High‐resolution secondary ion mass spectrometry analysis of carbon dynamics in mycorrhizas formed by an obligately myco‐heterotrophic orchid

Mycorrhiza formation represents a significant carbon (C) acquisition alternative for orchid species, particularly those that remain achlorophyllous through all life stages. As it is known that orchid mycorrhizas facilitate nutrient transfer (most notably of C), it has not been resolved if C transfer occurs only after lysis of mycorrhizal structures (fungal pelotons) or also across the mycorrhizal interface of pre‐lysed pelotons. We used high‐resolution secondary ion mass spectrometry (nanoSIMS) and labelling with enriched ¹³CO₂ to trace C transfers, at subcellular scale, across mycorrhizal interfaces formed by Rhizanthella gardneri, an achlorphyllous orchid. Carbon was successfully traced in to the fungal portion of orchid mycorrhizas. However, we did not detect C movement across intact mycorrhizal interfaces up to 216 h post ¹³CO₂ labelling. Our findings provide support for the hypothesis that C transfer from the mycorrhizal fungus to orchid, at least for R. gardneri, likely occurs after lysis of the fungal peloton.     

Scent-Matching Dogs Determine Number of Unique Individuals From Scat

ABSTRACT Noninvasive scat sampling methods can generate large samples sizes, collected over vast landscapes, ideal for addressing wildlife conservation and management questions. However, the cost of genotyping scat samples limits the accessibility of these techniques. We describe detection-dog methods for matching large numbers of scat samples to the individual, reducing or eliminating the need for sample genotyping. Three dogs correctly matched 25 out of 28 samples from 6 captive maned wolves (Chrysocyon brachyurus) of known identity. Sample scent-matching can increase overall accessibility and breadth of applications of noninvasive scat-collection methods to important landscape scale problems in wildlife sciences.     

Quantitative genetic and translocation experiments reveal genotype‐by‐environment effects on juvenile life‐history traits in two populations of Chinook salmon (Oncorhynchus tshawytscha)

Understanding the genetic architecture of phenotypic plasticity is required to assess how populations might respond to heterogeneous or changing environments. Although several studies have examined population‐level patterns in environmental heterogeneity and plasticity, few studies have examined individual‐level variation in plasticity. Here, we use the North Carolina II breeding design and translocation experiments between two populations of Chinook salmon to detail the genetic architecture and plasticity of offspring survival and growth. We followed the survival of 50 800 offspring through the larval stage and used parentage analysis to examine survival and growth through freshwater rearing. In one population, we found that additive genetic, nonadditive genetic and maternal effects explained 25%, 34% and 55% of the variance in larvae survival, respectively. In the second population, these effects explained 0%, 24% and 61% of the variance in larvae survival. In contrast, fry survival was regulated primarily by additive genetic effects, which indicates a shift from maternal to genetic effects as development proceeds. Fry growth also showed strong additive genetic effects. Translocations between populations revealed that offspring survival and growth varied between environments, the degree of which differed among families. These results indicate genetic differences among individuals in their degree of plasticity and consequently their ability to respond to environmental variation.     

Comparative phylogeography of two seastars and their ectosymbionts within the Coral Triangle

Repeated exposure and flooding of the Sunda and Sahul shelves during Pleistocene sea‐level fluctuations is thought to have contributed to the isolation and diversification of sea‐basin populations within the Coral Triangle. This hypothesis has been tested in numerous phylogeographical studies, recovering an assortment of genetic patterns that the authors have generally attributed to differences in larval dispersal capability or adult habitat specificity. This study compares phylogeographical patterns from mitochondrial COI sequences among two co‐distributed seastars that differ in their adult habitat and dispersal ability, and two seastar ectosymbionts that differ in their degree of host specificity. Of these, only the seastar Linckia laevigata displayed a classical pattern of Indian‐Pacific divergence, but with only moderate genetic structure (Φ_CT = 0.067). In contrast, the seastar Protoreaster nodosus exhibited strong structure (Φ_CT = 0.23) between Teluk Cenderawasih and the remainder of Indonesia, a pattern of regional structure that was echoed in L. laevigata (Φ_CT = 0.03) as well as its obligate gastropod parasite Thyca crystallina (Φ_CT = 0.04). The generalist commensal shrimp, Periclimenes soror showed little genetic structuring across the Coral Triangle. Despite species‐specific phylogeographical patterns, all four species showed departures from neutrality that are consistent with massive range expansions onto the continental shelves as the sea levels rose, and that date within the Pleistocene epoch. Our results suggest that habitat differences may affect the manner in which species responded to Pleistocene sea‐level fluctuations, shaping contemporary patterns of genetic structure and diversity.     

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

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. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 56–72.