Eco-geographic units, population hierarchy, and a two-level conservation strategy with reference to a critically endangered salmonid, Sakhalin taimen Parahucho perryi

Abstract

Hierarchical population structure can result from range-wide geographic subdivision under conditions of environmental heterogeneity and weak gene flow. While a lower level of structure can be formed by local populations within eco-geographic regions, an upper level can be characterized by variation between populations from different regions, and thus, be represented by evolutionarily significant units (ESUs) defined by environmental, ecological and genetic variation. Selection of ESUs may depend on the sequence of using these three sources of variation. We propose to determine ESUs by first using non-genetic, ecological and geographical gradients for defining preliminary population groups (eco-geographic units, EGUs) and then testing whether the boundaries of these units are genetically coherent and thus represent ESUs or warrant their further modification. We evaluate this approach using Sakhalin taimen, an East Asian endangered endemic fish. Forty-one samples (473 fish) were drawn from thirty populations across the species range and genotyped at microsatellite DNA markers. We assign the populations into ESUs based on geographic and life history criteria and subsequent application of genetic diversity analyses. The ESUs appeared to be greatly diverged genetically. Within ESUs, local populations are genetically differentiated, have low effective sizes, show signatures of demographic decline and extremely restricted gene flow. Conservation plans aimed to restore or maintain a specific threatened population should take into account such hierarchical structure, and in particular be based on the genetic resources drawn from each population or using ecologically and genetically similar populations from the same ESU as donors for restoration of the population.

Fish conservation in the land of steppe and sky: Evolutionarily significant units of threatened salmonid species in Mongolia mirror major river basins

“…For the initial demarcation of an ESU, researchers have focused on genetic markers including maternally transmitted, slowly evolving mtDNA, but also biparentally transmitted, quickly evolving microsatellites, as both yield relevant information on complementary spatiotemporal scales (O'Connell & Wright, ; Vogler & DeSalle, ). The identification of ESUs and genetically distinct populations of threatened and exploited fish stocks is increasingly used in fishery management to ensure that conservation actions and resources can be better matched with biological relevance (Xia, Chen, & Sheng, ; Geist, Kolahsa, Gum, & Kuehn, ; Escobar, Andrade‐López, Farias, & Hrbek, ; Zhivotovsky et al, ). While ESUs represent the upper hierarchical levels of intraspecific biodiversity, demographically independent groups that harbor an above average genetic variation or are more genetically distinct compared to the rest of the ESU are also important to identify.…”

Hierarchical genetic structure and implications for conservation of the world’s largest salmonid, Hucho taimen

“…Reproductive isolation has evolved within a number of salmonid species due to spatiotemporal differences in spawning (spring vs. fall Chinook salmon 26 ), or morphological specialization (dwarf and normal Coregonus clupeaformis 94 ; benthic and limnetic Salvinus alpinus 95 ; pelagic and littoral feeding Thymallus nigrescens 96 ). Additionally, although taimen populations typically do not differentiate at smaller spatial scales, anadromous Sakhalin taimen ( Parahucho perryi ) demonstrate population genetic structure arising from differences in spawning grounds and homing behavior 97 . While we are unaware of such mechanisms underlying divergence in taimen, our results indicate the potential for differentiation at smaller geographic scales than previously detected and the need for further study to understand its evolutionary causes and consequences for management.…”

Ecogeographic Units and Management Units of Chum Salmon Oncorhynchus keta of the Amur Zoogeographic Province

“…The EGU identification procedure consists of two stages (Zhivotovsky et al, 2015;Zhivotovsky, 2016aZhivotovsky, , 2017. At the first stage, one should preliminarily divide the distribution range of the species into ecologicalgeographical regions, using habitat features important for the studied species, and then subdivide the identified ecological-geographical regions into EGUs, taking into account the biology of the species.…”

“…A combinatory approach for determination of management units as intraspecific population groups would be based on biogeographic principles using data on the ecology and genetics of populations. In particular, the concept of ecogeographic units (EGUs) can be used to determine the management units (Zhivotovsky et al, 2015;Zhivotovsky, 2016aZhivotovsky, , 2017: each EGU is defined as a group of geographically close populations, the distribution range of which is characterized by similar ecological conditions, with possible exchange of gene flows between them, but significantly separated from other EGUs, which can be tested using DNA markers.…”