Population Genetics of the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) across Multiple Spatial Scales

Abstract

Conservation genetics is a powerful tool to assess the population structure of species and provides a framework for informing management of freshwater ecosystems. As lotic habitats become fragmented, the need to assess gene flow for species of conservation management becomes a priority. The eastern hellbender (Cryptobranchus alleganiensis alleganiensis) is a large, fully aquatic paedamorphic salamander. Many populations are experiencing declines throughout their geographic range, yet the genetic ramifications of these declines are currently unknown. To this end, we examined levels of genetic variation and genetic structure at both range-wide and drainage (hierarchical) scales. We collected 1,203 individuals from 77 rivers throughout nine states from June 2007 to August 2011. Levels of genetic diversity were relatively high among all sampling locations. We detected significant genetic structure across populations (Fst values ranged from 0.001 between rivers within a single watershed to 0.218 between states). We identified two genetically differentiated groups at the range-wide scale: 1) the Ohio River drainage and 2) the Tennessee River drainage. An analysis of molecular variance (AMOVA) based on landscape-scale sampling of basins within the Tennessee River drainage revealed the majority of genetic variation (∼94–98%) occurs within rivers. Eastern hellbenders show a strong pattern of isolation by stream distance (IBSD) at the drainage level. Understanding levels of genetic variation and differentiation at multiple spatial and biological scales will enable natural resource managers to make more informed decisions and plan effective conservation strategies for cryptic, lotic species.

Amphibian molecular ecology and how it has informed conservation

“…populations. For instance, in a riparian or riverine species, it could make sense to measure the physical distance along rivers to other populations (McCartneyMelstad et al 2012;Unger et al 2013). More generally, areas in the landscape that are relatively more or less hospitable to a particular species can be categorized as minimally or highly resistive to movement, respectively (Zeller et al 2012).…”

A genomic assessment of population structure and gene flow in an aquatic salamander identifies the roles of spatial scale, barriers, and river architecture

“…This pattern was evident in our explorations of population structure and general summary statistics (i.e., F ST ), as well as results from simple Mantel tests, which indicated a correlation between geographic and genetic distance across the study system. Species restricted to a continuously connected dendritic network generally are expected to follow this pattern [e.g., the Stream Hierarchy Model (Meffe & Vrijenhoek, 1988)], and population genetic studies in fully aquatic salamander species have consistently followed this expectation, including investigations of Cope's giant salamander, Dicamptodon copei (Dicamptodontidae; Steele, Baumsteiger, & Storfer, 2009), and the hellbender, Cryptobranchus alleganiensis (Cryptobranchidae; Unger, Rhodes, Sutton, & Williams, 2013). Necturus maculosus may have the ability to disperse long distances; it can inhabit a variety of habitats (Petranka, 1998) and is suggested to exhibit seasonal migration (Matson, 1998).…”

The importance of terrestrial dispersal for connectivity among headwater salamander populations

“…Desmognathine salamanders are small salamanders that rely on cutaneous respiration as juveniles and adults (Petranka 2010) and our results indicate limited dispersal along both within and out-of-network pathways. Other stream-associated salamanders with larger body sizes (e.g., Cryptobranchus alleganiensis; Unger et al 2013) or that maintain external gills as juveniles and adults (e.g., Dicamptodon copei; Steele et al 2009), exhibited reduced genetic population structuring (F st , 0.001-0.281) and conformed more closely to a stream hierarchy model when compared to D. fuscus, suggesting that larger size or external gills, or both may constrain dispersal to the stream corridor but allow greater movement within these corridors. The limiting role of external gills is also supported by genetic population structure of D. tenebrosis, a species of giant salamander that can exhibit a biphasic life cycle with a distinct, terrestrial adult stage and that exhibits no significant isolation between neighboring watersheds, unlike its predominately paedomorphic conspecific (D. copei; Steele et al 2009).…”