Variation and Ecological Fitness in the Woodlice
Is there any way to include a quote or two from source listed for discussion part of the lab. It is listed as a reference used and I believe it would be good to include a quote or two to answer the following:
Suggest other techniques that could be used for selection and how this might affect the frequency of specific alleles and the frequency distributions.
from Berkelhamer R. 1998. Variability and selection innatural populations of wood lice. Pages 245-254, in Tested studies for laboratory teaching, Volume 19 (S. J. Karcher, Editor).
Proceedings of the 19th Workshop/Conference of the Association for Biology Laboratory Education (ABLE), 365 pages.
Introduction
In ecological studies, variability in population enables natural selection and consequently evolution. A trait that lacks variation cannot evolve by natural selection, drift, migration, or non-random mating. Variability of traits in color, length, mass, number of segments, and sprint speed that populations may have increases the likelihood to experience selection and evolution (Thomas et al. 2001). The experiment was conducted to show the variable characteristics among individuals (traits) of woodlice (Crustacean Isopoda) that make them survive or not survive when exposed to a predation environment. The traits of woodlice that the experiment was based upon are color, length, number of segments, mass, and sprint speed. These traits were examined to establish their influence on predators or the selection of that trait by the simulated predators.
This paper seeks to explore variations and fitness as opposed to evolutionary response to selection. Evolution is examinable in more than one generation and entails a genetic composition change of a whole population (Berkelhammer, 1997). On the other hand, Selection implies a non-random survival of variants chosen randomly. We can define natural selection as variation in fitness so that the fittest individuals in a phenotype survive.
Selection helps contemporary populations to survive/persist better. Selection chooses a particular variant that gives individuals the higher fitness levels hence will suit the population for living in an environment (DeAngelis, & Mooij, 2005). The past selection has a great impact in shaping the behavior of the current population and without the previous selections; the contemporary individuals would be entirely unsuitable for living in an ecosystem.
The exercise in this paper will be completed by using statistical methods to help in data distribution (variation in woodlice – the terrestrial crustacean traits), to identify how traits confer a survival advantage on exposure to predators, and establish whether the survival advantages rely on the presence of predators, and, finally, recording data in a fashioned manner. The availability of woodlice and the readily available materials to examine them in for this exercise enabled the ease of carrying out this exercise. Variability in traits of organisms can be environmental, developmental, or heritable (Bock, 2003). This is an important point to note as discussed in the paper, though not dealt with explicitly.
Hypothesis
The woodlice survival or subjectivity as victims when exposed to predators relies on their variable traits in terms of color, length, number of segments, mass, and sprint speed. These traits inform the ability for the fittest to survive by means of variation and fitness (natural selection).
Mean and Variation
A population consists of individuals with variable traits. Since classical times, ecologists describe organisms by their mean for categorizing them (Grant, 1999). Also, mean compares either populations or samples. For example, a plant ecologist can use the mean height of shrubs in dumb and in dry land to understand growth response to moisture. Besides mean, variation is biologically very important in their natural selection. Darwin understood these variations and came up with natural selection and survival for the fittest in evolution (Campbell et al., 1991; Grant, & Grant, 2006). He suggested that the differences among species arise from variations in the traits among them. The variation and mean of population are easily seen by graphs of individual traits of particular values. The number of individuals in each class size is known as frequency distribution. The mean value should lie close to the bell-shaped curve middle while the distribution is seen in the distribution breadth.
Results and Analysis
Table 1: Victim Woodlice
Sow bug Sprint Speed (seconds) Length Number of Segments Color Mass Victim/Survivor
1 18.06 14.5 13 5 0.055 Victim
2 20.1 11.2 10 5 0.049 Victim
3 18 10.5 12 4 0.052 Victim
4 10.46 11.2 12 5 0.066 Victim
5 22.93 11.1 10 5 0.055 Victim
6 18.65 9.5 10 5 0.041 Victim
7 63 7.5 11 3 0.018 Victim
8 16.66 10.1 13 4 0.044 Victim
9 14.45 11.1 10 5 0.061 Victim
10 15.48 9.2 9 3 0.028 Victim
11 31.51 8.9 11 4 0.02 Victim
Minimum 10.46 7.5 9 3 0.018
Maximum 63 14.5 13 5 0.061
Range 52.54 7 4 2 0.043
Mean 22.66363636 10.436 11 4.364 0.044
Table 2: Survivor Woodlice
Sow bug Sprint Speed Length Number of Segments Color Mass Victim/Survivor
1 23.23 11.1 9 5 0.046 Survivor
2 16.48 11.9 12 5 0.066 Survivor
3 9.68 12.2 10 5 0.062 Survivor
4 19.93 10.5 10 4 0.038 Survivor
5 21.82 10.9 11 5 0.052 Survivor
6 27.59 10.7 10 5 0.046 Survivor
7 20.33 8.6 9 2 0.022 Survivor
8 14.35 7.4 11 4 0.023 Survivor
9 28.76 6.9 10 3 0.017 Survivor
10 7.98 12.1 12 5 0.064 Survivor
11 19.06 9.4 13 5 0.032 Survivor
12 12.16 9.7 10 3 0.038 Survivor
13 9.82 10.3 11 5 0.045 Survivor
14 22.73 11.1 10 4 0.045 Survivor
15 27.57 7.5 11 5 0.016 Survivor
16 14.5 7.4 9 4 0.018 Survivor
17 10.38 10.3 10 4 0.034 Survivor
Minimum 7.98 6.9 9 3 0.016
Maximum 28.76 12.2 13 5 0.066
Range 20.78 5.3 4 2 0.05
Mean 18.02176471 9.8824 10.47058824 4.294 0.039
Comparative Analysis for Victim and Survivor Woodlice
Table 3: Speed Distribution Table
Victim or Survivor Speed
Speed (seconds) Victims Survivors
4.0-14.0 1 5
14.1-19.0 6 4
19.1-24.0 2 5
24.1-63.0 2 3
Figure 1: Distribution of victims and survivors woodlice depending on speed
Table 4: Length Distribution Table
Victim or Survivor Length of
Length Victims Survivors
5.0-9.0 2 5
9.1-11.0 4 7
11.1-15.0 5 5
Figure 2: Distribution of victims and survivors woodlice depending on length
Table 5: Number of Segments Distribution
Victim or Survivor Number of Segments on
Number of Segments Victims Survivors
9.0-10.0 5 10
10.1-11.0 2 4
11.1-12.0 2 2
12.1-13.0 2 1
Figure 3: Distribution of victims and survivors woodlice depending on number of segments
Table 6: Color Codes Distribution table
Victim or Survivor Color codes for
Color Code Victims Survivors
2.0-3.0 2 3
3.1-4.0 3 5
4.1-5.0 6 9
Figure 4: Distribution of victims and survivors woodlice depending on color codes
Table 7: Mass distribution table
Victim or Survivor Mass of
Length Victims Survivors
0.01-0.02 2 3
0.021-0.03 1 2
0.031-0.04 0 4
0.041-0.05 3 4
0.051-0.06 3 1
0.061-0.07 2 3
Figure 5: Distribution of victims and survivors woodlice depending on mass
In the experiment, it was possible to identify how woodlice respond to predators by the traits of color, sprint speed, number of segments, mass, and color. The color values indicate the color codes as per the color scheme provided in the lab. The graphs showed victims that survived and those that became victims of predators following their traits.
Discussion
From the averages of woodlice sprint speeds, lengths, number of segment, color and mass, we can deduce that; the sow bugs with relatively faster speed, less mass, less conspicuous, fewer number of segments, and smaller lengths survived more than their counterparts with less speed, longer lengths, more mass, and conspicuous. The natural selection of the woodlice populations is basically influenced by the individual traits favoring selection. For instance speed enables individuals to have high selection intensity. Slower woodlice have low selection differentials. Moreover, selection of phenotypic trait such as mass, color, and size depend on predator type. High selection differentials should inform directional selection over time. On the contrary, low selection leads to little character change as a result of selection. Selection intensity relies on predator type. For instance, the visual predators are likely to select conspicuously colored populations and not the others. Also, predators that depend on size and mass may select against a certain class size while preying more strongly other sizes and mass class. For the exercise, the selection was limited to predation though there may be other environmental factors that survival of individuals in a population may rely upon. “Variability in some of the traits examined has a heritable component, while in others it may be strictly environmental and/or developmental” (Berkelhamer, 1998, p.248). The environment and developmental factor may affect the frequency distribution and specific alleles, for example, during harsh environments, food shortage, et cetera. Fast animals may escape predation because of the strength and more energy than their slower counterparts and they may be selected in times of food shortages.
Conclusion
The exercise shows that natural selection and survival of woodlice widely depends on their traits. The predators prey on individuals depending on the favorable traits on the population. For this exercise, as per the hypothesis, woodlice survival when subjected to simulated predator depended on the individual traits including color, length, number of segments, mass, and sprint speed. Slower, conspicuous, bigger, longer, and weighty woodlice had lower selection intensities than others. The traits, therefore, inform the ability sow bugs’ survival whereby only the fittest can survive by means of variation and natural selection.
References
Berkelhammer, R. (1997). Variability and Selection in Natural Populations of Wood Lice. Tested Studies for Laboratory Teaching, 18.
Berkelhamer R. (1998). Variability and selection in natural populations of wood lice. Pages 245-254, in Tested studies for laboratory teaching, Volume 19. (S. J. Karcher, Editor). Proceedings of the 19th Workshop/Conference of the Association for Biology Laboratory Education.
Bock, W. J. (2003). Ecological aspects of the evolutionary processes. Zoological science, 20(3), 279-289.
Campbell, D. R., Waser, N. M., Price, M. V., Lynch, E. A., & Mitchell, R. J. (1991). Components of phenotypic selection: pollen export and flower corolla width in Ipomopsis aggregata. Evolution, 45(6), 1458-1467.
DeAngelis, D. L., & Mooij, W. M. (2005). Individual-based modeling of ecological and evolutionary processes. Annu. Rev. Ecol. Evol. Syst., 36, 147-168.
Grant, P. R. (1999). Ecology and evolution of Darwin’s finches. Princeton University Press.
Grant, P. R., & Grant, B. R. (2006). Evolution of character displacement in Darwin’s finches. science, 313(5784), 224-226.
Thomas, C. D., Bodsworth, E. J., Wilson, R. J., Simmons, A. D., Davies, Z. G., Musche, M., & Conradt, L. (2001). Ecological and evolutionary processes at expanding range margins. Nature, 411(6837), 577-581.
