The decisions that a parent makes or conditions that a parent experiences can influence the survival and fitness of their offspring. These transgenerational effects, in which impacts of the environment on one generation impact subsequent generations, are widespread and can originate with both mothers and fathers. In organisms that make eggs, the environments mothers experience affect how they provision their eggs with a variety of substances that can help their offspring including energy, compounds that assist the immune system, and hormones. In reptiles, we know that high quality, well-provisioned eggs hatch into babies that are larger, grow better, are healthier, and likely have higher fitness. If mothers can fine tune these physiological impacts on their eggs (often called “maternal effects”) to match the needs of the environment that their offspring will experience, they may be able to increase the fitness of their offspring and themselves. Conversely, if environmental disruptions have negative impacts on mothers, these impacts may also affect their offspring.
Many species of lizards exploit urban habitats and thus may be good candidates for studying the impacts of urbanization on maternal effects on egg quality. Previous research has pioneered methods for assessing egg yolk contents in lizards, but we do not have a good understanding of how urbanization may impact lizard egg and hatchling quality. Emily Virgin, a graduate student in Susannah French’s lab at Utah State University chose to investigate how mothers and offspring of sideblotched lizards (Uta stansburiana) are affected by urbanization.
Emily captured groups of side-blotched lizards from the city core of St. George, UT and surrounding rural areas. Because these lizards make clutches with multiple eggs, Emily designed an experiment in which she took some eggs from each clutch to measure their physiological qualities while incubating others until hatching to measure offspring traits. She extracted yolk samples from eggs and measured energy content, immune function, and oxidative physiology.
Emily found that eggs from rural lizards had higher levels of bacterial killing ability (BKA), an integrative measure of immune function. This suggests that offspring from these eggs might have reduced immune function, a potential cost of having a mother from an urban area. These results also match previous work from the lab which has shown lower BKA in adult lizards living in urban areas. Emily did not, however, find differences in rural and urban eggs in measures of available energy (free glycerol) or oxidative stress, suggesting that for some egg traits, there is not a cost to occupying urban areas.
Emily also investigated reproductive outputs by attempting to quantify offspring quality and quantity. While urban lizards produced the same number of eggs as rural mothers, almost 30% of these eggs were unfertilized and thus unable to produce viable offspring. This suggests another potential cost to occupying urban areas may be reduced reproductive success. Because of this lower than expected hatching success, Emily was unable to quantify traits of offspring. However, in the future, Emily aims to continue to examine impacts of urbanization on lizards, perhaps by looking at hormone allocation to eggs. Follow her on Twitter to stay up-to-date on her work!
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