Telemetry and genetics reveal asymmetric dispersal of a lake‐feeding salmonid between inflow and outflow spawning streams at a microgeographic scale

Abstract

The degree of natal philopatry relative to natal dispersal in animal populations has important demographic and genetic consequences and often varies substantially within species. In salmonid fishes, lakes have been shown to have a strong influence on dispersal and gene flow within catchments; for example, populations spawning in inflow streams are often reproductively isolated and genetically distinct from those spawning in relatively distant outflow streams. Less is known, however, regarding the level of philopatry and genetic differentiation occurring at microgeographic scales, for example, where inflow and outflow streams are separated by very small expanses of lake habitat. Here, we investigated the interplay between genetic differentiation and fine‐scale spawning movements of brown trout between their lake‐feeding habitat and two spawning streams (one inflow, one outflow, separated by <100 m of lake habitat). Most (69.2%) of the lake‐tagged trout subsequently detected during the spawning period were recorded in just one of the two streams, consistent with natal fidelity, while the remainder were detected in both streams, creating an opportunity for these individuals to spawn in both natal and non‐natal streams. The latter behavior was supported by genetic sibship analysis, which revealed several half‐sibling dyads containing one individual that was sampled as a fry in the outflow and another that was sampled as fry in the inflow. Genetic clustering analyses in conjunction with telemetry data suggested that asymmetrical dispersal patterns were occurring, with natal fidelity being more common among individuals originating from the outflow than the inflow stream. This was corroborated by Bayesian analysis of gene flow, which indicated significantly higher rates of gene flow from the inflow into the outflow than vice versa. Collectively, these results reveal how a combination of telemetry and genetics can identify distinct reproductive behaviors and associated asymmetries in natal dispersal that produce subtle, but nonetheless biologically relevant, population structuring at microgeographic scales.

Stream inflows to lake deltas: A tributary junction that provides a unique habitat in lakes

“…For salmonids, the adfluvial life history with spawning in well-oxygenated streams and residence in lakes is common to populations of many species in the genera Oncorhynchus, Salmo, and Salvelinus (Arostegui & Quinn, 2019;Heim et al, 2019;Lennox et al, 2021). For example, brown trout in Ireland may show philopatry to particular inflow streams (Finlay et al, 2020). Brook trout also use lake-inlet stream areas for spawning (Curry & Devito, 1996).…”

Genetic structuring across alternative life‐history tactics and small spatial scales in brown trout (Salmo trutta)

“…Brown trout often form genetically differentiated populations separated by relatively short geographic distances (Carlsson et al, 1999;Finlay et al, 2020). Five populations were identified from three tributary rivers in this study: Bonds Glen, Killen Burn A, Killen Burn B, River Muff C and River Muff D. Thus, two coexisting populations were identified in each of the Killen Burn and River Muff.…”

“…In summary, the same genotype can result in different decisions regarding the life-history tactic as a consequence of environmental variability resulting in variation in the physiological condition cue (see Ferguson et al, 2019 for a comprehensive review). Thought to be a consequence of homing behaviour to natal breeding sites, brown trout have been shown to form genetically discrete populations over relatively short geographic distances (Bernatchez, Guyomard, & Bonhomme, 1992;Carlsson, Olsen, Nilsson, Øverli, & Stabell, 1999;Crozier & Ferguson, 1986;Ensing et al, 2011;Ferguson, 1989Ferguson, , 2006Finlay et al, 2020). In some places, this can lead to more than one brown trout population sharing the same local environment in the absence of obvious barriers to gene flow (Bernatchez et al, 1992;Carlsson et al, 1999;Finlay et al, 2020).…”

Hyper- and Hypo-Osmoregulatory Performance of Atlantic Salmon (Salmo salar) Smolts Infected With Pomphorhynchus tereticollis (Acanthocephala)

“…An incision was made along the midventral line and the alimentary tract was removed after severing its junctures with the anus and the esophagus. The phenotypic sex of each smolt was determined by visual inspection of the gonads and in any case where the designation was uncertain genetic methods were used to verify sex (as per Finlay et al (2020)).…”