Genetic divergence in morphology-performance mapping between Misty Lake and inlet stickleback

Different environments should select for different aspects of organismal performance, which should lead to correlated divergence in morphological traits that influence performance. The result should be genetic divergence in aspects of performance, morphology and associations ('maps') between morphology and performance. Testing this hypothesis requires quantifying performance and morphology in multiple populations after controlling for environmental differences, but this is rarely attempted. We used a common-garden experiment to examine morphology and several aspects of swimming performance within and between the lake and inlet populations of threespine stickleback (Gasterosteus aculeatus) from the Misty system, Vancouver Island, Canada. Controlling for body size, lake stickleback had shallower bodies, larger caudal fins and smaller pelvic girdles. With or without morphological covariates, lake stickleback showed greater performance in both sustained and burst swimming. In contrast, inlet stickleback showed greater manoeuverability than did lake stickleback in some analyses. Morphology-performance relationships were decoupled when considering variation within vs. between populations. Moreover, morphology-performance mapping differed between the two populations. Based on these observations, we advance a hypothesis for why populations adapting to different environments should show adaptive genetic divergence in morphology-performance mapping.     

Risk of predation as a promoting factor of species divergence in threespine sticklebacks (Gasterosteus aculeatus L.)

Icelandic freshwater systems are geologically young and contain only six species of freshwater fish. As these species colonized Icelandic fresh waters they were presented with a diversity of unique, uncontested habitats and food resources, promoting the evolution of new behaviour strategies crucial to the formation of new morphs and speciation. To determine the likelihood that predation threat could affect the antipredator behaviour and possibly the sympatric divergence of prey populations, we analysed antipredator behaviour of seven groups of Icelandic threespine sticklebacks ( Gasterosteus aculeatus ): two marine groups, one group from a lake without piscine predators, and two polymorphic lake populations, each with two groups occupying unique habitats. Shoaling cohesion, school formation and duration, and vigilance in predator inspection/avoidance behaviour varied greatly among groups. The differences appeared to be related to the risk of predation as well as to opportunities and constraints set by the different habitats. Antipredator behaviour was especially pronounced and differed extensively in two polymorphic forms from the lake Thingvallavatn, where predation risk is very high. By keeping the two morphs separate in their respective habitats, high predation risk may be a contributing factor in promoting the habitat-specific divergence of G. aculeatus seen in the lake. This suggests that in situations where refuge habitats are spatially separated, the risk of predation may contribute to the evolution of separate sympatric forms of small fish such as G. aculeatus .  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 189–203.     

Parasites of marine sticklebacks

A total of three specimens of Spinachia spinachia and 11 Gasterosteus aculeatus were caught in Loch Etive, Scotland. The salinity of the water at the capture site was 23%. Nine species of parasites were collected from individuals of the mixed population of sticklebacks, which included seven new parasite records for the British Isles.     

Covariation between predation risk, body size and fin elaboration in the green swordtail, Xiphophorus helleri

Natural and sexual selection can have either opposing or synergistic effects on the evolution of traits. In the green swordtail Xiphophorus helleri , sexual selection arising from female choice is known to favour larger males and males with longer swords. We examined variation in male and female size and fin morphology among 15 populations that varied in their predation environments. Males and females from populations in which piscivorous fishes were present had longer and deeper bodies than did males and females from populations in which piscivorous fishes were absent. Controlling for a positive effect of body size on sword length, males from populations in which piscivores were present had relatively shorter swords than did males from populations in which piscivores were absent. The associations between morphology and predation environment may be due to direct effects of predation, indirect effects of predation, other sources of selection that covary with predator presence, or other environmental effects on trait expression. These results suggest that while sexual selection favours longer swords, natural selection may have an opposing effect on sword length in populations with predators. Natural selection on body size, however, may act synergistically with sexual selection in populations with predators; both may favour the evolution of larger body size. The body size results for X. helleri contrast with related taxa that have become model systems for the study of life history evolution.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 87–100.     

Reduction of sexual dimorphism in stream-resident forms of three-spined stickleback Gasterosteus aculeatus

Sexual dimorphism in geometric body shape and external morphology was compared between marine and stream-resident forms of three-spined stickleback Gasterosteus aculeatus collected from North America and Japan. Some aspects of sexual dimorphism were shared between ecotypes: males had larger heads than females with no significant effect of ecotype on the magnitude of sexual dimorphism. By contrast, a significant sex-by-ecotype interaction was found for body depth. Males tended to have deeper bodies than females in both forms, but the magnitude of sexual dimorphism was reduced in stream-resident forms. Although females were generally larger in standard length and had larger pelvic girdles, significant sexual dimorphism in these traits was not consistently found across populations or ecotypes. These results suggest that some aspects of sexual dimorphism were shared between ecotypes, while others were unique to each population. The results further suggest that ecology may influence the evolution of sexual dimorphism in some external morphological traits, such as body depth.     

Inter-population variation in multiple paternity and reproductive skew in the guppy

We use microsatellite loci to detail the multiple paternity patterns in broods from 10 wild populations of the guppy ( Poecilia reticulata ) found in Northern Trinidad. The populations span two major drainages comprising the Caroni and the Oropouche, and include sites that are characterized by either high or low predation. Across the populations the frequency of multiple paternity is high with 95% (range: 70%–100%) of broods having multiple sires. Broods have an average of 3.5 sires (range: 1–9) and a mixed-model analysis suggests that broods from high predation sites have marginally more sires than do those from low predation sites, but this is true only in the Oropouche drainage. There is no difference in sire number between predation sites in the Caroni drainage. Brood size, but not female body length, is correlated with the number of sires and the correlation cannot be attributed solely to the stochastic process associated with sperm competition and a 'fair raffle'. Within broods there is significant skew in reproductive success among males, which may reflect variation in sperm competitiveness or female choice. There is, however, no difference in the skew among populations from different predation regimes or drainages. Finally, high predation populations were characterized by increased genetic variability at the microsatellite loci, suggesting a larger effective population size. We discuss explanations for the high degree of multiple paternity but the general lack of any major differences among broods from ecologically different populations.     

Predation of Lapwing Vanellus vanellus nests on lowland wet grassland in England and Wales: effects of nest density, habitat and predator abundance

There is concern that predation of Lapwing Vanellus vanellus nests may create additional pressure on declining populations of this species in Europe. At seven sites in England and Wales, daily nest predation rates on 1,390 nests were related to variables using Generalised Linear Mixed Models. The strongest predictor was Lapwing nest density (number of nests within 100 m): predation rates declined as nest density increased. Since nocturnal species, probably mammals, have been identified as the major predators of Lapwing nests at these sites, these results suggest that Lapwings are able to deter mammalian predators or may settle to nest at high densities in areas with low predation pressure. At the site level, there was no relationship between Lapwing nesting density and fox density, and a positive relationship with Carrion Crow Corvus corone nesting density. There was a weaker effect of distance to field boundary: nests closer to boundaries were more likely to be predated. Weak interactive effects between crow density and both nest visibility and distance to vantage point were identified in models using a reduced subset of nests. These were counter-intuitive, did not persist in the larger data set, and do not have obvious explanations. If Lapwings nesting at high density are able to deter predators, there are implications for land management. Smaller areas could be managed within potential breeding habitat to encourage Lapwings to nest in dense colonies. Selection of larger fields for such management, where nests could be located far from the field boundary should improve the value of such measures.     

Zooplankton in Loch Lomond: perspectives,predation and powan

Published and unpublished accounts of the zooplankton community of Loch Lomond are reviewed. Loch Lomond's zooplankton community is unique amongst those of Scotland's other large lochs. Holopedium gibberum appeared in Loch Lomond in the years between the studies of Slack & Hamilton in the 1950s and zooplankton surveys in the late 1970s.The annual cycles of Eudiaptomus gracilis, Cyclops strenuus abyssorum and Mesocyclops leuckarti are described for the mid basin of Loch Lomond. E. gracilis overwinter mainly as adult with variable egg production during their lifespan of 5–8 months. The cyclopoid copepods have variable life history characteristics. C. str. abyssorum produce a single generation per year, overwinter by means of resting eggs and a small population of planktonic adults, while M. leuckarti is present in the plankton throughout the year, but in low numbers during winter.Zooplankton populations in Loch Lomond are predated by the diverse fish community which includes a facultative planktivore in the powan, Coregonus lavaretus. Powan feed heavily on zooplankton from late spring until late autumn. Powan display selectivity in the prey species taken, in the size distribution and morph types taken within prey species. Zooplankton species, morphs and forms in Loch Lomond tend to reflect this predation.Zoology Department, University of St. AndrewsZoology Department, University of St. Andrews     

Do trade‐offs between predation pressures on females versus nests drive nest‐site choice in painted turtles?

Predation strongly influences reproductive behaviours because reproducing individuals must balance mortality risks to themselves and to their offspring. In many freshwater turtles, the nest predation risk decreases with nest distance from water, whereas the predation risk to females increases farther from water. To determine whether predation pressure influences the distance from water at which female turtles nest, we measured predation pressure on nesting females and on nests, as well as the distances of nests to water, in two populations of painted turtles. Using models, we found that female survival in both populations was high and did not vary with distance from water. Nest survival was also uncorrelated with nest distance to water, although it was significantly lower than adult survival in both populations and was only 1.2% in one population. Our results suggest that nest sites are not predictably safe from predators. Instead, turtles may hedge their bets by nesting over a wide range of distances from water because any distance is risky for nests and no distance is particularly risky for the nesting female. We suggest that other factors, such as suitable incubation conditions and/or post‐emergence hatchling survival, probably play a larger role than predation in driving nest‐site choice in painted turtles.     

Transplant experiments demonstrate that larger brains are favoured in high-competition environments in Trinidadian killifish

The extent to which the evolution of a larger brain is adaptive remains controversial. Trinidadian killifish (Anablepsoides hartii) are found in sites that differ in predation intensity; fish that experience decreased predation and increased intraspecific competition exhibit larger brains. We evaluated the connection between brain size and fitness (survival and growth) when killifish are found in their native habitats and when fish are transplanted from sites with predators to high-competition sites that lack predators. Selection for a larger brain was absent within locally adapted populations. Conversely, there was a strong positive relationship between brain size and growth in transplanted but not resident fish in high-competition environments. We also observed significantly larger brain sizes in the transplanted fish that were recaptured at the end of the experiment versus those that were not. Our results provide experimental support that larger brains increase fitness and are favoured in high-competition environments.     

Behavioral and physiological adjustments to new predators in an endemic island species,the Galápagos marine iguana

For the past 5 to 15 million years, marine iguanas (Amblyrhynchus cristatus), endemic to the Galápagos archipelago, experienced relaxed predation pressure and consequently show negligible anti-predator behavior. However, over the past few decades introduced feral cats and dogs started to prey on iguanas on some of the islands. We investigated experimentally whether behavioral and endocrine anti-predator responses changed in response to predator introduction. We hypothesized that flight initiation distances (FID) and corticosterone (CORT) concentrations should increase in affected populations to cope with the novel predators. Populations of marine iguanas reacted differentially to simulated predator approach depending on whether or not they were previously naturally exposed to introduced predators. FIDs were larger at sites with predation than at sites without predation. Furthermore, the occurrence of new predators was associated with increased stress-induced CORT levels in marine iguanas. In addition, age was a strong predictor of variation in FID and CORT levels. Juveniles, which are generally more threatened by predators compared to adults, showed larger FIDs and higher CORT baseline levels as well as higher stress-induced levels than adults. The results demonstrate that this naive island species shows behavioral and physiological plasticity associated with actual predation pressure, a trait that is presumably adaptive. However, the adjustments in FID are not sufficient to cope with the novel predators. We suggest that low behavioral plasticity in the face of introduced predators may drive many island species to extinction.     

Skate Bathyraja spp. egg predation in the eastern Bering Sea

Predation on skate eggs by snails was examined for three skate species at seven nursery sites in three regions (north, middle and south) of the eastern Bering Sea. Mean predation levels were 6·46% for the Alaska skate Bathyraja parmifera , 2·65% for the Aleutian skate Bathyraja aleutica and 22·25% for the Bering skate Bathyraja interrupta . Predation levels were significantly higher at the middle and north sites than the south sites for all species combined. Predation levels decreased with increasing egg-case densities at all nursery sites, and the highest predation levels occurred where egg-case densities were very low. Predated egg-case density increased with increasing snail densities across all nursery sites examined. The Oregon triton Fusitriton oregonensis was the most abundant snail species at all nursery sites and displayed ability to drill holes in the egg case of B. parmifera. Holes left by predatory snails in egg cases of B. parmifera were significantly larger, and of different shape at the middle site compared to the south site. Holes in B. parmifera were also significantly larger than those in egg cases of B. interrupta across all sites examined. Egg cases of B. aleutica possess surface spines that cover the egg case and may inhibit predation by snails at a greater rate than that of the B. parmifera and B. interrupta , which have a smoother egg-case surface.     

Parallel evolution of the sexes? Effects of predation and habitat features on the size and shape of wild guppies

Environmental gradients often lead to the parallel evolution of populations and species. To what extent do such gradients also lead to parallel evolution of the sexes? We used guppies (Poecilia reticulata) to examine the parallel and independent (sex‐specific) aspects of population divergence in response to predation and habitat features. Geometric morphometrics was used to analyse size and shape variation for 1335 guppies from 27 to 31 sites sampled in each of 2 years. Body size showed strong parallel population divergence; both sexes were larger at sites with a more open canopy and with higher flow. Body shape showed a mixture of parallel and independent population divergence. The strongest and most consistent effects were (1) high‐predation sites had males with smaller heads and deeper caudal peduncles, (2) open‐canopy sites had females with smaller heads and more distended abdomens and (3) high‐flow sites had males and females with smaller heads and deeper caudal peduncles.     

Prey selectivities of threespine sticklebacks (Gasterosteus aculeatus) and phantom midge larvae (Chaoborus spp.) in Newfoundland lakes

SUMMARY. 1. Threespine stickleback ( Gasterosteus aculeatus ) and Chaoborus ( C. punctipennis and C. trivittatus ) planktivore populations were sampled from several oligotrophic lakes on the Avalon Peninsula of Newfoundland, Canada. Pelagic zooplankton communities in these lakes consist of Daphnia catawba, Holopedium gibberum, Eubosmina longispina, Leptodiaptorma minutus, Epischura nordenskioldi, Cyclops scutifer and rotifers ( Conochilus unicornis, Keratella and Kellicottia spp.).
2. Comparison of gut contents of G. aculeatus and crop contents of later instar Chaoborus larvae with lake zooplankton communities indicated that the vertebrate and invertebrate plank tivores show contrasting species and size selectivities in their choice of zooplankton prey. Prey selectivities were quantified by means of the selectivity index α.
3. G. aculeatus showed positive selectivity for larger zooplankton (greater than 0.76 mm in length), typically the cladoceran D. catawba , while Chaoborus larvae showed positive selectivity for smaller zooplankton (less than 0.50 mm in length), typically the cladoceran E. longispina . While rotifers never featured in the diet of the sticklebacks, these zooplankters were a common component of the chaoborid diet. H. gibberum , with its gelatinous sheath, was rarely found in the gut contents of G. aculeatus and was never found in the crop contents of Chaoborus larvae.
4. Selective predation by these planklivores in the relatively shallow and well-mixed oligotrophic Avalon lakes may influence species composition and size structure of the pelagic zooplankton communities.     

Life-history consequences of predation for a subantarctic beetle: evaluating the contribution of direct and indirect effects

1. Recently, a small predatory beetle, Trechisibus antarcticus (Carabidae), was accidentally introduced onto the island of South Georgia, sub-Antarctic.
2. From the presumed site of introduction the beetle is invading the coastal lowland area, building up high densities locally in the tussock-forming grass Parodiochloa flabellata .
3. In the coastal area the endemic detritivorous/herbivorous beetle Hydromedion sparsutum (Perimylopidae) is common, especially in and beneath the tussocks.
4. The first three, out of six, larval instars of H. sparsutum are easily taken prey by the carabid.
5. In sites colonized by the carabid, total abundance and the ratio between larval and adult numbers of H. sparsutum are far lower, and its adult body size clearly larger, than in comparable sites where the carabid is absent.
6. Two hypotheses are proposed for explaining the increase in adult body size of H. sparsutum : (i) the increase is a direct effect of predation: selection by the predator favours large hatchlings and/or larvae with a high growth rate; and (ii) the increase is an indirect effect of predation: by lowering the density of H. sparsutum , predation has increased its per capita food supply, enabling a higher growth rate and a larger adult body size.
7. A food addition experiment in a carabid-free site showed availability of high quality food to be insufficient for sustaining the initial larval population.
8. In the laboratory, females from the predator-infested sites produced larger eggs and hatchlings than females from the carabid-free sites, but mass specific growth rates of the larvae were not higher.
9. Field and laboratory data give stronger support to the food hypothesis than to the size selectivity hypothesis.     

Feeding selectivity of four species of sympatric stickleback in brackish-water habitats in eastern Canada

Although sympatric populations of sticklebacks occur commonly along the north-eastern coast of North America, very few studies have considered the interspecific relationships within such populations. This paper investigates prey selectivity, feeding behaviour and potential prey availability within sympatric populations from five brackish-water sites in New Brunswick. Differences between the diets of species from different sites were related to differences in the range of prey available. Fish collected from sites with abundant aquatic vegetation consumed greater numbers of prey than those from vegetation-poor sites. The proportions of prey types eaten by both adults and juveniles reflected prey species abundance at the different sites; thus shifts in diet over time were found to be related to changes in the abundance of potential prey and not to shifts in prey preference on the part of the fish. The size of prey consumed was related to mouth size; adult and juvenile Gasterosteus wheatlandi , having the smallest mouths, consumed the smallest prey. Differences in prey size detected in the four species studied were due to differences in the types of prey consumed. Laboratory experiments on feeding behaviour showed that adult Apeltes quadracus and Pungitius pungitius were more efficient at capturing benthic prey than were Gasterosteus aculeatus and G. wheatlandi. Competition for food is thought not to occur in these populations, because of the abundance of potential prey and the morphological constraints on feeding behaviour.     

Differences in morphology, performance and behaviour between recently diverged populations of Podarcis sicula mirror differences in predation pressure

We investigated the possible role of variation in predation pressure in the phenotypic divergence of two island populations of the Italian wall lizard, Podarcis sicula . In 1971, ten adult specimens from the island of Pod Kopište (Adriatic Sea, Croatia) were transported to the island of Pod Mrčaru, 3.5 km east, where they founded a new population. Although the two islands resemble each other in general physiognomy (size, elevation, microclimate) and in the absence of terrestrial predators, lizards from the newly established population are now on average larger and have shorter hind limbs. They also exhibit lower maximal sprint speed as measured on a racetrack, and fatigue faster when chased in a torus track. In the field, lizards from the original population of Pod Kopište respond to a simulated predatory attack by fleeing at larger approach distances and by running further from the predator than lizards from Pod Mrčaru. These changes in morphology, behaviour and performance may result from the relaxed predation intensity on the latter island. Our analysis of the structural features of the microhabitats suggests that the vegetation on Pod Mrčaru offers more protection to lizards. Also, plasticine models of lizards, laid out on the islands, less often exhibited signs of being attacked by birds on Pod Mrčaru than on Pod Kopište. Our findings provide an example of how changes in (possibly a single) environmental factor may simultaneously produce responses in behaviour, morphology and whole-animal physiology, and this on a surprisingly small spatial and temporal scale.     

The contribution of abiotic and biotic factors to spatial and temporal variation in population density of the least killifish, Heterandria formosa

We report the results of a long-term examination of variation in adult density in the least killifish, Heterandria formosa, and the associations among adult density and a variety of ecological factors. We used data from 11 populations of H. formosa in Northwest Florida, collected between 2000 and 2010, to examine the relationships among temporal and spatial variation in adult density and (1) the composition of the aquatic fauna community among habitats (springs, ponds, and tidal marshes) where H. formosa are found, (2) an index of predation pressure and (3) the sampling season, distance from shore (cm), water depth (cm), and aquatic vegetation cover (%) in throw traps at each sampling event. We found clear evidence that adult densities of H. formosa vary widely but consistently among populations, with greater spatial variation than temporal variation in density estimates. Site identity explained most of the variation in density among populations, and there was no long-term consistent association of variation in density with different habitats; sites of the same habitat type were as likely to have characteristically different densities as were sites of different habitat types. Average adult densities of H. formosa increased as aquatic vegetation cover increased and as the index of predation pressure decreased, however assemblage structure was not a strong predictor of density. These results show that despite marked community, abiotic and biotic distinctions between habitat types, location-specific variation was the predominant signal in these data.     

10 000 years later: evolution of body shape in Haida Gwaii three-spined stickleback

The body shape of 1303 adult male three-spined stickleback Gasterosteus aculeatus from 118 populations on Haida Gwaii archipelago off the mid-coast of British Columbia was investigated using discriminant function analysis on partial warp scores generated from 12 homologous landmarks on a digital image of each fish. Results demonstrated geographical differences in adult body shape that could be predicted by both abiotic and biotic factors of the habitat. Populations with derived shape (CV1−), including thick peduncles, posterior and closely spaced dorsal spines, anterior pelvis, small dorsal and anal fins, were found in small, shallow, stained ponds, and populations with less derived shape (CV1+), with small narrow peduncles, anterior and widely spaced dorsal spines, posterior pelvis, large dorsal and anal fins were found in large, deep, clear lakes. This relationship was replicated between geographic regions; divergent mtDNA haplotypes in lowland populations; between predation regimes throughout the archipelago, and in each geographical region and between predation regimes in lowland populations monomorphic for the Euro and North American mtDNA haplotype. There were large-bodied populations with derived shape (CV2−), including small heads and shallow elongate bodies in open water habitats of low productivity, and populations with smaller size and less derived shape (CV2+), with large heads and deeper bodies in higher productivity, structurally complex habitats. This relationship was replicated between geographic regions, and partially between divergent mtDNA haplotypes in lowland populations. Field tests for phenotypic plasticity of body shape suggest that <10% of the total variation in body shape among populations throughout the archipelago can be attributed to plasticity.     

The influence of predation on horizontal distribution of zooplankton species

SUMMARY. 1. The horizontal distributions of Daphnia longispina and Bosmina tongispina in Lake Kvernavatn (Norway) were investigated twice in 1982. In late spring, when populations were small, the two species inhabited the same areas, and they were evenly distributed from the littoral to the pelagic. At high population densities, during midsummer, the species were spatially segregated, D. longispina being pelagic and B. longispina littoral in distribution.
2. The distribution and feeding of three-spined sticklebacks (Gasteros-teus aculeatus) were also studied. The sticklebacks were apparently forced into littoral areas by larger piscivorous predators in the pelagic and they were consequently restricted to foraging primarily on B. longispina, which formed dense swarms during daytime in summer.
3. We suggest that predation and competition influence the spatial distribution of zooplankton species. The feeding efficiency of fish foraging on high-density zooplankton populations can be reduced by spatial segregation of zooplankton species. Where high local densities occur, due to swarm formation, predation is changed from size-selective feeding to consumption of spatially isolated individuals.