March 11th, 2014
Environmental Biology Lab 4

Effect of Marine Environments on Bivalve Morphology

Abstract: The process of natural selection is dependent on the environment in which the selected organism resides. An individual’s phenotype determines how fit it is to survive in a given set of environmental conditions. Those individuals more fit than others are more able to survive and reproduce. This experiment is designed to explore the morphology of four species belonging to the class Bivalvia: Ensis directus, Mercenaria mercenaria, Mytilus edulis, and Spisula solidissima. These different species are vastly diverse and this diversity is directly related to the environments in which they live. Two questions will be addressed: how does the relative length of the mollusk ligament relate to the mobility of the animals and the environmental conditions under which they live, and how does intraspecific variation in shell morphology relate to habitat? The data collected in the experiment will be analyzed using the online ANOVA calculator. It can be found that ligament length relative to shell length is required by species living in the intertidal zone, where tides may make it difficult for individuals to remain stationary when necessary. It is also found that environment may not have as much effect on intraspecific variation as does the types of tasks performed by the species, such as locomotion and burrowing.
Hypothesis:
The first hypothesis I will propose is that mollusks with longer ligaments possess a greater locomotive ability. This seems intuitive because a longer ligament would allow greater range of movement for the mollusk to open and close its halves. The repeated opening and closing of the halves is the main method by which the mollusks move around. Environments where resources are dispersed over a large area or where predators are abundant would favor a longer ligament. Environments that would favor shorter ligament length might require the ability to burrow. In terms of intraspecific variation in shell morphology, the habitats where the mollusks live can be attributed to the deviation. I propose that species that live in the intertidal zone will have a much larger range of intraspecific variation. This is because organisms living in the intertidal zone are exposed to many more environmental challenges than those living in a strictly aquatic or terrestrial environment. A higher level of environmental “competition” demands much wider variety within species, in terms of size and other characteristics. More variation means there are more phenotypes that can be tested through natural selection, which leads to organisms that are fitter to survive. Although strictly aquatic environments have their own challenges, these obstacles are more standard when compared to hurdles in the intertidal zone, like predators and resource gathering.
Results:
Below are numerous tables and figures that show the collected data and mathematical analysis of that data.
Table 1: Original data of the measurements of the shell dimensions of the four species
ID
Species
Ligament length
Shell length
Shell height
Shell width
2R
ED
21.64
127.1
21.77
10.64
6R
ED
26.42
132.19
22.77
18.72
22R
ED
31.41
130.42
21.77
12.74
19R
ED
27.86
141.72
24.67
10.16
17R
ED
29.18
136.1
22.07
13.14
20R
ED
23.26
123.92
20.47
11.74
1R
ED
22.21
145.84
23.51
15.88
21R
ED
31.16
149.61
26.29
15.26
9R
ED
32.87
150.43
26.53
16.3
15R
ED
23.39
137.13
24.82
13.18
8R
ED
23.76
120.89
20.19
11.42
6R
ED
28.46
170.69
25.89
12.84
18R
ED
31.11
161.76
26.28
14.82
10R
ED
26.04
145.28
24.74
12.52
14R
ED
18.06
108.51
18.64
7.96
7R
ED
22.92
150.17
26.3
14.2
5R
ED
26.26
136.97
22.21
11.36
23R
ED
26.94
158.36
25.4
13.66
24R
ED
30.29
149.81
24.8
14.62
16R
ED
32.81
158.47
26.22
12.98
13R
ED
33.58
162.01
26.15
14.9
12R
ED
29.5
146.88
25.65
13.92
4R
ED
29.2
145.45
24.05
13.26
7R
ED
33.47
164.34
25.88
15.96
11R
ED
35.9
163.28
28.43
16.9
18R
ED
28.27
171.33
28.99
16.16
5R
ED
26.83
159.7
28.11
16.54
3R