Feeling disconnected: River fragmentation alters parenting, aggression, and risk-taking in threespine stickleback

Habitat fragmentation is a global challenge stemming from human-induced change. As habitat fragmentation is expected to worsen across time, there is a need to identify organism traits that can predict population persistence within fragments. Behavioral traits are primary candidates for understanding population response to fragmentation because behavior often serves as a first response to human-induced change. While behavior is a topic of interest in the context of habitat fragmentation, many studies are limited to investigating movement patterns. Parental care behaviors are directly tied to individual fitness and offspring survival, and may provide predictive value to population persistence under fragmentation. However, it remains unclear both whether and how parental care differs in organisms found in fragmented areas. We utilized the threespine stickleback (Gasterosteus aculeatus), a fish with obligatory paternal care, to examine the effects of aquatic fragmentation on parental care, territorial aggression, and juvenile risk-taking behavior. Following the identification of fragmented (pooled) and non-fragmented (connected) sites, we recorded parenting behaviors necessary for offspring survival. We then exposed territorial and parenting males to both a known and an unknown conspecific intruder to assess aggression. Finally, juveniles were measured in a risk-taking assay. Adult stickleback in fragmented sites showed a reduction in parental care and heightened aggression towards unknown conspecific intruders, while juveniles in fragmented sites were more hesitant to emerge into a novel environment. Altogether, our results provide support for changes in parental care within habitat fragments that may have generational consequences.

Methods
This study investigates differences in behavioral phenotypes in stickleback found in pooled and connected areas of the Navarro River, a single river system located in Philo, California. From May- July 2022, we collected behavioral data that can be placed into three major categories: parental care, aggression, and risk-taking. Adults males were used for parental care and aggression, while juveniles were used for risk-taking. All data was processed using R. Studio version 2023.03.0