Kleptoparasitic prey competition in shoaling fish: effects of familiarity and prey distribution

Familiarity is thought to stabilize dominance hierarchies andreduce aggressive interactions within groups of socially livinganimals. Though familiarity has been widely studied in shoalingfish, few studies have investigated changes in prey competitionas a function of time spent together within groups of initiallyunfamiliar individuals. In this study, we created shoals ofthree-spined stickleback (Gasterosteus aculeatus) and monitoredchanges in foraging rates and related competitive behaviorswithin shoals over a 4-week period in experimental series whereprey was spatially and temporally concentrated or dispersed.Prey share was unequal under both prey distribution modes, anddisparity in prey share was not seen to change as trials progressed.Interestingly, the contest rate for prey items fell over timewhen individuals were competing for dispersed prey but not whenprey were concentrated. We found no evidence that fish showedassociation preferences for either group members that had consumeda greater or lesser proportion of prey during trials. Thoughthe intensity of competition may be reduced by increased groupstability in nature, this is likely to be strongly dependenton the way prey resources are distributed through space andtime.     

Impacts of elevated terrestrial nutrient loads and temperature on pelagic food‐web efficiency and fish production

Both temperature and terrestrial organic matter have strong impacts on aquatic food‐web dynamics and production. Temperature affects vital rates of all organisms, and terrestrial organic matter can act both as an energy source for lower trophic levels, while simultaneously reducing light availability for autotrophic production. As climate change predictions for the Baltic Sea and elsewhere suggest increases in both terrestrial matter runoff and increases in temperature, we studied the effects on pelagic food‐web dynamics and food‐web efficiency in a plausible future scenario with respect to these abiotic variables in a large‐scale mesocosm experiment. Total basal (phytoplankton plus bacterial) production was slightly reduced when only increasing temperatures, but was otherwise similar across all other treatments. Separate increases in nutrient loads and temperature decreased the ratio of autotrophic:heterotrophic production, but the combined treatment of elevated temperature and terrestrial nutrient loads increased both fish production and food‐web efficiency. CDOM: Chl a ratios strongly indicated that terrestrial and not autotrophic carbon was the main energy source in these food webs and our results also showed that zooplankton biomass was positively correlated with increased bacterial production. Concomitantly, biomass of the dominant calanoid copepod Acartia sp. increased as an effect of increased temperature. As the combined effects of increased temperature and terrestrial organic nutrient loads were required to increase zooplankton abundance and fish production, conclusions about effects of climate change on food‐web dynamics and fish production must be based on realistic combinations of several abiotic factors. Moreover, our results question established notions on the net inefficiency of heterotrophic carbon transfer to the top of the food web.     

Comparison of the prolonged swimming performances of closely related, morphologically distinct three‐spined sticklebacks Gasterosteus spp.

Prolonged swimming performances of two as yet unnamed species of three‐spined stickleback, Gasterosteus spp., were compared. The two fishes (not yet formally described, referred to here as benthic and limnetic) inhabit different niches within Paxton Lake, Texada Island, British Columbia, Canada, and are recent, morphologically distinct species. Limnetics had longer endurance during prolonged swimming than did benthics. The mean regression of the log₁₀ of fatigue time (F_t, s) on swimming speed (U, standard length, L_S s^?1) for limnetics (log₁₀F_t = 7·03 ? 0·46U) had a similar slope, but a significantly higher intercept than that for benthics (log₁₀F_t = 5·55 ? 0·43U). Adult benthics were larger, heavier and deeper‐bodied fish than limnetics. Limnetics, however, had a significantly greater pectoral fin edge:base ratio (mean ± s .e .: limnetics, 4·58 ± 0·43; benthics, 3·63 ± 0·27). In addition, limnetics had significantly lower drag coefficients (C_D) than benthics (limnetics, log₁₀C_D = ?0·49log₁₀R_e + 0·66; benthics, log₁₀C_D = ?0·26log₁₀R_e ? 0·30) where R_e is the Reynolds number [(L_SU (ν^?1), where U and ν are swimming velocity and the kinematic viscosity of the water, respectively]. Compared to their ancestral form, the anadromous three‐spined stickleback Gasterosteus aculeatus L., limnetics and benthics had significantly longer and shorter endurance times, respectively. In addition, both these fishes had significantly higher fast‐start velocities than their ancestral form. Selection due to differential resource use may have lead to divergence of body form, and, therefore, of steady swimming performance. Therefore predation may be the selective force for the similar high escape performance in these two fishes.     

The ecology of an adaptive radiation of three‐spined stickleback from North Uist,Scotland

There has been a large focus on the genetics of traits involved in adaptation, but knowledge of the environmental variables leading to adaptive changes is surprisingly poor. Combined use of environmental data with morphological and genomic data should allow us to understand the extent to which patterns of phenotypic and genetic diversity within a species can be explained by the structure of the environment. Here, we analyse the variation of populations of three‐spined stickleback from 27 freshwater lakes on North Uist, Scotland, that vary greatly in their environment, to understand how environmental and genetic constraints contribute to phenotypic divergence. We collected 35 individuals per population and 30 abiotic and biotic environmental parameters to characterize variation across lakes and analyse phenotype–environment associations. Additionally, we used RAD sequencing to estimate the genetic relationships among a subset of these populations. We found a large amount of phenotypic variation among populations, most prominently in armour and spine traits. Despite large variation in the abiotic environment, namely in ion composition, depth and dissolved organic Carbon, more phenotypic variation was explained by the biotic variables (presence of predators and density of predator and competitors), than by associated abiotic variables. Genetic structure among populations was partly geographic, with closer populations being more similar. Altogether, our results suggest that differences in body shape among stickleback populations are the result of both canalized genetic and plastic responses to environmental factors, which shape fish morphology in a predictable direction regardless of their genetic starting point.     

The confusion effect from neural networks to reduced predation risk

The confusion effect is often cited as an antipredatory benefitof group living and has been demonstrated by numerous studiesacross a range of taxa. However, there have been relativelyfew studies examining the mechanisms behind the effect and noexperimental test of its supposed theoretical basis (informationdegradation in neural networks) using a natural predator–preypairing. In agreement with other studies, we demonstrate thatattack success of the three-spined stickleback (Gasterosteusaculeatus L.) is reduced by an increase in Daphnia magna groupsize. Neural network models attempt to explain this trend withmultiple prey inducing poor neural mapping of target prey, thusleading to an increase in the spatial error of each attack.We explicitly tested this prediction and demonstrate that thedecrease in attack success by sticklebacks does correspond toan increase in spatial targeting error with larger prey groupsize. Finally, we show that the number of targets, rather thanthe density or area occupied by the group, has the greatesteffect on reducing the rate of attack. These results are discussedin the context of the information processing constraints ofpredators, the ultimate cause of the confusion effect.     

Along the speciation continuum in sticklebacks

Speciation can be viewed as a continuum, potentially divisible into several states: (1) continuous variation within panmictic populations, (2) partially discontinuous variation with minor reproductive isolation, (3) strongly discontinuous variation with strong but reversible reproductive isolation and (4) complete and irreversible reproductive isolation. Research on sticklebacks (Gasterosteidae) reveals factors that influence progress back and forth along this continuum, as well as transitions between the states. Most populations exist in state 1, even though some of these show evidence of disruptive selection and positive assortative mating. Transitions to state 2 seem to usually involve strong divergent selection coupled with at least a bit of geographic separation, such as parapatry (e.g. lake and stream pairs and mud and lava pairs) or allopatry (e.g. different lakes). Transitions to state 3 can occur when allopatric or parapatric populations that evolved under strong divergent selection come into secondary contact (most obviously the sympatric benthic and limnetic pairs), but might also occur between populations that remained in parapatry or allopatry. Transitions to state 4 might be decoupled from these selective processes, because the known situations of complete, or nearly complete, reproductive isolation (Japan Sea and Pacific Ocean pair and the recognized gasterosteid species) are always associated with chromosomal rearrangements and environment‐independent genetic incompatibilities. Research on sticklebacks has thus revealed complex and shifting interactions between selection, adaptation, mutation and geography during the course of speciation.     

Three‐spined sticklebacks Gasterosteus aculeatus as a model for exploring behavioural biology

Niko Tinbergen chose the three‐spined stickleback Gasterosteus aculeatus for his classic behavioural studies because they are small, robust, common and easy to house in the laboratory under reasonably natural conditions and also because their behaviour, while sufficiently simple to be tractable, is still sufficiently complex to be interesting. An analysis of citation records shows that this was an inspired choice. Research on these small fish has addressed all four of Tinbergen's famous questions (causation, development, functions and evolution) and has contributed to the understanding of many different behavioural systems. The G. aculeatus literature is used here to explore several themes in fundamental behavioural biology (diet choice, shoaling, behavioural syndromes and sexual signalling) and the extent to which research using G. aculeatus has informed both fundamental and applied behavioural biology, the latter in the context of aquaculture research.