Morphological and genomic assessment of putative hybridization among deepwater ciscoes and between deepwater ciscoes and typical artedi in Lakes Michigan and Huron

Amanda Ackiss (USGS, aackiss@usgs.gov), Yu-Chun Kao(USFWS), Wendylee Stott (DFO), Andrew honsey (USGS), Randy Eshenroder (GLFC)

Species diversity can be lost through a combination of demographic decline and hybridization (Mallet 2005; Seehausen 2006). Regarding diversity losses among Ciscoes (subgenus Leucichthys, genus Coregonus) across the Great Lakes, the demographic decline in the 20th century has been well documented and was linked to anthropogenic stressors such as overexploitation and invasive species (see review in Eshenroder and Burnham-Curtis 1999). Hybridization also may have played a role in diversity losses among Ciscoes for various reasons. First, as recently diverged species in a young glacial-lake system, Ciscoes in the Great Lakes may not have strong post-zygotic barriers that impair the reproductive success of hybrids. Second, hybridization has been common in the genus Coregonus and has been reported in Ciscoes in the Great Lakes (Smith 1964; Todd and Stedman 1989; Eshenroder et al. 2016; Ackiss et al. 2020) and in European and Lake Whitefish (subgenus Coregonus) outside of the Great Lakes (Vonlanthen et al. 2012; Rougeux et al. 2017). Third, hybridization may result in reverse speciation, a process by which previously distinct forms/species collapse into a hybrid swarm, which has been observed in European Whitefish in several glacial lakes (Vonlanthen et al. 2012). Therefore, Cisco communities across the Great Lakes may have been shaped, at least in part, by hybridization. In Lakes Michigan and Huron, a major loss of Cisco diversity was associated with putative wide-scale hybridization events during the mid-1900s (Smith 1964; Todd and Stedman 1989; Eshenroder et al. 2016; Eshenroder and Jacobson 2020; Eshenroder et al. in press). These hybridization events may have led to the loss of five deepwater Ciscoes (C. alpenae, C. hoyi, C. kiyi, C. reighardi, and C. zenithicus) and a shallow-water Cisco, typical artedi (C. artedi artedi). The morphological evidence supporting claims of wide-scale hybridization (Lake Michigan: Smith 1964; Lake Huron: Todd and Stedman 1989), however, was not based on a comprehensive analysis of morphological data. Neither has there been any genetic evidence supporting claims of wide-scale hybridization in both lakes. Therefore, the importance of hybridization to the diversity of extant Ciscoes in Lakes Michigan and Huron remains unclear. Here we propose to carry out a comprehensive morphological and genomic assessment of the role of hybridization in the apparent loss of described forms of deepwater Ciscoes and extirpation of typical artedi from Lakes Michigan and Huron during the mid-1900s. The proposed project will contribute to our understanding of the taxonomy of extant deepwater Ciscoes, which in Lake Huron was inferred to be a hybrid swarm comprising the five deepwater Ciscoes listed above (Eshenroder et al. 2016), but which continue to be reported as C. hoyi (Favé and Turgeon 2008). It also will contribute to our understanding of the negative effects of hybridization, which has implications for Cisco restoration in the Great Lakes. For example, if the deepwater Ciscoes of Lakes Michigan and Huron hybridized as readily as described by Smith (1964) and Eshenroder et al. (2016), the prospects of reintroducing C. kiyi from Lake Superior are poor as those introduced may hybridize with extant deepwater Ciscoes. In addition, our results will clarify the role of hybridization in shaping morphological and genetic diversity of extant Ciscoes in the Great Lakes (Eshenroder and Jacobson 2020).