How feeding performance and energy intake change with a small increase in the body size of the three-spined stickleback

Changes in the foraging behaviour due to variation in the body size of the three-spined stickleback Gasterosteus aculeatus were investigated. All sizes of fish had a high probability of attacking prey whenever encountered. The probability of eating the prey increased with the size of the fish, as the larger fish had larger jaws and a greater stomach capacity. Therefore, as fish increased in size there was an increase in the probability of successful prey capture. The level of satiation did not have an effect on the prey handling time, which is contrary to other studies and is probably a result of the large prey sizes. The physical size of the prey meant that the handling times were long regardless of the motivational level of the fish. The larger fish took in more energy and at a faster rate, although the time to reach satiation was similar for all fish sizes. The advantage that large fish appear to have in successfully gaining large prey is negated by their greater metabolic requirement. The changes in feeding performance induced by small increases in body size could have important consequences for intraspecific competition, habitat Use and risk of predation.     

EVOLUTIONARY LOSS OF LARVAL FEEDING: DEVELOPMENT,FORM AND FUNCTION IN A FACULTATIVELY FEEDING LARVA,BRISASTER LATIFRONS

Species with large eggs and nonfeeding larvae have evolved many times from ancestors with smaller eggs and feeding larvae in numerous groups of aquatic invertebrates and amphibians. This change in reproductive allocation and larval form is often accompanied by dramatic changes in development. Little is known of this transformation because the intermediate form (a facultatively feeding larva) is rare. Knowledge of facultatively feeding larvae may help explain the conditions under which nonfeeding larvae evolve. Two hypotheses concerning the evolutionary loss of larval feeding are as follows: (1) large eggs evolve before modifications in larval development, and (2) the intermediate form (facultatively feeding larva) is evolutionarily short-lived. I show that larvae of a heart urchin, Brisaster latifrons, are capable of feeding but do not require food to complete larval development. Food for larvae appears to have little effect on larval growth and development. The development, form, and suspension feeding mechanism of these larvae are similar to those of obligate-feeding larvae of other echinoids. Feeding rates of Brisaster larvae are similar to cooccurring, obligate-feeding echinoid larvae but are low relative to the large size of Brisaster larvae. The comparison shows that in Brisaster large egg size, independence from larval food, and relatively low feeding rate have evolved before the heterochronies and modified developmental mechanisms common in nonfeeding echinoid larvae. If it is general, the result suggests that hypotheses concerning the origin of nonfeeding larval development should be based on ecological factors that affect natural selection for large eggs, rather than on the evolution of heterochronies and developmental novelties in particular clades. I also discuss alternative hypotheses concerning the evolutionary persistence of facultative larval feeding as a reproductive strategy. These hypotheses could be tested against a phylogenetic hypothesis.     

FECAL METHANOGENS AND VERTEBRATE EVOLUTION

It has been assumed that the feeding habits of vertebrates predispose the variety of intestinal differentiations and the composition of the microbial biota living in their intestinal tracts. Consequently, the presence of methanogenic bacteria in the various differentiations of the large intestine and the foregut of herbivorous vertebrates had been attributed primarily to the existence of anaerobic habitats and the availability of carbon dioxide and hydrogen originating from the fermentative microbial digestion of plant-based diets. However, Australian ratites, many murids, and several New World primates lack methanogens, despite their intestinal differentiations and their vegetarian feeding habits. Crocodiles, giant snakes, aardvarks, and ant-eaters on the other hand release significant amounts of methane. A determination of methane emissions by 253 vertebrate species confirmed that competence for intestinal methanogenic bacteria is shared by related species and higher taxa, irrespective of different feeding habits. In “methanogenic” branches of the evolutionary tree, a variety of differentiations of the large intestine evolved and, in some cases, differentiations of the foregut. In contrast, the lack of competence for methanogens in chiropterans/insectivores and carnivores apparently has precluded the evolution of specialized fermenting differentiations of the digestive tract. Our observations reveal that the presence of intestinal methanogenic bacteria is under phylogenetic rather than dietary control: competence for intestinal methanogenic bacteria is a plesiomorphic (primitive-shared) character among reptiles, birds, and mammals. This competence for methanogenic bacteria has been crucial for the evolution of the amniotes.     

Antixenotic resistance of subterranean clover cotyledons to redlegged earth mite, Halotydeus destructor

The short-term response of redlegged earth mite, Halotydeus destructor (Tucker) (Acarina: Penthaleidae) to cotyledons of different varieties of subterranean clover (Trifolium subterraneum subsp. subterraneum L.) was assessed by means of paired choice tests, and no-choice tests. H. destructor had lower numbers and fed less on detached cotyledons of resistant than susceptible varieties, yielding a correlation between the numbers of mites and feeding damage to the cotyledons during a three hour test period. For a number of resistant and susceptible varieties, there was a negative correlation between cotyledon deterrence in the three hour choice test and feeding damage to seedling after a two week period. Since the response of the mites to different subclover varieties occurred within three hours, it is concluded that the resistance is based on antixenosis.No evidence was obtained for antifeedant activity in organic solvent extracts from the variety DGI007 (resistant) in comparison with those from the variety Dalkeith (susceptible). Water soluble compounds from DGI007 cotyledons were preferred by mites, in feeding tests in terms of numbers, over those from Dalkeith (susceptible). Squeezed sap from the cotyledons of both varieties showed the same effects on mites as 5% glucose and were more phagostimulatory than water extracts. Mechanically damaged cotyledons of Dalkeith and DGI007 attracted more mites than the undamaged counterparts. The toughness of cotyledons in 17 varieties of T. subterraneum subsp. subterraneum was measured with a manual penetrometer. Results showed a negative correlation between toughness values and mite feeding damage scores (r²=0.752) for all varieties except S3615D (resistant). This implies a likely involvement of epidermal toughness as a contributor in the antixenotic resistance of these varieties. Other mechanisms may be involved in the resistance of S3615D.     

FEMALE CONTROL OF SPERM TRANSFER AND INTRASPECIFIC VARIATION IN SPERM PRECEDENCE: ANTECEDENTS TO THE EVOLUTION OF A COURTSHIP FOOD GIFT

Manipulation of ejaculates is believed to be an important avenue of female choice throughout the animal kingdom, but evidence of its importance to sexual selection remains scarce. In crickets, such manipulation is manifest in the premature removal of the externally attached spermatophore, which may afford females an important means of postcopulatory mate choice. We tested the hypothesis that premature spermatophore removal contributes significantly to intraspecific variation in sperm precedence by (1) experimentally manipulating spermatophore attachment durations of competing male Gryllodes sigillatus and (2) employing protein electrophoresis to determine the paternity of doubly mated females. The relative spermatophore attachment durations of competing males had a significant influence on male paternity, but the pattern of sperm precedence deviated significantly from the predictions of an ideal lottery. Instead, paternity data and morphological evidence accorded best with a model of partial sperm displacement derived here. Our model is similar to a displacement model of Parker et al. in that sperm of the second male mixes instantaneously with that of the first throughout the displacement process, but the novel feature of our model is that the number of sperm displaced is only a fraction of the number of sperm transferred by the second male. Regardless of the underlying mechanism, female G. sigillatus can clearly alter the paternity of their offspring through their spermatophore-removal behavior, and employ such cryptic choice in favoring larger males and those providing larger courtship food gifts. We discuss how female control of sperm transfer and intraspecific variation in sperm precedence may be important precursors to the evolution of gift giving in insects.     

The impact of food quantity on UV-B tolerance and recovery from UV-B damage in Daphnia pulex

UV-B (290 nm) tolerance of Daphnia pulex, conditioned to four different food levels (Chlorophyta), was tested under standardized conditions with an artificial radiation source. Parameters measured were survival, percentage of egg bearing Daphnia and the number of juveniles produced after irradiation. UV-B tolerance of Daphnia pulex was found to be significantly improved with increasing food concentrations at all three parameters. The impact of the four different food concentrations on the photoreactivation system was tested with simultanous UV-B and white-light irradiation of Daphnia. Survival rate improved significantly with increasing food levels compared to solely UV-B irradiation. Photoreactivation had no effect on the reproductive parameters.     

Redescription of Vorticella oceanica Zacharias, 1906 (Ciliophora: Peritrichia) with notes on its host, the marine planktonic diatom Chaetoceros coarctatum Lauder,1864

The late-spring quantitative relationship between epiphyton and macroinvertebrates was analyzed on the basis of units of colonizable plant surface of Typha angustifolia, Phragmites australis and Nuphar lutea (floating leaves) in the shallow euthrophic Lake Loosdrecht (the Netherlands), with a high seston load. The non-predatory chironomid larvae (Glyptotendipes viridis, Endochironomus albipennis, Pentapedilum sordens, Cricotopus sylvestris agg.) dominated among the macroinvertebrate taxa, controlling the diversity and resemblance of macroinvertebrate assemblages. There was a gradient in functional feeding groups among the chironomids from continuous filtering of the seston to prevailing utilization of epiphyton. We found no direct relationship between the total macroinvertebrate abundance and the epiphyton mass on the plants surface. We attribute this to the filter feeding-strategy of the most abundant species, Glyptotendipes viridis, that utilizes seston in the eutrophicated lake.     

Causal connection between detoxification enzyme activity and consumption of a toxic plant compound

Insect herbivores can increase their detoxification activities against a particular plant poison in response to prolonged ingestion of the same compound. For example, larval tobacco hornworms (Manduca sexta) experience a dramatic increase in cytochrome P450 activity against nicotine after ingesting nicotine. While it is generally assumed that this induction process permits increased consumption of toxic plant tissues, we are not aware of any direct experimental support for this assumption. Using a two-tiered approach, we examined the functional significance of P450 induction to M. sexta larvae ingesting a toxic but non-deterrent concentration of nicotine. First, we related the time-course of P450 induction in midgut microsomes to changes in nicotine consumption. When offered a nicotine diet, larvae failed to show a significant increase in consumption before 36 h, which was coincident with the time-course of the induction of midgut P450 activities against aldrin and nicotine. Second, we determined whether inhibiting the induced P450 activities affected nicotine consumption. We found that the increase in nicotine consumption following the induction of nicotine metabolism could be strongly inhibited by treatment with piperonyl butoxide, which by itself did not inhibit consumption. These results provide direct evidence for a causal connection between P450-mediated detoxification activity and consumption of a toxic plant compound.Abbreviation PB piperonyl butoxide     

Separating food and water deprivation in locusts: effects on the patterns of consumption, locomotion and growth

Abstract. In a factorial experiment, fifth-instar Locusta migratoria (L.) (Orthoptera: Acrididae) were given either dry food (lyophilized grass) and drinking water, food only, water only, or neither food nor water.Food consumption and insect weight were measured daily, and the behaviour of each locust was recorded for 5 h on each of four consecutive days and for 2.5 h on the fifth.Consumption declined progressively in locusts given food only, and those given water only were not observed to drink after the first day of food deprivation.The decline in food consumption on the first day was accounted for by a decrease in the average duration of feeds, which remained constant thereafter.The further decline in consumption over subsequent days was due to a progressive decline in the number of feeds.Although food availability did not slow weight loss relative to locusts given neither food nor water, the availability of water without food did.The proportion of time locomoting increased in all deprivation treatments, but the pattern of change across the five observation days differed markedly between treatments.Locusts given food but no water increased locomotion from 20% of the time budget (the value for controls) to 30% on the first day of deprivation, and by the second day had reached a plateau of approximately 65%.which was maintained until the experiment was terminated on day 5.In contrast, locusts given water but no food approached the 65% level of locomotion on the first day, which was stutistically greater than the 55% observed in those deprived of both food and water.This increase was due both to an increase in the number of locomotion bouts initiated and an increase in the average duration of locomotion bouts.On the second and third days, all deprivation treatments maintained locomotion at around 65%.By day 4, locomotion had decreased to approximately 15% in locusts deprived of both food and water, but not in those deprived of food only or water only.Unlike those given only food, locusts given only water showed a reduction in locomotion of c. 15% on the fifth day.