When resources are limited, organisms are often faced with trade-offs between energetically-expensive traits. Haley Ferguson, a recent graduate from Jerry Husak’s lab at the University of St. Thomas, presented a poster at SICB this week on an impressively comprehensive study investigating whether trade-offs exist among performance, reproduction, and immune function in the green anole (Anolis carolinensis). In her experiment, Haley divided green anoles into four treatment groups. One group experienced a normal diet (3-4 crickets, 4 times a week) and natural activity regime; one had a restricted diet (1 cricket, 4 times a week) and natural activity; one had a normal diet and strenuous exercise regime (running to exhaustion on a treadmill); and the final group had restricted diet and strenuous exercise.
Based on predictions from life history theory (see figure below), Haley and Jerry predicted that individuals who use more resources for locomotor activity will have fewer resources available for immune function or reproduction. Their results strongly supported this prediction. First, they showed that exercise training and diet restriction both inhibited the lizards’ capacity to grow in terms of size and mass. Immune function (measured by PHA swelling response and plasma bacterial killing assays) was also compromised in both trained and diet-restricted lizards. Female egg size and number, and male dewlap size and bite force were also reduced in lizards experiencing diet restrictions and exercise training. Surprisingly, Haley found that restricting lizard diet alone caused a more profound effect on immune function and reproductive output than training alone. Finally, to measure the trade-off between training and diet, Haley measured lizard endurance (time until exhaustion on a treadmill) in each group. She found endurance was higher in the trained groups regardless of a diet restriction. Future work in the Husak lab will follow up on these results by testing trade-offs among all of these traits among lizards with varying testosterone levels.
Note: This post was written by Brittney Andre, a research technician studying lizard behavior and physiology in the Johnson lab at Trinity University, and Michele Johnson.