From the FRI Field: Deciphering Differences for Biodiversity

The Freshman Research Initiative (FRI) at UT gives first-year students the opportunity to initiate and engage in real-world research experience with faculty and graduate students. Several students in the Biodiversity Discovery program this past fall semester have shared their research experiences on several species of chirping frogs in Texas and Mexico. In this two-part blog, students describe their work on the acoustic analysis of male advertisement calls (part 1) and digital measurements of preserved museum specimens (part 2) to look for distinguishing features among different species.

PART 1

by Arya Anagol and Mattie Sherwin 

Our research focuses on frog species of the genus Eleutherodactylus (subgenus Syrrhophus) ​that inhabit Mexico and the southern United States. ​Syrrhophus​ contains several cryptic species that are hard to distinguish from one another based on appearance. Deciphering differences between these species will provide new information about levels of biodiversity in the regions these species inhabit. Due to the threat of human activities to ecosystems through pollution, habitat destruction, and climate change, knowledge of biodiversity is of growing importance, which emphasizes the need to successfully delimit species. 

Typically, molecular and morphological data have been used to study ​Syrrhophus subgenus and delimit species boundaries to distinguish between the frogs. However, bioacoustic assessments have also been used in previous studies to distinguish and describe other amphibians. In the context of our research, a bioacoustical analysis includes a comparison of advertisement calls. Male frogs use advertisement calls to communicate with potential mates in the beginning of their reproduction process. Consequently, if frog advertisement calls diverge over time between populations, populations may become reproductively isolated as females no longer recognize the calls of certain males as the same species. This reproductive barrier to interbreeding leads to speciation.

Therefore, usage of bioacoustic evidence to distinguish between and describe frogs of the ​Syrrhophus​ subgenus can aid in affirming species boundaries and exploring the evolutionary history of these frogs. This deeper understanding of the ​Syrrhophus​ subgenus is required to garner a more extensive view of these frogs and to ensure that cryptic species are correctly distinguished. Thus, a combination of bioacoustic data analysis with morphometric measurement comparisons to explore species-level differences among ​Syrrhophus​ species could potentially be used to set species boundaries.

In our research we have worked to provide an application of bioacoustic analysis to determine if this line of evidence can effectively distinguish between species of ​Syrrhophus​ and identify intraspecific and interspecific variation. We processed bioacoustic data by measuring the spectral and temporal properties of the calls in order to garner information regarding the call structures. After gathering the measurement data, we created spectrograms and oscillograms of various calls in the software R as well as performing statistical analysis. The species boundaries set using bioacoustic data was compared to the species boundaries set using DNA sequencing data and morphometric data. Analysis of the spectral and temporal properties of the advertisement calls confirmed that bioacoustical data can be used to distinguish between different species of Syrrhophus. We expect that varying populations of the same species should have negligible differences in their call structure while frogs belonging to different species should have significantly dissimilar and unique call structures in comparison to each other. 

PART 2

by Linus Villareal and Leslie Sanchez

To morphologically assess the Syrrhophus subgenus, we used two open-source statistical data analysis programs, R (RStudio), and ImageJ and collected geometric morphological data. Our team measured various specimens in ventral, dorsal, and lateral angles from images provided by our instructor. We then used statistical methods to observe size and shape variability from many different measurements which include SVL (snout to vent length); HW (head width); HL (head length); IOD (inner-orbital distance); TYD (tympanum diameter); TYE (eye to tympanum distance); SL (snout length); EN (eye to narial distance); SN (narial to snout distance); IN (internarial distance); FAL (forearm length); HAL (hand length); FIIIL (third finger length); FIVL (fourth finger length); TL (thigh length); IMT (inner metatarsal tubercle length); OMT (outer metatarsal tubercle length). 

Analysis of these physical traits should lead to observations of similarities or differences between key body parts within the species. By obtaining the measurements digitally, we are able to acquire precise and unbiased data which would be rather difficult to obtain if it weren’t for Rstudio and ImageJ. Comparing the measurements of the various specimens allows us to distinguish features and how they vary between species and populations of the Syrrhophus subgenus.