Environmental drivers of spatiotemporal variation in the movement, performance, and genetic structure of brown trout and Atlantic salmon
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Date
2020-05
Authors
Finlay, Ross
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University College Cork
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Abstract
Environmental conditions vary spatially and temporally, providing organisms with
both challenges and opportunities. Animals have evolved a spectacular variety of
migratory behaviours to take advantage of environmental variation, particularly in
cases where this variation is predictable. The spatiotemporal pattern of migratory
movements displayed by a population or species can be thought of as the
evolutionary outcome of trade-offs amongst life history traits. As such, the study of
animal movement in relation to environmental heterogeneity can yield valuable
insights into the proximate and ultimate drivers of migratory behaviours as well as
the behavioural mechanisms underpinning genetic structure. Against this
background, the overarching aim of this thesis is to investigate the role of
environmental heterogeneity in shaping locally-adapted migratory behaviours, finescale
genetic structure and physiological performance in populations of wild brown
trout (Salmo trutta) and Atlantic salmon (Salmo salar).
Using telemetry data from passive integrated transponder (PIT) tags, I investigated
the fine scale spatiotemporal patterns of spawning-related movements of brown trout
between a feeding lake and two spawning streams (one inflowing, one outflowing,
separated by < 100 m) over two spawning seasons. The timing of seasonal, daily and
diel movements was strongly associated with variation in photoperiod, stream height
and moon phase. Movement activity was highest at night, and particularly on nights
with minimal lunar illumination and high water levels, suggesting that trout
synchronise their spawning movements with environmental conditions that minimise
their visibility to predators. Males began their movements between the lake and
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streams significantly earlier in the spawning season than females (protandry) and
were generally more active.
A substantial proportion of trout entered both spawning streams during the
spawning periods, providing potential sources of gene flow between the two streams.
However, Bayesian analyses revealed the existence of subtle genetic differentiation
between juvenile trout sampled in the two streams and indicated that gene flow was
strongly asymmetrical in a predominantly downstream (i.e. inflow to outflow)
direction. Thus, natal dispersal between the two streams appears to be more common
amongst trout that hatch in the inflow than the outflow. These findings have
important implications for genetic diversity and local adaptation of fish stocks in
fluvial and lacustrine environments.
The collection of PIT-derived data in fluvial habitats is often hindered by the
fragility of PIT antennae when exposed to high flows and flotsam. In Chapter 3 I
present a novel PIT antenna design I developed for use in flood-prone spatey rivers.
This design allows flotsam to pass without causing significant damage to antennae
and was crucial for collecting the data used in Chapters 4 and 5 and in Appendix A.
The performance of migratory populations can be strongly influenced by factors that
affect the physiology or survival of migrants in any encountered habitat. I therefore
investigated whether the acanthocephalan endoparasite Pomphorhynchus laevis
causes a habitat-specific (i.e. freshwater or saltwater) pathology in Atlantic salmon
smolts. Peculiarly for the species, the Irish strain of P. laevis uses salmonids, instead
of cyprinids, as its preferred definitive hosts. Despite observing high prevalence of
the parasite amongst wild smolts and high infection intensities in some individuals, I
found no evidence of a pathological effect of infection in fresh or salt water.
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However, I did demonstrate that this freshwater parasite can survive in smolts in
salinities similar to those found in coastal waters for at least 72 hours. Thus, the
coastal roaming behaviour of Irish sea trout may have facilitated the colonisation of
Irish river systems, resulting in the exceptionally widespread distribution of the
parasite in Ireland.
Collectively, these results contribute to our knowledge of how environmental
heterogeneity influences the movement, performance, distribution and genetic
structure of organisms in aquatic environments. As modern environmental changes
occur at an unprecedented pace, such knowledge may provide us with the ability to
anticipate, and perhaps even ameliorate, the impacts that anthropogenic activities
have on migratory species.
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Keywords
Population genetics , Salmonid , Migration , Behaviour , Telemetry , Parasites , Dispersal , Phenology , Salmo trutta , Salmo salar , Osmoregulation , Gene flow
Citation
Finlay, R. 2020. Environmental drivers of spatiotemporal variation in the movement, performance, and genetic structure of brown trout and Atlantic salmon . PhD Thesis, University College Cork.