Investigating Reproductive Strategies

There are two modes of

reproduction, sexual and

asexual.

There are advantages and

disadvantages to both sexual

and asexual reproduction.

Illustrated information sheets

for 12 organisms.

A reference list for more

information about the

organisms used in this activity.

A list of learning objectives

and key ideas to help you

guide classroom discussion

during the activity.

pecial Features

You’ll Find Inside

Class Time:

50 minutes

10 minutes to review activity and make

copies of student pages

Prep Time:

ogistics

Time Required

Copies of student pages

None

Materials

Prior Knowledge Needed

Appropriate For:

Students work in pairs to compare ﬁve aspects of

an organism that reproduces sexually with one that

reproduces asexually. As a class, students share

their comparisons and generate a list of general

characteristics for each mode of reproduction, and

discuss the advantages and disadvantages of both.

bstract

earning Objectives

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Investigating Reproductive Strategies

Primary Intermediate Secondary College

1. Divide students into pairs.

2. Hand each pair:

» The Investigating Reproductive Strategies worksheet (page S-1)

» 2 organism descriptions - one for an organism that reproduces sexually and one for an organism that

reproduces either asexually or using both strategies - (see chart below).

3. Instruct each pair to read about their assigned organisms and complete the comparison table on the

Investigating Reproductive Strategies worksheet.

4. When all pairs have completed the comparison table, have them post their tables around the room.

5. Ask students to walk around the room and read the comparison tables with the goal of creating a list of

general characteristics for organisms that reproduce sexually and one for organisms that reproduce

asexually.

6. As a class, compile lists of general characteristics

for organisms that reproduce sexually and

asexually on the board. Learning objectives and

discussion points for each category on the Investigating Reproductive Strategies worksheet are listed on

pages 2-4 to help you guide the discussion.

7. Ask students to discuss the advantages and disadvantages of each mode of reproduction in their pairs.

Have them prepared to support their reasoning.

8. Add advantages and disadvantages to the list of general characteristics for each mode of reproduction.

9. Lead a discussion on the types of situations or conditions in which each mode of reproduction would be

most advantageous or disadvantageous. Do students think one reproductive mode is generally beer?

Why?

lassroom Implementation

Sexual Asexual Both Sexual and Asexual

Blue-headed wrasse Amoeba Brittle star

Duck leech Salmonella Meadow garlic

Grizzly bear Whiptail lizard Spiny water eas

Leafy sea dragon

Red kangaroo

Sand scorpion

Reproductive strategies used by organisms described in this ac-

Tip: You may wish to have students record their

ideas on a sheet of paper while they read the

comparison tables

Investigating Reproductive Strategies

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Sexual Asexual

Relative

complexity

of organism

(including size)

Learning Objectives/Discussion Points:

• Complex organisms tend to reproduce

sexually.

Learning Objectives/Discussion Points:

• Simple organisms tend to reproduce

asexually.

Number of

parents who

contribute

genetic

information to

the offspring

Learning Objectives/Discussion Points:

• Two parents contribute genetic

information.

• Ospring are unique from their parents

and from each other.

Learning Objectives/Discussion Points:

• One parent contributes genetic

information.

• Ospring are exact genetic copies

(clones) of the parent.

Reproductive

mechanism

Learning Objectives/Discussion Points:

• Gametes from two parents join.

• With sperm fertilize eggs inside the

body, the chances of gametes meeting

are increased. Each individual may

produce fewer eggs and/or sperm.

• When eggs and sperm are released to

join outside the body, the gametes have

a lower chance of meeting. Organisms

that reproduce in this way must produce

many gametes.

Learning Objectives/Discussion Points:

• Asexual reproduction does not involve

gametes.

• Reproduction is by splitting in half,

or forming new individuals that are

released from the “parent.”

What are the advantages and disadvantages of sexual and asexual reproduction?

Is one “better” than the other? You are an Ecologist who wants to nd out. You decide to compare

5 aspects of organisms that reproduce sexually with ones that reproduce asexually. You will begin by

looking at two organisms. Once you make your comparisons, you will share your information with all of

the other ecologists in your class to draw general conclusions about each method of reproduction.

Fill in the table below with information for each organism you have been assigned.

Investigating Reproductive Strategies

This activity was downloaded from: hps://teach.genetics.utah.edu

Print-and-Go™

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Learning Objectives

Sexual Asexual

Relative

amount of

parental care

Learning Objectives/Discussion Points:

• Ospring tend to have longer gestation

periods, and developing ospring are

protected.

• Parents tend to care for their young,

increasing the chances that ospring

will survive.

• Organisms that invest time and energy

in caring for their young tend to have

fewer ospring.

• Some sexually reproducing organisms

neither gestate nor care for their young.

These ospring are vulnerable to

predators or the environment. These

organisms tend to produce large

numbers of gametes and/or ospring.

This increases the chances that some

ospring will survive and reproduce.

Learning Objectives/Discussion Points:

• Ospring receive little or no parental

care.

• Organisms that reproduce by forming

new individuals that separate from the

parent do provide a form of parental

care before the ospring are released.

• Organisms that do not care for their

young tend to produce large numbers of

ospring.

• Organisms where few ospring survive

to reproduce have large numbers of

ospring.

• Organisms that split to produce an

“adult” ospring often can rapidly

reproduce again.

Genetic

variation in

offspring

Learning Objectives/Discussion Points:

• Genetic variation comes only from

sexual reproduction, in which genetic

information from two parents combines.

• Genetic variation helps a species (as

a whole) survive. In the event of a

change in environment or increased

competition for resources, some

organisms may have slight trait

variations (due to genetic variation) that

allow them to survive. Over time, natural

selection may favor these dierences,

resulting in new adaptations.

Learning Objectives/Discussion Points:

• Ospring have little to no genetic

variation. (note: variation does still arise

through random mutation)

• In the event of a change in environment

or competition for resources, ospring

may not have trait variations that will

allow them to survive.

• If a parent has traits that are well

adapted to a particular environment,

its ospring will have these same traits,

which may provide them with a survival

advantage.

Investigating Reproductive Strategies

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Learning Objectives

Overall Learning Objectives/Discussion Points

• There are advantages and disadvantages to both sexual and asexual reproduction.

• For an individual it is “best” if the greatest number of its ospring survive to reproduce, carrying its genes into

the next generation.

• Some species produce large numbers of ospring, but only a few may survive to reproduce. Other species

produce few ospring, but parents provide extended care to improve each ospring’s chance of survival.

• For a species it is “best” if individuals survive and reproduce so that the species does not go extinct.

• Genetic variation, through new combinations of alleles, results only from sexual reproduction. Certain

variations may help individuals survival and reproduce, giving the population the potential to adapt to new

and changing environments.

• Organisms that can use both sexual and asexual modes of reproduction may be most adaptable to dierent

conditions.

Investigating Reproductive Strategies

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(All websites accessed May 2008)

Amoeba (Amoeba proteus)

Anderson OR. 1988. Comparative Protozoology: Ecology, Physiology, Life History. Springer-Verlag.

Sleigh M. 1989. Protozoa and other protists. Edward Arnold Publishers.

Tree of Life Web Project: hp://tolweb.org/accessory/Amoebae?acc_id=51

Rogerson A. 1980. Generation times and reproductive rates of Amoeba proteus as inﬂuenced by temperature

and food concentration. Canadian Journal of Zoology 58(4): 543-548.

hp://www.allsands.com/science/animals/whatisamoeba_ves_gn.htm

hp://www.bartleby.com/65/am/ameba.html

hp://www.tulane.edu/~wiser/protozoology/notes/morph.html

Grizzly Bear (Ursus arctos horribilis)

Defenders of Wildlife, Grizzly Bear Fact Page: hp://www.kidsplanet.org/factsheets/grizzly_bear.html

Craighead JJ, Sumner JS and Mitchell JA. 1995. The grizzly bears of Yellowstone: their ecology in the

Yellowstone ecosystem. Island Press.

hp://www.bear.org/Grizzly/Grizzly_Brown_Bear_Facts.html

hp://www.bcadventure.com/adventure/wilderness/animals/grizzly.htm

hp://sbsc.wr.usgs.gov/cprs/research/projects/grizzly/grizzly_bears.asp

Red Kangaroo (Macropus rufus)

Dawson TJ. 1995. Kangaroos: biology of the largest marsupials. Comstock Publishing.

theBigZoo.com. hp://www.thebigzoo.com/Animals/Red_Kangaroo.asp

Yue M. 2001. “Macropus rufus” (On-line), Animal Diversity Web. hp://animaldiversity.ummz.umich.edu/site/

accounts/information/Macropus_rufus.html

Duck Leech (Theromyzon tessulatum)

Sawyer RT. 1986. Leech biology and behaviour. Volume I: anatomy, physiology, and behaviour. Clarendon

Press.

Davies RW. 1991. Annelida: leeches, polychaetes, and acanthobellids. In: [Thorp JH and Covich AP. eds

Ecology and Classiﬁcation of North American Freshwater Invertebrates. Academic Press, Inc.

Wilkialis J and Davies RW. 1980. The population ecology of the leech (Hirudinoidea: Glossiphoniidae)

Theromyzon tessulatum. Canadian Journal of Zoology 58: 906-911.

Wilkialis J and Davies RW. 1980. The reproductive biology of Theromyzon tessulatum (Glossiphoniidae:

Hirudinoidea), with comments on Theromyzon rude. Journal of Zoology London. 192: 421-429.

Meadow Garlic (Liliaceae: Allium canadense)

Connecticut Botanical Society: hp://www.ct-botanical-society.org/galleries/alliumcana.html

eferences

Investigating Reproductive Strategies

This activity was downloaded from: hps://teach.genetics.utah.edu

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Wildﬂowers of the Southeastern US: hp://2bnthewild.com/plants/H134.htm

Prairie Wildﬂowers of Illinois, by John Hilty: hp://www.illinoiswildﬂowers.info/prairie/plantx/wild_garlicx.htm

Desert Grassland Whiptail Lizard (Cnemidophorous uniparens)

Crews D. 1987. Courtship in unisexual lizards: A model for brain evolution. Scientiﬁc American 255: 116-121.

Blanchard DL. Everything you wanted to know about whiptail lizards (Genus Cnemidophorus) and quite a lot

that you didn’t. hp://home.pcisys.net/~dlblanc/whiptail.html

hp://media.www.dailytexanonline.com/media/storage/paper410/news/2006/02/06/LifeArts/Ut.Lab.Studies.

GenderBending.Lizard.Mating-1599792.shtml

Salmonella (Salmonella typhimurium)

Saeed AM. 1999. Salmonella enterica Serovar Enteridis in Humans and Animals. Iowa State University Press.

Bell C and Kyriakides A. 2002. Salmonella: a practical approach to the organism and its control in foods.

Blackwell Science.

Guthrie R. 1992. Salmonella. CRC Press.

Centers for Disease Control, salmanellosis. hp://www.cdc.gov/nczved/dmd/disease_listing/salmonellosis_

gi.html

Sand Scorpion (Paruroctonus mesaensis)

Polis G and Farley R. 1979. Characteristics and environmental determinants of natality, growth and maturity in

a natural population of the desert scorpion, Paruroctonus mesaensis (Scorpionida: Vaejovidae). Journal of

Zoology. London. 187: 517-542.

Farley R. 2001. Structure, reproduction, and development. In: Scorpion Biology and Research. Eds: Brownell P

and Polis G, Oxford University Press.

Polis G and Sissom D. 1990. Life History. In: Biology of Scorpions. Ed. Polis G. Stanford University Press.

How the Sand Scorpion Locates its Prey. hp://ﬂux.aps.org/meetings/YR00/MAR00/vpr/layy3-03-04.html

Ivars Peterson’s MathTrek. July 17, 2000. Pinpointing prey. hp://www.maa.org/mathland/mathtrek_7_17_00.

html

Leafy Sea Dragon (Phycodurus eques)

Groves P. 1998. Leafy sea dragons. Scientiﬁc American. 279 (6): 84-89.

Brile Star (Ophiactis savignyi)

Marine Invertebrates of Bermuda, Lile Brile Star. hp://www.thecephalopodpage.org/

MarineInvertebrateZoology/Ophiactissavignyi.html

Smithsonian Tropical Research Institute. hp://striweb.si.edu/bocas_database/details.php?id=1274

Hendler G, Miller JE, Pawson DL, and Kier PM. 1995. Sea stars, sea urchins, and allies. Smithsonian Institution

Press.

Investigating Reproductive Strategies

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Spiny Water Flea (Bythotrephes longimanus)

Smith DG. 2001. Pennak’s Freshwater Invertebrates of the United States. Wiley & Sons.

Dodson SI and Frey DG. 1991. Cladocera and other Branchiopoda. In: [Thorp JH and Covich AP (eds)] Ecology

and Classiﬁcation of North American Freshwater Invertebrates. Academic Press, Inc.

Caceres CE and Lehman JT. Life history and eﬀects on the Great Lakes of the spiny tailed Bythotrepes.

University of Minnesota Sea Grant. hp://www.seagrant.umn.edu/exotics/spiny.html

Sikes BA. June 2002. Species of the Month: Spiny water ﬂea. Institute for Biological Invasions. hp://invasions.

bio.utk.edu/invaders/ﬂea.html

Blue-Headed Wrasse (Thalassoma bifasciatum)

Warner RR. Mating behavior and hermaphrodism in coral reef ﬁshes. American Scientist 72: 128-136.

Warner RR and Hoﬀman SG. 1980. Population density and the economics of territorialdefense in a coral reef

ﬁsh. Ecology 61(4): 772-780.

Louch C. Fish Tales. Port Townsend Marine Science Center. hp://ptmsc.org/science/topicspages/ﬁshtales.

html

Louisa Stark, Genetic Science Learning Center

Molly Malone, Genetic Science Learning Center

Mel Limson, Genetic Science Learning Center

Sheila Avery, Genetic Science Learning Center

Lee Clippard (Writer)

A Howard Hughes Medical Institute Precollege Science Education Initiative for

Biomedical Research Institutions Award.

redits

unding

Investigating Reproductive Strategies

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Print-and-Go™

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What are the advantages and disadvantages of sexual and asexual reproduction?

Is one “better” than the other? You are an Ecologist who wants to nd out. You decide to compare

5 aspects of organisms that reproduce sexually with ones that reproduce asexually. You will begin by

looking at two organisms. Once you make your comparisons, you will share your information with all of

the other ecologists in your class to draw general conclusions about each method of reproduction.

Fill in the table below with information for each organism you have been assigned.

Sexual Asexual

Relative

complexity

of organism

(including size)

Number of

parents who

contribute

genetic

information to

the offspring

Reproductive

mechanism

Relative

amount of

parental care

Genetic

variation in

the offspring

Investigating

Reproductive Strategies

Name

Date

S-1

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Permission granted for classroom use.

Reproductive Strategies

AMOEBA (Amoeba proteus)

Take a look through a microscope at a drop of

healthy pond water. You’ll likely nd a ton of

one-celled organisms zooming about. Some of

these cells move by uttering tiny hair-like cilia.

Others propel themselves with large whip-like

agella. You’ll also come across blobby cells that

creep about and engulf other cells with their

bodies. These one-celled critters are amoebas,

and they move and feed by extending pseudo-

podia (false feet). To move, an amoeba reaches

pseudopodia away from its edges and anchors

them at their tips. The cell’s insides stream into the pseudopodia until the entire amoe-

ba has slurped into a new place.

Amoebas live all over, from oceans to soil. They play an important ecological role by

making meals of the huge numbers of bacteria, algae, and small protists found on this

planet. One common amoeba is the giant amoeba, Amoeba proteus. Giant amoebas

reproduce by binary ssion, a fancy word that means splitting in two. When a giant

amoeba begins to divide, it pulls its pseudopodia in to form a kind of ball. After its nu-

cleus doubles, the amoeba constricts in the middle, as if a belt were being pulled tight

around it. Finally, the two new cells pinch apart, send out pseudopodia, and slink away

from each other. In this way, two identical “daughter” cells are made from one. When

conditions are right, this amoeba can divide every 48 hours.

Animal Prole:

Steve Durr

Amoeba proteus with several green algae trapped

inside food vacuoles.

Name

Date

S-2

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Reproductive Strategies

BLUE-HEADED WRASSE

(Thalassoma bifasciatum)

Many animals are born male or female and stay that way for the

rest of their lives. Not so with the blue-headed wrasse, a tropi-

cal sh that darts about amongst the corals and sponges in shallow Caribbean waters.

Females of this sh can completely transform into males when the conditions are right.

Blue-headed wrasses, like many reef sh, are small and brightly colored. Most of

them—young males and females—are yellow with a greenish-black stripe on their

sides. The others—the few, the proud, and the pow-

erful—are older males. They have showy blue heads,

green bodies, and thick black and white stripes

around their collars.

Big blue-headed males defend territories around the

reefs. There, they strut their stuff until the smaller

yellow females nd them attractive. When this hap-

pens, the female swims with the male and spawns

(releases her eggs). The male quickly fertilizes them

with his sperm before they oat away into the

ocean. Blue-headed males can mate with as many as

100 females per day!

Of course, these big males can lose their territories

because of nasty little things like death and rivalry.

When that happens, the largest yellow female in the

area may morph into a blue-headed male. So, some

of the blue-headed males were born male, while

others were born female.

For the females that transform into males, this is a

great deal. They can get a lot of their genes into the

next generation. First they lay eggs when they are younger, then they fertilize eggs as

males when they’re older.

Animal Prole:

Adult male Blue-Headed Wrasse

Adult female or young male Blue-Headed Wrasse

Virginia O. Skinner

Juvenile Blue-Headed Wrasse

Virgina O. Skinner

Name

Date

S-3

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Reproductive Strategies

BRITTLE STAR (Ophiactis savignyi)

Peer into the hole of a sea sponge and you may

catch a glimpse of the brittle star Ophiactis savignyi.

These creatures are tiny: only an inch or two across

with arms stretched. They inhabit virtually all of the

world’s tropical and sub-tropical ocean habitats.

Brittle stars are related to starsh. They have a

similar body structure. The central disk holds all the

important stuff like the mouth, stomach and re-

productive organs. Then there are the arms—long,

slender, wavy and edged with short spines. These

arms are what give brittle stars their name. They

can break off and regenerate.

O. savignyi takes regeneration a step further. It actu-

ally splits in half to reproduce. When ssion hap-

pens, the brittle star breaks down the middle of its

disk to make two identical 3-armed halves. These

half-stars then grow three new arms.

But this isn’t the only way O. savignyi reproduces.

Like all brittle stars, they also reproduce sexually. At

certain times of the year, large females and males

raise their disks off the surface, balance on their legs,

and release sperm and eggs into the ocean. When

the sperm and eggs meet, they make larvae that

oat away to new habitats.

Fission is the main way that Ophiocomella repro-

duce. But since they don’t move far or fast, large

groups of brittle star clones build up in one area.

Scientists think sexual reproduction might help

brittle stars move into new areas far from their

clone-lled sponge homes.

Animal Prole:

Ellen Muller - www.pbase.com/imagine

Brittle star spawning.

Michael Roy

Ophiactis savignyi

Tamara McGovern

A recently divided Ophiactis savignyi. Three tiny arms

are beginning to regenerate.

Name

Date

S-4

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Reproductive Strategies

DUCK LEECH (Theromyzon tessulatum)

Leeches are the stuff of horror movies and

doomed journeys into infested waters. This

leech is no exception. It has the disgusting habit

of attaching itself to nostrils, eyes, throats, and

even brains. Thankfully for humans, it only does

this to ducks and other waterfowl. This has

earned it the common name “duck leech.”

The duck leech does a good job getting around. It probably gets spread as ducks y

from pond to pond. Like all leeches, this leech is a hermaphrodite: it has both male and

female reproductive parts. But that doesn’t mean it can move into a pond all alone, re-

produce with itself, and start a new leech population. It still takes two to tango, as they

say. A leech requires sperm from another leech to fertilize its eggs.

When the duck leech reproduces, two leeches

rub together and give each other their sperm.

Each leech will use the other’s sperm to fertilize

its eggs. They they place as many as 400 fertil-

ized eggs into gooey cocoons for protection. A

leech attaches its cocoons to a rock or other

sheltered place, then waves its body over them.

This delivers fresh, oxygen-rich water.

After 21 days, all 400 of the developing young

leeches attach to their parent’s belly. They re-

main attached until the parent nds a suitable bird for a meal. When that happens, the

young bloodsuckers leave their parent behind and attach to the host for their rst

blood meal. The parent dies shortly thereafter, but not before giving hundreds of new

eyeball-suckers a shot at the game of life.

Animal Prole:

Young attached to the underside of a parent leech.

Biopix.dk Biopix.dk

Name

Date

S-5

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Reproductive Strategies

GRIZZLY BEAR (Ursus arctos horribilis)

Grizzly bears used to roam throughout the

Great Plains of North America. They hunted elk

and moose, and nibbled on berries and grasses.

Grizzly bears still do these things, of course. But

habitat loss and hunting have left the bears only

in rough, mountainous areas.

Grizzly bears are enormous animals. They need

large territories, especially when food is hard to

nd. Males can weigh as much as 453.6 kg (1000

pounds). Females can clock in around 317.5 kg

(700 pounds). A grizzly bear’s territory can be as large as 906.5 square kilometers (350

square miles). Though grizzlies spend most of their days wandering alone, they come

together in early summer to mate.

During mating, the male deposits his sperm into

the female, where they fertilize her eggs. Fe-

males delay implantation of the fertilized eggs

until late fall. This way, the embryos don’t begin

developing until the females are nestled into

their warm dens. Mothers give birth 8 weeks lat-

er to between 1 and 4 cubs. Until they leave the

den in late spring, the cubs live off their mom’s

milk. This means mom has to eat enough in the

summer and fall to survive hibernation and to

feed her cubs, too! Cubs stay with their mother for about 3 years. She won’t repro-

duce again until they leave her side.

Bears grow and reproduce slowly. This, and their need for large territories with a lot of

food, makes grizzlies sensitive to over-hunting and habitat loss. Thankfully, they’re pro-

tected by the Endangered Species Act. And many conservation and wildlife biologists

Animal Prole:

US Fish and Wildlife Service/Larry Aumiller US Fish and Wildlife Service/ Terry Tollefsbol

Name

Date

S-6

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Reproductive Strategies

LEAFY SEA DRAGON (Phycodurus eques)

Dragons lurk in the cool waters off the

southwestern Australian coast. But they

aren’t the mythical beasts that devour huge

ships before slipping away into the deep.

These dragons are calm, graceful sh known

as leafy sea dragons (Phycodurus eques).

Though smaller than mythical dragons, leafy

sea dragons can be pretty big. They grow

up to 51 cm (1.7 feet) long, and they have

long leaf-like appendages sprouting from

their bodies. This leaness helps them blend in with their seaweed habitat. It hides

them from predators and helps them hunt for food. Like their cousins the seahorses,

leafy sea dragons have long snouts they use to suck up tiny shrimp. To hunt, they drift

around camouaged as a piece of seaweed and ambush their small, crunchy prey.

Leafy sea dragons and their relatives repro-

duce in a way that’s rare in the sh world.

The males carry and hatch the young in-

stead of the females! When sea dragons

mate, the female nds a potential dad and

deposits her eggs underneath his tail. There,

his sperm fertilize them. Pregnant dads can

carry as many as 200 incubating eggs. It

pays to have a dad that looks like seaweed,

because the eggs are protected from preda-

tors there. The eggs cling for 4–5 weeks,

then they hatch.

The young are less than 2.5 cm (1 inch) long at hatching. Sadly, many will become little

shy snacks for larger sh. But the lucky ones who survive will grow up to be beautiful

adults. Having protection from dad during development likely gave leafy sea dragons a

n up in the big ocean world.

Jeff Jeffords - divegallery.com

www.stuarthutchison.com.au

Eggs attached under a male sea dragon’s tail.

Animal Prole:

Name

Date

S-7

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Reproductive Strategies

MEADOW GARLIC

(Liliaceae: Allium canadense)

Before Europeans brought their garlic and

onions to North America, Native Americans

were likely spicing up their cooking with a na-

tive plant known as meadow garlic. This garlic,

Allium canadense, grows wild from Florida to

Canada. Surprisingly, it belongs to the same

family as garden lilies—those big, bright ow-

ers that sit in vases and gardens around the

world. Even though it’s called meadow garlic, it really smells and tastes more like an

onion. Rubbing the leaves and stems releases a pungent onion smell.

Meadow garlic, also known as wild garlic, grows from bulbs like other lilies in its family.

The bulbs lie dormant underground over winter, storing energy. Spring and early sum-

mer bring a burst of growth and reproduction. Bees don’t mind the onion smell, and

they buzz around pollinating the small, pink or white owers. Although each ower has

both male and female reproductive parts, it can’t mate with itself. The bees are needed

to move pollen from one plant to another. Gametes join to form fertile seeds that will

spread and grow into new plants. The offspring have a mix of genes from the two par-

ent plants.

But meadow garlic doesn’t rely only on bees or other pollinators to spread itself

around. Perched underneath the owers are clusters of little, nubby growths called

bulblets. The bulblets are outgrowths of the plan. When they drop off, they sprout into

new plants identical to their parent. The bublets provide enough start-up energy for

the new plants to grow. Eventually, they produce owers and bulblets of their own.

Since plants in the lily family reproduce both with and without fertilization, they can

spread easily. Some lilies have actually become pests by taking over pastures, gardens,

and roadsides across the country.

Plant Prole:

Larry Allain @ USGS National Wetlands

Research Center

Name

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S-8

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Reproductive Strategies

RED KANGAROO (Macropus rufus)

In the remote, dry plains of central Australia,

mobs roam the countryside. But these aren’t

mobs to be feared. Mobs are the ofcial name

for groups of red kangaroos, Macropus rufus.

And unlike angry mobs of people, red kanga-

roos are skittish and will scatter when fright-

ened. When they’re really moving, red kangaroos

can leap as far as 3.7 meters (12 feet) in one

jump and reach speeds of 56 kph (34.8 mph)!

Red kangaroos are one of the largest marsupials. Herbivorous mobs of them bounce

about eating grasses and other vegetation. Mobs are usually led by the most mature

female and include lots of other females and young kangaroos, called joeys. When it’s

mating time, males will sometimes box each other for females with their powerful legs.

The winning male deposits his sperm in the

female, where it fertilizes an egg.

After mating, females gestate for about 33 days,

then give birth to one baby kangaroo. Young

red kangaroos are born very undeveloped. Like

most marsupials, they will spend a lot of time

growing in their mom’s pouches. Though tiny,

pink, hairless, and blind, the newborn knows to

head straight for the pouch. It swims through

mom’s fur to get there, then attaches to a nipple

and nishes developing.

After about 7 months, a joey outgrows mom’s pouch and leaves to bounce around

next to her. Once this happens, the mom gives birth to another tiny pink baby. Females

can continuously give birth. They usually have about 3 joeys every two years.

Animal Prole:

Geoff Shaw - http://kangaroo.genome.org.

A newborn kangaroo in its mother’s pouch.

Chris Willis

A mother red kangaroo with a joey in her pouch.

Name

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S-9

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Reproductive Strategies

SALMONELLA (Salmonella typhimurium)

There are times when we eat something and

our stomachs hurt. And then there are times

when it hurts REALLY badly. When it hurts

dreadfully bad and includes fever, nausea and

diarrhea, it could be food poisoning. Yick. And

that’s a mild case of food poisoning! Some of

the more life-threatening cases can send a per-

son to the hospital.

The interesting thing is, it’s not poisoning at all. It is the result of a sinister bacteria

known as Salmonella. This one-celled, rod-shaped bacteria is fairly common. It can be

found naturally in raw eggs, raw meats, on the bodies of some reptiles, and in animal

feces. It’s when Salmonella nds itself in the warm growth chambers of our bodies that

it hits pay dirt.

When Salmonella reaches our small intestine, it begins to make copies of itself through

simple division. These bacteria continue to rapidly divide, increasing in number and

infecting other cells. It takes about 12–72 hours to feel the effects of a Salmonella inva-

sion. Our immune system responds, but Salmonella does a good job of fending it off.

Our bodies can ght off some Salmonella infections, but we often need antibiotics to

overcome them.

Thankfully, Salmonella is not one of those extreme bacteria that can survive the freez-

ing temperatures of the Arctic or the boiling heat of volcanic thermal vents. We can kill

Salmonella by cooking, pasteurizing, and freezing our foods and drinks. Still, Salmonella

infection is common enough. It usually turns up where people aren’t washing their

hands or cooking meat thoroughly.

Bacteria Prole:

Salmonella (rod-shaped) invading human cells.

Rocky Mountain Laboratories, NIAID,

Name

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S-10

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Reproductive Strategies

SAND SCORPION (Paruroctonus mesaensis)

When the sun goes down in the Mojave Desert,

sinister beasts lurk underfoot. The sand scorpion

spends its days in a burrow underground, then

comes out at night to sting, kill, and munch its prey.

Shine an ultraviolet light and the ground will come

alive with glowing scorpions. They hunt beetles,

crickets, other scorpions, and even cannibalize their

own kind. If it’s the right time of year, glowing scorpi-

ons might also be dancing the night away.

Yep, that’s right—sand scorpions dance during

courtship. Males grasp the females by their pinch-

ers and move them around in circles. After a while,

the male deposits a packet of sperm onto a stick or

other surface. Then he moves the female until she is

on top of the sperm. She takes it in and fertilizes her

eggs internally. The dance ends here, and the male

usually skitters off to nd more mates. But every

now and then, the female rears back, stings the male,

and eats him for her next meal!

Young sand scorpions spend about 12 months

developing inside their mother, then they are born

alive. They quickly crawl onto their mom’s

back, where they stay until they’re big

enough to leave the burrow. On aver-

age, a sand scorpion mom has about 33

newborns. But things aren’t always easy

for them. Sometimes the young eat each

other or the mom eats the young. Clearly,

stingers don’t make life trouble-free for

the sand scorpion. But they’re still very

successful in their dry, sandy habitats.

Animal Prole:

Mother scorpion (syntropis)

carrying babies on her back.

http://scorpion.amnh.

Spermatophor from a male

scorpion.

http://scorpion.amnh.

Scorpions (Tityus trinitatis) engaged in courtship dance.

Sand scorpion (Paruroctonus mesaensis) capturing a bur-

rowing cockroadh. Photo taken under UV illumination..

Philip H. Brownell, Ph.D.

Name

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S-11

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Reproductive Strategies

SPINY WATER FLEA (Bythotrephes longimanus)

There’s a tiny, transparent crustacean that swims

jerkily around in the Great Lakes. It spikes sh

in the mouth with its long tail and gobbles up

microscopic aquatic animals (zooplankton). It’s

called the spiny water ea, but it’s more related

to crabs and lobsters than to insects.

Though other kinds of water eas are common

in ponds and streams, the spiny water ea is not

a welcome visitor. It’s an invader from European

waters, and it competes with local sh and wa-

ter eas for food. Its defense is its nasty barbed

tail, which makes up 70% of its 2 cm long body.

Spiny water eas are a threat to ecosystems

in part because they reproduce rapidly. Like all

water eas, this one alternates between asexual

and sexual phases. Most of the time, a female

produces eggs without fertilization. She releases

about 10 eggs into the brood chamber on her

back. They develop over several days, then the

young clones hatch. In the warm days of sum-

mer, females can make a batch of clones every 2

weeks.

When food is scarce or temperatures drop,

some females produce spiny little males. The males mate with females that have pro-

duced special eggs used for fertilization. Once fertilized, these so-called “resting eggs”

leave the mom and stay dormant until conditions improve. Resting eggs can survive

drying or being eaten by sh.

Spiny water eas seem to have a lot on their side, and they’re in the Great Lakes to

stay. Still, biologists are working hard to keep them from spreading into more lakes.

Animal Prole:

Pieter Johnson, University of Colo-Pieter Johnson, University of Colo-

Different reproductive forms of spiny water eas.

Male (left), female with asexual eggs (center), and

female with sexual eggs (right).

Name

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S-12

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Reproductive Strategies

DESERT GRASSLANDS WHIPTAIL

LIZARD (Aspidoscelis uniparens)

Things are often not what they seem in the

world of reproduction. Take the example of the

desert grassland whiptail, a lizard that lives in the

southwestern United States. These lizards have

long sleek bodies with lines from nose to tail.

They race around in the dry leaves and branches

eating termites, grasshoppers, beetles, and other

insects. Like other lizards, the whiptails perform

courtship, mate, and lay eggs.

Sounds pretty ordinary, right? But if we took a

closer look, we’d nd that not a single one of

these lizards is a male! This all-female whiptail

species can reproduce without fertilization—a

process called parthenogenesis.

Pairs of females take turns playing male during

courtship and mating. If the female is interested,

the “male” will wrap around her and grip “his”

jaws around her body. The couple will stay like

this for 5 to 10 minutes. This is called pseudo-

copulation, or false mating. No actual males or

sperm are involved.

The “female” from this mating pair lays 2 to 3 eggs, which all hatch into copies of their

mom. Females will “mate” and lay eggs about 3 times over the breeding season. It turns

out that females who lay eggs after “mating” with another female lay more eggs than

females who don’t mate. Laying a few more eggs is denitely an advantage in the harsh

desert where survival is difcult.

Animal Prole:

at Austin

Two female desert grasslands whiptail lizards en-

gaged in pseudocopulation.

Name

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S-13

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