Morphological Variation of Cisco across Gradients of Lake Productivity

Abstract

The effects of lake productivity and late‐summer hypolimnetic oxygen on the size and shape of Cisco Coregonus artedi were examined in 27 Minnesota lakes. Geometric morphometry analyses of specimens captured in vertical gill nets indicated that Cisco in more productive lakes with hypoxic hypolimnia were larger, with deeper bodies, shorter snouts and caudal peduncles, and longer fins. Cisco in unproductive lakes with oxygenated hypolimnia were smaller, with slender bodies, longer snouts and caudal peduncles, and shorter fins. The effect of hypolimnetic oxygen on depths utilized by Cisco and the resulting vulnerability to predation was an important driver of shape and fin length. Deeper body depths and longer fin lengths were possibly a response to greater vulnerability to predation when hypoxic hypolimnia limit coldwater refugia for Cisco, which are forced to inhabit shallower depths near warmwater predators such as Walleye Sander vitreus and Northern Pike Esox lucius. Differences in size and shape relationships of Cisco in lakes on and off the Canadian Shield were also detected. The availability of late‐summer habitat, depth‐mediated predation risk, and growth potential appear to be important ecological drivers of morphological variation in Cisco.

Oxythermal habitat as a primary driver of ecological niche and genetic diversity in cisco (Coregonus artedi)

“…Phenotypic plasticity likely aided the selection pressures that enable Cisco to inhabit a wide range of lakes ranging from oligotrophic to eutrophic (Jacobson et al 2020). In Minnesota, cisco are found in 648 lakes that range from oligotrophic to eutrophic moving from the northeastern to central part of the state (Jacobson et al 2010).…”

“…The dual effects of eutrophication and climate change across the lake productivity gradient causes cisco to inhabit the upper water column possessing higher temperatures in impacted lakes, which in turn has been shown to impact cisco morphology (Jacobson et al 2020) and stable isotope patterns regardless of diets (Zimmer et al 2020). A useful metric for quantitatively measuring thermal habitat quality for cold-water fishes is the water temperature at which dissolved oxygen drops below 3 mg L -1 (T DO3 ; Jacobson et al 2010).…”

“…T DO3 is positively related to lake productivity (Zimmer et al 2020) with lower T DO3 values indicating higher habitat quality (Jacobson et al 2010). T DO3 has also been shown to influence both average capture depth and body shape of cisco across lakes (Jacobson et al 2020), as well as likelihood of cisco summer kill when cisco are forced to inhabit waters that do not meet their respiration demand (Jacobson et al 2012). An example of how T DO3 relates to oxythermal habitat and its influence on habitat use of cisco is shown in Figure 1.…”

“…In this study we sampled cisco in 32 Minnesota lakes that ranged from oligotrophic to eutrophic. These lakes have been the focus of previous research that provided insights on the morphological response of cisco to productivity gradients (Jacobson et al 2020), the influence of lake productivity on stable isotope patterns across lakes (Zimmer et al 2020), and the ability of cisco to retain morphological and ecological traits when translocated from Lake Superior to inland lakes (Jacobson et al 2018). The present study aims to build upon this body of work by assessing effects of the oxythermal habitat on cisco habitat use, isotopic patterns, diets, genetic D r a f t diversity, and their physical-chemical environment within and across lakes.…”

Isotopic niche size of Coregonus artedi (sensu lato) Increases in the presence of Mysis diluviana, expanded habitat use and phenotypic diversity

“…In Chaoborus ‐based food webs, cisco size is related to zooplankton density with complex diel patterns of movement including no diel movement (Ahrenstorff et al., 2013). In non‐ Mysis food webs in a Minnesota lake region ( Chaoborus may or may not be present), size and shape of cisco are related to overall lake productivity with use of shallow habitat occurring in lakes with inadequate hypolimnetic oxythermal habitat (Jacobson et al, in review). In response, cisco fin shape and size shifted to accommodate a more substrate‐based food source.…”