Intraspecific Variation in Reproductive Ecology and Success of a Keystone Stream Fish, Bluehead Chub

• Main Author: Kim, Seoghyun
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Biology; Ecology; Limnology; Natural Resource Management
• ISBN: 9781392372500; 139237250X

Individuals differ in many traits, and such variation affects reproductive tactics to maximize fitness. Variation in reproductive success influences not only population dynamics and genetic structure, but also community and ecosystem structure when the species plays an important functional role such as keystone species. Key topics in investigations of individual variation are to quantify the degree of variation and its implications on fitness, which are the ultimate goals in my research focusing on reproductive ecology of a keystone stream fish, bluehead chub Nocomis leptocephalus.Understanding the timing of spawning is a key topic in fish ecology because reproduction is a determinant of life history and population structures. The timing of spawning has evolved to maximize offspring survival in response to optimal biotic and abiotic conditions. However, environmental control on spawning timing, particularly in fine spatial scale (e.g., local scales) and temporal scales (e.g., daily trends), are poorly understood for most native stream fishes. (Chapter 1) The first chapter aimed to characterize spawning periodicity of bluehead chub and yellowfin shiner among local streams. I conducted daily observations to address daily spawning patterns and examine the impacts of environmental drivers such as water temperature and flow conditions. I expected that the timing of spawning would be synchronous among local streams if regional factors, such as weather patterns, are the key drivers of reproduction. Results showed that fish spawned periodically within the same stream and across different streams. Water temperature affected the timing of spawning in all streams, whereas the effects of flow varied by stream. Specifically, spawning was triggered by a short-term increase in water temperature and observed under stable flow conditions.While environmental fluctuations affect daily spawning patterns, these may play an important role in variation in nesting behavior and reproductive interactions with nest associates. Nest construction is a distinct reproductive strategy, which can attract females and maximize offspring survival, and this can be affected by environmental fluctuation and resource availability. Further, understanding how nesting behavior attracts nest associates is crucial for understanding how nesting behavior may determine positive reproductive interactions (i.e., nest association). However, questions still remain about how abiotic and biotic factors affect variation in nest size and interactions with yellowfin shier. (Chapter 2) I investigated the effects of abiotic and biotic factors on nest size and utilization by associates, which were related to the reproductive success of bluehead chub. I developed a conceptual hypothesis of causal relationships among abiotic and biotic factors and two key variables (i.e., nest size and yellowfin shiner abundance), then which I tested multiple hypotheses using a path analysis. The results showed that male size was positively related to various biotic variables, including nest sharing, duration of spawning, and re-use of nesting resources. Larger male size and nest sharing behavior led to larger nest size and attracted more yellowfin shiner.While various abiotic and biotic factors affected nesting behaviors and reproductive interactions, these findings (Chapter 2) considered the fitness proxies but not individual fitness such as reproductive success (i.e., the number of offspring sired by each individual). Although individual traits play the main role in reproductive success, studying reproduction in the wild is notoriously difficult due to the cryptic spawning and aggregation of multiple individuals. (Chapter 3) For my third chapter, I investigated how individual variation led to differences in mating system and reproductive success in a natural stream using passive integrated transponder (PIT) tags and microsatellite markers. I hypothesized that larger males would reproduce more successfully than smaller males in a field experiment, but other individual traits such as cooperative behavior could mediate the size-dependent reproductive success in the natural stream. I predicted that female reproductive success is associated with body size, but the female choice could mediate this relationship. Lastly, I expected some key individual traits such as body size and cooperative nest sharing to lead to successful nest construction, which could influence reproductive success. I observed that nest size and nesting effort led to successful reproduction in males, and nest sharing (i.e., the number of males on nests) was an important behavioral trait that led to successful nest construction and attracting females. However, I found little evidence that male body size had significant effects on reproductive success and nest construction, while body size was positively associated with female reproductive success. Overall, my findings suggest that male body size is not always a primary factor for constructing larger nests, female choice, or reproductive success. Perhaps cooperative behavior (i.e., nest sharing) could mediate the size-dependent reproductive success.Collectively, my three chapters advance reproductive ecology of a keystone stream fish, bluehead chub. My dissertation research demonstrates that two key environmental variables (i.e., water temperature and flow) associated with weather conditions have a major influence on spawning activities and nesting behaviors lead to variation in reproductive outcomes. Chapter 1 demonstrated that fish responded to a range and short-term increase of environmental cues. Chapter 2 and 3 demonstrated the relative importance of environments and individual traits (i.e., body size and nesting behavior) to nest construction, female choice, and reproductive outcomes. While male body size was a significant factor for constructing larger nests in Chapter 2, I found little evidence that body size was determinant of reproductive success in Chapter 3. Environmental impacts could mediate the size-dependent reproductive success, but the notable pattern was that cooperative reproduction among males (i.e., nest sharing) was the most important factor leading to successful reproduction. This is one of the few studies that demonstrates male-male cooperation in nest-building fishes, because occupying and defending nests through aggressive behaviors are common reproductive strategies in nest-building males. Further, my findings have valuable insights in complex relationships among males; they act cooperatively but competitively engage in efforts to increase fitness that may cause reproductive skew within a cooperative male group.Individual variation provides the very basis for evolutionary adaptation and population resiliency, which are critical in species conservation as organisms respond to environmental changes. However, basic biology and life history are still poorly understood on native freshwater fishes, while this knowledge is critical for conservation and management of stream ecosystems. This study illustrates that reproductive ecology and success were affected by a complex interplay of environmental conditions, phenotypic variation, and behavior in bluehead chub, whose nests are also used by other fish species in the Southeast USA. In addition, my study designs, including intense observations and monitoring nests using PIT antenna array coupled with genetic analysis, would shed light on a novel approach in behavioral ecology and fisheries research.