In species that provide parental care, care for offspring is often accompanied by an increase in locomotor activity and a decrease in feeding opportunities which can negatively impact endogenous energy reserves. Depletion of parental energy stores and declines in nutritional condition can cause physiological disturbances, such as an imbalance between free radical production and available antioxidants, known as oxidative stress. Using the teleost smallmouth bass (Micropterus dolomieu) as a model, we tested if the energetic challenge associated with sole paternal care was associated with oxidative stress. Blood samples from parental males were collected throughout parental care, during egg, embryo, and larval stages of offspring development, and assayed for both antioxidant capacity and oxidative damage. A reduction in oxygen radical absorbance capacity was observed during the parental care period, indicating a decrease in resistance to oxidative stress. Although no change was observed in the reduced:total thiol ratio, a significant increase in the concentration of both oxidized and total thiols occurred during the parental care period. No increase in the oxidative stress markers 8-hydroxy-2-deoxyguanosine, protein carbonyls and lipid peroxides was observed. We concluded that oxidative stress did not occur as a result of parental care in the male smallmouth bass. This study provides evidence that participation in energetically taxing activities, such as parental care, can result in a decrease in antioxidant resources, but may not always result in oxidative stress.
All research was conducted in accordance with guidelines of the Canadian Council of Animal Care as administered by Carleton University and Queen's University (B09-06) and with a scientific collection permit from the Ontario Ministry of Natural Resources. Blood samples from wild adult male smallmouth bass were collected between May 11th and June 5th, 2009, on Indian Lake (44°35′N, 76°19′W) at three time points, determined by the developmental stage of their offspring: fresh eggs, embryonic and larval fry. The fresh egg stage was considered to be the cleavage phase of embryo development (Balon, 1975) and was characterized by near-transparent eggs with no obvious organogenesis or fungal deposition. The embryonic stage was considered to be the transition from the last embryo stage, (eleuthro-embryonic) to first larval stage (protopterygiolarval) and was characterized by loss of egg-sack and development of swimming ability. Finally the larval stage was considered to be the late protopterygiolarval stage (Balon, 1975) and was characterized by black coloration, and development of schooling behaviors. Characterization of each stage was completed by visual observation of physical traits and behaviors of offspring in the nest. Snorkeling surveys were completed whereby snorkelers located and marked smallmouth bass nests, which had eggs that were determined to be in the fresh egg stage of development, with numbered polyvinylchloride (PVC) tags. Nest location was recorded and the number of eggs was categorized between a low value of 1 to a high value of 5 (Suski and Philipp, 2004). For the purpose of this study we focused on fish with intermediate egg scores (i.e., 3 or 4) to control for variation in brood size which is known to be positively correlated with parental vigilance and nest aggression (e.g., Suski and Philipp, 2004, Hanson et al., 2009b). The majority (> 90%) of nests for smallmouth bass have an egg score of either 3 or 4. In total 29 parental males were sampled during this study. Nests were all between 1 and 3 m in depth on a cobble-gravel substrate. Marked nests were returned to at each of the three aforementioned stages of offspring development. At each stage different males were captured and sampled. Parental male smallmouth bass were caught by rod and reel from either the boat, or by the snorkeler and landed within 20 s of capture. Fish were placed in a foam lined trough filled with fresh lake water and blood was sampled via caudal venipuncture using a vacutainer tube (3 mL, lithium–heparin anticoagulant, Becton-Dickson; 21 G, 11/2′ long syringe; BD, NJ, USA). All fish were sampled within 2 min from time of initial hooking. Approximately 2 mL of blood was obtained, placed on ice water slurry for < 1 min, and immediately centrifuged for 5 min at 1500 rpm (Clay Adams Compact II Centrifuge, Becton-Dickson; Sparks, MD, USA). Erythrocytes and plasma were separated and flash frozen in liquid nitrogen and transferred to an ultra-cold freezer where they were stored at − 80 °C until analysis. Fork length of fish was then measured and fish was immediately released.