Effects of head shape variation on growth, metamorphosis and survivorship in larval salamanders (Hynobius retardatus)

The effects of head shape variation on growth and metamorphosis in larval salamander (Hynobius retardatus) were examined by a laboratory experiment and a field experiment. In the laboratory experiment, each larva was fed equal amounts and was prevented from accessing others in both the solitary and group treatments, although chemical cues could be transmitted through water in the group treatment. The relative head width of larvae became larger in the group treatment during the early periods but having a large head width did not finally influence growth rate and days for metamorphosis. In the field experiment, larvae were allowed to contact each other directly in two density conditions. The enlarged relative head width was linked to high growth rate in the high-density treatment but not in the low-density treatment. The larval body size distribution in the high-density condition tended to be smaller, and there was a small proportion of large-sized individuals with a broad head width. Moreover, the small number of large larvae metamorphosed much earlier than the others. The mortality of larvae in high-density conditions was much higher than that in the low-density treatments. This would be a consequence of cannibalism in the high-density condition. From the experimental results obtained, it is argued that for the larvae of H. retardatus having a large head is an adaptive tactic that maximizes fitness, particularly in temporary ponds with an unpredictable environment and in crowded conditions.     

Growth, dynamics, and distribution of a population of the brook lamprey Lampetra planeri in a South Swedish stream

Size and structure of a South Swedish population of Lampetra planeri larvae were studied during 5 yr. Population size fluctuated considerably within the studied section of stream with a general decline. The fluctuations were positively and strongly correlated (multiple R²= 0.85) with the population density at the beginning of each analysed period, while poorly correlated with such variables as heavy precipitation and temperature. Several factors suggest the entire larval population drifts downstream: fluctuations in the studied stream section, increasing mean size downstream, and incongruity in longitudinal distribution in surveys, performed with a 5-yr interval. Growth, estimated both in caged larvae and from length frequency data, occurred mainly in autumn. High density in cages reduced the growth rate of larvae.     

Age,growth, and sex ratio among populations of least brook lamprey,Lampetra aepyptera,larvae: an argument for environmental sex determination

Synopsis Sex ratios of least brook lamprey,Lampetra aepyptera, larvae varied widely among 12 geographically-diverse streams of the eastern United States. The extremes were 29 and 71% male, and the proportion of males increased significantly with relative population density, which was estimated among the streams from the number of larvae collected per m2 of substrate. The skewed sex ratios were not likely due to differential mortality between the sexes or differential recruitment to the adult stock, since they were established at the time of gonadal differentiation (at ca. 2 years of age) and remained relatively constant over the subsequent 2–3 years of larval life. Furthermore, although females seemed to predominate in the oldest larval age class, thus appearing to metamorphose later than males, their numbers were small and were omitted from the overall sex ratio. Sex ratio did not vary significantly with water hardness, pH, annual thermal units, or latitude. The possible adaptive significance of density-dependent sex determination in lampreys, however, remains elusive. It has been proposed that growth-promoting conditions might yield female-biased sex ratios as a tactic for ensuring that relatively large individuals become females, thereby increasing their fecundity. As predicted, larval size at a given age was generally greater in low-density populations, but there was no relationship between sex ratio and larval size, and female larvae were not consistently larger than the males.     

Growth and survival rate of the larvae ofHynobius nebulosus Tokyoensis Tago (Amphibia,Hynobiidae)

Growth and population density of the larvae, Hynobius nebulosus tokyoensisTago , were estimated in a small pond within the study site settled in Habu village of Hinodemachi, a suburb of Tokyo City, during the period from 1975 to 1980. The mortality factors which influenced the survival rate of larvae were also evaluated from the ecological point of view. Laboratory experiments on the growth of larvae and predation by newts were conducted in pararell with the field survey. The results showed that growth rate of larvae under the natural condition was very slow, as compared with that under the laboratory condition with sufficient food supply, and mean body size at metamorphosis was negatively correlated with the density at that time. This suggested that food resources were in short supply in the pond, and there occurred a severe intraspecific competition for food among larvae. The mortality rate of larvae was so high, 80–99% in each year, and the density of larvae survived until metamorphosis varied so greatly from year to year that the larval stage was the most important stage throughout the life cycle to the maintenance of a population for this salamander. The most important factors which contributed to this high mortality were the predation by the newt, Triturus pyrrhogaster pyrrhogasterBoie , and cannibalism. From the laboratory experiment, it was found that predators could attack only small larvae successfully, and successful attack rate decreased sharply as larvae grew larger. This relationship resulted in the characteristic L-shaped pattern of survivorship curve of larvae; that is, heavy mortality just after hatching period.     

Rearing density and susceptibility of Rana pipiens metamorphs to cercariae of a digenetic trematode

Cercariae of many digenean trematodes target particular developmental stages of their hosts. For some digeneans that are parasites of amphibians, infection appears timed to host metamorphosis. The success and timing of metamorphosis is itself affected by a number of factors, including host density. We investigated the degree to which rearing density of Rana pipiens larvae influenced time to metamorphosis and snout-to-vent length and mass at metamorphosis, as well as establishment of cercariae of the trematode Manodistomum syntomentera Stafford, 1905. As expected, individuals metamorphosed later, were smaller, and weighed less at metamorphosis if they were reared under intermediate to high densities compared with low densities, in experimental outdoor mesocosms. Cercariae establishment was higher in smaller metamorphs that took longer to metamorphose within the low-density treatment. Additionally, cercariae establishment was lower in larvae from the low-density tanks compared with larvae from the intermediate- to high-density tanks. However, more tadpoles had failed to metamorphose in the intermediate to high rearing densities by the time cercariae were no longer available from natural collections of first intermediate hosts, Physa spp. Larval amphibians under crowded conditions should experience increased susceptibility to trematode establishment in nature, but only if they metamorphose within the time period when cercariae are still available.     

Effect of delayed metamorphosis on larval competence, and post-larval survival and growth, in the abalone Haliotis iris Gmelin

Marine invertebrate species vary in their ability to delay metamorphosis, and in the degree to which delayed metamorphosis compromises juvenile performance. Abalone (Haliotis iris) larvae were deprived of metamorphosis cues and the effects of delayed metamorphosis on larval competence, and post-larval growth and survival were quantified. Larvae were exposed to a metamorphosis inducer (the coralline alga Phymatolithon repandum (Foslie) Wilks and Woelkerling) on Days 11, 18, 22, 26, 30 and 34 post-fertilisation (temperature 16-17 degrees C). Post-larvae were reared on diatoms (Nitzschia longissima Grunow) for 3-4 weeks post-metamorphosis. Delayed metamorphosis caused progressive negative effects on post-larval performance. Virtually all larvae initiated metamorphosis in response to P. repandum, regardless of larval age. The proportion of post-larvae that developed post-larval shell growth within 2 days of metamorphosis induction dropped only approximately 20% from Day 11 to Day 26 (P>0.05), but was significantly lower by Day 30 and Day 34 (P<0.001). Larvae that metamorphosed on Days 11, 18 and 22 showed high survival (>80%) and growth rates (means of 20-22 μm shell length per day). In contrast, larvae that metamorphosed on Day 26 and Day 30 had poor survival (30-40%) and lower (P<0.05) growth rates (15-16 μm/day). Of the larvae that metamorphosed on Day 34, only 7 (30%) survived their first week post-metamorphosis, and they grew only 2 μm/day on average. Only one of these post-larvae (4%) survived the second week. The visible yolk supply diminished over the life of the larvae and was near zero by Day 34. Nearly all larvae had died by Day 38. H. iris larvae remained competent to metamorphose for at least 3 weeks after they attained competence. Post-larval growth and survival were not reduced if metamorphosis occurred within 3 weeks of fertilisation. This extended period of larval competence implies that H. iris larvae can potentially disperse for up to several weeks before successful metamorphosis.     

Density reductions by predatory trout increase adult size and fecundity of surviving caddisfly larvae in a detritus-based stream food web

1. In some situations, individuals surviving in environments where predation is intense can grow faster because the benefits of release from intraspecific competition outweigh costs associated with anti-predator responses. Whether these 'thinning' effects of predation occur in detritus-based food webs where resource renewal occurs independently of consumption by consumers was studied. We investigated how effects of predatory brown trout ( Salmo trutta ) on the larvae of the detritivorous stream caddisfly, Zelandopsyche ingens , influenced the size and fecundity of the caddisfly adults.
2. Trout substantially reduced the abundance of Z. ingens larvae, but adult male and female Z. ingens were significantly larger in trout streams compared to fishless streams. Females in trout streams had 33% more eggs than fishless stream females, and egg sizes were not significantly different. In mesocosms, Z. ingens larvae in low density treatments reflecting trout stream abundances grew significantly faster than larvae in high density treatments that were characteristic of fishless stream abundances. Non-lethal trout presence did not influence case building behaviour, feeding rates or growth or Z. ingens larvae, indicating non-lethal effects of predators were negligible.
3. Increased adult size and fecundity associated with trout stream individuals were probably a result of predator thinning of larval density indirectly releasing surviving Z. ingens from intraspecific competition. Thus, predator thinning did influence interactions between larvae in this detritus-based food web as larval growth was strongly density-dependent. However, extrapolating the total number of eggs potentially produced indicates the increased fecundity of females in trout streams would not compensate for losses of larvae to trout predation.     

HABITAT DURATION,LENGTH OF LARVAL PERIOD,AND THE EVOLUTION OF A COMPLEX LIFE CYCLE OF A SALAMANDER,AMBYSTOMA TEXANUM

In many organisms, genotypic selection may be a less effective means of adapting to unpredictable environments than is selection for phenotypic plasticity. To determine whether genotypic selection is important in the evolution of complex life cycles of amphibians that breed in seasonally ephemeral habitats, we examined whether mortality risk from habitat drying in natural populations of small-mouthed salamanders (Ambystoma texanum) corresponded to length of larval period when larvae from the same populations were grown in a common laboratory environment. Comparisons were made at two levels of organization within the species: 1) among geographic races that are under strongly divergent selection regimes associated with the use of pond and stream habitats and 2) among populations within races that use the same types of breeding habitats. Morphological evidence indicates that stream-breeding A. texanum evolved from pond-breeding populations that recently colonized streams. Larvae in streams incur heavy mortality from stream drying, so the upper bound on length of larval period is currently set by the seasonal duration of breeding sites. We hypothesized that selection would reduce length of larval period of pond-breeders that colonize streams if their larval periods are inherently longer than those of stream-breeders. The results of laboratory experiments support this hypothesis. When grown individually in a common environment, larvae from stream populations had significantly shorter larval periods than larvae from pond populations. Within races, however, length of larval period did not correlate significantly with seasonal duration of breeding sites. When males of both races were crossed to a single pond female, offspring of stream males had significantly shorter larval periods than offspring of pond males. Collectively, these data suggest that differences in complex life cycles among pond and stream-breeders are due to genotypic selection related to mortality from habitat drying. Stream larvae in the common-environment experiment were significantly smaller at metamorphosis than pond larvae. Yet, the evolution of metamorphic size cannot be explained readily by direct selection: there are no intuitively obvious advantages of being relatively small at metamorphosis in streams. A positive phenotypic correlation was observed between size at metamorphosis and length of larval period in most laboratory populations. A positive additive genetic correlation between these traits was demonstrated recently in another amphibian. Thus, we suspect that metamorphic size of stream-breeders evolved indirectly as a consequence of selection to shorten length of larval period.     

Variable effects of goitrogens in inducing precocious metamorphosis in sea lampreys (Petromyzon marinus)

The ability of different goitrogens (anti-thyroid agents) to induce precocious metamorphosis in larval sea lampreys (Petromyzon marinus) was assessed in four separate experiments. Two of these goitrogens (propylthiouracil [PTU] and methimazole [MMI]) are inhibitors of thyroid peroxidase-catalyzed iodination, and three (potassium perchlorate [KClO(4)], potassium thiocyanate [KSCN], and sodium perchlorate [NaClO(4)]) are anionic competitors of iodide uptake. Because, theoretically, all of these goitrogens prevent thyroid hormone (TH) synthesis, we also measured their influence on serum concentrations of thyroxine and triiodothyronine. All goitrogens except PTU significantly lowered serum TH concentrations and induced metamorphosis in some larvae. The incidence of metamorphosis appeared to be correlated with these lowered TH concentrations in that KClO(4), NaClO(4), and MMI treatments resulted in the lowest serum TH concentrations and the highest incidence of metamorphosis in sea lampreys. Moreover, fewer larvae metamorphosed in the KSCN and low-KClO(4) treatment groups and their serum TH concentrations tended to be greater than the values in the aforementioned groups. MMI treatment at the concentrations used (0.087 and 0.87 mM) was toxic to 55% of the exposed sea lampreys within 6 weeks. The potassium ion administered as KCl did not alter serum TH concentrations or induce metamorphosis. On the basis of the results of these experiments, we have made the following conclusions: (i) In general, most goitrogens other than PTU can induce metamorphosis in larval sea lampreys, and this induction is coincident with a decline in serum TH concentrations. (ii) The method by which a goitrogen prevents TH synthesis is not directly relevant to the induction of metamorphosis. (iii) PTU has variable effects on TH synthesis and metamorphosis among lamprey species. (iv) Unlike in protochordates, potassium ions do not induce metamorphosis in sea lampreys and are not a factor in the stimulation of this event.     

Induction of metamorphosis of pediveliger larvae of the mussel Mytilus galloprovincialis Lamarck, 1819 using neuroactive compounds, KCl, NH4Cl and organic solvents

Pediveliger larvae of Mytilus galloprovincialis were subjected to a series of bioassays to investigate the induction of metamorphosis using neuroactive compounds, K(+), NH(4)(+) and organic solvents. Growth and survival of post-larvae obtained using ethanol and methanol were also observed. Epinephrine, phenylephrine, clonidine and metanephrine induced larval metamorphosis at 10(-6) to 10(-4) M in both 24-h and continuous exposure assays. In 24-h exposure assays, alpha-methyldopa at 5 x 10(-5) M and methoxyphenamine at 5 x 10(-5)-10(-4) M induced 55-94% metamorphosis. Similarly, excess K(+) at 3 x 10(-2) M induced 39% metamorphosis and NH(4)(+) at 1-5 x 10(-2) M induced 63-78% metamorphosis. The EC50s of seven organic solvents ranged from 0.04 to 0.82 M. Post-larvae that metamorphosed using ethanol and methanol survived as juveniles and grew at the same rate as those from microbial biofilm. Thus, the above compounds can be useful inducers of metamorphosis for antifouling studies using larvae and juveniles of M. galloprovincialis.     

Theory on the evolutionary history of lamprey metamorphosis: role of reproductive and thyroid axes

Metamorphosis is a developmental strategy used by only a small number of extant fishes and little is known about its phylogenetic development during the evolution history of this large group of vertebrates. The present report provides a putative evolutionary history of metamorphosis in the lamprey, an extant agnathan with direct descendancy from some of the oldest known vertebrates. The study reviews recent data on the role of the thyroid gland and its hormones in metamorphosis, summarizes some recent views on the evolution of the endostyle/follicular thyroid in lampreys, and provides new data on the content of two gonadotropin-releasing hormones (GnRH-I and -III) in brain during goitrogen-stimulated, precocious metamorphosis. These new data support an earlier viewpoint of a relationship between thyroid and reproductive axes during metamorphosis. It is proposed that the earliest lampreys were paedomorphic larvae and they lived in a marine environment; as such, they resembled in many ways the larvae from which the ancient protochordates, Larvacea, are derived. The iodide-concentrating efficiency of the endostyle was a critical factor in the evolution of metamorphosis and this gland was replaced by a follicular thyroid, for postmetamorphic animals needed to store iodine following their invasion of freshwater. Larval growth and postmetamorphic reproduction in freshwater became fixtures in the lamprey life cycle; a non-parasitic adult life-history type appeared later. The presence among extant lampreys of two different adult life-history types, and examples of the lability of the timing of sexual maturation in some species, imply that there has been a complex interplay between the thyroid and reproductive axes during the evolution of metamorphosis in lampreys. This proposal is consistent with what we know of interplay of these axes in extant adult lampreys and with the long-held viewpoint that thyroid function and sexual maturation are an association with an ancient history.     

Observations on the age, growth, reproduction and food of the chub Squalius cephalus (L.) in the River Stour, Dorset

Opercular bones from 399 chub from the River Stour, Dorset were used for age and backcalculated growth measurements. Scales were only used to aid the interpretation of difficult operculars. Annuli were laid down through the period mid-April to mid-June. Growth in length was minimal between October and March. Growth rates were similar to those published for chub in other European waters, but the Stour chub were longer-lived and attained a greater ultimate size. Female chub grew faster than the males. Spawning occurred from late May into June and elaboration of the gonads took place between September and May. Immature chub had an annual cycle of condition; the 0 group having a maximum in August and older immature fish reaching their maximum in June. Both categories had a minimum condition in early spring. The cycle of gonad development affected the condition of mature fish. The numbers of eggs in chub of lengths 359–467 mm ranged from 27 000–65 000. Some females attained sexual maturity at age V or VI, but most by age VII. The majority of males matured at age V, though some at ages III or IV. Growth rates and year-class strengths varied from year to year but independently of one another. Thirty-one per cent of chub aged II and over belonged to the 1959 year class. Young chub ate insect larvae and small crustacea, but the occurrence of fish and macrophytes was greater in the diet of older fish.     

Development of salinity tolerance in the marine pulmonate Amphibola crenata (Gmelin)

Growth and survival of veligers of Amphibola crenata (Gmelin) were followed in a range of salinities from 4 to 35%. In salinities of 18%. and below, growth was slowed and a large proportion of veligers died. In 4 to 12%., no larvae survived to metamorphosis, but these low salinities were tolerated for short periods.Newly post-metamorphic snails and juveniles collected from the field survived well even at 4%., showing that greater tolerance of low external salinities developed at metamorphosis. Examination of the physiology of adult snails suggested that this may be due to the development of osmoregulating mechanisms, because the adults maintain the blood hyperosmotic to the medium in 4 and 9%. The kidney, however, does not seem to be involved in this regulation because urine is isosmotic with the blood. An extra-renal mechanism of salt uptake is, therefore, postulated.     

Growth patterns of a stream vertebrate differ between urban and forested catchments

1. Urban development results in the decline of amphibian density and species richness. A logical next step towards understanding why urbanisation negatively impacts amphibians is to track species‐specific demographic responses to urbanisation. 2. We monitored growth of two‐lined salamander (Eurycea cirrigera Green) larvae over two complete cohorts (2006 and 2007) in nine western Georgia, U.S.A. streams. 3. We found that salamanders in streams surrounded by urbanised and developing catchments hatched at the same size as their reference‐stream counterparts, but achieved larger sizes within the first few months of growth. We evaluated the effect of four variables that correlate with the urban‐forest gradient and found that elevated temperatures in the urban environment, coupled with decreased intraspecific competition because of lower survivorship in these same habitats, were two of the most likely explanations for increased growth rates. 4. Such an increase in growth of surviving larvae may maintain population viability in urban areas where it has been shown survival is difficult because of increased in‐channel flow during flood events. Because larvae that do survive in urban streams undergo metamorphosis at large sizes, they may recoup a component of fitness (i.e. increased adult survivorship and reproduction) through growth.     

Exclusion size and material have minimal effects on stream benthic algae and macroinvertebrate colonization within submerged cages

Despite their widespread use in grazer–biofilm studies, stream exclusion cages have inherent physical properties that may alter benthic organism colonization and growth. We used laboratory studies and a field experiment to determine how exclusion cage design (size and material) alters light availability, water velocity, and benthic organism colonization. We measured light reduction by various plastic cage materials and flow boundary layer thickness across a range of exclusion cage sizes in the laboratory. We also deployed multiple exclusion cage designs based on commonly available materials into a second-order stream to assess algae and macroinvertebrate colonization differences among exclusion cages. All plastics reduced some light (190–700 nm wavelengths) and blocked more ultraviolet light than photosynthetically active radiation. Exclusion cage size did not influence flow boundary layer thickness, but larger exclusions tended to have higher velocity at the substrata surface. Despite light and water velocity differences, algal biomass, macroinvertebrate density, and community composition were similar between exclusion cage types. However, algal assemblages outside exclusion cages differed in composition and had higher biomass compared to inside exclusion cages. In terms of algal and macroinvertebrate colonization, plastic exclusion cage size and material appear to be flexible within the sizes tested, but differences can still exist between exclusion cage communities and those within the stream. Overall, artifacts of screened exclusion cages do not appear to introduce large bias in results of grazer–biofilm studies, but efforts to design exclusion cages that better mimic the natural system should continue.     

Growth,fecundity, and egg size of least brook lamprey,Lampetra aepyptera

Synopsis Eight geographically-diverse (33°11N to 39°14N) populations of least brook lamprey varied significantly in density of larvae and mean length of metamorphosing and adult lampreys (101–152 mm). Absolute fecundity (503–5900 eggs) did not change significantly with stage of post-larval development, suggesting little post-metamorphic atresia; egg dry weight increased to stage 6, the penultimate stage of metamorphosis. Absolute fecundity increased with the cubic power of total length. Relative fecundity (250–1124 eggs per gram total body weight) decreased significantly with increasing length within two streams. Relative fecundity, adjusted to a common length, increased with mean length of the population. Conversely, mean egg dry weight (0.09–0.24 mg, stages 6–8) increased with maternal length within three streams, and decreased with length among streams. In populations where spawning occurs at a small body size, females produce comparatively fewer but larger eggs. Large eggs may be required to counter the effects of an unproductive environment and the accompanying reduction in relative fecundity is compensatory. No relationship was evident between latitude, annual thermal units, or density and relative fecundity or egg size. Mean length of a population was also unrelated to these environmental factors.     

Colonization of artificial substrata by macro-invertebrates in a stream and variations according to stone size

SUMMARY. Plastic cages containing artificial substrata were placed on the stony bottom of a stream in a section where the environmental conditions appeared to be homogeneous. The section was divided into eight equal sub-sections (A-H) and four cages were placed in each sub-section. The stone-size of the artificial substrata was similar within each cage but differed between the four cages with average diameters of 14, 24, 48 and 96 mm, respectively. The baskets were removed one month later and the catches of macro-invertebrates were recorded.
Analysis of the catches (density and number of taxa in each cage) revealed no significant differences in connection with the position of the cages in the section of stream. Cages with 48-mm stones contained the least abundant fauna. The taxa which colonized cages with 14- or 24-mrn stones were more numerous than those collected from cages with 48- or 96-mm stones.
Statistical analysis by laxon confirmed the preceding results. Variability in connection with the position of the cages along the section of stream was never significant. A little more than half the taxa were distributed independently of stone size but always showed a contagious type distribution. The density of the other taxa was higher, either in cages with 14- or 24-mm stones (particularly Gammarus ) or only in cages with 96-mm stones (especially Hydropsyche ). Only one taxon was more abundant in cages with 48-mm stones, the type of substratum in which the overall density was lowest.
Catches in the cages were not the same as those taken with a Surber sampler because the two samplers did not take samples from the same habitats and also because the baskets offered a more specialized habitat than the surrounding bottom. The basket with 24-mm stones gave the least distorted picture of the natural population.     

Models of metamorphic timing: an experimental evaluation with the pond-dwelling salamander Hemidactylium scutatum (Caudata: Plethodontidae)

Amphibian larvae vary tremendously in size at metamorphosis and length of larval period. We raised pond-dwelling four-toed salamander (Hemidactylium scutatum) larvae to test two models that predict a larva’s age and size at metamorphosis. The Wilbur-Collins model proposes that the developmental rate of a larva responds to changes in growth rate in an adaptive manner throughout the larval period, and that metamorphosis can be initiated after a minimum size has been reached. The Leips-Travis or fixed-rate model states that developmental rate is set early in the larval period, perhaps by early growth rate or food availability and their positive correlation with developmental rate, and that changes in growth rate during the larval period affect size at metamorphosis, but have no effect on the age of an individual at metamorphosis. A modified version of the Wilbur-Collins model suggests that a larva’s developmental rate becomes fixed about two-thirds of the way through the larval period, with changes in growth rate after that point only affecting size at metamorphosis. Larvae were raised on eight different feeding regimes which created two constant and six variable growth histories. Growth history did significantly affect size at metamorphosis. However, an a posteriori statistical test revealed a group of seven and an overlapping group of six treatments with indistinguishable lengths of larval period, indicating a general picture of a fixed developmental rate regardless of growth history. This result is unique among similar studies on invertebrates, fish, and frogs. There was no association between early growth or food level and development rates. Neither the Wilbur-Collins nor the Leips-Travis fixed-rate models were supported. The invariable developmental rate of Hemidactylium and recent osteological evidence from the literature suggest that larvae begin the process of metamorphosis as soon as they hatch, probably a trait selected for by strong predation pressure in the aquatic environment. A variety of different approaches (ecological, developmental, phylogenetic) are necessary to fully evaluate the adaptive nature of the timing of transitions between life cycle stages. Received: 3 June 1999 / Accepted: 18 March 2000     

The influence of environmental variables on larval growth of stoneflies (Plecoptera) in natural and deforested streams

A total 14 streams located in the Tatra Mts (Slovakia) were investigated. The studied river basins have different deforestation range (0–45.5%) influenced by windstorm. Daily and annual water temperature suggested that in streams overflowing through the area deforested by windstorm the temperature was higher than in selected non-disturbed streams. Higher average nutrient concentrations in samples from these streams are connected with nutrient mobilization from disturbed forest soils after the windstorm. Most of the damaged streams have higher trophic status, including POM and biofilms. The growth of the most abundant larvae increases with deforestation. Growth of species Leuctra rauscheri, Protonemura Montana, and Perlodes intricatus correlates with the sum of daily temperatures over a given time interval. Growth of species Brachyptera seticornis, Leuctra autumnalis and Isoperla sudetica are affected by stream trophy.     

Variation in food availability mediate the impact of density on cannibalism,growth, and survival in larval yellow spotted mountain newts (Neurergus microspilotus): Implications for captive breeding programs

In this study, we examined cannibalistic behavior, growth, metamorphosis, and survival in larval and post‐metamorph endangered yellow spotted mountain newts Neurergus microspilotus hatched and reared in a captive breeding facility. We designed a 2 × 2 factorial experiment, crossing two levels of food with two levels of density including high food/high density, high food/low density, low food/high density, and low food/low density. The level of cannibalistic behavior (including the loss of fore and hind limbs, missing toes, tail, gills, body damage, and whole body consumption) changed as the larvae grew, from a low level during the first 4 weeks, peaking from weeks 7 to 12, and then dropped during weeks 14–52. Both food level and density had a significant effect on cannibalism. The highest frequency of cannibalism was recorded for larvae reared in the low food/high density and lowest in high food/low density treatments. Growth, percent of larval metamorphosed, and survival were all highest in the high food/low density and lowest in low food/high density treatment. Food level had a significant effect on growth, metamorphosis, and survival. However, the two levels of density did not influence growth and metamorphosis but showed a significant effect on survival. Similarly, combined effects of food level and density showed significant effects on growth, metamorphosis, and survival over time. Information obtained from current experiment could improve productivity of captive breeding facilities to ensure the release of adequate numbers of individuals for reintroduction programs. Zoo Biol. 35:513–521, 2016. © 2016 The Authors. Zoo Biology published by Wiley Periodicals, Inc.