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

local. Changes in shape, size and weight can so easily be seen between examples such as the 1st

and 2nd 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

measured to 1x103 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

y = 0.1375x - 1.3271!R² = 0.57895!

0.00!1.00!2.00!3.00!4.00!5.00!6.00!7.00!8.00!9.00!

0.00! 10.00! 20.00! 30.00! 40.00! 50.00! 60.00! 70.00!

Cla

w W

eigh

t (g)!

Total Weight of Neophrop (g)!

y = 0.1168x3.4522!R² = 0.55359!

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Wei

ght o

f Cla

w (

to L

og10

) (g)

Total Weight of Nephop (to Log10) (g)

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

data was recorded, the first incision was made between uropod and the 4th pleopod. The uropod, was

then examined and laid aside, the 4th pleopod was then removed and examined. The process was

repeated until the eye was reached.

RESULTS

Figure 1. A relationship between total weight of Nephrop norvegicus and weight of

claw. Samples from the Irish Sea: 14th December 2010.

Figure 2. A power relationship between total weight of Nephrop norvegicus and weight

of claw using values to Log10. Samples from the Irish Sea: 14th December 2010.

 

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.

• Although the R2 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.

• Interestingly though the R2 value for fig 5 is significantly lower than all other R2 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.

• 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

negative slope and very small R2 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.