Evaluating the genetic consequences of river fragmentation in lake sturgeon (Acipenser fulvescens Rafinesque, 1817) populations

Abstract

SummaryFragmentation of formerly continuous habitats can have significant consequences on subpopulations in isolated fragments. This study examined the temporal genetic consequences of historical river fragmentation by hydroelectric dams on lake sturgeon (Acipenser fulvescens Rafinesque, 1817), using temporal samples from two Ontario river systems. Temporal genetic analyses of samples from the Ottawa (dammed) and Kenogami (unregulated) river systems were used to (1) compare changes in genetic structure and diversity within and between free-flowing and regulated systems; (2) assess how impoundments have influenced the spatial and temporal genetic structure and diversity within these contrasting systems; and (3) estimate effective population sizes (N e ) in both rivers using temporal genetic estimators. Levels of genetic diversity did not differ between impounded and free-flowing rivers, nor did genetic diversity differ through time within a river system. Levels of genetic divergence over time were similarly minimal. We did, however, detect a 65% decline in effective population size in the impounded Ottawa River over two generations. Moreover, over the same time period the Ottawa River had substantially lower N e estimates for Lake Sturgeon than the free-flowing Kenogami River system. This study represents one of the first to observe genetic consequences of fragmentation on Lake Sturgeon. As such, this work reinforces the importance of maintaining or restoring habitat connectivity and availability for this migratory species, and mitigating other demographic threats that could compound, or be compounded by the effect of reduced genetic variation.

Translocation as a mitigation tool: Demographic and genetic analysis of a reintroduced lake sturgeon (Acipenser fulvescensRafinesque, 1817) population

“…Many lake sturgeon populations have undergone significant historical declines in abundance without significant decreases in genetic diversity (DeHann, Librants, & Elliot, ; Drauch & Rhodes, ; McDermid, Wozney, Kjartanson, & Wilson, ; McDermid et al., ; Welsh, Hill, Quinlan, Robinson, & May, ; Wozney et al., ). The unique life history characteristics of sturgeon, such as longevity, long generation time, and overlapping generations, may buffer against loss of genetic diversity (McDermid et al., , ; Wozney et al., ). Potential losses of genetic diversity may be lessened by rapid population growth after reintroduction (Allendorf & Luikart, ), which may be the case for the reintroduced Mattagami population.…”

“…The marked reduction in N e of the reintroduced population compared to its source was expected due to the limited number of translocated adults. N e has been shown to be a sensitive measure of genetic loss compared to other diversity metrics in lake sturgeon populations (McDermid et al., ) and other reintroduced species (Miller, Towns, Allendorf, Ritchie, & Nelson, ; Ottewell et al., ). This result indicates that the limited number of founding adults has left a genetic signature and that without rapid growth or additional reintroductions, the population may eventually be susceptible to loss of genetic diversity over time (Ottewell et al., ).…”

“…Similar to most translocations, this effort reintroduced a small number of adults, which is often associated with increased genetic drift and inbreeding in future generations, resulting in loss of diversity (Frankham, Ballou, & Briscoe, 2010;Leberg, 1993;Wolf, Griffith, Reed, & Temple, 1996). Many lake sturgeon populations have undergone significant historical declines in abundance without significant decreases in genetic diversity (DeHann, Librants, & Elliot, 2006;Drauch & Rhodes, 2007;McDermid, Wozney, Kjartanson, & Wilson, 2011;McDermid et al, 2014;Welsh, Hill, Quinlan, Robinson, & May, 2008;Wozney et al, 2011). The unique life history characteristics of sturgeon, such as longevity, long generation time, and overlapping generations, may buffer against loss of genetic diversity (McDermid et al, 2011(McDermid et al, , 2014Wozney et al, 2011).…”

Genetic estimation of evolutionary and contemporary effective population size in lake sturgeon (Acipenser fulvescensRafinesque, 1817) populations

“…Contemporary abundance of lake sturgeon varies within the 10 fragmented river reaches along the lower 580 km border section (Lake Temiscaming to Carillon) with the greatest relative abundances remaining in the unimpounded river reaches (Haxton, ; Haxton and Findlay, , ). Despite the extensive fragmentation of the Ottawa River, lake sturgeon in the dammed river segments as yet show no evidence of genetic fragmentation or substructure (Wozney et al., ), although a temporal analysis of N e from historical and contemporary samples showed evidence of a decline in effective population size (McDermid et al., ).…”

“…It may not be possible to empirically determine the historical genetic diversity of these ancestral populations, due to substantial losses and population declines across much of their natural range in the 19th and early 20th centuries (Harkness and Dymond, ; Auer, ). Previous studies have differed in the extent of documented genetic losses as evidenced by genetic bottlenecks (DeHaan et al., ; McDermid et al., , ), but the drastic historical population reductions and losses were catastrophic, in many cases exceeding losses of over 90% (Harkness and Dymond, ; Auer, ; COSEWIC, ).…”