Phylogenetic Diversity of Certain Dendropsophus Hylids Through Phylogenetic and Chromosomal Analysis

This is not Dendropsophus. I don't have any photographs
of that frog. Rather, this is Rana aurora, the red-legged
frog. This picture was taken May 31st, 2009 near Campbell
River on Vancouver Island, BC.

There has been an increase in genetic interest in recent years. While the medical application of genetic knowledge has proved invaluable, there are other reasons scientists study genetics. One of these is for the purpose of understanding how closely related species are and the practical application to evolutionary biology. Many researchers view phylogenetic and chromosomal analysis a definitive authority illustrating trends through the evolutionary tree. However, some evidence suggests that these trends are not consistant.

In a 2013 paper entitled “Comparative Cytogenetic Analysis of Some Species of the Dendropsophus microcephalus group (Anura, Hylidae) in Light of Phylogenetic Inferences,” Medeiros and her associates argued for a reconsideration of the taxonomy of Dendropsophus species, particularly D. nanus and D. walfordi. These two species had an identical karyotype, with the same fundamental number (visible number of arms per chromosome set) of 52, exactly 30 diploid chromosomes, four pairs of telocentric chromosomes (chromosomes with the centromere at the terminal end), and a nucleolar organizer (were the nucleus begins to form) on the metacentric chromosome pair 13 (1). This lack of dissimilarity may indicate that D. nanus and D. walfordi are more closely related than previously thought, possibly even belonging to the same species.

            In the past, Dendropsophus was thought to be a distinct genus from Hyla on the grounds that it had 30 chromosomes. Following, the many species were divided into nine species groups. Later, many authors disputed the assignments of certain species, moving them from one group to another. Others doubted the very status of some species, suggesting that they be synonymous with, or a subspecies of, another species (2). A phylogenetic and chromosomal analysis, it was hoped, would clear up some of this confusion.

            With so much confusion over the relationship of these amphibians, it is not surprising that Medeiros et al. felt another more conclusive study was necessary. Most other analyses were based on phenotypic variations such as pattern, color, voice, and tadpole morphology (2). The Medeiros et al. study attempted to fill in some of these gaps with karyotyping. Because the ordering of genes on chromosomes determines the phenotype of an organism, karyotypes that prove to be the same may indicate that the two species are indeed one and the same.

            Interestingly, the authors of the said paper hold that identical karyotypes do not necessarily dictate that two specimens belong to the same species. For example, in their phylogenetic analysis of the various Dendropsophus species, the authors concluded that the species D. jimi and D. sanborni are not closely related. However, when a karyotype was performed for these species, they proved to be identical. The authors chose to disregard the karyotype and align with the phylogenetic analysis (6). There were other features that could not be seen in the karyotype which were evident in the sequenced ribosomal DNA.

            The authors concluded that, while karyotyping could be useful in determining valid species, there are certainly exceptions to this. They wrote that, “in some cases the obtained cytogenetic data do not help to distinguish between valid species of Dendropsophus” (8). In other words, if two species are clearly different from a phylogenetic perspective, then karyotypes that are identical can be disregarded. Rather, they gave priority to phylogenetic analysis.

However, they did accept karyotyping as considerable evidence of a dissimilar ancestry when it illustrated significant differences. In the case of the species D. nanus and D. sanborni, the karyotypes were so different that they were taken as significant evidence for these two species being unrelated (8). This biased may be due to the evolutionary presuppositions, which would predict a traceable spreading out and increase of diversity, as apposed to a limiting or narrowing of diversity predicted by creationism.

            The article was well prepared and conservative with its conclusion, even suggesting that much more work was needed before a conclusion could be made. However, there was some inconsistency with regards to the importance or reliability of chromosomal analysis. The authors expected to see distinct subgroups of Dendropsophus in accordance with the expected function of new traits in a population rising up and persisting. This was not the case for chromosomal analysis. The karyotypes of some species were not consistent with phylogenetics.

Given a creationist standpoint, this seeming discrepancy is not unexpected, as all species of Dendropsophus would have started with the same genes and potential for diversity. In this view, the species were degraded through generations as information was lost and only fragments of that original diversity were left over. While populations would be similar, having come from the same descendants, given species could have any limited number of left over genes from the original descendants. Thus, though such research is done with an evolutionary worldview, the results nearly always provide invaluable data for science.

Bibliography:

Medeiros, Lilian Ricco, Luciana Bolsoni Lourenc, Denise Cerqueira Rossa-Feres, Albertina Pimentel Lima, Gilda Vasconcellos Andrade, Ariovaldo Antonio Giaretta, Gabriel Toselli Barbosa Tabosa Egito, et Shirlei Maria Recco-Pimentel. 2013. “Comparative Cytogenetic Analysis of Some Species of the Dendropsophus microcephalus group (Anura, Hylidae) in light of Phylogenetic Inferences.” BMC Genetics. Vol. 14, No. 59. From http://www.biomedcentral.com/content/pdf/1471-2156-14-59.pdf (accessed October 13, 2013). Level 1

Hartwell, Leland H., Leroy Hood, Michael L. Goldberg, Ann E. Reynolds, et Lee M. Silver. 2011. Genetics: From Genes to Genomes, Fourth Edition. McGraw Hill Companies, Inc. New York. Level 3.