This is for Aoife RE: our conversations about lobsters xoxo

1. 11/02/2011 13:53
“Investigation of allometric growth and modification of a basic metameric plan
in the Dublin Bay Prawn”
Hugo Kieran-1E7 Group: DEF
INTRODUCTION
As stated in the title, this experiment deals with the allometric study of Nephrops Norvegicus.
Allometry is defined as “change in a measurable aspect of an organism (such as shape) with increase
or decrease in size,” (Charest, 2005). Nephrops novegicus is great example to demonstrate allometry
from the view that the modifications are very apparent; it's relatively inexpensive, readily available and
st
local. Changes in shape, size and weight can so easily be seen between examples such as the 1
nd
and 2 chelipads. Given their structure is identical it is allometry that has caused such a dramatic
contrast. It is this juxtaposition that perfectly highlights the transformation of the basic metameric plan,
that is, the primitive appendages into specialised, sensory, walking, swimming and burrowing limbs
through allometry.
During the course of this experiment, data was collected from 15 samples of prawns. Each student
then used this data to plot the growth rates of their samples.
MATERIALS AND METHODS
Very few materials are actually needed to perform this experiment satisfactorily. The materials used in
this experiment were:
1. A dissection tray.
2. A scalpel.
3. A forceps.
4. A Vernier calipers.
5. A weighing scales.
6. A pair of gloves.
7. A Specimen.
After a safety talk, the sample was unwrapped. It was weighed and recorded. The larger claw was
then broken at the propodus. The larger claw was then weighed and recorded. All weights were
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measured to 1x10 g. following this; several other aspects of the sample must be recorded for
comparison. Firstly, the length of the propodus of the larger claw was measured. Subsequently: the

2. maximum width of the carapace; the maximum length of the carapace and the maximum diameter of
the eye were also measured. All measurements were then pooled between ~15 other students to
ensure replication of this experiment.
A piece of paper was labeled with the numbers 1~20 vertically. These numbers represent the
appendages of the Nephrop. The numbers allow one to work systematically, beginning at either end
and working through the numbers. After each appendage was removed, it was placed beside the
corresponding number and left for later analysis and sketching.
The prawn was placed upside down, before any incisions were made, the sex of the nephrop had to
be determined. This was done by examining the structure and texture of the pleopods. Once all the
th
data was recorded, the first incision was made between uropod and the 4 pleopod. The uropod, was
th
then examined and laid aside, the 4 pleopod was then removed and examined. The process was
repeated until the eye was reached.
RESULTS
9.00!
8.00! y = 0.1375x - 1.3271!
R² = 0.57895!
7.00!
Claw Weight (g)!
6.00!
5.00!
4.00!
3.00!
2.00!
1.00!
0.00!
0.00! 10.00! 20.00! 30.00! 40.00! 50.00! 60.00! 70.00!
Total Weight of Neophrop (g)!
Figure 1. A relationship between total weight of Nephrop norvegicus and weight of
th
claw. Samples from the Irish Sea: 14 December 2010.
1
Weight of Claw ( to Log10) (g)
y = 0.1168x3.4522!
0.9
R² = 0.55359!
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Total Weight of Nephop (to Log10) (g)
Figure 2. A power relationship between total weight of Nephrop norvegicus and weight
th
of claw using values to Log10. Samples from the Irish Sea: 14 December 2010.

3. Thus, using a figure-by-figure break down, results are as follows:
Figure 1: !"#$% (!) = 0.1375. !"#", ! < 1.
• This implies that the organs or shape are increasing in size more slowly than the
reference dimension (i.e. the claw weight is increasing faster than the total weight).
• There is a dispersed band of data along the trendline with several outliers, which
indicates a large diversity among the nephrops for example a prawn with abnormally
large claws for a relatively low weight.
Figure 2:Reasoning behind the formula = {log ! = log ! + b. log ! → log ! = log ! + log ! ! →
log ! = log ! . ! ! ∴ ! = !. ! ! } !": ! = 3.45 ⇒ > 1
• This slope implies that the claw weight is actually increasing faster than the reference
value (total weight) This makes sense in terms of allometry as the claws are
significantly larger than their cheilipad counterparts.
• There is little or no evidence of any inflection points in this graph.
Figure 3: ! = 0.1526 ⟹ ! < 1
• This slope is similar to that of figure 1 showing the carapace width increasing faster
than the propodus length.
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• Although the R value is fairly standard (i.e. there’s nothing particularly surprising
about this graph), there are a number of outliers as well, reflecting a large diversity
between carapace width and carapace length among these prawns.
Figure 4: ! = 0.445 ⟹ ! < 1:
• This slope has also been shown to be less than one this shows the same result as
above using Log10 values.
• An interesting point to note here however is the concentration of values with a small
range packed towards the upper end of the trendline with relatively few (<5) outliers.
Figure 5: ! = −0.0032 ⟹ ! < 1:
• Figure 5 gives us a slope that has a very small number and a negative value. Firstly:
the negative value implies that the growth of the eyes is slowing down to in relation to
the carapace width.
2 2
• Interestingly though the R value for fig 5 is significantly lower than all other R values
seen so far. This implies a poor fit of the trendline, which in itself suggests a huge
degree of variety among the sample prawns.

4. • On examining the graph, our theory is reinforced not only by the sheer range of
values [x (carapace) = 13mm; y (eye diameter) = 7mm as far as x = 66.12mm y =
8.22mm] with huge outliers on either side perpendicular to the trendline too.
Figure 6: ! = −0.14 ⟹ ! < 1:
• The same phenomenon, as above, is confirmed by the Log10 values and graph with a
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negative slope and very small R value.
• However there is a more concentrated cluster at the end of the trendline in fig. 6.
• Little or no evidence of inflection.
DISSCUSION
On examining the graph data, I would propose that we can see clear evidence of isometric allometry.
It is corroborated by the results of figures 1~4. These figures show a standard growth or reduction in
size between the total weight of the body and various appendages or between the size of the
carapace (which is a central body part) and appendages. The problematic part, as far as I can see is
the growth of the Nephrop’s eyes. These do not seem to conform to any standard trend.
The question this then raises is why? Perhaps it is the fact that the eyes serve as an organ serving a
sensory purpose. It could also be that the eyes are derived from a different material i.e. they’re not
made from a hard shell. Another possibility could be the depth at which the organisms live: if one lives
at 300m and another at 500m; we would expect the Nephrop living at 300m to have smaller eyes as
they receive more light from the surface. It’s hard to say. The only way to find out is to test these
possibilities. A number of other factors could also be measured e.g. antennules length/thickness.
As we know from studying biology, there is always the problem of experimental error. For instance,
there is a problem in measuring the “maximum width” of something. This is not only asking a number
of different people to choose different points on a Nephrop but it is coupled with the problems of
inaccurate measurement and potential error of parallax.
Another interesting aspect to this experiment to note is the fact that all the Nephrops graphed are
male. Would there be differences in the allometry of females? Are they adapted to play different roles
in the habitat? Judging by the lack of females in this sample group, that these Nephrops were caught
during winter as the females burrow during the winter months. This makes different areas of the
population accessible to fisherman at different times.