Freshwater Fish Biogeography In The Bering Glacier Region, Alaska

Abstract

Bering Glacier, Alaska, is Earth's largest surging glacier, with surges occurring approximately every 20-30 years since 1900. Surges and subsequent retreats lead to a dynamic environment for aquatic communities, as glacial ice over-rides landscapes and new habitats form during glacial retreat. Lands around Bering Glacier are administered by the State of Alaska and the U.S. Bureau of Land Management (BLM). Purposes of this study are to characterize fish communities and provide information relevant to their management for BLM. Given Bering Glacier's remoteness, little information exists regarding its fish communities. Fish were collected over five summer field seasons (2002-2006), with 10 fish species collected in 80 lakes and streams. Results indicate that Dolly Varden (Salvelinus malma), threespine stickleback ( Gasterosteus aculeatus), prickly sculpin (Coitus asper), and coho salmon (Oncorhynchus kisutch) are first to colonize new habitat after glacial retreat. Ten locations with sympatric populations of anadromous and resident freshwater threespine stickleback were found. Geometric morphometrics and genetic analyses were conducted on these species pairs to test hypotheses regarding their formation. Possible origins include sympatric speciation, double invasion of anadromous fish, and independent colonization by resident freshwater fish from pre-existing lakes and streams along with anadromous fish. Body shape analyses of anadromous vs. resident freshwater stickleback supported the independent colonization hypothesis, because of a lack of body shape co-variation between groups, a lack of correlation of geometric morphometric variables with site age, and few fish with intermediate body shape at each site. Origin hypotheses were tested by use of the frequency of the Euro-North American Clade (ENAC) vs. the Trans North Pacific Clade (TNPC) in the mtDNA as well as sequence divergence of a portion of the mtDNA gene NADH2. A greater proportion of TNPC fish exist in resident freshwater populations at all sites, supporting the independent colonization hypothesis. The NADH2 sequence data did not help to clarify the origins. Future research at Bering Glacier should examine broader scale sequence divergence in genomes of stickleback and other colonizing fishes to advance the understanding of contemporary evolution and management implications in this newly formed aquatic landscape.