Introduction

Brief motivation

Project is about affect of stress in Rock agamas on their development, phys- iology, behavior and other ecologically relevant features (like sprint speed, bite force and wound healing). This study was crucial as it gives us insights on how urban lizards cope with stress that comes as a consequence of staying in human dominated areas. Maturity (from juvenile to adult) is an important stage that determines sev- eral life history traits of an organism. However, it remains largely unstudied how changes in physiology, behavior and phenotypes are caused by difference in stress levels during development till sexual maturity.

Experimental setup

Approach

Implants are given to wild caught juvenile P. dorsalis. These implants either release cortisol (hence refered to as CORT treatment) or don’t release any- thing (hence refered to as SHAM treatment). Note that the juvenile phase is the peak developmental phase of P. dorsalis and implants are given to both male and female lizards. After surgical implantation, these animals are left to grow in an enclosed space. Collection of data (mentioned in the next section) occurs during the developmental phase as well as after adulthood is reached.

Data collected

The following data were collected from the P. dorsalis under experimental treatment.

1. Morphometric data : X-Ray images were taken after capture using dental X-Ray tools, every 3 weeks after implantation. The X-Ray is then landmarked, and the skeletal structure is further analyzed and is used to compare the difference between CORT and SHAM treatment as they develop from juveniles to adults. This will be discussed in later sections.
2. Immune Response : A wound is given to a lizard, post numbing, to see how fast the lizard heals it back. Photographs are taken on a daily basis for 10 days to capture the healing process of the wound. The area of the wound is measured using the photographs. The healing capabilities are then compared between CORT and SHAM treatments.
3. Sprint speed : After adulthood is reached, P. dorsalis are brought back to the lab. These lizards are then allowed to run on a track one by one, video of which is recorded. The track is marked at regular known lengths so that the speed of the bouts can be digitally computed. The lizards run away from humans (which simulates a predator-encounter like condition) which is used to make them run on the track. This is done to test predator avoidance capabilities of the lizard, to see if stress at early stage affects their survival in the wild.
4. Bite force : This is collected by making the lizard bite a machine, which outputs the bite strength in pressure. Biting is a common strategy employed in male-male aggression interaction and defensive mechanism.
5. Behavior data : This is about the number of head bops, push-ups and other behaviors expressed by the lizards, in the presence of con- specifics. This is to verify if mating behavior is affected by stress at juvenile phase.
6. Hormonal Response : To check if there are any effects on levels of testosterone and cortisol, blood tests are run on the test animals. Blood is collected by inserting a capillary tube behind the eye socket and tapping into a vein. The blood hormone level is compared with the baseline blood hormone level.

Work Done

Data Collection

Sprint Speed Analysis

I developed the protocol for annotating the lizard sprinting data. Using this protocol I annotated the data and the analysis of the data is still underway. (Here’s a link to the protocol developed for scoring of the sprint speed videos.)[https://drive.google.com/file/d/14dO4wofYg4UtzMAyEoD3jQYwkt1xmnmE/view?usp=drive_link]

Landmarking

X-Ray images were collected of the lizards in captivity post implantation. The X-Ray images were taken once every 3 weeks to capture growth rates and development of different body structures of the lizards. These X-Ray images need to be landmarked (annotation of data) so that further morphometric analysis can be carried out on them. Landmarking was done using tpsDig software of over 180 images and repeated thrice in order to minimize human error.

Immune Response

Photographing of wounds were done for 10 days after the day of wound- ing. Imaging was done using phone camera (Galaxy M12) directly from the lizard tanks. To ensure that the lizards do not move during the photograph- ing process, images were taken early in the morning (before sun rise) while the lizards were still asleep. P. dorsalis are diurnal animals, that are physi- ologically constrained to be active when the sun is out. The photographs of the wounds will be used the measure the wound size and thus used to compute rate of healing based on how much the area has reduced over the span of 10 days. The rates are then compared between SHAM and CORT treatment, to see if continued exposure to stress from juvenile phase effects the wound healing capabilities of adult lizards.

Others

Field work

Field work involved capturing lizards and measuring different morphometrics. Majority of the field work was carried out in the rocky terrain of Kolar, India. These lizards were caught and bagged, using modified fishing rods as nooses.

Data collection in lab

Lizard X-Ray data and blood samples were collected in the lab. The videos for sprint speed analysis were also recorded in a lab setting. Also, I was involved in care-taking of lizards in the lab enclosure, which involved feeding them and cleaning.

Acknowledgments

I would like to thank Subhasmita Patro for the guidance and support. I would also like to thank Prof. Maria Thaker and the Macrophysiology lab for being very inclusive and for making my summer experience memorable.