Adaptive Radiation along a Thermal Gradient: Preliminary Results of Habitat Use and Respiration Rate Divergence among Whitefish Morphs

Abstract

Adaptive radiation is considered an important mechanism for the development of new species, but very little is known about the role of thermal adaptation during this process. Such adaptation should be especially important in poikilothermic animals that are often subjected to pronounced seasonal temperature variation that directly affects metabolic function. We conducted a preliminary study of individual lifetime thermal habitat use and respiration rates of four whitefish (Coregonus lavaretus (L.)) morphs (two pelagic, one littoral and one profundal) using stable carbon and oxygen isotope values of otolith carbonate. These morphs, two of which utilized pelagic habitats, one littoral and one profundal recently diverged via adaptive radiation to exploit different major niches in a deep and thermally stratified subarctic lake. We found evidence that the morphs used different thermal niches. The profundal morph had the most distinct thermal niche and consistently occupied the coldest thermal habitat of the lake, whereas differences were less pronounced among the shallow water pelagic and littoral morphs. Our results indicated ontogenetic shifts in thermal niches: juveniles of all whitefish morphs inhabited warmer ambient temperatures than adults. According to sampling of the otolith nucleus, hatching temperatures were higher for benthic compared to pelagic morphs. Estimated respiration rate was the lowest for benthivorous profundal morph, contrasting with the higher values estimated for the other morphs that inhabited shallower and warmer water. These preliminary results suggest that physiological adaptation to different thermal habitats shown by the sympatric morphs may play a significant role in maintaining or strengthening niche segregation and divergence in life-history traits, potentially contributing to reproductive isolation and incipient speciation.

Life history traits of the fish community in Lake Annecy: evidence from the stable isotope composition of otoliths

“…Furthermore, the δ 13 C oto value of otoliths is correlated with the specific respiration rate of individual fish estimated with δ 18 O oto values Solomon et al, 2006;Wurster and Patterson, 2003). These values have been used to track ontogenetic changes in diet, trophic level over life or temperature habitat of different morphs of a species (Jamieson et al, 2004;Schwarcz, et al, 1998;Kahilainen et al, 2014). However, applications have been restricted due to uncertainties regarding the nature of the relationship with controlling parameters .…”

Visual pigments of Arctic charr (Salvelinus alpinus (L.)) and whitefish (Coregonus lavaretus (L.)) morphs in subarctic lakes

“…The increase in A2 from June to September might then be interpreted as a phase-lagged response to the favourable light conditions of the summer months (starting with the ice-break in early June), when quantum catch may be more important than thermal noise control. It should also be noted that the measured profundal temperature of 9.5°C represents the highest annual temperature in this habitat, briefly obtained in late September during the vertical mixing of the water column (Kahilainen et al, 2014).…”

“…This seasonal tuning of chromophore system and rod absorbance spectra would require a follow-up study using an annual sampling design. Whitefish is prone for some ontogenetic habitat shifts as at least pelagic and littoral morphs use near surface habitats during their first year of life and thus should be exposed to the widest range of underwater wavelength distribution compared to older individuals inhabiting deeper and colder water layers in their respective habitats (Kahilainen et al, 2014). Overall, the sample sizes (numbers of individuals) for determining rod spectra for each condition (e.g.…”

“…Additionally, the profundal morph of Arctic charr is a more effective predator on chironomids than the littoral morph, suggesting heritable behavioural traits . Physiological traits related to profundal feeding include higher food conversion efficiency of the profundal Arctic charr morph in cold-water temperatures (Knudsen et al, 2015) and generally low metabolism of the profundal SSR whitefish (Kahilainen et al, 2014). Traits for permanent dwelling in the profundal habitat seem to be numerous in both Arctic charr and whitefish and thus may not be purely dependent on visual capabilities.…”

“…The morphs are named according to body size and gill raker traits: the small sparsely rakered (SSR) whitefish is a profundal dwelling morph with the lowest number of gill rakers, the large sparsely rakered (LSR) whitefish a littoral morph having intermediate numbers of gill rakers and the densely rakered whitefish (DR) is a small sized pelagic morph with the highest number of gill rakers (Kahilainen & Østbye, 2006;Kahilainen et al, 2011). Furthermore, SSR whitefish dwell in the coldest habitat and have the lowest respiration rate and largest eye size (Kahilainen & Østbye, 2006;Kahilainen et al, 2014). The eyes of profundal morphs are larger than those of the other morphs throughout their ontogeny Harrod et al, 2010).…”