Article Review
Chelini, M. C., Brock, K., Yeager, J., & Edwards, D. L. (2021). Environmental drivers of sexual dimorphism in a lizard with alternative mating strategies. Journal of Evolutionary Biology, 34(8), 1241-1255. Web.
Summary
Paper’s Content
Most of the various evolutionary mechanisms discussed as the causes leading to sexual differentiation of males and females in the lizard population are reduced to the habitat in the paper. The research conducted by scientists is aimed at identifying the dependence between the sexual dimorphism of lizards on environmental conditions. The difference between the average values of the frequency and severity of the trait in males and females in warm and cold climates is established. Signs such as the size of the limbs, tail, head, the number of scales and shields, coloring, and pattern are considered.
Major Points
The main points of the article were the accumulation and analysis of data on morphological divergence between males and females in populations under different environmental conditions. The paper provides a detailed description and discussion of the morphology of the lizard Uta stansburiana, which lives in different climatic conditions (Chelini et al., 2021). After that, the adaptive value of certain characteristics for a particular sex is revealed, as well as the directions and patterns in the formation of sexual dimorphism.
Main Question
The main questions that the researchers were interested in was to determine the environmental conditions in which lizard populations would have more pronounced sexual dimorphism. In addition, scientists were faced with the task of finding out whether only the degree of morphological differentiation would change, or whether its structure would also differ (Chelini et al., 2021). In addition, the paper should have answered the question of the relevance of existing data and new experimental studies.
Sampling And Methods
Both empirical and theoretical research methods are used in the work; each of the methods has a special section in the paper. First of all, observation is applied: purposeful and attentive perception of the studied signs in lizards with subsequent fixation of the data obtained. Next, the analysis of data recorded in specimens living in different climatic conditions is applied. At the final stage of the study, the synthesis of information obtained by other researchers with the results of this work is used.
The sample of species is rather narrow, since only one specimen of lizard – Uta stansburiana – is taken into account. However, its entire habitat has been studied in great detail, so the sample of climatic conditions is wide, which is very appropriate for the study (Chelini et al., 2021). Quantitative research methods were very competently selected, which made it possible to qualitatively collect and analyze the necessary data. However, the method of analogy raises some doubts: the conclusions obtained are proposed to be used as a universal model in relation to other lizard species.
Findings
During the observation and analysis of the literature, it was revealed that sexual dimorphism is more pronounced in a population of lizards living in a cold temperature regime. It was found that in individuals who are in unfavorable environmental conditions, sexual characteristics are more pronounced. At the same time, the sexual characteristics of lizards living in warm climatic zones are less noticeable in both males and females. The results are well explained: the conclusion summarizes statistical data from the current and other studies. In addition, each section of the article ends with a summary of the results of the considered stage of the study. Thus, the work is well structured and ideas presented in it are easy to follow.
Interpretation
Based on the data of the fluctuating asymmetry analysis, it was shown that the optimal natural zone for the lizard is a warmer climate. Consequently, the cold climate turns out to be more extreme conditions for the lizard population. Scientists note the tendency of populations to increase sexual dimorphism in terms of increasing the size and proportions of the body in males living there. Cold climate populations are characterized by high density and limited habitat area. This is true for many populations in unfavorable environmental conditions, because in such populations the pressure of sexual selection is stronger. Thus, the severity of sexual dimorphism becomes clearer in unfavorable environmental conditions at the border of the range, where higher evolutionary plasticity of the population is required.
Conclusions clearly follow from the results, they briefly outline the main points of the data obtained, and an explanation to them. They summarize the author’s position on the problem posed, and confirm the hypotheses given at the beginning of the study. Summing up the results is quite logical and reasoned, cause-and-effect relationships can be easily traced there.
Evaluation of Evidence and Reasoning
Strongly Evidence-Supported Statements
The strengths of the study are a detailed illustrated list of sexual dimorphisms in the features of coloring, and pattern, as well as sexual dimorphism by metric and meristic signs. The data of the analysis are in general agreement with those from the literature, and no significant differences were found. In addition, a strong argument is presented when determining the reasons for the more pronounced expression of signs of sexual dimorphism in individuals of cold climates. The proof by contradiction is used very competently: arguments are given in favor of the insolvency of the socio-behavioral causes of sexual dimorphism.
More Weakly Supported Statements
Weaker arguments are presented in favor of the fact that the conclusions obtained in the article are universal and applicable to other lizard species. According to the Lofeu, all models of ecological niches have a limited and probabilistic nature (Lofeu et al., 2020). When studying rare species and isolated populations of lizards inhabiting areas with difficult terrain, it is impossible to visit their habitat areas to collect information. Thus, it is possible that the dependence of the severity of sexual characteristics established in the article depending on the habitat climate is only applicable to Uta stansburiana.
Providing Background on the Investigated Question
The introduction, with which the article begins, provides a scientific background regarding the known causes of sexual dimorphism in various populations. However, it is mentioned that mainly the biological origins of sexual dimorphism in animals have been investigated, while environmental influences are less common as the main causes studied (Siliceo-Cantero et al., 2020). The results of previous studies on the signs of sexual dimorphism in lizards are also summarized.
Ignored Aspects
The work ignores the habitat features of some lizard species, for which the findings may not be suitable. For example, there are populations of lizards living exclusively in warm climates, but there is also a division among them regarding the severity of sexual characteristics. This may be due to the size of the territory they inhabit (Naretto et al., 2020). Thus, island lizards are in conditions of more strictly natural selection than mainland ones, so their environment leads to the need for more active development of sexual characteristics.
Conflicting Results
Many specific mechanisms for the formation of sexual dimorphism on one or another trait remain controversial or have not been identified at all. Thus, the connection between sexual dimorphism and the nature of sociosexual relationships among lizards is denied, but other reasons remain unknown. Despite the fact that the article focuses on the relationship of this phenomenon with the environment, scientists recognize the existence of other potential causes.
References
Chelini, M. C., Brock, K., Yeager, J., & Edwards, D. L. (2021). Environmental drivers of sexual dimorphism in a lizard with alternative mating strategies. Journal of Evolutionary Biology, 34(8), 1241-1255. Web.
Lofeu, L., Brandt, R., & Kohlsdorf, T. (2020). Digit identity matters: origin and evolution of sexual dimorphism in the digit lengths of tropidurid lizards. Biological Journal of the Linnean Society, 131(1), 109-121. Web.
Naretto, S., & Chiaraviglio, M. (2020). Factors driving sexual dimorphism and colour variability in Achala Copper Lizard (Pristidactylus achalensis), an endemic species to the highland mountains in Central Argentina. Canadian Journal of Zoology, 29(3), 1-46. Web.
Siliceo-Cantero, H. H., Benítez-Malvido, J., & Suazo-Ortuño, I. (2020). Insularity effects on the morphological space and sexual dimorphism of a tropical tree lizard in western Mexico. Journal of Zoology, 311(4), 277-285. Web.