Phylogenetic trees have become an important component of biology education, but their utility in the classroom is compromised by widespread misinterpretations among students. One factor that may contribute to student difficulties is style, as diagonal and bracket phylogenetic trees are both commonly used in biology. Previous research using surveys found that students performed better with bracket phylogenetic trees across a variety of interpretation tasks. The present study builds on prior research by comparing how students interpret diagonal and bracket phylogenetic trees in the context of an introductory biology course and by expanding the style comparison to include construction tasks. Students performed significantly better with bracket phylogenetic trees for some, but not all, interpretation tasks. In addition, students who constructed bracket phylogenetic trees were significantly more accurate compared to those who used the diagonal style. Thus, our results reinforce previous research for interpretations, and the performance gap between styles extended to construction tasks. It remains to be seen, however, if such differences persist after instruction that balances the use of diagonal and bracket phylogenetic trees.

Introduction

Phylogenetic trees are essential in nearly all disciplines of biology (Baum et al., 2005; Omland et al., 2008), and consequently, learning about phylogenetic trees is also an important component of biology education (O'Hara, 1997). Phylogenetic trees provide a powerful framework for thinking and learning about biology from an evolutionary perspective by serving as visual representations, analytical tools, and conceptual models (Novick & Catley, 2007; Baum & Offner, 2008; Wiley, 2010; Smith et al., 2013). However, the utility of phylogenetic trees for education is diminished by widespread misinterpretations among high school, introductory, and upper-division students (Morabito et al., 2010; Halverson, 2011; Catley et al., 2013; Novick & Catley, 2013; Blacquiere & Hoese, 2016). Such misinterpretations often persist through explicit instruction (Phillips et al., 2012; Dees et al., 2014) and create or reinforce student difficulties with understanding evolution (Meir et al., 2007; Gregory, 2008). The importance of phylogenetic trees for biologists and lack of interpretation skills among students is a disparity that warrants further investigation, such that researchers and teachers can determine the best course of action for instruction.

Students inevitably encounter two equivalent styles of phylogenetic tree, diagonal and bracket, in textbooks, journals, and other resources (Figure 1; Catley & Novick, 2008). Based on classroom observations, style can impact how students interpret phylogenetic trees (Baum & Offner, 2008; Halverson et al., 2011). However, only two studies have explicitly examined the effects of style on student comprehension. Novick and Catley (2007) used translation tasks to reveal perceptual differences between diagonal and bracket phylogenetic trees. Students with varying backgrounds in biology translated different visual representations of evolution, including diagonal and bracket phylogenetic trees, from one representation to another while retaining the same information. The investigators found that accuracy decreased whenever diagonal phylogenetic trees were involved in translations, and the effect was larger for students with less experience in biology. In a second study, Novick and Catley (2013) used a variety of tasks, such as identifying traits shared by taxa, recognizing monophyletic groups, and evaluating relatedness, to compare how students interpret diagonal and bracket phylogenetic trees. Accuracy was lower for the diagonal style across nearly all interpretation tasks, and this effect was often observed regardless of background in biology.

Figure 1.
Diagonal (top) and bracket (bottom) phylogenetic trees with identical branch patterns.
Figure 1.
Diagonal (top) and bracket (bottom) phylogenetic trees with identical branch patterns.

Although the results of Novick and Catley (2007; 2013) are intriguing for biology instructors, the data for these innovative studies were obtained through surveys in which students had no stake in the outcome. Such data are valuable as a starting point, but students may not be motivated to take surveys that will not affect their academic standing as seriously as graded coursework (Sundberg, 2002). Thus, one goal of this study was to reinforce and build on existing, survey-based research by comparing how students interpret diagonal and bracket phylogenetic trees in the context of an introductory biology course. Specifically, we asked the following research question: (1) Do introductory biology students demonstrate differential interpretation abilities for provided phylogenetic trees based on style?

Beyond reinforcing existing research on student interpretations, we also investigated style effects for phylogenetic tree construction, which is of particular interest to teachers. Construction tasks, in which students build phylogenetic trees from various forms of data, are common instructional activities for phylogenetic trees (e.g., Singer et al., 2001; Goldsmith, 2003; Julius & Schoenfuss, 2006; Burks & Boles, 2007; Lents et al., 2010; Eddy et al., 2013; Bokor et al., 2014; Lampert & Mook, 2015). Although several studies examined how accurately students construct phylogenetic trees from data (Meir et al., 2007; Halverson, 2011; Hobbs et al., 2013; Young et al., 2013), only one investigation accounted for style (Dees & Momsen, 2016). However, students were allowed to choose which style to use and overwhelmingly constructed diagonal phylogenetic trees (80%), resulting in an inadequate sample of bracket phylogenetic trees for comparison. Thus, the second goal of this study was to determine if style impacts how accurately introductory biology students construct phylogenetic trees. Specifically, we asked the following research question: (2) Do introductory biology students demonstrate differential construction abilities for phylogenetic trees based on style?

To summarize, we expanded on existing research that investigated the effects of style on student understanding of phylogenetic trees in two ways. First, data for this study were collected through introductory biology coursework rather than through surveys. Second, we included phylogenetic tree construction in addition to interpretation tasks. Our results inform researchers and teachers who are working to develop phylogenetic tree instruction that best facilitates student learning.

Methods

Data for this study were collected during an introductory biology course (n = 107) for science and related majors (Table 1) at a large, public university in the midwestern United States. The course served students at different stages in their academic programs (24% freshmen, 37% sophomores, 20% juniors, 19% seniors) and focused on evolution, form and function, and ecology. Instruction was learner-centered with an emphasis on collaboration (Johnson et al., 1998). Students regularly worked in assigned groups to build and evaluate conceptual models (Dauer et al., 2013), discuss clicker questions (Caldwell, 2007), and construct scientific arguments (Driver et al., 2000).

Table 1.
Course enrollment by major group (n = 107).
Major GroupPercentage of Students
Agricultural sciences 25 
Biological sciences 43 
Natural resource management 12 
Pre-professional healthcare 10 
Other majors (non-science) 10 
Major GroupPercentage of Students
Agricultural sciences 25 
Biological sciences 43 
Natural resource management 12 
Pre-professional healthcare 10 
Other majors (non-science) 10 

Data Collection

We designed an instrument to assess and compare student understanding of diagonal and bracket phylogenetic trees. Students were asked to interpret two equivalent phylogenetic trees (Figure 1) in a number of ways, including identifying traits possessed by taxa, determining the most recent common ancestor of taxa, recognizing monophyletic groups, and evaluating taxa relatedness. We designed much of the instrument based on the work of Novick and Catley (2013), who suggested these interpretations are core skills associated with understanding phylogenetic trees. In addition, students were asked to use the diagonal and bracket phylogenetic trees to determine if extant taxa are descended from other extant taxa, which we refer to as contemporary descent. Earlier studies showed that students often view the straight lines of phylogenetic trees as single entities (Novick & Catley, 2007) that represent no evolutionary change (Meir et al., 2007). For example, students might assume the line from American alligators to node C in Figure 1 (top) represents American alligators rather than part of their evolutionary history. Based on this assumption, students could wrongly infer that bald eagles evolved from American alligators. Because diagonal phylogenetic trees are drawn with straight lines rather than brackets, students may demonstrate contemporary descent reasoning more often when interpreting diagonal phylogenetic trees. Thus, we designed questions that directly assess contemporary descent to test this prediction. Finally, students were asked to construct a phylogenetic tree of plants from provided morphological data in the style of their choice, such that construction accuracy could be compared across styles. All interpretation and construction tasks that were used for this investigation are available in the  Appendix.

We distributed the instrument as a pencil-and-paper homework in an introductory biology course before classroom instruction on phylogenetic trees. In conjunction with the homework, students were assigned a short reading on phylogenetic trees that described their purpose and associated terminology (e.g., nodes and monophyletic groups). The reading, Bioskills 3: Reading a Phylogenetic Tree by Freeman (2011), was modified to include examples of both phylogenetic tree styles. No reading was assigned from the online course textbook (Nature Education, 2013), which contained only bracket phylogenetic trees. Students were allowed to use any resource except each other and were given one week to submit the homework. Note that the order of assessment items was the same for all students: (1) diagonal phylogenetic tree and associated questions, (2) bracket phylogenetic tree and associated questions, and (3) construction task. Students were awarded full credit in the course for completing each question, but to avoid impacting motivation, the grading scheme was not disclosed prior to homework submission. Unfortunately, subsequent instruction on phylogenetic trees, which included a variety of interpretation and construction activities, was not explicitly controlled for style. Instructional materials collected from the course included both styles but were heavily biased toward bracket phylogenetic trees. Thus, we were unable to collect post-instructional data that would provide an unbiased measure of style effects.

Data Coding

Student responses to the trait possession, most recent common ancestor, and monophyletic group questions were coded as correct or incorrect. Questions about contemporary descent (extant taxa evolved from other extant taxa) required a yes or no answer with reasoning. Student answers and reasoning were each coded as correct or incorrect, where correct reasoning suggested extant taxa evolved from a common ancestor rather than each other (e.g., “No, bald eagles and the American alligator are in the same monophyletic group and share a recent common ancestor, but eagles did not evolve from alligators.”). Questions about taxa relatedness asked students to choose which of two taxa is more closely related to a reference taxon and provide reasoning. Answers were coded as correct or incorrect, and student reasoning was coded as correct, incorrect, or mixed using a published rubric (Dees et al., 2014). Correct reasoning referenced most recent common ancestry or monophyletic groups, whereas incorrect reasoning included comparing distances between taxa (branch tip proximity), counting nodes and synapomorphies between taxa, and using information that was not provided by phylogenetic trees (external insights). In some cases, student responses included correct and incorrect reasoning for taxa relatedness, which resulted in the mixed code.

At the end of the instrument, students were asked to construct a phylogenetic tree from provided data in the style of their choice. Phylogenetic trees constructed by students were first coded for style as diagonal or bracket (e.g., Figure 1). Rare cases (n = 4) containing both diagonal and bracket features were coded as the predominant style. Student responses were coded for accuracy as correct, adequate, or incorrect using a published rubric (Dees & Momsen, 2016). Phylogenetic trees that contained major errors, such as incorrect relatedness or incorrect traits, were considered incorrect. Student responses that included only minor errors, such as empty branches or extra nodes, were coded as adequate. The distinction between major and minor errors was based on whether or not the errors impeded the ability of students to interpret taxa relatedness or trait possession, which were skills assessed by our instrument. Finally, phylogenetic trees containing no major or minor errors were considered correct. Student responses to each interpretation and construction task were coded by two independent raters with greater than 92 percent agreement (κ > 0.89; Cohen, 1960).

Statistical Analyses

We treated student responses to the isomorphic interpretation questions associated with diagonal and bracket phylogenetic trees as paired, nominal data. For dichotomous categories (e.g., correct or incorrect), we used the exact version of McNemar's test, which takes the paired nature of our data into account (McNemar, 1947; Rufibach, 2011). The null hypothesis is that an equal number of students switched in one direction (e.g., incorrect to correct) as in the other direction from one phylogenetic tree style to the other (McDonald, 2014). For trichotomous categories (e.g., correct, incorrect, or mixed), we used an extension of McNemar's test known as the Stuart-Maxwell test (Stuart, 1955; Maxwell, 1970). An exact binomial test was used to determine if students preferred to construct diagonal or bracket phylogenetic trees, where the null hypothesis is an equal number of each style (i.e., no preference). Because students constructed only one phylogenetic tree in the style of their choice, accuracy results were nominal (correct, adequate, or incorrect) but unpaired for the construction task. Thus, we used a Fisher's exact test (Fisher, 1934) to compare accuracy across styles, with the null hypothesis that accuracy is independent of style (McDonald, 2014).

Results

Data were collected through a pre-instructional homework that was distributed in an introductory biology course. Of 107 enrolled students, 92 (86%) responded to the interpretation tasks for both phylogenetic tree styles, which enabled within-student comparisons for accuracy across styles. In addition, 85 students (79%) completed the single construction task using the style of their choice, which facilitated a between-student comparison for accuracy across styles.

Interpretations

Students were significantly more accurate when interpreting bracket phylogenetic trees for some, but not all, interpretation tasks (Table 2). There was no difference in accuracy between styles for recognizing traits possessed by taxa. However, students were more accurate in determining most recent common ancestors of taxa and identifying monophyletic groups when interpreting bracket phylogenetic trees. In addition, students were less likely to endorse contemporary descent (extant taxa are descended from other extant taxa) when interpreting bracket phylogenetic trees. Finally, there was no difference in accuracy between styles for evaluating taxa relatedness. However, we found that students were largely unable to determine taxa relatedness, regardless of phylogenetic tree style. For some insight into why performance was poor for taxa relatedness, we tabulated the specific forms of reasoning used by students (Table 3). Counting the number of synapomorphies between taxa was by far the most common approach, followed by counting nodes and comparing distances between taxa (branch tip proximity). Other forms of reasoning were relatively rare, and students generally used the same approach for diagonal and bracket phylogenetic trees.

Table 2.
Number of correct student responses to each interpretation task for diagonal and bracket phylogenetic trees (percentages in parentheses; n = 92 paired responses).
Interpretation TaskDiagonal StyleBracket StyleComparison
Trait possession 83 (90%) 81 (88%) p = 0.791 
Most recent common ancestor 75 (82%) 91 (99%) p < 0.001 
Monophyletic group 63 (68%) 77 (84%) p = 0.003 
Contemporary descent answer 65 (71%) 82 (89%) p < 0.001 
Contemporary descent reasoning 55 (60%) 74 (80%) p < 0.001 
Taxa relatedness answer 12 (13%) 15 (16%) p = 0.250 
Taxa relatedness reasoning 7 (8%)# 10 (11%)# p = 0.368* 
Interpretation TaskDiagonal StyleBracket StyleComparison
Trait possession 83 (90%) 81 (88%) p = 0.791 
Most recent common ancestor 75 (82%) 91 (99%) p < 0.001 
Monophyletic group 63 (68%) 77 (84%) p = 0.003 
Contemporary descent answer 65 (71%) 82 (89%) p < 0.001 
Contemporary descent reasoning 55 (60%) 74 (80%) p < 0.001 
Taxa relatedness answer 12 (13%) 15 (16%) p = 0.250 
Taxa relatedness reasoning 7 (8%)# 10 (11%)# p = 0.368* 
#

Mixed reasoning was found in less than 5% of responses for each style of phylogenetic tree.

*

P-value was calculated using a Stuart-Maxwell test due to trichotomous categories (correct, incorrect, or mixed reasoning). All other p-values were derived from exact McNemar's tests.

Table 3.
Number of student responses that contained specific forms of reasoning to evaluate taxa relatedness for each phylogenetic tree style (percentages in parentheses; n = 92 paired responses).
Taxa Relatedness ReasoningDiagonal StyleBracket Style
Most recent common ancestry 6 (7%) 7 (8%) 
Monophyletic grouping 5 (5%) 6 (7%) 
Counting nodes 20 (22%) 20 (22%) 
Counting synapomorphies 46 (50%) 41 (45%) 
Branch tip proximity 19 (21%) 16 (17%) 
External insights 5 (5%) 2 (2%) 
Other responses 8 (9%) 6 (7%) 
Taxa Relatedness ReasoningDiagonal StyleBracket Style
Most recent common ancestry 6 (7%) 7 (8%) 
Monophyletic grouping 5 (5%) 6 (7%) 
Counting nodes 20 (22%) 20 (22%) 
Counting synapomorphies 46 (50%) 41 (45%) 
Branch tip proximity 19 (21%) 16 (17%) 
External insights 5 (5%) 2 (2%) 
Other responses 8 (9%) 6 (7%) 

Note: Student responses could include multiple forms of reasoning for taxa relatedness. See Dees et al. (2014) for complete descriptions and student-generated examples of reasoning categories.

Construction

Students showed a strong preference for building diagonal phylogenetic trees. Of the 85 students who completed the construction task, 59 (69%) used the diagonal style (p < 0.001 versus an equal number of each style). The majority of phylogenetic trees constructed by students were correct or adequate in terms of accuracy (Figure 2). However, there was a significant difference in accuracy between diagonal and bracket phylogenetic trees (p = 0.002). This style effect disappeared entirely when adequate phylogenetic trees were treated as correct (p = 1.00), indicating the difference was driven by the adequate category. Specifically, diagonal phylogenetic trees included considerably more minor errors, but the incidence of major errors was similar between styles (Table 4).

Figure 2.
Accuracy of phylogenetic trees constructed by students (n = 85 responses).
Figure 2.
Accuracy of phylogenetic trees constructed by students (n = 85 responses).
Table 4.
Major and minor errors in phylogenetic trees constructed by students (n = 85 responses).
Major ErrorDiagonal Style (n = 59)Bracket Style (n = 26)
Incorrect relatedness 16 (27%) 6 (23%) 
Incorrect traits 19 (32%) 6 (23%) 
Contemporary descent 2 (3%) 2 (8%) 
Minor Error Diagonal Style (n = 59) Bracket Style (n = 26) 
Empty branches 30 (51%) 3 (12%) 
Extra nodes 44 (75%) 6 (23%) 
Side branches 0 (0%) 2 (8%) 
Major ErrorDiagonal Style (n = 59)Bracket Style (n = 26)
Incorrect relatedness 16 (27%) 6 (23%) 
Incorrect traits 19 (32%) 6 (23%) 
Contemporary descent 2 (3%) 2 (8%) 
Minor Error Diagonal Style (n = 59) Bracket Style (n = 26) 
Empty branches 30 (51%) 3 (12%) 
Extra nodes 44 (75%) 6 (23%) 
Side branches 0 (0%) 2 (8%) 

Note: Phylogenetic trees constructed by students could include multiple major and minor errors. See Dees and Momsen (2016) for complete descriptions and student-generated examples of errors.

Discussion

We expanded on existing research that examined the effects of style on student understanding of phylogenetic trees in two ways. First, rather than using surveys in which students had no stake in the outcome, we collected data through a pre-instructional homework in an introductory biology course for science and related majors. Second, we included a phylogenetic tree construction task in addition to a series of interpretation tasks. Our results inform researchers and teachers who are working to develop phylogenetic tree instruction that best facilitates student learning.

Interpretations

Using surveys, Novick and Catley (2013) found that students performed significantly better with bracket phylogenetic trees across a variety of interpretation tasks. We collected data as part of an introductory biology course and used a different instrument, but our results largely agree with the previous investigation. For most interpretation tasks, students performed significantly better with bracket phylogenetic trees. However, there was no difference between styles for identifying traits possessed by taxa and evaluating taxa relatedness. For trait possession, students could answer the questions simply by reading information that was explicitly provided by the diagonal and bracket phylogenetic trees (Figure 1). In contrast, the other interpretation tasks required students either to use symbolic information provided by the phylogenetic trees (e.g., nodes and branches) or to apply external knowledge (e.g., monophyletic groups and taxa relatedness). Thus, it was not surprising that students were generally able to identify traits possessed by taxa, regardless of style. For taxa relatedness, the lack of a significant difference between styles was probably due to a floor effect. The vast majority of students were unable to evaluate taxa relatedness, due in large part to using incorrect reasoning strategies, which resulted in style having no impact. Further, the poor overall performance for determining taxa relatedness aligns with previous research, as students typically struggle with this interpretation (Novick & Catley, 2013; Smith et al., 2013; Dees et al., 2014).

Construction

As part of an earlier investigation, Dees and Momsen (2016) found that accuracy of phylogenetic trees constructed by students was independent of style. However, few students chose to construct bracket phylogenetic trees, which resulted in an inconclusive outcome. During the present study, students again favored the diagonal style for construction, but enough students chose the bracket style to enable a meaningful comparison. Although students performed well overall, construction accuracy differed significantly by style. Specifically, there was no difference in major errors, but diagonal phylogenetic trees included considerably more minor construction errors, such as empty branches and extra nodes. While these minor errors should not affect student performance on the interpretation tasks we used for this study (e.g., trait possession and taxa relatedness), such errors could impact other interpretations. For example, empty branches could reflect the common belief that evolutionary changes occurred only at nodes (Baum et al., 2005; Meir et al., 2007; Gregory, 2008). Thus, minor errors are not necessarily inconsequential, and the prevalence of minor errors in diagonal phylogenetic trees constructed by introductory biology students is concerning.

Limitations and Future Research

We recognize this study is limited in a number of ways. First, for the single construction task, students were asked to use the style of their choice. Thus, each student constructed one phylogenetic tree, and the accuracy comparison across styles is between-student. Future investigations should use a stronger within-student approach by asking students to construct equivalent diagonal and bracket phylogenetic trees during separate tasks.

Second, the order of assessment items was the same for each student: (1) diagonal phylogenetic tree and associated questions, (2) bracket phylogenetic tree and associated questions, and (3) construction task. Therefore, it is possible that prompt order affected student responses. For example, some students could have performed better on questions associated with the bracket phylogenetic tree due to experience gained by attempting to interpret the diagonal phylogenetic tree. However, students also could have performed worse on questions associated with the bracket phylogenetic tree due to assessment fatigue or loss of motivation over time. Future research should control for these possible order effects by systematically varying the order of assessment items.

Third, we collected data from one introductory biology course at one university, and the results may not reflect undergraduate biology students as a whole. Students at other institutions may have different academic backgrounds and motivations that could influence their performance. Thus, there is a need for further research at a variety of schools to accumulate additional evidence from which we can make more robust and generalizable claims.

Finally, our use of terminology may vary from that used by practicing systematists. However, we used language consistent with undergraduate biology educators and introductory textbooks (e.g., Baum & Offner, 2008; Freeman, 2011; Novick & Catley, 2013).

Implications for Instruction

Most current introductory biology textbooks, in response to research similar to this study (Novick & Catley, 2007; 2013), use only bracket phylogenetic trees. However, many instructors may be unaware of this publishing decision, and many more are likely unfamiliar with the empirical research related to style effects and phylogenetic trees. A typical introductory biology instructor uses a variety of resources to develop curricula, including but not limited to the course textbook. As a result, instruction may use diagonal and bracket phylogenetic trees somewhat interchangeably. Thus, although introductory biology textbooks are consistent in their use of bracket phylogenetic trees, instruction often includes a mixture. Research on style effects, therefore, serves to inform instructors of the potential for phylogenetic tree style to impact student reasoning.

Further, research focused on the interaction of instruction with style effects is currently quite limited. For example, data for this study were collected before instruction on phylogenetic trees, and previous research on style effects either did not document instruction (Novick & Catley, 2007; 2013) or resulted in an inconclusive outcome (Dees & Momsen, 2016). Thus, the direct impact of instruction remains unknown, and we advise against making instructional decisions regarding phylogenetic tree style without additional data. It is possible, for example, that balancing the use of diagonal and bracket phylogenetic trees during instruction could reduce or eliminate performance differences between styles. Future investigations should collect data before and after instruction on phylogenetic trees that is controlled for style. Such research is needed to determine the course of action for teachers who are working to develop phylogenetic tree instruction that best facilitates student learning.

This research was conducted in compliance with Institutional Review Board regulations (protocol SM12217) and was funded by a STEM education fellowship from North Dakota State University and the National Science Foundation (DRL-1420321 and DUE-1156974).

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Appendix: Interpretation and Construction Tasks that were used for this Investigation

The following interpretation questions from the pre-instructional homework accompanied the diagonal phylogenetic tree in Figure 1 (top).

Trait Possession

According to the phylogenetic tree of chordates in Figure 1, which of the following traits do bald eagles possess? Draw an X inside the box below each possessed trait.

Most Recent Common Ancestor

Which node of the phylogenetic tree in Figure 1 represents the most recent common ancestor of platypuses and American alligators?

  • node A

  • node B

  • node C

  • node D

Monophyletic Group

Draw a circle around one monophyletic group (clade) on the phylogenetic tree in Figure 1.

Contemporary Descent

According to the phylogenetic tree of chordates in Figure 1, did bald eagles evolve from American alligators? Explain your reasoning below.

Taxa Relatedness

According to the phylogenetic tree of chordates in Figure 1, how would you describe the relatedness of American alligators to fire salamanders and red kangaroos?

  • American alligators are more closely related to fire salamanders than red kangaroos.

  • American alligators are more closely related to red kangaroos than fire salamanders.

  • American alligators are equally related to fire salamanders and red kangaroos.

  • American alligators are not related to fire salamanders and red kangaroos.

Explain the reasoning for your choice below.

The following interpretation questions from the pre-instructional homework accompanied the bracket phylogenetic tree in Figure 1 (bottom).

Trait Possession

According to the phylogenetic tree of chordates in Figure 1, which of the following traits do griffon vultures possess? Draw an X inside the box below each possessed trait.

Most Recent Common Ancestor

Which node of the phylogenetic tree in Figure 1 represents the most recent common ancestor of short-beak echidnas and Siamese crocodiles?

  • node A

  • node B

  • node C

  • node D

Monophyletic Group

Draw a circle around one monophyletic group (clade) on the phylogenetic tree in Figure 1.

Contemporary Descent

According to the phylogenetic tree of chordates in Figure 1, did griffon vultures evolve from Siamese crocodiles? Explain your reasoning below.

Taxa Relatedness

According to the phylogenetic tree of chordates in Figure 1, how would you describe the relatedness of Siamese crocodiles to marbled newts and koalas?

  • Siamese crocodiles are more closely related to marbled newts than koalas.

  • Siamese crocodiles are more closely related to koalas than marbled newts.

  • Siamese crocodiles are equally related to marbled newts and koalas.

  • Siamese crocodiles are not related to marbled newts and koalas.

Explain the reasoning for your choice below.

The following construction task was placed at the end of the pre-instructional homework.

Use the morphological traits in Table A1 to construct a phylogenetic tree of plants. Any style of phylogenetic tree is fine. Be sure to label all shared, derived characters (synapomorphies).

Table A1.
Morphological traits of plants (X = trait possessed by plant).
PLANTS
Ginkgo BilobaCreeping FingerwortGreen AlgaeLady TulipTufted LacefernBishop Pine
TRAITS Stomata   
Needles      
Cuticle  
Seeds    
Flowers      
Cones     
PLANTS
Ginkgo BilobaCreeping FingerwortGreen AlgaeLady TulipTufted LacefernBishop Pine
TRAITS Stomata   
Needles      
Cuticle  
Seeds    
Flowers      
Cones