Does Breeding Site Fidelity Drive Phenotypic and Genetic Sub-Structuring of a Population of Arctic Charr?

Fine-scale genetic structure reflects limited and coordinated dispersal in the colonial monk parakeet, Myiopsitta monachus

The genetic structure of animal populations has considerable behavioural, ecological and evolutionary implications and may arise from various demographic traits. Here, we use observational field data and molecular genetics to determine the genetic structure of an invasive population of monk parakeets, Myiopsitta monachus, at a range of spatial scales, and investigate the demographic processes that generate the observed structure. Monk parakeets construct large nests that can house several pairs occupying separate chambers; these nests are often aggregated within nesting trees. We determined patterns of relatedness within compound nests, within nesting trees and between trees. Spatial autocorrelation analyses of pairwise genetic relatedness revealed fine-scale genetic structure with relatives of both sexes spatially clustered within, but not beyond, nesting trees. In addition, males were more related to males sharing their compound nests than to other males occupying the same nesting tree. By contrast, males and females within compound nests were not significantly more closely related than elsewhere in the same tree, and we found no evidence for inbreeding. Adults showed high breeding site fidelity between years despite considerable disturbance of nest sites. Natal dispersal was female-biased, but dispersal distances were relatively short with some natal philopatry observed in both sexes. Sibling coalitions, typically of males, were observed amongst both philopatric and dispersing birds. Our results show significant clustering of kin within compound nests and nesting trees resulting from limited and coordinated natal dispersal, with subsequent breeding site fidelity. The resulting genetic structure has implications for social behaviour in this unusual parrot species.

Asymmetrical habitat coupling of an aquatic predator-The importance of individual specialization

Predators should stabilize food webs because they can move between spatially separate habitats. However, predators adapted to forage on local resources may have a reduced ability to couple habitats. Here, we show clear asymmetry in the ability to couple habitats by Eurasian perch-a common polymorphic predator in European lakes. We sampled perch from two spatially separate habitats-pelagic and littoral zones-in Lake Erken, Sweden. Littoral perch showed stronger individual specialization, but they also used resources from the pelagic zone, indicating their ability to couple habitats. In contrast, pelagic perch showed weaker individual specialization but near complete reliance on pelagic resources, indicating their preference to one habitat. This asymmetry in the habitat coupling ability of perch challenges the expectation that, in general, predators should stabilize spatially separated food webs. Our results suggest that habitat coupling might be constrained by morphological adaptations, which in this case were not related to genetic differentiation but were more likely related to differences in individual specialization.

Genetic evidence for panmixia in a colony-breeding crater lake cichlid fish

Fine-scaled genetic structuring, as seen for example in many lacustrine fish, typically relates to the patterns of migration, habitat use, mating system or other ecological factors. Because the same processes can also affect the propensity of population differentiation and divergence, assessments of species from rapidly speciating clades, or with particularly interesting ecological traits, can be especially insightful. For this study, we assessed the spatial genetic relationships, including the genetic evidence for sex-biased dispersal, in a colony-breeding cichlid fish, Amphilophus astorquii, endemic to Crater Lake Apoyo in Nicaragua, using 11 polymorphic microsatellite loci (n = 123 individuals from three colonies). We found no population structure in A. astorquii either within colonies (no spatial genetic autocorrelation, r ~0), or at the lake-wide level (pairwise population differentiation FST = 0-0.013 and no clustering), and there was no sex-bias (male and female AIc values bounded 0) to this lack of genetic structure. These patterns may be driven by the colony-breeding reproductive behaviour of A. astorquii. The results suggest that strong philopatry or spatial assortative mating are unlikely to explain the rapid speciation processes associated with the history of this species in Lake Apoyo.

Ecosystem size predicts eco-morphological variability in a postglacial diversification

Identifying the processes by which new phenotypes and species emerge has been a long‐standing effort in evolutionary biology. Young adaptive radiations provide a model to study patterns of morphological and ecological diversification in environmental context. Here, we use the recent radiation (ca. 12k years old) of the freshwater fish Arctic charr (Salvelinus alpinus) to identify abiotic and biotic environmental factors associated with adaptive morphological variation. Arctic charr are exceptionally diverse, and in postglacial lakes there is strong evidence of repeated parallel evolution of similar morphologies associated with foraging. We measured head depth (a trait reflecting general eco‐morphology and foraging ecology) of 1,091 individuals across 30 lake populations to test whether fish morphological variation was associated with lake bathymetry and/or ecological parameters. Across populations, we found a significant relationship between the variation in head depth of the charr and abiotic environmental characteristics: positively with ecosystem size (i.e., lake volume, surface area, depth) and negatively with the amount of littoral zone. In addition, extremely robust‐headed phenotypes tended to be associated with larger and deeper lakes. We identified no influence of co‐existing biotic community on Arctic charr trophic morphology. This study evidences the role of the extrinsic environment as a facilitator of rapid eco‐morphological diversification.

Oncology practice trends from the national practice benchmark

In 2011, we made predictions on the basis of data from the National Practice Benchmark (NPB) reports from 2005 through 2010. With the new 2011 data in hand, we have revised last year's predictions and projected for the next 3 years. In addition, we make some new predictions that will be tracked in future benchmarking surveys. We also outline a conceptual framework for contemplating these data based on an ecological model of the oncology delivery system. The 2011 NPB data are consistent with last year's prediction of a decrease in the operating margins necessary to sustain a community oncology practice. With the new data in, we now predict these reductions to occur more slowly than previously forecast. We note an ease to the squeeze observed in last year's trend analysis, which will allow more time for practices to adapt their business models for survival and offer the best of these practices an opportunity to invest earnings into operations to prepare for the inevitable shift away from historic payment methodology for clinical service. This year, survey respondents reported changes in business structure, first measured in the 2010 data, indicating an increase in the percentage of respondents who believe that change is coming soon, but the majority still have confidence in the viability of their existing business structure. Although oncology practices are in for a bumpy ride, things are looking less dire this year for practices participating in our survey.

Panmixia in Zoarces viviparus: implications for environmental monitoring studies

In this study, the genetic population structure of the eelpout Zoarces viviparus was investigated by using microsatellites. Samples were collected at 10 sites in the Baltic Sea, covering a distance of c. 90 km. Ten newly developed microsatellite loci were used to infer the population structure. No global spatial genetic differentiation was found (global F(ST) = 0·0001; D(est) = -0·0003), indicating strong gene flow at this scale, nor any clear pattern of isolation by distance. The results suggest that gene flow among the studied populations of Z. viviparus is stronger than usually thought, which might be caused by environmental homogeneity. This is important for planning and evaluating monitoring activities in this species and for the interpretation of ecotoxicological studies. Strong migration might lead to wrong conclusions concerning the pollution in a given area. Therefore, reference stations should be placed at a larger distance than presently practiced.

Population connectivity: dam migration mitigations and contemporary site fidelity in arctic char

BACKGROUND

Animal feeding and spawning migrations may be limited by physical barriers and behavioral interactions. Dam constructions (e.g. hydropower) commonly include gateways for fish migrations to sustain ecological connectivity. Relative genetic impacts of fish passage devices versus natural processes (e.g. hybrid inferiority) are, however, rarely studied. We examined genetic (i.e. microsatellite) population connectivity of highly migrating lake-dwelling Arctic char (Salvelinus alpinus), introduced 20 generations ago, across and within two subalpine lakes separated by a dam with a subterranean tunnel and spill gates after 7 generations. Due to water flow regime, the time window for fish migration is highly restricted.

RESULTS

Char populations, with similar genetic structuring and diversity observed across and within lakes, were admixed across the dam with fishways during feeding. For spawning, however, statistically significant, but very low population differentiation (θ; 0.002 - 0.013) was found in nine out of ten reproductive site comparisons, reflecting interactions between extensive migration (mean first generation (F0) = 10.8%) and initial site fidelity. Simulations indicated that genetic drift among relatively small effective populations (mean N(e) = 62) may have caused the observed contemporary differentiation. Novel Bayesian analyses indicated mean contributions of 71% F0 population hybrids in spawning populations, of which 76% had maternal or paternal native origin.

CONCLUSIONS

Ecological connectivity between lakes separated by a dam has been retained through construction of fishways for feeding migration. Considerable survival and homing to ancestral spawning sites in hybrid progeny was documented. Population differentiation despite preceding admixture is likely caused by contemporary reduced reproductive fitness of population hybrids. The study documents the beginning stages of population divergence among spatial aggregations with recent common ancestry.

Phenotypic plasticity, heterochrony and ontogenetic repatterning during juvenile development of divergent Arctic charr (Salvelinus alpinus)

Phenotypic plasticity is a developmental process that plays a role as a source of variation for evolution. Models of adaptive divergence make the prediction that increasing ecological specialization should be associated with lower levels of plasticity. We tested for differences in the magnitude, rate and trajectory of morphological plasticity in two lake populations of Arctic charr (Salvelinus alpinus) that exhibited variation in the degree of resource polymorphism. We reared offspring on diet treatments that mimicked benthic and pelagic prey. Offspring from the more divergent population had lower levels of morphological plasticity. Allometry influenced the rate of shape change over ontogeny, with differences in rate among ecomorphs being minimal when allometric variation was removed. However, plasticity in the spatial trajectory of development was extensive across ecomorphs, both with and without the inclusion of allometric variation, suggesting that different aspects of shape development can evolve independently.

Morphometric and genetic analyses of two sympatric morphs of Arctic char (Salvelinus alpinus) in the Canadian High Arctic

Multivariate morphometric analyses were used to examine variation in head, body, and fin shape between two sympatric morphotypes of Arctic char ( Salvelinus alpinus (L., 1758)) from Lake Hazen, Ellesmere Island, Nunavut, Canada. Population structure of the Lake Hazen Arctic char was examined using five microsatellite loci. The “small” morph was found to have a larger (primarily deeper) head, larger and more elongate fins, and a deeper lateral profile than the “large” morph. The morphs also differed in allometric growth patterns. The large and small morphs do not appear to represent genetically distinct populations. The head morphology of the Lake Hazen small and large morphs exhibited similarities to benthic and pelagic morphs (respectively) from other lakes. We hypothesize that the large morph may be adapted to high-efficiency swimming and that the small morph may be adapted to low-efficiency, high-acceleration swimming. Such functional trade-offs are not uncommon among fish specializing in dispersed or mobile prey (fish and plankton) and benthic prey, respectively. The lack of apparent genetic differentiation between the morphs may suggest that the morphological differences result, to some extent, from phenotypic plasticity. Based on these results and previous analyses, it seems reasonable to conclude that Lake Hazen Arctic char represent a resource polymorphism.

Interaction of landscape and life history attributes on genetic diversity, neutral divergence and gene flow in a pristine community of salmonids

Landscape genetics holds promise for the forecasting of spatial patterns of genetic diversity based on key environmental features. Yet, the degree to which inferences based on single species can be extended to whole communities is not fully understood. We used a pristine and spatially structured community of three landlocked salmonids (Salvelinus fontinalis, Salmo salar, and Salvelinus alpinus) from Gros Morne National Park (Newfoundland, Canada) to test several predictions on the interacting effects of landscape and life history variation on genetic diversity, neutral divergence, and gene flow (m, migration rate). Landscape factors consistently influenced multispecies genetic patterns: (i) waterfalls created strong dichotomies in genetic diversity and divergence between populations above and below them in all three salmonids; (ii) contemporary m decreased with waterway distance in all three species, while neutral genetic divergence (theta) increased with waterway distance, albeit in only two taxa; (iii) river flow generally produced downstream-biased m between populations when waterfalls separated these, but not otherwise. In contrast, we expected differential life history to result in a hierarchy of neutral divergence (S. salar > S. fontinalis > S. alpinus) based on disparities in dispersal abilities and population size from previous mark-recapture studies. Such hierarchy additionally matched varying degrees of spatial genetic structure among species revealed through individual-based analyses. We conclude that, whereas key landscape attributes hold power to predict multispecies genetic patterns in equivalent communities, they are likely to interact with species-specific life history attributes such as dispersal, demography, and ecology, which will in turn affect holistic conservation strategies.

Contrasting patterns of spatial genetic structure in sympatric rock-dwelling cichlid fishes

The cichlid fish of Lake Tanganyika in Eastern Africa are a celebrated example of both ecological and species diversification. Because population subdivision is likely to play an important role in the speciation process, understanding how habitat features interact with species' demographic, behavioral and ecological attributes to influence gene flow and population divergence may help explain the causes of high species richness in this and other systems. Here, we test the roles of isolation-by-habitat and isolation-by-distance in generating fine-scale population genetic structure in three sympatric species of habitat-restricted cichlids in Lake Tanganyika. Using multilocus microsatellite genotypes, we contrast patterns of population differentiation in these habitat specialists along a mosaic coastline of both favorable and unfavorable habitat. Despite their close phylogenetic relationship and shared habitat affinity, these species show striking differences in their pattern of genetic subdivision within the same geographical region, suggesting substantially different patterns of gene flow. In particular, two trophically specialized species exhibit much more restricted gene flow over sandy habitat than a trophically opportunistic species. This result suggests that ecological and behavioral traits have a strong influence on the scale and degree of population subdivision, a finding that has potentially important implications for understanding differential propensities for diversification among lineages and phylogenetic patterns of diversity.

Cryptic barriers to dispersal within a lake allow genetic differentiation of Eurasian perch

Gene flow between coexisting or nearby populations normally prevents genetic divergence and local adaptation. Despite this, there are an increasing number of reports of sympatric sister taxa, indicating potential divergence and speciation in the face of gene flow. A large number of such reported cases involve lake-dwelling fish, which are expected to run into few physical barriers to dispersal within their aquatic habitat. However, such cases may not necessarily reflect sympatric speciation if cryptic dispersal barriers are common in lakes and other aquatic systems. In this study, we examined genetic differentiation in perch (Perca fluviatilis L.) from nine locations in a single, small lake (24 km(2)), using microsatellites. We detected significant genetic differentiation in all but two pairwise comparisons. These patterns were not consistent with divergence by distance or the existence of kin groups. Instead, they suggest that cryptic barriers to dispersal exist within the lake, allowing small-scale genetic divergence. Such an observation suggests that allopatric (or parapatric) divergence may be possible, even in small, apparently homogenous environments such as lakes. This has important consequences for how we currently view evidence from nature for sympatric speciation.

Fine spatial scale phenotypic divergence in wood frogs (Lithobates sylvaticus)

I studied local divergence in growth, a trait previously shown to be both phenotypically plastic and heritable, among wood frog (Lithobates sylvaticus (LeConte, 1825)) tadpoles inhabiting four ponds within a continuous woodland. Mark–recapture results revealed very low levels of migration among ponds as close as 35 m and no more than 185 m apart. Common garden experiments conducted at two temperatures revealed consistent year-to-year patterns of phenotypic divergence in tadpole growth performance among the four pond populations. The divergence in growth performance was conserved when controlling for parental effects via half-sibling experiments. Results of cross-transplant experiments suggest that the divergence in tadpole growth reflected either genetic drift or adaptation to local pond conditions. Taken together, the results suggest that divergence in growth performance among the tadpoles from the four ponds is the result of selection or genetic drift reinforced by low levels of gene flow among pond populations.