Pluvial Drainage Patterns and Holocene Desiccation Influenced the Genetic Architecture of Relict Dace, Relictus solitarius (Teleostei: Cyprinidae)

Abstract

Changing drainage patterns have played a significant role in the evolution of western North American aquatic taxa. Relict dace, Relictus solitarius, is a Great Basin endemic cyprinid with a native range that is restricted to four valleys in eastern Nevada. Relictus solitarius now occupies spring systems that are the remnants of Pleistocene-era pluvial lakes, although it may have occurred in the area for much longer. Here we use mitochondrial DNA sequence data to assess range-wide genetic diversity of R. solitarius, and to estimate divergence times to determine whether pluvial drainages played an important role in shaping intraspecific genetic diversity. Genetic diversification within R. solitarius began during the early to mid-Pleistocene, separating populations within two sets of valleys (Butte/Ruby and Goshute/Steptoe). Additional diversification in each of the two sets of valleys occurred more recently, in the mid- to late-Pleistocene. Holocene desiccation has further isolated populations, and each population sampled contains unique mtDNA haplotypes. Pluvial drainage patterns did contribute to the genetic structure observed within R. solitarius, but most of the intraspecific diversification does not appear to be associated with the Last Glacial Maximum. Holocene desiccation has also contributed to the observed genetic structure. The relict dace populations we sampled are all unique, and we recommend that future management efforts should strive to preserve as much of the genetic diversity as possible.

Broad‐ and fine‐scale structure across the distribution of the relict dace (Relictus solitarius) in the Great Basin desert, USA

“…GSTS is located in the southern end of Goshute Valley between JSWC and Steptoe Valley, but our analyses do not indicate it is most closely related to either JSWC or Steptoe Valley Relict Dace (Figure 2e). Previously with mtDNA data, Houston et al (2015) found most fish from GSTS to have the same haplotype and the sampling location was monophyletic and nested within generally polyphyletic JSWC and Steptoe Valley sampling locations. The complex evolutionary history of GSTS including a loss of diversity due to drift and the rapid separation of Relict Dace into refugia results in few shared sites to inform branching patterns, and the few phylogenetically informative sites that do support a “true” topology may at times be less abundant than the sites that support a “false” topology.…”

“…Nevada Department of Wildlife (NDOW) biologists collected fin clips from 396 morphologically identified Relict Dace in the Butte, Ruby, Goshute, Steptoe, and Spring Valleys in 2017 (Table 1; Figure 1). Locations used in Houston et al (2015) are noted, as well as alternative names for locations. Fin clips were dried and stored in envelopes until DNA extraction using the Qiagen DNeasy kit (Qiagen) according to the manufacturer's protocol.…”

“…Throughout their range, Relict Dace show very high levels of structure and diversity and more recent admixture in the eastern valleys when compared to the western valleys (Houston et al, 2015), likely due to more available habitat in Goshute and Steptoe Valleys. Previous mtDNA data suggest an initial split between the eastern (Goshute and Steptoe) and western (Butte and Ruby) Valleys ~1 million years ago, followed by significant diversification during the Pleistocene and increased isolation through the Holocene from drying, and more recently through habitat alteration and introduced species (Houston et al, 2015).…”

“…Detailed views are included for collection sites at (c) JSWC in Goshute Valley, (d) Ruby Lake in Ruby Valley, and (e) Phillips ranch in Steptoe Valley. Asterisks denote locations sampled by Houston et al (2015)…”

“…At the time of range‐wide sampling for Houston et al (2015), managers were primarily concerned with hybridization between Speckled Dace and Relict Dace in Butte and Ruby valleys, and it was assumed that most of the JSWC were occupied by a single population which could be represented by Big Springs. However the high habitat diversity of JSWC, results on the range‐wide distribution of genetic variation from Houston et al (2015), and recent comprehensive surveys uncovering significant habitat diversity prompted managers to question (1) Is JSWC is a single large population or multiple populations, (2) Is there evidence of local adaptation in the form of outlier loci? and (3) to What extent are populations within JSWC connected, if at all?…”