Date of Thesis
Spring 2025
Description
Parental care behaviors have a significant impact on the survivorship of offspring and therefore the inclusive fitness of the parent. These behaviors are broad and varied and include defending against predators, acquiring food, and choosing where to lay their eggs. The latter, oviposition site selection, has significant impact on embryo survivorship in oviparous animals, as the chosen sight can impact factors such as incubation temperature, predation risk, and resource availability. For amphibians, oviposition site selection is particularly crucial as their eggs lack a calcareous shell, leaving them more susceptible to environmental conditions and predation. In response to this, amphibians have evolved diverse and adaptive oviposition site selection behaviors to keep their aquatic embryos and larvae protected and hydrated.
Though most oviparous amphibians lay their eggs in large masses, many newt species in the family Salamandridae lay individual eggs that they then wrap in materials found in the water. This unique behavior likely has a higher parental cost compared to laying in masses, but may offer some benefits, such as predator defense. With this oviposition site selection behavior comes a distinct choice: female newts wrap their eggs in either live aquatic vegetation or dead leaf litter, and each material chosen may confer unique benefits to the embryos. While some benefits of egg-wrapping have been studied, the effects of different wrapping materials on embryo development and predation rates remain undocumented.
The goal of this thesis is to investigate the benefits and mechanisms of the unique egg-wrapping behavior by female newts. Eastern Newts (Notophthalmus viridescens) were chosen as a model species because they wrap their eggs in two 6 different materials: aquatic vegetation and dead leaves. Aquatic vegetation might supply additional oxygen to developing embryos while dead leaves may offer enhanced predator protection. We hypothesized that these two different wrapping materials would result in differing impacts on egg predation and embryonic development, and that predator presence would influence oviposition material choice in female newts. In the case of material choice, we hypothesized that females’ oviposition site selection would be influenced by the presence of egg predators, and that they would choose to lay eggs in either dead leaves or aquatic vegetation at differing rates depending on predator exposure. In the case of predation, we hypothesized that the predation rate would change depending on the material the eggs were wrapped in, if any. And in the case of development, we hypothesized that the two different egg wrapping materials used by newts would impact embryonic growth and development. To test these hypotheses, we ran three experiments in the springs of 2023 and 2024.
The first laboratory experiment, outlined in Chapter 1, investigated whether the presence of an egg predator - Wood Frog (Lithobates sylvaticus) tadpoles - would affect females’ oviposition site choice of dead leaves or live aquatic vegetation. To do this, we utilized growth chambers and individual aquariums to provide controlled conditions that would allow the females to be exposed to visual and chemical cues from the tadpoles without the tadpoles able to access the eggs laid. We predicted that females housed with tadpoles (N = 10) would choose to wrap their eggs in dead leaves presumably because of enhanced predator protection by deal leaves, and females housed without tadpoles (N = 10) would choose to wrap their eggs in live aquatic vegetation presumably because of 7 additional oxygen provision to the embryo. I ran this experiment twice, and both times there were not enough eggs laid to test these predictions.
Chapter 2 outlines a laboratory predation experiment to investigate whether different egg-wrapping materials affected predation rates using Wood Frog tadpoles and Eastern Newt eggs. I collected Eastern Newt eggs that were wrapped in either dead leaves or aquatic vegetation, a portion of which I then unwrapped. I then exposed groups of these eggs (N = 25 per treatment) to Wood Frog tadpoles for them to predate. We predicted that eggs wrapped in dead leaves would be eaten at the lowest rate, unwrapped eggs at the highest rate, and eggs wrapped in live aquatic vegetation between the two. Eggs wrapped in dead leaves were eaten significantly less than eggs with no wrapping, but there was no significant difference between eggs wrapped in live aquatic vegetation and eggs with no wrapping, and no significant difference between eggs wrapped in dead leaves and eggs wrapped in live aquatic vegetation.
Finally, Chapter 3 outlines a laboratory experiment investigating whether the two different egg-wrapping materials - dead leaves or live aquatic vegetation - impact newt embryo development. We collected Eastern Newt eggs wrapped with the two different materials from mesocosms, in which gravid female newts were kept, and placed them in individual containers in growth chambers programmed to mimic outdoor conditions (N= 20 per treatment), then measured body size and larval period of the hatchlings. We predicted that eggs wrapped in live aquatic vegetation would hatch faster and larger than eggs wrapped in dead leaves. Embryos from eggs wrapped in live aquatic vegetation hatched on average three days earlier than those wrapped in dead leaves. However, the embryos from eggs 8 wrapped in live aquatic vegetation had shorter body length compared to those from eggs wrapped in dead leaves. Despite their smaller body sizes, the growth rate for eggs wrapped in live aquatic vegetation was significantly higher than that of eggs wrapped in dead leaves.
The results from the studies outlined above suggest that the types of wrapping materials, dead leaves and live aquatic vegetation, have varying effects on larval development and predation rates. The results indicate that live aquatic vegetation confers developmental benefits to the embryos such as increased growth rate and shorter hatching time, while dead leaves are likely to provide improved protection from aquatic predators. We also found that larvae from live aquatic vegetation hatched smaller than larvae from eggs wrapped in dead leaves, and the predation rates between eggs wrapped in live aquatic vegetation and dead leaves were similar. These findings underscore the need for further research with increased sample sizes into the mechanisms underlying the unique oviposition site selection behaviors of Eastern Newts.
Keywords
oviposition site selection, embryonic development, eastern newt, predation
Access Type
Masters Thesis
Degree Type
Master of Science
Major
Animal Behavior
First Advisor
Dr. Mizuki Takahashi
Second Advisor
Dr. Reggie Gazes
Third Advisor
Dr. Mark Haussmann
Recommended Citation
Prohofsky, Anna, "All Wrapped Up: How Choice of Egg Wrapping Substrate During Oviposition Site Selection Affects Predation and Embryonic Growth in Eastern Newts" (2025). Master’s Theses. 297.
https://digitalcommons.bucknell.edu/masters_theses/297