R. J. Wootton

Appetite and growth compensation in the European minnow,Phoxinus phoxinus (Cyprinidae), following short periods of food restriction

SynopsisChanges in the daily appetite and weekly growth rates of individual adult minnows,Phoxinus phoxinus, on ad libitum rations were recorded before and after they had experienced 4 or 16 days of food restriction. Feeding levels during the restriction periods were either starvation or a maintenance ration. The latter was estimated from a previously determined regression model. Water temperature was 15°C and the photoperiod 9L15D in all experiments. The mean weight of fish used ranged from 1.06 to 2.15 g. The 4 day restriction had no detectable effects on appetite or growth. After the 16 day restriction, the minnows showed hyperphagia and had increased specific growth rates and growth efficiencies compared with control fish. The compensatory increases in appetite and growth were not sustained and within three weeks had declined to levels not significantly different from those of the control fish. At the end of the experiments, there were no significant differences between the mean weights or cumulative food consumption of the restricted and control groups. The results suggest that adult minnows regulate their appetite and growth rate in relation to their previous nutritional history.

The costs of parental care in teleost fishes

Introduction Definitions Parental care in teleost fishes Parental investment in teleost fishes Cost to survival Cost to batch fecundity Cost to breeding frequency Tactics to reduce parental costs Mate desertion and bigamy Brood cannibalism and abandonment Brood mixing Reducing the level of care Reducing energy expenditure Using camouflage Using helpers Costs and the evolution of parental care Summary Acknowledgements References

Constraints in the Evolution of Fish Life Histories

Species and populations of species are viewed as occupying positions in a multi-variate space whose dimensions are defined by life history traits. Some constraints that limit which positions can be occupied are reviewed: they include physical, allometric, physiological, demographic and genetic constraints. The need for good-quality data on life history traits and the physiological mechanisms that lie behind the traits is emphasized.

Growth and energetics in the stickleback-Schistocephalus host-parasite system: a review of experimental infection studies

Summary Three-spined sticklebacks in natural lacustrine populations are often infected with plerocercoids of the indirectly transmitted pseudophyllidean cestode Schistocephalus solidus. Field studies typically show infections to be associated with reduced host condition, gonadogenesis and energy reserves, though infection phenotypes can vary considerably both between and within host populations. Experimental infection studies allow the impact of infections on hosts to be studied under a variety of rearing conditions, and so can be used to determine the environmental component of infection phenotypes. Here, we review recent laboratory studies undertaken by our group, examining the growth and condition of experimentally infected fish reared under conditions that differed in terms of absolute ration, temporal pattern of feeding and level of competition between fish. We compare infection phenotypes generated in our experimental studies with those of fish sampled in field based studies. Experimental studies in which infected fish were reared under competition for limited food resources, or were fed a restricted diet, generated infection phenotypes that most closely resembled those found in the majority of natural populations. When access to food was unrestricted, however, infected fish were able to sustain high growth rates and lay down energy reserves. If experimental studies are to be used to understand the impact of infection under natural conditions, husbandry protocols that closely match field conditions must be designed. We suggest that a full understanding of the impact of parasites on their hosts can only be gained by integrating controlled laboratory experiments with detailed field studies. The stickleback‐Schistocephalus system is ideally suited to examining these questions, and we provide several suggestions for future research.

Variation in the Mating System of a Biparental Cichlid Fish, Cichlasoma Panamense

Cichlasoma panamense is a biparental, substrate-spawning cichlid which breeds during the dry season in Panamanian streams. In one population some males helped to defend their offspring throughout the period of parental care but many deserted their mates to achieve additional spawnings leaving females to guard alone. The proportion of C. panamense guarding in pairs increased throughout the breeding season. This was associated with an increase in the rate with which parental cichlids attacked potential brood predators and an increase in brood size. The increase in attack rate was due to the crowding of fishes as water levels receded during the dry season and especially to the increasing numbers of newly independent cichlids which congregated in the shallow water areas where C. panamense brood. The sex ratio in the population was strongly biased towards females. Males spent more time away from the brood than females which enabled them to find and spawn with unmated females. The attack rate of females brooding alone was not significantly higher than that of those with mates and their foraging rate not significantly lower although they spent less time away from their brood. In a more productive stream where population density was high, breeding was almost entirely in monogamous pairs. The rate at which parents attacked potential predators was higher, the sex ratio was 1:1 and brood size was large. The males decision to guard or desert appears to depend on his opportunities for further matings, the ability of the female to guard alone and the value of a current brood. These results agree with the predictions of game theory models of parental care.

The Darwinian stickleback Gasterosteus aculeatus: a history of evolutionary studies.

The history of studies on the taxonomy and evolutionary biology of the three-spined stickleback Gasterosteus aculeatus from the 18th century to the present is reviewed. After the publication of Darwins Origin of the Species, four important dates, 1925, 1947, 1967 and 2001, are identified as marking major gains in the understanding of the evolution of the diversity in morphological, life-history, physiological and behavioural traits that characterizes G. aculeatus. The period 1925-1970 led to the identification of the main themes of research: status and adaptive significance of lateral-plate morphs; inter and intrapopulation trait variation in freshwater resident G. aculeatus and the adaptive significance of the variation. Between 1970 and 2001, these themes were investigated using variation observed particularly along the Pacific coast of the U.S.A. and Canada, notably in the Cook Inlet region of Alaska and the Haida Gwaii Archipelago. Studies on adaptive radiation and reproductive isolation in lacustrine, ecomorph pairs (limnetics and benthics) discovered in the Strait of Georgia region have been particularly productive. From 2001, the application of genomic studies to these problems began to open up the study of the relationships between genotype, phenotype and selective advantage to causal analysis.

Ecological causes of morphological evolution in the three-spined stickleback

The central assumption of evolutionary theory is that natural selection drives the adaptation of populations to local environmental conditions, resulting in the evolution of adaptive phenotypes. The three-spined stickleback (Gasterosteus aculeatus) displays remarkable phenotypic variation, offering an unusually tractable model for understanding the ecological mechanisms underpinning adaptive evolutionary change. Using populations on North Uist, Scotland we investigated the role of predation pressure and calcium limitation on the adaptive evolution of stickleback morphology and behavior. Dissolved calcium was a significant predictor of plate and spine morph, while predator abundance was not. Stickleback latency to emerge from a refuge varied with morph, with populations with highly reduced plates and spines and high predation risk less bold. Our findings support strong directional selection in three-spined stickleback evolution, driven by multiple selective agents.

Effects of Food and Density On the Reproductive Biology of the Threespine Stickleback With a Hypothesis On Population Limitation in Sticklebacks

Changes in the abundance of a stickleback population over a decade are described. A review of the experimental evidence suggests that, in principle, changes in the reproductive output of males and females in response to changes in food supply and fish density could account for the changes in abundance.

A LONG-TERM STUDY OF A SHORT-LIVED FISH: THE DEMOGRAPHY OF GASTEROSTEUS ACULEATUS

(1) We present the results of the first long-term investigation on the demography of a population of three-spined sticklebacks. This study describes the changes in the abundance of a population from a backwater of the Afon Rheidol in mid-Wales, based on mark-recapture data collected in October of each year from 1972 until 1998. (2) The population showed quasi-cyclical changes in abundance around a trend line with a period of approximately 6 years. Over the duration of the study there was a tendency for the population to decline. During the unusually dry summers of 1976, 1983, 1984 and 1989 the population was either at a minimum size or was below the estimated trend line. Estimates of stickleback densities varied between 7-28 m -2 . (3) Analysis of length-frequency data showed there were two cohorts present. These were assumed to represent two age classes, 0+ and 1+, with the population consisting largely of the 0+ class. Thus the population was essentially annual. (4) There was evidence of density-dependent mortality and growth of 0+ sticklebacks during and shortly after the spawning period.

Calcium and salinity as selective factors in plate morph evolution of the three‐spined stickleback (Gasterosteus aculeatus)

Identifying the causal factors underlying natural selection remains a key challenge in evolutionary biology. Although the genetic basis for the plate morph evolution of three‐spined stickleback (Gasterosteus aculeatus) is well described, the environmental variables that form the basis for different morphs are not understood. We measured the effects of dissolved calcium and salinity on the growth of sticklebacks with different plate morphs from Scotland and Poland. There was a significant interaction of calcium with plate morph for fish from both regions, with complete morph sticklebacks growing more slowly at low calcium concentrations and low morph sticklebacks showing divergent responses to calcium concentration. A Scottish anadromous population showed evidence of local adaptation to high salinity, which was independent of plate morph. Polish and Scottish populations diverged in their response to salinity, suggesting a difference in osmotic regulation. The results implicate a role for calcium in selecting for plate morph evolution in sticklebacks, possibly as a limiting element in skeletal growth.