Experience of natural prey and feeding efficiency in three-spined sticklebacks (Gasterosteus aculeatus L.)

The possibility that efficiency of feeding on different prey in three-spined sticklebacks ( Gasterosteus aculeatus L.) increases by experience of such items was investigated experimentally by comparing sticklebacks reared with only non-moving prey (frozen brine shrimps) with sticklebacks caught in the wild from localities where a wide range of prey species was available. Fish without experience of natural food scored less well than those from the wild on various components of foraging and so had reduced feeding efficiency. However, feeding efficiency in naive fish improved after just a few days of experience with natural prey. Such experience-induced changes in foraging efficiency will alter the profitability of prey items for individual fish.     

Female mate choice and male red coloration in a natural three-spined stickleback (Gasterosteus aculeatus) population

Under laboratory conditions, female three-spined sticklebacks(Gasterosteus aculeatus L.) show a mating preference for intenselyred-colored males. We verified this female choice in the fieldby observing a freshwater stickleback population in its naturalhabitat. During the egg collection phase, individual courtingmales were localized with the aid of a dummy of a ripe female,caught and photographed under standardized conditions, and released.After males had stopped collecting eggs, we counted the numberof eggs in the nests. The more intense a male's red breedingcoloration, the more eggs he received. Simultaneous female choiceexperiments in the laboratory suggested that ripe females ofthis population preferred redder males. Breeding activitiesof the males in the field were clustered and seem to be synchronizedwithin clusters. At one of the breeding sites, more intensered males were in better physical condition, but this was notthe case at another site. Although several synchronized breedingcycles were observed, the majority of males seem to completeonly one breeding cycle.     

ADAPTIVE RADIATION ALONG GENETIC LINES OF LEAST RESISTANCE

Are measurements of quantitative genetic variation useful for predicting long-term adaptive evolution? To answer this question, I focus on g_max, the multivariate direction of greatest additive genetic variance within populations. Original data on threespine sticklebacks, together with published genetic measurements from other vertebrates, show that morphological differentiation between species has been biased in the direction of g_max for at least four million years, despite evidence that natural selection is the cause of differentiation. This bias toward the direction of evolution tends to decay with time. Rate of morphological divergence between species is inversely proportional to θ, the angle between the direction of divergence and the direction of greatest genetic variation. The direction of greatest phenotypic variance is not identical with g_max, but for these data is nearly as successful at predicting the direction of species divergence. I interpret the findings to mean that genetic variances and covariances constrain adaptive change in quantitative traits for reasonably long spans of time. An alternative hypothesis, however, cannot be ruled out: that morphological differentiation is biased in the direction g_max because divergence and g_max are both shaped by the same natural selection pressures. Either way, the results reveal that adaptive differentiation occurs principally along “genetic lines of least resistance.”     

Parasitism, oddity and the mechanism of shoal choice

When choosing between shoals differing in Schistocephalus solidus infection status, uninfected test sticklebacks Gasterosteus aculeatus showed a preference for joining uninfected conspecifics when shoal sizes were equal, but reversed this preference when the relative size of the infected shoal was increased by a factor of 3. When given a choice between a shoal composed of size-matched minnows Phoxinus phoxinus and a shoal composed of the same number of all uninfected or all S. solidus -infected sticklebacks, test fish always preferred the sticklebacks, regardless of their infection status, over the minnow shoal. These observations suggest that species, parasite status and shoal size are all of importance when fish decide which shoal to join.     

Association between integration structure and functional evolution in the opercular four‐bar apparatus of the threespine stickleback,Gasterosteus aculeatus (Pisces: Gasterosteidae)

Phenotypes may evolve to become integrated in response to functional demands. Once evolved, integrated phenotypes, often modular, can also influence the trajectory of subsequent responses to selection. Clearly, connecting modularity and functionally adaptive evolution has been challenging. The teleost skull and jaw structures are useful for understanding this connection because of the key roles that these structures play in feeding in novel environments with different prey resources. In the present study, we examined such a structure in the threespine stickleback: the opercular four‐bar lever that functions in jaw opening. Comparing oceanic and two fresh‐water populations, we find marked phenotypic divergence in the skull opercular region, and the major axes of morphological and functional variation of the lever are found to be highly correlated. All three populations share the same global skull integration structure, and a conserved, strongly‐supported modular organization is evident in the region encompassing the lever. Importantly, a boundary between two modules that subdivides the lever apparatus corresponds to the region of most prominent morphological evolution. The matched modular phenotypic and functional architecture of head and jaw structures of stickleback therefore may be important for facilitating their rapid adaptive transitions between highly divergent habitats. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 375–390.     

SEX DIFFERENCES IN MATE RECOGNITION AND CONSPECIFIC PREFERENCE IN SPECIES WITH MUTUAL MATE CHOICE

Sexual isolation is often assumed to arise because choosy females recognize and reject heterospecific males as mates. Yet in taxa in which both males and females are choosy, males might also recognize and reject heterospecific females. Here, we asked about the relative contribution of the sexes to the strong sexual isolation found in limnetic–benthic species pairs of threespine sticklebacks, which show mutual mate choice. We asked whether males and females of the two species recognize conspecifics and also prefer to mate with them. We found evidence for mate recognition by both sexes but only females prefer conspecifics. The nature of male courtship depended on which species of female they were courting, indicating that males recognized conspecific females and differentiated them from heterospecifics. However, males courted both species of females with equal vigor and changed courtship in a manner that would increase the chance of mating with heterospecifics. Females both recognized conspecifics and strongly preferred them. They responded very little to heterospecific male courtship and almost never mated with them. Therefore, males are likely to undermine sexual isolation, but females uphold it. Despite mutual mate choice and mate recognition in both sexes, females are primarily responsible for sexual isolation in these taxa.     

The ontogeny of predatory mechanisms in the fifteen-spined stickleback, Spinachia spinachia (L.)

Predatory behaviour is similar in juvenile and adult fifteen-spined sticklebacks. Despite achieving velocities up to 20.2 times faster than the prey, juvenile fish do not employ low-energy attacks. This contrasts with adults which adjust predatory behaviour according to prey-type, but may be a result of the unpredictable prey escape response.     

Fathead minnows avoid conspedfic and heterospedfic alarm pheromones in the faeces of northern pike

Groups of fathead minnows Pimephales promelas were tested to determine if they avoided areas of a test tank labelled with the faeces of a predator (northern pike, Esox lucius ) which had recently been fed minnows, brook sticklebacks Culaea inconstans , or swordtails Xiphophorus helleri. Minnows exhibited a fright reaction upon presentation of sponges labelled with faeces, when the pike had consumed minnows or sticklebacks, but not swordtails (which lack alarm pheromones). The fright reaction was characterized by increased shoal cohesiveness and increased dashing and freezing behaviour. Minnows avoided the area of the tank containing the faeces from pike on diets of minnows or sticklebacks, but not from pike fed a diet of swordtails. These data demonstrate that: (1) minnows actively avoid the faeces of pike fed minnows or brook sticklebacks, and (2) minnows exhibit a fright reaction to the faeces of a pike fed brook sticklebacks.     

Physiological effects in juvenile three-spined sticklebacks feeding on toxic cyanobacterium Nodularia spumigena-exposed zooplankton

Feeding rate, growth and nutritional condition as well as nodularin concentration of juvenile three-spined sticklebacks Gasterosteus aculeatus were assessed in an experimental study where field-collected fish were given a diet of zooplankton fed with toxic Nodularia spumigena for 15 days. Food consumption was higher in N. spumigena bloom conditions compared with the cyanobacterium-free control, but despite this the growth rate of exposed fish did not improve. Control fish and fish fed N. spumigena -exposed zooplankton had higher RNA:DNA ratios and protein content than fish grown in cyanobacterial bloom conditions indicating good nutritional condition and recent growth of fish, whereas in bloom conditions metabolic transformation of nodularin to less toxic compounds may cause an energetic cost to the fish affecting the growth rate of the whole organism. Juvenile three-spined sticklebacks collected from the field contained higher concentrations of nodularin at the beginning of the experiment (mean 503·1 μg kg⁻¹). After 15 days, the lowest nodularin concentrations in fish were measured in the control treatment, suggesting that fish fed with non-toxic food are able to detoxify nodularin from their tissues more effectively than fish in continuing exposure.