Strong isolation by distance argues for separate population management of endangered blue duck (Hymenolaimus malacorhynchos)

Abstract

Knowledge of genetic diversity and population structuring represents a key component for the conservation of endangered species, especially where translocations and re-introduction operations are integral tools for population management. The blue duck (Hymenolaimus malacorhynchos) is a threatened riverine specialist that is endemic to New Zealand. Populations from the North and South Island form two distinct mitochondrial lineages, which currently necessitate separate conservation management. Here we examine the patterns of variability at 11 microsatellite loci and mitochondrial control region data to assess the range-wide genetic diversity and population structure of blue duck. Our data suggest that North and South Island blue duck populations likely diverged in the late Pleistocene with very limited gene flow, strongly reinforcing the current management strategy to avoid translocation between islands. Genetic diversity within both islands follows a pattern of isolation by distance with relatively high levels of gene flow among populations, likely driven by male-juvenile dispersal. The overall genetic diversity in blue duck is low and effective population size is small. These data will provide important information for conservation management of this species.

Contrasting patterns of population structure at large and fine geographical scales in a migratory avian disturbance specialist of braided river ecosystems

“…Black‐fronted terns have so far still relatively high nuclear and mitochondrial genetic diversity despite continuing population declines (O'Donnell & Hoare, ). The level of genetic diversity is similar to other threatened New Zealand avian species, for example kea ( Nestor notabilis ; Dussex, Wegmann, & Robertson, ) and blue duck (whio/ Hymenolaimus malacorhynchos ; Grosser, Abdelkrim, Wing, Robertson, & Gemmell, ). Moreover, it is also similarly high to other Chlidonias species (Dayton, Ledwoń, Paillisson, Atamas, & Szczys, ; Szczys, Lamothe, et al, ).…”

When genetic and phenotypic data do not agree: the conservation implications of ignoring inconvenient taxonomic evidence

“…There is 1.9% divergence (i.e. 17 step-wise differences) between mitochondrial DNA haplotypes in North Island and South Island populations of this species (Grosser et al 2017). Also, nuclear data for blue duck/ whio suggest a distinct North Island and South Island genetic cluster.…”

“…In spite of these genetic differences and in the face of limited morphological data (Robertson et al 2007), researchers have taken a conservative approach, pointing out that gaps in sampling mean they cannot rule out a genetic cline rather that two discrete subspecies. They advocate for additional secure conservation sites based on genetic distinctiveness, but at no point suggest these are two different subspecies (Grosser et al 2017).…”

Old divergence and restricted gene flow between torrent duck (Merganetta armata) subspecies in the Central and Southern Andes

“…Additionally, as referred in the second hypothesis, torrential river systems inside watersheds are analogous to islands (islands on mountain slopes) that isolate and sustain populations and communities (Black, 1997;Naiman, Magnuson, McKnight, Stanford, & Karr, 1995;Omernik & Bailey, 1997;Sullivan, Watzin, & Keeton, 2007), similarly observed in lakes (Barbour & Brown, 1974), marshes (Brown & Dinsmore, 1988), caves (Culver, Holsinger, & Baroody, 1973), mountaintops (Nores, 1995), or woodlots (Holland, 1978). Similar population structure patterns have been described in the blue duck (Hymenolaimus malacorhynchos) in New Zealand with a regional genetic differentiation (region around 100 km) associated with isolation-by-distance pattern (Grosser et al, 2016). Finally, it is possible that different watershed (sub)-populations may be genetically more connected or completely differentiated depending on the distance among them and the dispersal capacity of the ducks.…”

“…Among torrent duck riverine (sub)-populations it appears that dispersal is most likely to occur at close range (Cerón & Capllonch, 2016;Paradis, Baillie, Sutherland, & Gregory, 1998), which could also reduce their differentiation and resemble a metapopulation model (Hanski & Gaggiotti, 2004;Levins, 1968). Similar population structure patterns have been described in the blue duck (Hymenolaimus malacorhynchos) in New Zealand with a regional genetic differentiation (region around 100 km) associated with isolation-by-distance pattern (Grosser et al, 2016). To test these hypotheses, future work would benefit from measures of relatedness on increased sampling of individuals across rivers, including multiple adjacent river systems stratified by elevation.…”