Metabolic traits of westslope cutthroat trout, introduced rainbow trout and their hybrids in an ecotonal hybrid zone along an elevation gradient

Abstract

In the Upper Oldman River, Alberta, introduced non-native hatchery rainbow trout (Oncorhynchus mykiss) hybridize with native westslope cutthroat trout (O. clarkii), resulting in a hybrid swarm. Rainbow trout dominate at low elevations (< 1250 m) in the river mainstem, cutthroat in high-elevation tributaries (> 1400 m), and hybrids are numerically dominant in the mid-elevation range. We hypothesized that metabolism of rainbow trout would exceed that of cutthroat trout, and that the elevation gradient in genetic makeup would be mirrored by a gradient in metabolic traits, with intermediate traits in the hybrid-dominated ecotone. Metabolic traits were measured and regressed against the genetic makeup of individuals and elevation. Rainbow trout had higher oxygen consumption rates (OCRs), higher white muscle lactate dehydrogenase (LDH), and citrate synthase (CS) activity, and higher plasma acetylcholinesterase (AchE) than cutthroat trout. Hybrids had intermediate OCRs and AchE, but LDH activity as high as rainbow trout. While hybrid zones are usually modelled as a balance between cross species mating and selection against hybrids, ecotonal hybrid zones, where hybrids proliferate in intermediate habitats and have traits that appear well suited to ecotonal conditions, have been proposed for some plants and animals, and may have important implications for resource management and conservation.

Dispersal and selection mediate hybridization between a native and invasive species

“…Across riverscapes, RBT Â WCT hybridization is often prevalent in low elevation streams with warmer water temperatures, whereas non-hybridized populations occur in colder, headwater streams [25,26]. This led to the hypothesis that cold temperatures in headwater streams impart a competitive advantage to native WCT [27,28]. We found evidence for selection against RBT admixture in two streams with contrasting thermal characteristics; Cyclone Creek is considerably warmer than Langford Creek but has a much lower pRBT.…”

Cold tolerance performance of westslope cutthroat trout (Oncorhynchus clarkii lewisi) and rainbow trout (Oncorhynchus mykiss) and its potential role in influencing interspecific hybridization

“…Westslope cutthroat trout with some level of admixture of RT alleles grow more quickly and mature faster than nonadmixed WSCT, and a trade-off exists between metabolic scope (RT) and growth efficiency (WSCT) such that RT are favoured at high temperatures by their increased metabolic scope and WSCT are favoured at low water temperatures by increased growth efficiency (Rasmussen et al 2010). Subsequently, Rasmussen et al (2012) documented interspecific differences in metabolism in terms of rates of oxygen consumption, and the activity of metabolically relevant enzymes, lactate dehydrogenase and citrate synthase, and concluded that fish with RT alleles tended to have higher metabolic demands than fish comprised primarily of a WSCT genomic background. Hybrids generally had intermediate metabolic traits and were better able to balance the trade-off between energetic scope and growth efficiency, allowing them to be successful in cooler, more upstream locations than RT (Rasmussen et al 2012).…”

“…Subsequently, Rasmussen et al (2012) documented interspecific differences in metabolism in terms of rates of oxygen consumption, and the activity of metabolically relevant enzymes, lactate dehydrogenase and citrate synthase, and concluded that fish with RT alleles tended to have higher metabolic demands than fish comprised primarily of a WSCT genomic background. Hybrids generally had intermediate metabolic traits and were better able to balance the trade-off between energetic scope and growth efficiency, allowing them to be successful in cooler, more upstream locations than RT (Rasmussen et al 2012). Consequently, nonadmixed WSCT may be observed to persist predominately in high-elevation tributaries as a function of the physiological and metabolic limitations of RT and interspecific hybrids in these habitats (Rasmussen et al 2010(Rasmussen et al , 2012.…”

“…Hybrids generally had intermediate metabolic traits and were better able to balance the trade-off between energetic scope and growth efficiency, allowing them to be successful in cooler, more upstream locations than RT (Rasmussen et al 2012). Consequently, nonadmixed WSCT may be observed to persist predominately in high-elevation tributaries as a function of the physiological and metabolic limitations of RT and interspecific hybrids in these habitats (Rasmussen et al 2010(Rasmussen et al , 2012.…”

“…Our study is a natural next step in trying to understand the processes behind the consistent spatial patterns in hybridization between these two species in nature (e.g., Rasmussen et al 2012;Yau and Taylor 2013).…”