Small
Animal
Study
© Copyright
This resource is owned by the New Zealand Marine Studies Centre. Photocopying of this
resource is restricted to the purchasing school. Teachers may photocopy work sheets only for
students in their class, provided the copyright footer is maintained.
Small Animal Study
Table of Contents
A conceptual framework ..................................................................................................
Investigation # 1 Adaptive Radiation in Crustaceans.......................................................
Investigation # 2 Classification of Shore Crabs...............................................................
Investigation # 3 Morphology of Half-Crabs...................................................................
Investigation # 4 A Context: Distribution of Shore Crab Species....................................
A Context: Sketch of Location, Sheltered Rocky Shore, Circatidal Periodicity..............
Investigation # 5 Reproduction of Petrolisthes enlongatus..............................................
Investigation # 6 Protective Responses of the Half-Crab, Petrolisthes enlongatus.........
On the Completion of Your Experimental Work..............................................................
Glossary of Experimental Terms......................................................................................
Validity, Reliability and Ethics.........................................................................................
Statistical Analysis............................................................................................................
Using Excel for Analysis..................................................................................................
3
4
8
14
18
21
22
25
26
27
29
30
31
List of data sheets
Adaptive Radiation in Crustaceans Data Sheet #1...........................................................
Adaptive Radiation in Crustaceans Data Sheet #2...........................................................
Classification of Shore Crab Data Sheet #1......................................................................
Classification of Shore Crab Data Sheet #2......................................................................
Morphology of Half-Crabs Data Sheet #1........................................................................
Shore Survey for inter-tidal shore crabs...........................................................................
6
7
12
13
17
20
List of Figures
Figure 1. Dorsal view of the half-crab, Petrolisthes elongatus........................................
Figure 2. Ventral view of the abdomen of the half-crab, Petrolisthes elongatus.............
Figure 3. Mean activity per 30-min periods of 6 Hemigrapsus sexdentatus....................
Figure 4. Life history of the half cab Petrolisthes enlongatus..........................................
Figure 5. An example of what your data should look like when entered into excel.........
Figure 6. An example of calculating the average, SD and SE for your data....................
Figure 7. The selection process to create a scatter plot of your data................................
Figure 8. The basic plot generated by excel which requires more edits to be usable.......
Figure 9. Drop down menu for adding chart elements.....................................................
Figure 10. A completed and presentable graph of the example data................................
15
16
21
23
31
31
32
32
33
33
List of Tables
Table 1. Mean sea water temperatures (oC) in three locations.......................................... 24
© New Zealand Marine Studies Centre, University of Otago, Dunedin
2
Small Animal Study
A Conceptual Framework
The Hypothesis - 7-point Check
1. Is it a statement?
2. Does it have a subject?
3. Does it clearly state the independent variable?
4. Does it clearly state a dependant variable?
5. Is it a prediction of a relationship between the independent and dependant variable?
6. Can you sketch a graph of this prediction?
7. Does it have an explanatory cause?
Example:
That (1) as temperature (3) increases (5) the time taken (4) for the half-crab, Petrolisthes
elongatus,(2) to turn over (4) will decrease (5) because muscle function of a poikilotherm is
affected by rate of cellular respiration which will increase as temperature increases (7).
© New Zealand Marine Studies Centre, University of Otago, Dunedin
3
Small Animal Study
Investigation # 1
Adaptive Radiation in Crustaceans
Crusty Creatures – and why are there more of them than us
As humans we like to think of ourselves as up there and at the top of the evolutionary ladder.
After all, surely the sheer number of us on the planet must prove that we have successfully
evolved to fit our environment. Physiologically speaking our bodies can be a bit limited, drop
us in the sea or in the middle of a desert and we won’t survive for too long without a few
aids. We use our highly evolved brains to compensate for the limitations of our very complex
but somewhat limited bodies so that one species – Homo sapiens, can spread around the
globe.
Crustaceans, on the other hand, are a bit limited in the brain department but a simple body
allows them to live in a wide range of habitats, mostly marine but also freshwater and
terrestrial environments. Crustaceans belong to the phylum Arthropoda, a vast group of
animals who all have body armour in the form of an exoskeleton and show definite
segmentation in their body plan. They all have very small brains, but physiological and
morphological variation means that 31,000 different species of crustaceans have evolved to
fit into local environments.
In this investigation you will look at how variation in body design and function suits the
habitat of a species.
Key points to remember:
Phylum Arthropoda:
• Includes spiders, mites, insects,
crustaceans, millipedes, ticks and
scorpions.
• The largest animal group in the
world with over 750,000 species
described.
Subphylum Crustacea:
• Includes crabs, shrimp, lobsters,
crayfish and wood lice.
• Over 31,000 species described.
• Most species are marine, a smaller
number live in freshwater and a few
are terrestrial.
Features that all Crustacea share –
their basic body design:
•
A segmented body – the head has:
2 pairs of antennae
1 pair of mandibles
2 pairs of maxillae also used for
feeding.
•
Trunk bears many appendages –
may include crawling, walking or
swimming legs, and specialised
appendages for sperm transmission
and egg brooding called pleopods.
•
Trunk often covered dorsally by a
single piece of skeleton called a
carapace, and one can usually
determine thorax and abdomen on
the ventral side.
•
No single method of feeding.
•
All have eyes, tactile receptors and
chemoreceptors.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
4
Small Animal Study
Adaptive Radiation in Crustaceans
Objective:
To examine adaptive radiation in Crustaceans.
Conceptual connection:
Evolutionary adaptation.
Morphological – behavioural integration.
Time:
Allow 30 – 40 minutes
Active summary:
You will be provided with a variety of species of Crustacea. Species may be viewed in the
aquarium, in the laboratory, on the shore, as preserved specimens or from pictures. Look at
how each species varies from the basic crustacean body plan and how these variations help it
fit into its habitat. It is up to you to make the most detailed observations you can. Try and
imagine the species in its natural habitat and think about how the features you observe might
help it to survive.
Methods:
1. You will need:
Adaptive Radiation data sheets 1 & 2, a pencil and a variety of crustacean species. For
small animals you may need a hand lens or binocular microscope.
•
Compare the body form of shrimp, crayfish and a crab.
Complete data sheet 1 with your observations.
•
Compare the body form of the five crab species. For each, make observations of their
morphology and behaviour, and describe their natural habitat. How do the features
you have observed help them to survive in their local habitat?
Complete data sheet 2.
Discussion:
• List four features that the crabs have in common.
•
What advantages do these variations in body forgive to the different species?
•
How do these variations develop?
© New Zealand Marine Studies Centre, University of Otago, Dunedin
5
Small Animal Study
Adaptive Radiation in Crustaceans Data Sheet #1
Crabs, shrimp and crayfish are closely related and evolved from the same basic body plan.
Observe these animals in the aquarium. Describe how the body form is adapted for their
lifestyle.
Shrimp
How do they move?
Role of the abdomen?
How do they catch their food?
Other observations:
Crab
How do they move?
Role of the abdomen?
How do they catch their food?
Other observations:
Crayfish
How do they move?
Role of the abdomen?
How do they catch their food?
Other observations:
© New Zealand Marine Studies Centre, University of Otago, Dunedin
6
Small Animal Study
Adaptive Radiation in Crustaceans Data Sheet #2
Observe the crabs highlighted below. Describe how their body form varied from the basic
body form. What advantage has the change in body plan given the species?
Crab Type
Half-crab
Explain colour &
special features of the
carapace & abdomen
-Blue grey to blend in
with the rocky shore
-Flat body to move
under rocks
-Smooth, nothing
encrusting shell
-Abdomen flapped to
turn crab right side up
Describe the chelae
& explain use
-Large and flattened for
getting under rocks
-Used in defense
Describe the shape &
use of the 5th pair of
walking legs
-Small, reduced, foldd
in half and tucked
under body
-Used for cleaning
carapace and gills
Paddle crab
(or cancer crab)
Camouflage crab
(or spider crab)
Hermit crab
Pea crab
© New Zealand Marine Studies Centre, University of Otago, Dunedin
7
Small Animal Study
Investigation # 2
Classification of Shore Crabs
SKILL: Information gathering
Objectives:
To identify two common shore crabs to species level using a dichotomous key.
Conceptual connection:
Evolutionary adaptation
Adaptive radiation
Speciation-extinction = biodiversity
Adaptation = niche
Time:
Allow 45-60 minutes
What’s in a name?
Being able to accurately name a plant or animal is something that challenges all biologists at
some time. You need to understand the basic principles of taxonomy, the process of placing
an organism in decreasing sixed groups with similar features until you end with a description
that is unique to a species. There may well be some variations between individuals of the
same species but remember the definition of a species – Individuals who can undertake
reproduction and produce fertile offspring. This exercise gives you the chance to gain
experience using scientific dichotomous keys and understand the process of taxonomy.
Method:
1. You will need: common shore crab species, crab identification keys, and shore crab
data sheets #1 & 2.
2. Begin with the phylum key and choose the descriptions which best fit with the halfcrab. As you work through the key record the major features that you notice (for
example, all crabs will show bilateral symmetry) at each taxonomic level on shore
crab data sheets #1.
3. Continue to work through the keys to determine subphylum, class, order and
infraorder. Record your information in shore crab data sheets #1.
4. Once you have identified the half-crab move onto the other species. Complete shore
crab data sheets #2 with notes that will help you identify the crabs when you are on
the beach.
Key points to remember:
•
Handle animals with care; look
carefully for evidence of damage
such as missing limbs, which may
confuse your observations.
•
Remember to bring Table 2 to the
seashore when you do your crab
survey. It will help you identify the
crabs when you find them on the
beach.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
8
Small Animal Study
Crab Identification Keys
Key to Major Marine Invertebrate Phylum
1.
a.
b.
Body symmetry radial (body arranged around a central axis e.g. Jellyfish) ...... go to 3
Body symmetry not radial .................................................................................. go to 2
2.
a.
b.
Body symmetry bilateral (two sides form almost mirror images) ...................... go to 4
Body without apparent symmetry ....................................................................... go to 9
3.
a.
b.
Soft body, individuals with a circle of feeding tentacles around mouth (may be
retracted and therefore not visible) ................................................................... go to 10
Body usually hard and spiny or leathery, pentaradial symmetry (symmetry based on
5), tiny tube feet usually present, tentacles usually absent .............................................
...................................................................................... PHYLUM ECINODERMATA
4.
a.
b.
Body covered by a hard shell or exoskeleton ..................................................... go to 5
Body not covered by a hard shell or exoskeleton ............................................... go to 7
5.
a.
Body enclosed in a tube-like structure of calcium, mucous or sand, body usually with
numerous tentacles which can extend beyond the opening of the tube (may be
retracted) ................................................................................. PHYLUM ANNELIDA
Body enclosed in a hard shell or exoskeleton, not a tube structure .................... go to 6
b.
6.
a.
b.
7.
a.
b.
8.
a.
b.
9.
a.
b.
10.
a.
b.
11.
a.
b.
Body covered by a hard exoskeleton with jointed appendages or legs ..........................
............................................................................................PHYLUM ARTHROPODA
Body covered by a hard shell(s) and without jointed appendages of legs ........ go to 11
Soft, elongate body divided into a long series of similar segments, each segment
usually with small lateral fleshy extensions (parapodia) ................................................
.................................................................................................. PHYLUM ANNELIDA
Soft, flattened body, not divided into segments ................................................. go to 8
Body slug-like with a single muscular foot on the ventral surface. Finger-like or gill
like structures may be visible on the upper surface .......................................................
................................................................................................ PHYLUM MOLLUSCA
Body very flat and uniform, without a foot or projections on the upper surface ...........
............................................................................... PHYLUM PLATYHELMINTHES
Body without apparent symmetry and with numerous small pores on the surface,
rough and spongy to the touch ...................................................PHYLUM PORIFERA
Body solitary or colonial, with pairs of pores or siphons, jelly-like and solid to the
touch. If colonial usually large and encrusting with pores usually arranged in pairs
(may be able to recognise bilateral symmetry in large individuals) ...............................
................................................................................................ PHYLUM CHORDATA
................................................................................ SUBPHYLUM UROCHORDATA
Body long and cylindrical with feeding tentacles at one end (may not be visible), may
have tube feet ............................................................ PHYLUM ECHINODERMATA
Body attached to substrate with tentacles on upper body, or free floating with
tentacles hanging down..............................................................PHYLUM CNIDARIA
Body attached to rock (sessile) with a series of white overlapping plates, may have a
Stalk................................................................................... PHYLUM ARTHROPODA
Body covered with 1, 2, or 8 shells......................................... PHYLUM MOLLUSCA
© New Zealand Marine Studies Centre, University of Otago, Dunedin
9
Small Animal Study
Key to Subphylum
1.
a.
b.
2.
a.
b.
3.
a.
b.
Appendages present on most body segments .................................................................
..............................................SUBPHYLUM UNIRAMIA (centipedes and millipedes)
Some body segments without appendages, or with appendages other than walking
legs ...................................................................................................................... go to 2
Body divided into cephalothorax and abdomen; the first pair of appendages are
feeding chelicerae ...........................................................................................................
SUBPHYLUM CHELICERATA (horseshoe-crab, spiders, sea spiders)
Body divided into cephalothorax and abdomen and the first pair of appendages are
antennae .............................................................................................................. go to 3
Two pairs of antennae and branched (biramous) appendages ........................................
SUBPHYLUM CRUSTACEA (shrimp, lobsters, crabs, barnacles, isopods,
amphipods, copepods etc.)
One pair of antennae and unbranched (uniramous) appendages ....................................
............................................................................ SUBPHYLUM UNIRAMIA (insects)
Key to Major Class and Order
1.
a.
b.
2.
a.
b.
3.
a.
b.
Permanently attached to a hard surface: animals enclosed totally in a carapace of
several calcareous plates which form a conical shell ("test") .........................................
..............................................................CLASS CIRRIPEDIA, ORDER THORACICA
Motile animals..................................................................................................... go to 2
Carapace present as single unit covering the head and thorax but not the abdomen ......
................................................... CLASS MALACOSTRACA, ORDER DECAPODA
Carapace absent .................................................................................................. go to 3
Body flattened dorso-ventrally; no thoracic gills, legs generally all alike .....................
........................................................ CLASS MALACOSTRACA, ORDER ISOPODA
Body flattened from side to side (i.e. laterally compressed); thoracic gills present;
legs of more than on type.................................................................................................
................................................. CLASS MALACOSTRACA, ORDER AMPHIPODA
Key to Major Infraorder
1.
a.
b.
Body covered by a snail shell or sponge... INFRAORDER ANOMURA (hermit crab)
Body not covered in this manner......................................................................... go to 2
2.
a.
b.
Body with well-developed tail or abdomen region ........................................... go to 3
Body with reduced abdomen region, usually held folded under the cephalothorax .......
............................................................................................................................. go to 4
3.
a.
b.
Swimming form ................ INFRAORDER STENOPODIDEA, CARIDEA (shrimps)
Crawling form .......................... INFRAORDER ASTACIDEA, PALINURA (lobster)
4.
a.
Abdomen greatly reduced and is held tightly under the body, with 5 pairs of walking
legs including the large claws ................. INFRAORDER BRACHYURA (true crabs)
Abdomen not held tightly under the body, and is often not reduced in size, great
variation in body forms, with four pairs of walking legs include the large claws. If
fifth pair present, they are much reduced .......................................................................
...................................................... INFRAORDER ANOMURA (‘asymmetrical tails')
b.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
10
Small Animal Study
Key to common shore crab species found in Otago region
1.
a.
b.
Abdomen reduced and carried under thorax (crab like form) ............................ go to 2
Abdomen not as above ...................................... Hermit crabs and shrimps and prawns
2.
a.
b.
Free living ........................................................................................................... go to 3
Found inside mussels ...................................... Pea crab Pinnotheres novazealandiae
3.
a.
Antennae long, chelae large and flattened, abdomen bent loosely under thorax, four
pairs of walking legs, including chelae (claws) ..... Half-crab Pertrolisthes elongatus
Antennae short, abdomen small and tightly pressed against underside of thorax, five
pairs of walking legs including chelae (claws) ................................................... go to 4
b.
4.
a.
b.
5.
a.
b.
6.
a.
b.
7.
a.
b.
8.
a.
b.
9.
a.
b.
10.
a.
b.
Small delicate crabs, carapace thin and flat with a rostrum projecting between the
eyes, legs long and thin (carapace length <15mm) .........................................................
.............................................................................Small sea spider Halicarcinus white
Not as above ....................................................................................................... go to 5
Carapace square, eyestalks relatively long (project out from carapace), construct
burrows (muddy shore species) .......................................................................... go to 6
Carapace more rounded, eyestalks short (set in hollow on carapace), does not
construct burrows ............................................................................................... go to 7
Eyestalk length less than distance between eyestalk bases, no setal fringe (hair like
growth) on walking legs and chelae (claws) grey or brown in colour (carapace width
2–18 mm) .......................................................... Tunnelling mud crab Helica crassa
Eyestalk length equal to distance between bases, setal fringes present on walking legs
and chelae, carapace with black speckles, terminal segment of chelae may be light
orange ................................................. Stalk eye mud crab Macrophthalmus hirtipes
carapace thumbnail shaped, dull grey-green with blotches of orange, brown and white
carapace with three lateral spines (pointed projections from the edges of the
carapace), walking legs with dense fringe of setae (hair like growth) on front edge.
Male chelae with pad of setae on inner surface (carapace width 7-34 mm) ...................
.............................................................. Hairy handed crab Hemigrapsus crenulatus
Legs and chelae lack fringe setae ....................................................................... go to 8
Carapace purple with white markings (carapace width may be >30mm) ......................
.............................................................. Purple shore crab Hemigrapsus sexdentatus
Not purple ........................................................................................................... go to 9
Sides of carapace smooth with no lateral spines, cuticle looks polished and chestnut
brown colour (carapace width 6-16 mm) .. Smooth shore crab Cyclograpsus lavauxi
Side of carapace with lateral spines or rounded “pie crust” appearance .......... go to 10
Five lateral spines on each side of carapace, final segment of last pair of walking legs
flattened into paddles ................................................ Paddle crabs Ovalipes catharus
Blunt crenulations on carapace give pie crust appearance, tips of chelae black ............
............................................................................ Cancer crab Cancer novozealandiae
© New Zealand Marine Studies Centre, University of Otago, Dunedin
11
Small Animal Study
Classification of Shore Crab Data Sheet #1
Classification of the half-crab
Classification
Group
Description of Key Features
KINGDOM
PHYLUM
SUBPHYLUM
CLASS
ORDER
INFRAORDER
GENUS
SPECIES
© New Zealand Marine Studies Centre, University of Otago, Dunedin
12
Small Animal Study
Classification of Shore Crab Data Sheet #2
Descriptions of common shore crabs
Scientific name:
Scientific name:
Common name:
Common name:
Features:
Colour:
Features:
Colour:
Chelae (size, shape):
Chelae (size, shape):
Spines on edge of carapace?
Spines on edge of carapace?
Legs – Number:
Legs – Number:
Legs hairy?
Legs hairy?
Scientific name:
Scientific name:
Common name:
Common name:
Features:
Colour:
Features:
Colour:
Chelae(size, shape):
Chelae (size, shape):
Spines on edge of carapace?
Spines on edge of carapace?
Legs – Number:
Legs – Number:
Legs hairy?
Legs hairy?
© New Zealand Marine Studies Centre, University of Otago, Dunedin
13
Small Animal Study
Investigation # 3
Morphology of Half-Crabs
Objectives:
To examine external structures and sexual dimorphism of the half-crab, Petrolisthes
elongatus.
Conceptual connection:
Morphology-behavioural integration
Adaptation = niche
Time:
Allow 45-60 minutes
Method:
1.
You will need an adult Petrolisthes elongatus, diagram of an adult, pencil and eraser.
Once you have completed the first part of this exercise you will need a crab of the
opposite sex to compare.
2.
*
Observe the external features of Petrolisthes elongatus under the microscope.
On Figure 1 (dorsal view) label:
•
•
•
•
•
•
•
•
•
•
•
Antenna (1st antenna, small, at front of carapace – you will need to draw on the diagram).
Antennule (2nd antenna, long at side of eyes).
3rd maxillipeds (mouth parts).
Compound eye.
Chelipeds (1st pair of limbs with chelae attached).
Chelae (claws).
Walking legs (2nd to 4th pair of limbs).
Cleaning legs (5ht pair of limbs, hidden under tail)
Carapace (shield-like exoskeleton that covers the head and thorax).
Abdomen (tail).
Rostrum (part of carapace between the eyes.
3.
Add a scale to the diagram and note relevant information about colour and function of
the structures. How does Petrolisthes elongatus differ from other common shore crabs
found in the same habitat?
4.
Hold the carapace of the crab using your thumb and forefinger and turn over to view
the ventral side. Gently unfold the abdomen and note the features.
On Figure 2 (ventral view) label:
*
•
•
•
•
•
Abdomen.
Anus.
Pleopods (appendages on the abdomen of females for egg attachment).
Copulatory pleopods (male reproductive organs).
Telson
5.
Observe the abdomen of a crab of the opposite sex and label Figure 2. What are the
differences between male and females?
6.
Fill out the morphology data sheet.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
14
Small Animal Study
Morphology of Half-Crabs
Figure 1. Dorsal view of the half-crab, Petrolisthes elongatus.
Image credit: Monterey Bay Aquarium – Crabs: Claws and Shells
© New Zealand Marine Studies Centre, University of Otago, Dunedin
15
Small Animal Study
Morphology of Half-Crabs
Figure 2. Ventral view of the abdomen of the half-crab, Petrolisthes
elongatus.
Male:
Female:
Discussion:
1.
Petrolisthes elongatus is not considered a true crab. How does it differ in morphology
from true crabs?
2.
Explain the reasons for the differences in male and female morphology (sexual
dimorphism).
3.
Sea stars, mussels, and kina do not exhibit sexual dimorphism. Why not?
Image credit: Jones, 1977.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
16
Small Animal Study
Morphology of Half-Crabs Data Sheet #1
Complete the morphological feature-niche/behavioural integration table.
Morphological adaptation
Antenna
Niche or behavioural integration
Active “water sampling”, chemosensory
structures = potential food detection.
Antennule
3rd maxilipeds
Compound eye
Chelipeds
Walking legs
Cleaning legs
Carapace
Abdomen
Pleopods
Telson and uropods
Flat enlarged surface area = enhanced
“swimming” locomotion.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
17
Small Animal Study
Investigation # 4
A Context: Distribution of Shore Crab Species
SKILL: Focussing, information gathering, processing and interpreting
Objectives:
To investigate the ecological niche and the distribution of Petrolisthes elongatus and three
other intertidal crab species in the intertidal zone in relation to the physical environment.
Conceptual connection:
Niche
Adaptation = niche
Biotic and abiotic factors
Habitat distribution models
Selection process = patterns in nature
Adaptation processes = patterns in nature
Ecological adaptation = selection by the individual among behavioural responses
Evolutionary adaptation = differential survival among population responses
Biological clock/circadian rhythm
Zeitgeber
Time:
Allow 60-90 minutes
Background:
Equipment:
Transect line (measured line)
Quadrat (square frame, 0.5m x 0.5 m)
3-4 plastic buckets (ice cream containers)
Clipboard with shore data sheets
pencils
Method:
1.
Organise yourselves into groups of 3 and make sure you have all the equipment listed.
2.
Start at the water’s edge and extend your transect line perpendicular to the shoreline.
Place the first quadrat at the start of the transect line (0m) and record the number of
different crabs found within the quadrat. Return the crabs to the location of collection.
Take care not to hurt or step on the crabs! If it starts in your quadrat and moves
out of your quadrat, count it, if it starts outside your quadrat and it moves inside
your quadrat, do not count it!
3.
The bottom edge of the second quadrat should be placed at the next metre mark and the
same information collected. Continue the procedure every metre until you have reached
the cliff. Remember to switch roles so that everyone has the chance to record data, look
for crabs etc.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
18
Small Animal Study
A Context: Distribution of Shore Crab Species
Results:
1.
Graph the combined class data for the distribution of each species of crab using a kite
diagram.
2.
•
•
•
•
Summarise any observations you made:
Were any of the crabs carrying eggs?
Did the size of crabs change from low to high tide?
Any correlation between substrate type and crab species/numbers?
Were different species found under the same rock?
Discussion:
1.
How did the physical conditions vary between the quadrats? Think about time
exposed to air, temperature, substrate, variations in salinity etc.
2.
Describe the adaptations which allow the crabs to survive at different levels on the
intertidal zone. Think about morphological, behavioural, and physiological
adaptations.
3.
Describe the distribution pattern of Petrolisthes elongatus and other crab species:
Was there any correlation between height on the shore and the species? Suggest
reasons for this distribution pattern.
Any correlation between crab species and substrate type?
•
•
4.
What are some of the limitations or biases of this survey technique. Suggest
alternative methods and outline the advantages and disadvantages of each.
5.
What would you expect to find if you were able to put on dive gear and continue the
survey to a depth of 5m?
6.
Imagine the shoreline at high tide. What would you expect the crabs to be doing?
7.
Imagine the shoreline at night. What would you expect the crabs to be doing?
8.
Is this the reproductive season for Petrolisthes elongatus or any other crab species?
How might you determine when the reproductive season is?
© New Zealand Marine Studies Centre, University of Otago, Dunedin
19
SHORE SURVEY FOR INTERTIDAL SHORE CRABS, PORTOBELLO PENINSULA
LOCATION___________________________DATE__________TIME_________
PREDICTED TIME AND LEVEL OF HIGH TIDE_________QUADRAT SIZE_______
HABITAT DESCRIPTION____________________________________________
SEASONAL/ANNUAL RANGE AND VARIATIONS
SALINITY
sea ______________________ intertidal ________________
TEMPERATURE sea ______________________ exposed ________________
LIGHT
blue skies _________________ overcast ________________
QUADRAT #
DISTANCE (m from waters edge)
SUBSTRATE (solid rock/
boulder/cobble/gravel/sand in %)
# CRABS PER QUADRAT
Hemigrapsus crenulatus –
Hairy-handed crab
Petrolisthes elongatus –
Half-crab
Hemigrapsus sexdentatus –
Common (purple) shore crab
Cyclograpsus lavauxi Smooth shore crab
Other
1
2
3
4
Salinity, sea________________
Salinity, intertidal___________
Temperature, sea___________
Temperature, rock top_______
Temperature, under_________
Light, rock top______________
Light, under________________
pH_______________________
O2_______________________
5
6
A Context: Sketch of Location, Sheltered Rocky Shore, Circatidal
Periodicity
Histogram showing activity of a group of common shore =crabs (Hemigrapsus sexdentatus) over a 5day period immediately following their removal from the shore. (Williams, B. G. (1969). The
rhythmic activity of hemigrapsus edwardsi. Journal of experimental marine biology and ecology 3(3),
215-223.
Figure 3. Mean activity per 30-min periods of 6 Hemigrapsus sexdentatus in constant conditions
from 14h30 on 11th Jan 1967 until 10h00 16th Jan 1967. The natural tide height in the environment
during the recording period is indicated above.
By referring to the histogram of Hemigrapsus sexdentatus activity above comment on how this
response may be a confounding variable in practical investigations and how you might design and
carryout an investigation so as to counteract or account for this.
© New Zealand Marine Study Centre, University of Otago, Dunedin
21
Small Animal Study
Investigation # 5
Reproduction of Petrolisthes enlongatus
SKILL: Focussing and information gathering
Objective: To investigate the reproductive strategy and life cycle of Petrolisthes elongatus.
Conceptual connection:
Morphological, physiological and behavioural integration
Niche=adaptation
Biological clocks
Time: Allow 45-60 minutes
Methods:
1.
Examine female crabs carrying eggs "in berry". Estimate how many eggs are present.
Describe how the eggs are attached to the mother?
2.
Look at the developing eggs (embryos) under the microscope. Are all the embryos at
the same stage of development? Are they in the early stages of development (no
structures visible) or close to hatching (eyes and limbs visible)?
3.
Observe the planktonic larval stages under the microscope. On Reproduction of
Petrolisthes elongatus Figure 4 please label the following parts:
On Zoea larva:
- Rostrum (anterior spine)
- Posterior spines
- Compound eye
- Jointed legs
- Cephalothorax
- Abdomen
On Megalopa larva:
- Antenna (1st antennae)
- Antennule (2nd antennae)
- Cephalothorax
- Abdomen
- Eye
- Cheliped
- Appendages
Discussion:
1.
Crabs have internal fertilisation. What are the advantages and disadvantages of this
method compared with external fertilisation?
2.
What are the advantages and hazards of having a planktonic larval stage?
3.
List 3 ways that you think the larvae are adapted for life in the plankton.
4.
Petrolisthes elongatus is found living on the intertidal zone with as many as five other
crab species. How does each species maintain reproductive isolation? Think about pre
and post mating mechanisms (behavioural, morphological and ecological methods).
© New Zealand Marine Studies Centre, University of Otago, Dunedin
22
Small Animal Study
Reproduction of Petrolisthes enlongatus
Figure 4. Life history of the half cab Petrolisthes enlongatus.
0.1mm
0.1mm
5mm
Image credits: Smith & Jensen, 2015; García-Guerrero et al.,
2005; Monterey Bay Aquarium – Crabs: Claws and Shells.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
23
Small Animal Study
Reproduction of Petrolisthes enlongatus
1.
How many eggs would you expect a crab with a carapace length of 11mm to be
carrying?
2.
Using Table 1, can you identify any relationship between mean seawater temperatures
around Kaikoura and breeding cycles? How would you expect seawater temperatures
for Dunedin to compare?
Table 1.
(Jones, 1977)
3.
How would seawater temperature effect the breeding cycle of Petrolisthes enlongatus?
© New Zealand Marine Studies Centre, University of Otago, Dunedin
24
Small Animal Study
Investigation # 6
Protective Responses of the Half-Crab, Petrolisthes enlongatus
SKILL: Focussing and information gathering, awareness of biorhythm
Objectives:
To look at recovery response of the half-crab when disturbed by being inverted.
Conceptual connections:
Autopoiesis
Behaviour is the end point of ecological stress (toxicology)
Morphological - behavioural integration
Niche
Niche—adaptation
Abiotic and biotic (environmental factors)
Habitat distribution models
Selection processes = patterns in nature
Adaptation processes = patterns in nature
Ecological adaptation = selection by individual among behavioural responses
Time:
45 minutes
Methods:
1.
Based on your study of the morphology of the crab and observations made during the
shore survey, list your ideas about the sensory abilities and protection behaviours of the
crab. For example:
-
What biotic factors do you think might threaten its survival in this environment?
How might it aid its survival if manipulated by a potential predator?
What abiotic factors might compromise its safety and survival in the intertidal
environment?
How do you think it responds to some of these factors and how do these responses
increase its chances of survival?
What factors might affect the efficiency of the half-crab’s response to these threats to
survival?
2.
We will design an experiment to test some of your predictions. Use page 1 to help you
develop your experimental plan.
3.
If time permits, carry out the pilot experiment and record your results. You will need
to design a data table to do this. If time does not allow, just share your plan with the
rest of the class for constructive comment.
4.
What were the problems with your experimental design? How would you modify it if
you had time to repeat it?
© New Zealand Marine Studies Centre, University of Otago, Dunedin
25
Small Animal Study
On the Completion of Your Experimental Work
You are required to submit a formal scientific report. This should be structured into sections,
which could include abstract, hypothesis, methods, results (including data sheets, graphs etc.),
conclusions, discussion, references and appendices.
Outline of a scientific report
The report must contain each of the following components:
Abstract:
Provides an overview by stating the principal objectives and briefly
describing the methodology. It should summarise the results and state the
principal conclusion. An abstract is usually written last.
Introduction: Gives the rationale for doing the study. It should include the relevant
background that gives valid reason for your hypothesis with reference to
observation, text, personal communication. Also include i) the problem or
question and ii) a clearly stated hypothesis iii) Introduction of the biological
concept that will be linked to your discussion of your results.
Method:
Write what you did in the order that you did it. Methods should be described
so someone else could repeat your experiment just as you have done it.
Results :
Present data in the form of graphs or tables and use the text to draw attention
to major observations and trends.
Discussion:
An interpretation of your results explaining how they improve your
knowledge of the subject. How you minimized bias and error and steps you
took to maximize validity and reliability of your data. Any statistical test of
reliability of data is referred to.
Conclusion:
List your conclusions concisely with reference back to original hypothesis.
References:
List references and sources of any quotes using the format used in the
reference list adds booklet.
Appendices:
May be included if more detailed information is to be presented than is
needed for understanding (e.g. tables of raw data).
© New Zealand Marine Studies Centre, University of Otago, Dunedin
26
Small Animal Study
Glossary of Experimental Terms
ACCLIMATION:
A period of time needed in a new set of conditions for an animal's physiology
to adjust to those conditions. (A minimum of 40 Minutes in the new
condition; pers. comm. Dr. Amanda Bates —thermal tolerance in submarine
hydrothermal vent species).
AVERAGE /
MEAN
A calculated "central" value of a set of numbers. To calculate it: add up all
the numbers, then divide by how many numbers there are.
CONFOUNDING
VARIABLE:
A factor, other than the independent variable under investigation that might
impact on the response that is being observed or measured. The effect of
these variables needs to be eliminated or minimized to maximize the validity
and reliability of results.
CONTROL:
The part of an experiment which is the same as the treatment in every way
except for the factor being tested. Controls are used as a comparison point
for the experimental treatment.
DEPENDANT
VARIABLE:
The measured variable. The response of subject animal that is hypothetically
linked to the manipulated variable.
EXPERIMENT:
A situation where one or more factors are varied by a researcher in order to
test the effects of the factor on one or more subjects:
Manipulative experiment: An experiment in which the factors are varied
by the researcher according to a preconceived plan in an artificial set-up.
Mensurative experiment: An experiment in which the researcher compares
two or more already-existing subjects which appear to differ only in the
factor being tested.
EXPERIMENTAL
DESIGN:
The preconceived, systematic framework in which the effects of factors on
subjects are tested.
FACTOR:
The item which a researcher believes will have an effect on the subject. (see
also independent variable)
HYPOTHESIS:
A conjectural proposition set forth as an explanation for a specific
phenomenon or observation. A supposition as the basis for reasoning usually a statement starting with "That.... Needs to state animal subject,
independent variable (manipulated), dependant variable (measured),
relationship between them.
INDEPENDENT
VARIABLE:
The manipulated variable. The factor that will be altered by the experimenter
(or altered by aspects of environment) that is postulated will have an effect
on some aspect of the subject animal.
NULL
HYPOTHESIS:
A re-statement of the hypothesis which assumes that factor of interest NULL
has no effect on the subject. This is tested by the experiment and of the
results. accepted or rejected on the basis It is the null hypothesis that is tested
by a statistical test.
PILOT STUDY:
A small-scale study run before a major study, used to evaluate the
experimental design.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
27
Small Animal Study
Glossary of Experimental Terms
PROTOCOL:
The detailed steps to be carried out as part of the overall experimental plan
to increase consistent process and reduce error.
RANGE OF
TREATMENTS:
The different conditions or levels the Independent variable is set at . A.S.
assessment requires at least four in the range. These need to make sense in
relation to the animal's environment and meet ethical requirements.
R2 VALUE
Represents how close the data are to the fitted regression line anywhere in
between 0.0 to 1.0. 0.0 indicates that the model explains none of the
variability of the response data, and 1.0 indicates that the model explains all
the variability of the response data
RELIABILITY:
Is your experimental design and practice such that the data collected is a
most dependable and fair representation of the actual relationship under
investigation? Have all sources and causes of error, bias, and confounded
results been identified, defined, measured, recorded and managed?
REPEAT:
The same experimental protocol is carried out again using the same sample
set of the subject (animals).
REPLICATE:
The same experimental protocol is carried out again using a new and
different sample set of the subject (animals). The repeated unit of each
treatment and control in an experiment. "Why once is not enough".
SAMPLE:
A subset of the population under study.
Random Sampling: Sampling in a manner such that the selection of one
sample has no effect on the selection of any other sample. In random
sampling, all units in the population have an equal chance of being sampled.
Systematic Sampling: Sampling according to a predetermined and
systematic plan. The population units are sampled at regular intervals or
multiples thereof.
STANDARD
DEVIATION
Measures the amount of variability, or dispersion, for a subject set of data
from the mean
STANDARD
ERROR
measures how far the sample mean of the data is likely to be from the true
population mean
SUBJECT:
That which the researcher believes may be affected by a factor (see also
dependent variable).
THEORY:
An explanation of a phenomenon or observation which is based on all known
facts concerning that phenomenon. NOT a supposition.
VALIDITY:
Does the Animal response, the Niche variable, and their relationship
hypothesized, make sense in terms of the animal’s experience in the niche
and in terms of known biological science? Is your hypothesis a sensible
statement in the context of the animal and its niche?
VARIABLE:
A characteristic which takes on different values for different individuals or
measurements (see Dependent Variable & Independent Variable)
© New Zealand Marine Studies Centre, University of Otago, Dunedin
28
Small Animal Study
Validity, Reliability and Ethics
Validity
•
Does the independent variable vary in the environment and does the study
subject experience that variation?
•
Can at least four treatments of the independent variable be defined within
the parameters we expect to see in the environment?
•
Does the study subject's response make sense in terms of its biology?
Reliability
•
Is your investigation set up in a way so it can measure the outcome of
your hypothesis?
•
Have all sources of confounding variables been identified and managed?
•
Have all sources of error and bias been identified and managed?
•
Is your sample size the maximum that time, space and resource allow?
Ethics
•
Is your treatment of the animal within its normal environmental range?
•
Does your setup allow the animal to display its normal behaviour?
•
Do you minimize stress and suffering of the animal by keeping in water and changing to
new seawater when possible (each new treatment), ( handling with cold wet hands?)
•
does the benefit outweigh the harm?
•
Do you diagnose undue stress or damage and deal with it quickly?
© New Zealand Marine Studies Centre, University of Otago, Dunedin
29
Small Animal Study
Statistical Analysis
H1...H0...H1...H0 its off to stats we go!
1.
No amount of statistical analysis will make your results, analysis or interpretation meaningful
or reliable or excellent if you haven't addressed the practical necessities of validity and
reliability when carrying out your testing of your hypothesis, H1 (in the normal course of
science the appropriate statistics is determined before carrying out the investigation!)
2.
Obtain (via excel spreadsheet) or calculate descriptive statistics (average and standard
errors of the average).
3.
Graph the data! A graph shows you if there are any outlier individuals, shows you if any
individual is distorting the trend you may see in the means, shows if there is congruence
between individuals, shows you the spread of the data and therefore its usefulness in
interpreting a trend or relationship and a graph is essential for interpreting any later statistical
test result you may do.
4.
It is of little use to graph means only. You need to either graph as a scatter plot or graph as
means with standard error of the means error bars. These methods show spread of the
data and the value of the experimental means in representing the likely species population
mean.
5.
Perform (or preferably get your computer to perform) a stats 'mining' operation to determine
the statistical significance of differences between the means. If a scatter plot is used a
regression line is helpful in determining how closely the data fits a trend. R2 value then
becomes the measure of statistical significance.
6. What stats test?
Chi square test :
Raw numbers (e.g. number of crabs). Sample size 20 or more with a
normal distribution.
ANOVA (analysis
of variance):
Derived values (e.g. Time, speed, mg/L). Sample size can be less
than 20, with a normal distribution
7.
The test will ask a question of your data. This question relates to your null Hypothesis, H0.
Your hypothesis has predicted a relationship between independent and dependant variables.
Your null hypothesis is that there is NO relationship between the variables, in other words the
response measured will be random in relation to the independent variable. The statistical test
asks, "How probable is it that these results represent random chance?" i.e. What is the
probability of the data supporting the NULL hypothesis, H0?
8.
You are looking for a P-value less than 0.05. This would mean that there would be a less than
5% probability that the data is random. This is regarded as a low probability that the H0 is
supported; therefore, it means a high probability that the data shows a relationship between
the variables. A P-value greater than 0.05 means that the results should be interpreted as a
relationship very cautiously.
However, P<0.05 does not necessarily mean that the hypothesis is supported. You will need
to refer back to the graph to interpret where this statistically significant relationship is and it
may lead to a new or refined hypothesis. You should refer back to the experimental method to
critique the validity and reliability of the data.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
30
Small Animal Study
Using Excel for Analysis
1.
Data should be organised with the first column labelled “Crab” with the number of
crabs you used in your experiment. The treatments should be in the top row from
lowest to highest (not the order you tested). See Figure 5.
Figure 5. An example of what your data should look like when entered into excel.
2.
Below your data in column A create a label for ‘Treatments’, ‘Average’, ‘Standard
Deviation’, and ‘Standard Error’ (see the glossary for definitions of these if you are
unfamiliar with these). See figure 6. To calculate the average, standard deviation, and
standard error the following formulas are used:
Average
Statistic
Formula
=AVERAGE(XX:XX)
Standard deviation
=STDEV(XX:XX)
Standard error
=(STDEV(XX:XX))/SQRT(COUNT(XX:XX))
Note: XX:XX designates a cell value range e.g. B2:B11 as in figure 6.
Figure 6. An example of calculating the average, SD and SE for your data.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
31
Small Animal Study
Using Excel for Analysis
3.
Once you have calculated the descriptive statistics you are ready to graph your data.
Click and drag to select your treatment and average values (not the labels), select the
insert tab at the top of the window and select the scatter chart icon (see figure 7).
Figure 7. The selection process to create a scatter plot of your data.
The resulting plot looks like figure 8.
Chart Title
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
18
20
Figure 8. The basic plot generated by excel which requires more edits to be usable.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
32
Small Animal Study
Using Excel for Analysis
From the plot in figure 8 you can already clearly see a pattern for this example data,
but this plot needs more editing to make it fully interpretable and presentable. You
need to:
o
o
o
o
Delete the title, horizontal, and vertical guide lines.
Add axis titles with units (e.g. time (s); temperature (oc); salinity (ppt) ).
Add error bars using your Standard Error as a custom positive and negative value.
Note that you will have to delete the horizontal bars that are generated.
Add a trend line and an R2 value.
To add elements to the graph (titles, lines and error bars) select the plot by clicking on
it, then click the add chart element for a dropdown of options (figure 9).
Figure 9. Drop down menu for adding chart elements.
Once that is all done the resulting figure should look similar to figure 10 and will be usable in
your report.
12
R² = 0.9256
10
Time (s)
8
6
4
2
0
0
5
10
Temperature
15
20
(oc)
Figure 10. A completed and presentable version of the example data that can be interpreted
using the average, standard error and R2. Axes are labelled and show units.
© New Zealand Marine Studies Centre, University of Otago, Dunedin
33