become specialized cells.  Specialized Cells differ in Structure and Function from the cells from which they originated.

G. REPRODUCTION refers either to the formation of new cells for Growth, Repair, or Replacement or to the making of a New Individual.

H. Others Include:
Respiration – obtaining Oxygen.
Digestion – Chemically and Mechanically breaking down food substances.
Absorption – The passage of substances through certain membranes.
Circulation – the movement of substances within the body in Body Fluids.
Excretion – Removal of wastes that the body produces.

MAINTENANCE OF LIFE OR SURVIVAL NEEDS

1. The structures and functions of almost all body parts help maintain the Life of the Organism. The ONLY Exceptions are an Organisms Reproductive Structures, which ensure that its species will continue into the future.

2. Life requires certain Environmental Factors, including the Following:

A. WATER – this is the most abundant chemical in the body and it is required for many Metabolic Processes and provides the environment in which Most of them take place. Water also transports substances within the organism and is important in regulating body temperature.

B. FOOD – the Substances that provide the body with necessary Chemicals (Nutrients) in addition to Water. Food is used for Energy, supply the raw materials for building new living matter, and still others help regulate vital chemical reactions.

C. OXYGEN – It is required to release Energy from food substances. This energy, in turn, drives metabolic processes. Approximately 20% of the air be breathe is oxygen.

D. HEAT (BODY TEMPERATURE) –  a form of energy, it is a product of Metabolic Reactions. Normal Body Temperature is around 37 C or 98 F. both low or high body temperatures are dangerous to the organism.

E. PRESSURE (ATMOSPHERIC) – Necessary for our Breathing.

PRINCPAL ORGAN SYSTEMS OF THE HUMAN BODY (TABLE 46-1)

1. INTEGUMENTARY SYSTEM

A. The Skin and Structures derived from it, such as hair, nails, and sweat and oil glands.

B. Is a barrier to pathogens and chemicals (Protects the body), Helps regulate body temperature, Eliminates waste, Helps synthesize vitamin D, and receives certain stimuli such as Temperature, Pressure, and Pain.

2. SKELETAL SYSTEM

A. All the Bones of the body (206), their associated Cartilage, and the Joints of the Body.

B. Bones Support and Protect the body, assist in body movement, They also house cells that produce blood cells, and they store minerals.

3. MUSCULAR SYSTEM

A. Specifically refers to Skeletal Muscle Tissue and Tendons.

B. Participates in bringing about movement, maintaining posture, and produces heat.

4. CIRCULATORY A nd CARDIOVASCULAR SYSTEM

A. The Heart, Blood and Blood Vessels.

B. Transports oxygen and nutrients to tissues and removes waste.

5. LYMPHATIC SYSTEM- Sometimes included with the Immune System or Circulatory System becuase it works closely with Both Systems.

A. The Lymph, Lymphatic Vessels, and Structures or Organs (Spleen and Lymph Nodes) containing Lymph Tissue.

B. Cleans and Returns tissue fluid to the blood and destroys pathogens that enter the body.

6. NERVOUS SYSTEM

A. The Brain, Spinal Cord, Nerves, and Sense Organs, such as the eye and ear.

B. Interprets sensory information, Regulates body functions such as movement by means of Electrochemical Impulses.

7. ENDOCRINE SYSTEM

A. ALL Hormone producing Glands and Cells such as the Pituitary Gland, Thyroid Gland, and Pancreas.

B. Regulates body functions by means of Hormones.

8. RESPIRATORY SYSTEM

A. The Lungs and a series of associated passageways such as the Pharynx (Throat), Larynx (Voice Box), Trachea (Windpipe), and Bronchial Tubes leading into and out of them.

B. Exchange oxygen and carbon dioxide between the air and blood.

9. DIGESTIVE SYSTEM

A. A long tube called the Gastrointestinal (GI) Tract and associated organs such as the Salivary Glands, Liver, Gallbladder, and Pancreas.

B. Breaks down and absorbs food for use by cells and eliminates solid and other waste.

10. URINARY And EXCRETORY SYSTEMS

A. The Kidneys, Urinary Bladder, and Urethra that together produce, store, and eliminate Urine.

B. Removes waste products from the blood and regulates volume and pH of blood.

11. IMMUNE SYSTEM

A.  The Immune System Consists of Several Organs, as well as White Blood Cells in the Blood and Lymph.
Includes the Lymph Nodes, Spleen, Lymph Vessels,Blood Vessels, Bone Marrow, and White Blood Cells (Lymphocytes).

B. Provides protection against Infection and Disease.

12. REPRODUCTIVE SYSTEM

A. Organs that produce, store, and transport reproductive cells (Sperm and Eggs).

B. Produces eggs and sperm, in women, provides a site for the developing embryo-fetus.

HOMEOSTASIS

1.  All of the above systems function together to help the Human Body to Maintain HOMEOSTASIS.

2.   A person who is in good health is in a state of Homeostasis.

3.   Homeostasis reflects the ability of the body to maintain relative Stability and to Function Normally despite constant Changes.

4.   Changes may be External or Internal, and the body must Respond Appropriately.

5.   As we continue to study the Human Body, keep in mind that the Proper Functioning of each Organ and Organ System has a role to perform in maintaining HOMEOSTASIS.

6.  The Human Body uses Homeostasis Mechanisms to maintain its stable internal environment. Homeostasis Mechanisms work much like a Thermostat (NEGATIVE FEEDBACK) that is sensitive to temperature and maintains a relative constant room temperature whether the room gets to Hot or Cold.

BODY CAVITIES

1. Many  organs and organ systems in the human body are housed in compartments called BODY CAVITIES. (Figure 46-2)

2.  These cavities protect delicate internal organs from injuries and from the daily wear of walking, jumping, or running.

3.  The body cavities also permit organs such as the lungs, the urinary bladder, and the stomach to expand and contract while remaining securely supported.

4.  The human body has FOUR Main Body Cavities:

A.  CRANIAL CAVITY – encases the brain.

B.  SPINAL CAVITY – extending from the cranial cavity to the base of the spine, surrounds the Spinal Cord.

THE TWO MAIN CAVITIES IN THE TRUNK OF THE HUMAN BODY ARE SEPARATED BY A WALL OF MUSCLE CALLED THE DIAPHRAGM.

C. THORACIC CAVITY – The upper compartment, contains the heart, the esophagus, and the organs of the respiratory system – the lungs, trachea, and bronchi.

D.  ABDOMINAL CAVITY – The lower compartment, contains organs of the digestive, reproductive, and excretory systems.

ANATOMICAL TERMINOLOGY

To communicate effectively with one another, researchers and clinicians have develop a set of Terms to describe anatomy that have precise meaning.  Use of these terms assumes the body in the ANATOMICAL POSITION.  This means that the body is standing erect, face forward with upper limbs at the sides and with the palms forward.

RELATIVE POSITION

Terms of Relative position describe the location of one body part with respect to another.  The include the following:

1. SUPERIOR – means that a body part is above another part or is closer to the head.

2. INFERIOR – means that a body part is below another body part or toward the feet.

3. ANTERIOR – means toward the front.

4. VENTRAL – also means toward the front

5. POSTERIOR – is the opposite of anterior; it means toward the back.

6. DORSAL – also is the opposite of anterior; it means toward the back.

7. MEDIAL – relates to an imaginary midline dividing the body in equal right and left halves. Sample:  The nose is medial to the eyes.

8. LATERAL – means toward the side with respect to the imaginary midline.  Sample:  The ears are lateral to the eyes.

9. PROXIMAL – describes a body part that is closer to a point of attachment or closer to the trunk of the body than another part.  Sample:  The elbow is proximal to the wrist.

10. DISTAL – is the opposite of proximal.  It means that a particular body part is farther from the point of attachment or farther from the trunk of the body than another part.  Sample:  The fingers are distal to the wrist.

11. SUPERFICIAL – means situated near the surface.

12. PERIPHERAL – also means outward or near the surface.

13. DEEP – describes parts that are more internal.

14. CORTEX  –  the outer layer of an organ

15. MEDULLA –  the inner portion of an organ.

Battle of the Hermaphrodites

Sexes Clash Even When Sharing the Same Body

DUELING FLATWORMS. Two hermaphroditic flatworms, Pseudobiceros bedfordi, each with pale, side-by-side penises, show their undersides as they square off to mate. Michiels

Many snails, slugs, and worms are so-called internally fertilizing, simultaneous hermaphrodites. In any encounter, such creatures can deliver sperm, receive it for fertilizing eggs internally, or do both.  Nico Michiels, an evolutionary ecologist at the University of Tübingen in Germany , offers the striking example of hermaphroditic polyclad flatworms called Pseudobiceros bedfordi.  When two of these small, speckled sea worms meet to mate, there’s no taking turns. Each worm, 2 to 6 centimeters long, wields its pair of side-by-side penises like a weapon. One worm tries to fertilize the other by ejaculating anywhere on its partner’s body, splashing it with sperm in a cocktail that dissolves flesh. After the brew eats a hole through the skin, the sperm work their way through various tissues until they reach the eggs.

In many P. bedfordi encounters, only one member of the pair gets its sperm to the other’s eggs. The recipient of the sperm eventually deposits clutches of hundreds of eggs on some suitable surface and glides away. The holes and wrinkly streaks on many worms’ bodies are ejaculate burns, says Michiels. It’s not that the duelists could choose a less violent way to couple. In these worms, the reproductive tract has an opening, but it doesn’t lead to the eggs.

And in many other simultaneous hermaphrodites, if one partner deposited sperm into the other’s reproductive tract, elaborate plumbing would divert a sizable portion of the sperm to digestive organs, presumably as a snack for the recipient. Of course, animals with separate sexes can be rough and tumble too, says Michiels. However, he and a colleague propose that gender wars are more likely to flare into bodily harm among simultaneous-hermaphrodite species with internal fertilization than among their separate-sex counterparts.

In the violence that’s evolved in many of these simultaneous hermaphrodites, says Michiels, “the result is an almost ridiculous escalation.”  The mating quirks of simultaneous hermaphrodites are attracting growing interest. Researchers are exploring the sexual conflicts that escalate into bodily harm. A few species, however, have gone in the other direction, developing systems for cooperative bouts of mutual insemination or for taking turns. From Michiels’ perspective, though, hermaphrodites “tell us it’s very useful to have the sexes separate.”

Formerly Benign

Roughly 15 percent of animal species live a hermaphroditic lifestyle of some form, Michiels estimates. Many of them are sequential hermaphrodites, such as clown fish that spend their young adulthood as one gender and then switch to the other. Among the animals that are simultaneously male and female, Michiels distinguishes between hermaphrodites where partners make contact to achieve internal fertilization and those in which at least one of the partners releases a cloud of gametes, so the partners don’t themselves make physical contact. According to Michiels, the fertilizers without partner contact are less likely to careen into a violent conflict than are hermaphrodites with full-contact internal fertilization.

For years, biologists didn’t think much about sexual conflict, even in species with separate sexes, says Nils Anthes, also of Tübingen. Mating seemed “benign,” as Anthes puts it. Both males and females have urges for offspring, so at first glance, producing youngsters should be a happy, family project.

That rosy view began fading in 1948, when fruit fly researcher Angus John Bateman of England argued that males invest much less energy in producing offspring than females do. That investment gap suggested that the best reproductive strategy for one sex isn’t equally good for the other. Bateman argued that the average male would do well to mate as widely as possible, while a female should be particular about whose sperm she accepts. What could make better tinder for conflict between the sexes?

In 1979, theorist Eric Charnov, now at the University of New Mexico in Albuquerque , proposed that these ideas could apply to simultaneous hermaphrodites. For example, conflicts could arise as individuals of those species sort out when to play each sexual role.

For years, theorists assumed that tactics in the hermaphrodite gender war would be fairly consistent within an individual or even a species, says Anthes. However, in the July Animal Behaviour, Michiels, Anthes, and Annika Putz, offer what they call a new framework for thinking about hermaphrodites. It urges theorists to compare his and hers benefits under changeable, thus realistic, conditions. Strategies could vary, for example, with the characteristics of available partners. In another paper, Michiels and Anthes report that sea slugs donate more sperm to a partner that’s been isolated than to one that’s recently mated and so already carries plenty of sperm.

Mate This

Some of the mating habits of simultaneous hermaphrodites can be difficult for humans to understand. For that reason, the University of California , Santa Cruz doesn’t emphasize that its athletic teams’ mascot, a hermaphroditic banana slug, has been reported to practice apophally, or penis biting. Theorists have proposed several dramatic hypotheses about the conflicted sex lives of the big, land-living, bright-yellow slugs. One focused on the possible value of a detached organ as a barrier to the recipient mating with others.

Heike Reise of the State Museum of Natural History in Görlitz , Germany , suggests something simpler: The worms just get stuck. The reproductive-tract muscles may sometimes grip its partner’s penis too tenaciously. This would explain reports of slugs appearing to strain apart before one bites off its partner’s penis.

These and other hermaphroditic matings that look like maulings have inspired many scientific publications in recent years. Michiels and Leslie Newman described in 1998 what has become a classic example, called penis fencing, in the Pseudoceros bifurcus marine worm from Australia ‘s Great Barrier Reef . When potential mates meet, they rear up and face off, feinting and dodging.

The researchers argued that each worm was trying to fertilize the other’s eggs while minimizing the sperm it receives. A worm delivers its sperm by using its penis to punch a hole in the partner’s skin, anywhere on the body. As in the ejaculate-splashing polyclad worms, the sperm’s navigational prowess gets it to the eggs. Since 1998, the scientists have found relatives of P. bifurcus that mate even more aggressively, says Michiels.

“Everybody wants to be male, and nobody wants to be female,” is Michiels’ basic explanation. The species keep evolving tactics, some of them violent, to maximize fatherhood. Michiels and Joris Koene of the Free University in Amsterdam present a mathematical model in the August Integrative and Comparative Biology predicting that hermaphrodite species face an extra-high risk of evolving violence between mates.

If the species had separate sexes, females would act as a safety brake, says Michiels. When the male function starts taking a big toll on female reproduction, females take countermeasures. But that doesn’t happen when each individual is both male and female. To Michiels, the prospects for creatures living this way look so perilous that he speculates that they’re headed for “an evolutionary dead end.”

Doping scandals

Some hermaphrodites have a literal take on Cupid’s arrows. The common brown garden snail (Cantareus aspersus) and members of at least four families of land snails shoot what’s popularly called a love dart.

IT MUST BE LOVE. The sharp calcium spike stuck through the head of the common garden snail on the left was launched during courtship by its mating partner. Chase & Koene

Over some 7 days, a garden snail forms a 9-millimeter-long, sharpened shaft in a gland near the opening of its reproductive tract. As two snails wriggle around, positioning themselves to pump sperm into the reproductive tract of each other, each launches its dart toward each other’s body.

“It’s a strange thing to do to your prospective mate,” notes neurobiologist Ronald Chase of McGill University in Montreal .

Chase got curious about the snails’ darts in the 1980s. The prevailing explanation at the time, he says, had been floating around since the early 18th century: The dart would make the partner more willing to mate.

That explanation was “easy to refute,” says Chase. First, virgin snails don’t shoot a dart when they first mate, and other snails flub the shot about half the time. They either botch the launch so that the dart bounces off the partner without embedding or they miss the partner entirely. In various studies, he and a colleague compared aspects of mating, for example, the length of time that the snails courted before copulating, when snails mated with and without dart piercing. “It made absolutely no difference,” he says.

Having undermined the previous explanation of the dart, Chase began seeking others. He found that snails triumphing at the dart thrust gained an advantage. They sired twice as many offspring as did snails whose darts missed their targets.

Among garden snails, a sticky substance coats the darts, and Chase and a series of collaborators have experimented to see whether the darts deliver some mate-managing chemical. When researchers dissected out snail reproductive ducts that receive sperm and smeared them with dart mucus, the ducts began contracting in ways that Chase speculates would send sperm toward the storage organs on the route to fertilization rather than toward a gland that digests sperm.

These findings suggested that darts deliver snail drugs, but Chase still wondered whether the stabbing itself had an effect. Chase’s McGill colleague Katrina Blanchard has just ruled out that possibility. She removed the dart-making gland and its contents from about 200 garden snails. When these snails mated, she did the stabbing herself, using a syringe to inject either a saline solution or an extract of dart goo. The stabbing and saline injection didn’t boost paternity, but a shot of dart goo did, Chase and Blanchard report in the June 22 Proceedings of the Royal Society B.

Garden snails do well if they make one jab, but other species hold on to their love darts and wield them as daggers. A Japanese hermaphroditic snail stabs its partner some 3,000 times during a single mating encounter, report Koene and Satoshi Chiba of Tohoku University in Sendai , Japan . In work released online for the October American Naturalist, the researchers say that the pattern of darts and daggers throughout the snail family tree shows that among hermaphroditic species, repeated stabbing probably evolved before single-use darts did.

Koene has used dart-stabber family trees to look for evidence of arms-race escalation in sexual traits. He and Hinrich Schulenburg of Tübingen found that among Helicoidea snails, two traits tend to occur in the same species. Fancified darts with flanges deliver extra goo, and elongated sperm-receiving organs diminish the goo’s power by requiring it to act on a greater area of tissue. That pairing looks like the aftermath of escalating conflict, the researchers argued in the March 30, 2005 BMC Evolutionary Biology.

Although the examples are striking, Chase says that he’s not convinced that the males’ and females’ interests clash. Chase and his McGill colleague Kristin Vaga reported in the April Behavioral Ecology and Sociobiology that they haven’t found clear behavioral signs of conflict, such as avoidance, in the mating of garden snails.

Until now, snail love darts have dominated research on mate-controlling chemicals. But other structures are now being considered. A study of common earthworms (Lumbricus terrestris), which are simultaneous hermaphrodites, has found that some 30 of each individual’s 40 special hairs pierce its partner’s skin, according to Koene, Michiels, and Tina Pförtner of Westfaelische Wilhelms University in Münster, Germany. These hair stabs change the partner’s uptake of sperm, possibly by injecting chemicals, the team reported in the December 2005 Behavioral Ecology and Sociobiology.

Anthes is working with the sea slug Siphopteron quadrispinosum. Its penis has an attached stylet that plunges into a partner’s body during mating. The slug taking the hit slows down, so Anthes speculates that the syringelike prong injects a sedative.

Although many simultaneous hermaphrodites play the guy’s role more aggressively than the girl’s, Michiels notes that in a few cases the sperm receiver seems to take charge. He’s found early–20th-century accounts of a rare freshwater European flatworm without a functional penis. Instead, according to the reports, the individual acting as a female thrusts a faux penis into its partner and draws out a supply of sperm.

Equal Partners?

Sex isn’t all conflict, though. Some hermaphrodites take turns being male and female or simultaneously deliver and receive sperm. Scientists had proposed that one partner might become more or less cooperative depending on what the other one just did. Anthes and Michiels have come up with a new method for testing this idea. They studied a “very beautiful” sea slug that’s a simultaneous hermaphrodite, says Anthes.

FAIR TRADE. Two hermaphroditic Chelidonura hirundinina sea slugs prepare for one of several simultaneous sperm exchanges. (Red arrows indicate female openings; yellow arrow shows male organs.) Anthes & Michiels

Yellow and blue lines shimmer along the black body of Chelidonura hirundinina, but what the researchers find even more beautiful is a little fold of skin lined with hairs that guide blobs of sperm from a worm’s testes along a brief trip in the outside world to its penis. The researchers cauterized the groove in a few worms so that sperm wouldn’t reach the penis.

Mating slugs normally exchange some sperm, back off, and then return for another round. They reciprocally transfer sperm five to eight times during a mating. When researchers cauterized the sperm-guiding groove of one slug, so that it no longer provided sperm, the partner broke off the exchanges after only two to four rounds, the researchers reported in the Oct. 11, 2005 Current Biology.

When the researchers have tried the experiment in another species, Chelidonura sandrana, cauterization produced no change in mating. That might have been a disappointment, but Michiels says that the difference between the two species might hold clues to the value of reciprocity.

Such unexpected twists, Michiels says, attracted him to the study of hermaphrodites. “I really had the feeling that we know about males and females,” he says. For hermaphrodites, though, “it’s a completely different world.”

Citation:

Michiels, Nico. “Battle of the Hermaphrodites”. Science News. Sept. 16, 2006; Vol. 170, No. 12.