Increased parental care cost for nest-guarding fish in a lake with hyperabundant nest predators

Although parental care increases offspring survival, providingcare is costly, reducing parental growth and survival and, thereby,compromising future reproductive success. To determine if anexotic benthic predator might be affecting parental care bynest-guarding smallmouth bass (Micropterus dolomieu), we comparednest-guarding behavior and energy expenditures in two systems,one with a hyperabundant recently introduced predator, the roundgoby (Neogobious melanostomus). In Lake Erie, USA, smallmouthbass vigorously defended their nests from benthic round gobies.In Lake Opeongo, Canada, smallmouth bass were exposed to fewerand predominantly open-water predators and were less activein their nest defense. From scuba and video observations, wedocumented that nest-guarding smallmouth bass chased predators(99% of which were round gobies) nine times more frequentlyin Lake Erie than in Lake Opeongo. This heightened activityresulted in a significant decline in weight and energetic contentof guarding males in Lake Erie but no change in Lake Opeongomales. Bioenergetic simulations revealed that parental careincreased smallmouth bass standard metabolic rate by 210% inLake Erie but only by 28% in Lake Opeongo. As energy reservesdeclined and offspring became increasingly independent, malesin both lakes consumed more prey and spent more time foragingaway from their nests; however, nest-guarding smallmouth bassconsumed few prey and, in Lake Erie, rarely consumed round gobies.Therefore, increased parental care costs owing to the presenceof round gobies could affect future growth, reproduction, andsurvival if smallmouth bass approach critically low energy reserves.