Investigating the link between morphological characteristics and diet in an island population of omnivorous reptiles (Sphenodon punctatus)

Abstract

The morphological characteristics that impact feeding ecology in ectotherms, particularly reptiles, are poorly understood. We used morphometric measures and stable isotope analysis (carbon-13 and nitrogen-15) to assess the link between diet and functional morphology in an island population of an evolutionarily unique reptile, the tuatara (Sphenodon punctatus). First, we established a significant positive correlation between overall body size, gape size, and fat store in tuatara (n=56). Next, we describe the relationship between stable isotope profiles created from whole blood and nail trim samples and demonstrate that nail trims offer a low-impact method of creating a long-term dietary profile in ectotherms. We used nitrogen-15 values to assess trophic level in the population and found that tuatara on Takapourewa forage across multiple trophic levels. Finally, we found a significant relationship between gape size and carbon-13 (linear regression: P<0.001), with tuatara with large gapes showing dietary profiles that suggest a higher intake of marine (seabird) prey. However, whether body size or gape size is the primary adaptive characteristic allowing for more optimal foraging is yet unknown. This article has an associated First Person interview with the first author of the paper.

Gut microbiome of the sole surviving member of reptile order Rhynchocephalia reveals biogeographic variation, influence of host body condition and a substantial core microbiota in tuatara across New Zealand

“…However, our study found no link between sites with or without seabirds (data not shown), and no link between sites which were closer geographically. As males on Takapourewa would also have finished a season where fairy prions made up a large part of their diet (Lamar et al., 2022), this indicates a lack of significant influence from expected sources such as diet, habitat and other species (Jin et al., 2021; Sullam et al., 2012; Zhang et al., 2021) with which the tuatara shares its burrow, further identifying tuatara as a species with unexpected drivers of its microbiota.…”

“…Tuatara body condition was significantly associated with bacterial community composition, as was tick abundance (Figure 2b). Body condition is potentially linked to diet: tuatara eating a more nutritious diet may be consuming different dietary items and gaining better body condition as a result (Lamar et al., 2022), while also introducing different bacteria to their gut compared with tuatara of poorer body condition. Likewise, microbiota differences associated with parasitism could either indicate that parasitism changes the microbiota present in tuatara, or that tuatara with sub‐optimal microbiota are more vulnerable to parasitism.…”

“…Each animal was then weighed by spring balance and measured for snout‐vent length (SVL), vent‐tail length (VT) and tail regrowth. Snout‐vent length and VT were summed to obtain total length, and body condition was calculated as $$$ \frac{\log \left(\mathrm{weight}\right)}{\log \left(\mathrm{SVL}\right)} $$$ (Lamar et al., 2022). The average daily maximum and minimum temperatures for each site during the sampling period were obtained using the nearest National Institute of Water and Atmospheric Research (NIWA) stations through the NIWA CliFlo database.…”

First person – Sarah K. Lamar

“… ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Biology Open, helping researchers promote themselves alongside their papers. Sarah K. Lamar is first author on ‘ Investigating the link between morphological characteristics and diet in an island population of omnivorous reptiles ( Sphenodon punctatus ) ’, published in BiO. Sarah is a PhD candidate and personal research assistant to the Head of the School of Biological Sciences in the lab of Professor Nicola Nelson and Dr. Diane Ormsby (co-chairs) at Victoria University of Wellington.…”

Reproductive Fitness in Male Tuatara (Sphenodon punctatus) and its Implications

“…Non-viable sperm cells with damaged plasma membranes absorb the eosin compound and exhibit a red stain, while viable cells appear white against the nigrosine counterstain (see Lamar et al, 2022).…”