Summary
Parental care requires a complex integration of physiology and behaviour, yet little is known about the physiological and energetic consequences or correlates of these behaviours. Using two species of male black bass (smallmouth bass, Micropterus dolomieu; largemouth bass, M. salmoides) as a model, the focus of this study was to determine the biochemical and hematological indicators of change in nutritional status and potential for chronic stress. This was accomplished by randomly sampling individuals at four stages across parental care. Additionally, a subset of individuals was repeatedly sampled at three brood development stages to track changes in biochemical factors within the individual. Though there were changes in physiological factors across parental care in randomly sampled fish of both species (declines in plasma glucose in largemouth bass; decreases in hematocrit and plasma chloride in smallmouth bass), repeated sampling of individuals was determined to be a more appropriate sampling technique due to natural variability in biochemical factors among individual fish. Repeated sampling of smallmouth bass did not adversely influence physiological metrics or brood abandonment. However, there were higher incidences of nest abandonment in repeatedly sampled largemouth bass. Amongst the repeatedly sampled smallmouth bass, nutritional indicators such as plasma triglyceride levels decreased indicating individual fasting across the majority of parental care. Increases in plasma calcium and magnesium towards the end of care indicated that feeding most likely resumed when the brood was close to independence after ~3 weeks of care. Lastly, several indicators of chronic stress, such as plasma glucose and chloride levels, increased throughout the parental care period. These sublethal stressors are indicative of decreasing body condition associated with prolonged activity and fasting which may have marked impacts on the ability of an individual to continue parental care for the current brood and impact subsequent individual fitness. Further research into the mechanistic relationships between behaviour, physiology, and energetics during the parental care period will provide a better understanding of the decisions by individuals facing multiple trade-offs that ultimately lead to differences in individual fitness.
Methodology
This study was carried out from May 1st to June 1st, 2006 on Lake Opinicon, eastern Ontario, Canada (44°30′N, 76°20′W). Daily snorkel surveys of the littoral zone were conducted to locate largemouth and smallmouth bass that were actively guarding nests with newly deposited eggs. Upon locating an active bass nest [defined as male guarding newly deposited (<1 day old) eggs], the snorkeler placed a numbered PVC tile near the nest and recorded nest location, nest depth, and number of eggs within the nest (visual, categorical assessment ranging from low of 1 to high of 5; Suski and Philipp 2004). At the time of nest discovery, individuals were randomly assigned to sampling groups. Control fish were not handled beyond that as described above to provide a baseline estimate of nest abandonment within the lake for each species. Subsets of individuals were sampled at each of the four brood developmental stages [eggs (sampled within 1 day of spawning), egg sac fry (newly hatched embryos, approximately 1.5 weeks after spawning), swim up fry (larvae begin to swim >0.5 m above the nest, approximately 2 weeks after spawning), and free swimming fry (larvae swim <1 m above and around the nest, prior to independence, approximately 3 weeks after spawning]. Fish were captured using heavy-action recreational fishing equipment that could be used to angle fish from the boat or underwater (by the diver). In total, 41 largemouth bass (total length mean ± SD; 381 ± 40 mm) and 50 smallmouth bass (total length mean ± SD; 366 ± 38 mm) were blood sampled for this study. All fish were landed within 20 s of hooking to minimize non-parental care related anaerobic exercise. During the entire period that angled fish were held on the boat, they were always in water. Upon capture, fish were quickly blood sampled by the caudal puncture method using a 1.5″, 21 gauge vacutainer syringe (Houston 1990) while being held within a foam lined trough containing fresh lake water. Up to 1.5 ml of blood (representing approximately 3.7% of total blood volume) was collected in a 3-ml, flat-bottomed vacutainer containing lithium heparin to prevent blood coagulation. Total length was recorded as well as the presence or absence of any injury. Individuals were then released within 5 m of the nest in less than 2 min. During the sampling procedure, a snorkeler remained at the nest site and defended the brood until the male returned (typically in under 5 min). Blood samples were centrifuged immediately at 10,000× gravity for 5 min (Clay Adams Compact II Centrifuge). Hematocrit was assessed in the field by measuring the volume of red blood cells by volume of total liquid on centrifuged blood collection tubes using micrometer calipers. Plasma samples were stored in liquid nitrogen for subsequent analysis. Individuals in the last treatment group, repeatedly sampled fish, were sampled at each stage of brood development (with the exception of the swim up fry stage). At the final stage of brood development, due to the fact that fish at this stage roam across large areas and capture by angling becomes ineffective, fish were captured by a snorkeler using a spear gun. Following sampling, fish were euthanized by cerebral percussion. After non-lethal sampling, a snorkeler revisited each nest every 2 days to record presence or absence of the male as well as the progression of the brood through developmental stages.