Microbial community diversity patterns are related to physical and chemical differences among temperate lakes near Beaver Island, MI

Lakes are dynamic and complex ecosystems that can be influenced by physical, chemical, and biological processes. Additionally, individual lakes are often chemically and physically distinct, even within the same geographic region. Here we show that differences in physicochemical conditions among freshwater lakes located on (and around) the same island, as well as within the water column of each lake, are significantly related to aquatic microbial community diversity. Water samples were collected over time from the surface and bottom-water within four freshwater lakes located around Beaver Island, MI within the Laurentian Great Lakes region. Three of the sampled lakes experienced seasonal lake mixing events, impacting either O2, pH, temperature, or a combination of the three. Microbial community alpha and beta diversity were assessed and individual microbial taxa were identified via high-throughput sequencing of the 16S rRNA gene. Results demonstrated that physical and chemical variability (temperature, dissolved oxygen, and pH) were significantly related to divergence in the beta diversity of surface and bottom-water microbial communities. Despite its correlation to microbial community structure in unconstrained analyses, constrained analyses demonstrated that dissolved organic carbon (DOC) concentration was not strongly related to microbial community structure among or within lakes. Additionally, several taxa were correlated (either positively or negatively) to environmental variables, which could be related to aerobic and anaerobic metabolisms. This study highlights the measurable relationships between environmental conditions and microbial communities within freshwater temperate lakes around the same island.

Colonization of the Beaver Island Archipelago by deer mice (Peromyscus maniculatus gracilis): mtDNA evidence for multiple origins

The Beaver Island group in Lake Michigan comprises nine islands ranging from 0.3 to 144 km2, lying approximately 30 km west of Michigan’s Lower Peninsula (LP) and 15 km south of the Upper Peninsula (UP). The islands have been isolated from mainland Michigan for most of their postglacial history, but were connected to the mainland LP during the low-water Chippewa stage (ending about 7400 years before present (YBP)). Although plants and animals could have colonized the islands during the Chippewa period, flooding during the subsequent Nipissing high-water stand means that the smaller islands have been colonized more recently. We analyzed 481 bp of mitochondrial D-loop sequences from woodland deer mice (Peromyscus maniculatus (Wagner, 1845)) on six of these islands in northern Lake Michigan to elucidate the mainland origin and minimum number of colonization events for this species. Surprisingly, the distribution of haplotypes on the islands suggests that the populations on most islands likely had separate recent origins on the mainland UP. Approximate Bayesian computation supports a scenario in which individual islands were colonized separately by distinct groups of mice. Together, the data suggest multiple colonization events from the UP, rather than expansion from a bottlenecked population or a single colonization event.