Critical Analysis of primary literature BIOLOGY

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Research paper: Androgen-dependent male vocal performance influences female preference in Neotropical singing mice

Abstract and Introduction

Reasons for conducting the Study

The motive behind the study was to determine the effects of androgen-mediated vocal signals produced by neotropical male mice on female mice. The researchers wanted to know whether variations in bandwidth frequencies of the melodies or trill made by male mice have different effects on female mice. Since neotropical male produce sounds that attract female mice, the authors suspected that variations in the frequency or tone of the trills could have a corresponding varying effects or levels of attraction on female mice. Further, the research was intended to demonstrate the effects of androgen hormones on modulating male mice’s vocal performance. The researchers also wanted to determine whether female mice would respond to versions of trills that closely mimic those of male mice that have been treated with androgens. They also wanted to find out if the neotropical mice shows vocal performance correspondence with trill rates and the bandwidth of the frequencies. The relevance of the study is in mating amongst mice in that the louder the trills produced by males, the higher the attraction rates at which female mice are attracted.

Hypothesis and Prediction

The researchers predicted that removal of androgen from male mice would negatively impact on their singing ability. Further, they hypothesized female rats are likely to prefer vocal trills of higher performance with regards to loudness than poorly performed songs or melodies (Pasch, George, Campbell & Phelps, 2011). The hypothesis and predictions are found on page 178 of the article. The hypothesis and predictions are clearly stated and understandable. The researchers choose appropriate experiments and observations to prove their predictions because manipulation of androgen levels in rats could only be best achieved through castration of the rats, and elevating androgen levels required injecting the male rats with androgens. The cage setting in which the experiment was conducted was conducive since it made it easy for the researchers to monitor the behavior of male and female rats throughout the experiments.

Materials and Methods

Experimental Methods

The experimental method that was used involved capturing, uniquely coding, and releasing the mice into their respective habitats. In order to manipulate androgen levels in male mice, the researchers castrated laboratory reared off springs of wild mice. A group of the mice were treated with dihydrotestosterone to assess if androgens levels were adequate to bring about aromatization (Pasch, George, Campbell & Phelps, 2011). The researchers then used non-lactating female mature mice that usually show the highest response rates to trills, which were caged 48 hours before the experiment was done. Fast and slow trill stimulus was recorded and played using a laptop and a speaker to the female rats (Pasch, George, Campbell & Phelps, 2011). Each trill for different male rat with different androgen levels was recorded and played using different frequency bands.

Statistical Methods Used

The statistical method used to analyze results was linear regression. It was applied to evaluate the way trill rates relate to different bandwidths, and also to compute the performance limits as well as to evaluate the way body conditions of the mice affected the melodies of the mice in the fields (Pasch, George, Campbell & Phelps, 2011). The researchers used ANOVA software to measure variance of the frequencies and bandwidth of the melodies or trills. A paired t-test was applied to analyze trills prior to and after androgen treatment. The significant alpha values were between 0.25 and 0.5 (Pasch, George, Campbell & Phelps, 2011). Chi-square test was then applied to determine variations or deviation from the expected values. In the experiment, positive values for the t-test meant that females preferred fast stimuli whereas a negative value indicated that females preferred slow stimuli, and 0 was a sign that there was no preference (Pasch, George, Campbell & Phelps, 2011).

Figures and Tables

Figure 2 (a) and (b) illustrate different bandwidth and frequencies of the quality of trill performance against trill rates. From figure (a), it can be observed that the frequency bandwidth before androgen treatment was lower than after treatment. In figure (b), the frequency bandwidth has been plotted against trill rates. From the figure, it can be seen that were highest among mice that were castrated but were treated with dihydrotestosterone after the treatment, and the trill durations were longest among Costa Rican rats that were released to their natural habitats. The diagrams look simple and understandable but help to explain the values presented in the results in that females were likely to approach speakers with fast stimulus trills than low stimulus, and they had a short latency of approaching fast trills (Pasch, George, Campbell & Phelps, 2011). The figures also indicate that androgen levels have an effect on trill frequencies.

Evaluation of the Results and Discussion

The results show mixed outcomes. However, the figures that support the hypothesis and predictions of the authors are significantly higher than those that oppose their predictions. As such, the results indicate that there is a direct relationship between the presence of and high androgen levels with the trills produced (Pasch, George, Campbell & Phelps, 2011). From the results, it can be authoritatively concluded that androgens modulate the frequencies and rates of melodies produced by male mice. Furthermore, the results imply that female mice spend long durations of time around the sound sources that broadcast trills regarded as high performance according to frequency bandwidths and trill durations. However, there was a negative relation between frequency bandwidth and trill duration, which is normal in nature and has also been documented on birds.

References

Pasch, B., George, A. S., Campbell, P., & Phelps, S. M. (2011). Androgen-dependent male vocalperformance influences female preference in Neotropical singing mice. Animal Behaviour82(2), 177-183.