Breeding pond fidelity in the common toad, Bufo bufo

Two independent studies of adult common toad, Bufo bufo , movements between different spawning ponds/populations both within and between years were made in England and Sweden during the spring breeding periods of1987–1990. The results of the two studies were subsequently combined since they were found to be complementary. In addition, in England during 1984 and 1985, large numbers of 'toadlets' were marked so that they could be identified if recaptured as breeding adults.
The degree of relocation between ponds was negatively correlated to the distance between ponds. The proportion of both males and females that moved between ponds within a particular year was significantly less than the proportion relocating between years. In any year, between 79% and 96% of adults that survived to breed the following year, returned to the original pond. Similarly, of the toadlets marked during1984–85, 81% of the males that subsequently returned as breeding adults were captured in their pond of origin.
Isolation, in relation to both population dynamics and population genetics, is defined and its implications for the management of common toad populatins discussed.     

Intraspecific competition in tadpoles of Rana arvalis: does it matter in nature? A field experiment

Tadpole growth and development are easily affected by intraspecific competition in tank experiments, provided treatment density is sufficiently high. Is this a phenomenon also observed in nature? A pond was divided into four tadpole-proof sections. Each year for 8 years, all spawn laid by moorfrogs (Rana arvalis) in this pond was relocated to create relative spawn and tadpole densities of 1 : 4 : 1 : 4. No direct effect of the density manipulation on survival, tadpole size, and development and metamorph timing and size could be demonstrated. However, I also measured actual tadpole density during the time of development. Apart from the experimental density manipulation, this measure included effects of between-year variation in amount of spawn, natural tadpole mortality, and pond drying (which concentrated the tadpoles by decreasing the area of the pond sections). Actual density had limited but significant effects on tadpole size and development. I suggest that density regulation, acting on the tadpole stage, may be present in the population but was of less short-term importance than abiotic factors and, possibly, adult density regulation. Consequences of the findings for conservation are discussed.     

Hydrological Status of the spawning ground of Acipenser sinensis underneath the Gezhouba Dam and its relationship with the spawning runs

The spawning runs of Chinese Sturgeon (CS; Acipenser sinensis) were observed 37 times below Gezhouba Dam of Yangtze River between 1983 and 2004. Five hydrological factors (water temperature, water level, flow discharge, silt content and current velocity) were monitored on a daily basis at the spawning ground between October and November for 22 consecutive years (1983–2004). The effect of current velocity on the spawning ground at the bottom layer of the river, where CS was spawning for four years, was measured (1996–1999). The authors of this study analyzed the relationship between the five hydrological factors and the respective spawning runs. Twenty-two years of continuous observations indicated that the daily mean values of all the five hydrological factors fluctuated within a certain range when CS was spawning. It was concluded that the optimal values for the hydrological factors during the spawning runs are 18.0–20.0°C for temperature, 14100 m³/s for discharge volume, 42.0–45.0 m for water level above the sea level, and 0.2–0.3 kg/m³ for silt content in the water, wherein the current velocity above the bottom layer to stimulate the fish to spawn should be between 1.0–1.7 m/s. The optimal water temperature might provide an essential precondition for other factors to trigger spawning. As water temperature reaches the optimal values and most of the other parameters are at the brink of deviation from their optimal range of values (water level, current velocity and silt content in the water), CS would begin to spawn. By 2009, when the Yangtze Three Gorges Project, which is located 45 km upstream of the Gezhouba Dam, is completed and begins to operate normally, changes in the downstream water temperature are expected to occur, which may have a negative effect on the development of gonad and the stimulation of spawning of CS; however, the anticipated decrease of the silt content in the water may be considered favorable for the performance of the spawning site.     

Influence of temperature on the spatial distribution of first spawning dates of the common frog (Rana temporaria) in the UK

Between 1998 and 2007, the UK Phenology Network collected nearly 70 000 records of the first spawn dates of the common frog Rana temporaria . Annual national mean dates varied by more than 2 weeks and were closely related to January–March temperatures. A 1 °C increase in Central England Temperature advanced national mean spawning by 5.1 days. The temporal pattern of spawning records varied between years; sometimes unimodal in form, sometimes multimodal, seemingly associated with steady or erratic rises in spring temperatures, respectively. Spatial patterns of frogspawn were similar in different years, the earliest records occurring in the southwest with records progressively later in the north and east. On average, 100 km of eastwards progression took 7.4 days and 100 km of northwards progression took 4.7 days. A composite map for the 1998–2007 period is constructed and compared with an earlier published map based on data 60 years previously. The similarity and dissimilarity of these two maps is discussed; the general progression pattern of frogspawn phenology is similar but an advance of a 10-day contour category is apparent. We anticipate further advances of frog spawning dates in the future and an increase in the numbers of pre-January 1 records of frog breeding.     

The date of spawning in populations of the Common frog (Rana temporaria) from different altitudes in northern England

A series of ponds in the Wear Valley in northern England, ranging in altitude from 46 to 838 m, were visited regularly over a four-year-period, and a record was kept of the dates on which spawn from the Common frog, Rana temporaria , was first seen in each of the ponds. On average. spawning was delayed by six days for every 100 m increase in altitude. The date of spawning at each of the ponds was fairly consistent from year to year; only in 1974 was the date of spawning noticeably different from other years. A theory was proposed which could account for the variation in the date of spawning with altitude and the annual variation in the date of spawning, observed in the present study. It is proposed that frogs from nothern England become sensitive to environmental temperature in the middle of February and emerge in the spring after experiencing a temperature-sum of 106 degree(C)-days. The onset of temperature sensitivity is probably initiated by a circannual endogenous rhythm. The time at which the rhythm switches on the temperature-sensing mechanism in frogs probably varies in different populations, and may well be locally adapted. For spawning to follow emergence, a certain minimum water temperature may be required. In the present study, most frogs in the wild spawned when the water temperature in the ponds was above 7°C, but frogs could spawn at 3·1°C. Alternative theories for the control of emergence and spawning are also discussed.     

Effects of predator interactions, prey palatability and habitat structure on survival of natterjack toad Bufo calamita larvae in replicated semi-natural ponds

The significance of predation and aquatic habitat structures to the survivorship of natterjack toad Bufo calamita larvae was investigated by manipulating predator numbers and pond characteristics in a series of replicated semi-natural pools over three consecutive years Two species of fish (common carp Cyprinus carpio and perch Perca fluviatilis) increased the survival of small tadpoles severalfold by selectively consuming predatory invertebrates, but a third species of fish (rudd Scardinius erythrophthalmus) devoured tadpoles and invertebrates indiscriminately Survival of larger tadpoles later in larval development was less affected by the reduction of invertebrate predation pressure from carp and perch, probably because abiotic factors (pond desiccation and anoxia) were stronger agents of tadpole mortality In ponds of low pH (ca 4 5) there was greatly increased spawn mortality and reduced tadpole growth rates but no significant change in tadpole predation compared with circumneutral controls Neutralisation of acid ponds to pH 7 by addition of Ca(OH)₂ restored spawn viability and tadpole growth rates to control levels without affecting predation level Addition of organic nutrients stimulated tadpole growth rates significantly m ohgotrophic ponds but not sufficiently to improve survival of small larvae in the face of predation Extensive growths of macrophytes increased predator numbers up to more than twofold but effects on tadpole mortality rates differed between experiments Replacement of natural substrates by concrete basins substantially increased tadpole survival throughout development, probably because both predation by invertebrates and abiotic mortality factors were ameliorated Predation was a strong force early in natterjack tadpole development irrespective of chemical and biological conditions within ponds, but became much less important compared with abiotic factors as an agent of mortality at later tunes     

Seasonal changes in the pituitary- gonad axis of feral goldfish, Carassius auratus L., from Ontario, Canada

Apparently healthy, feral goldfish, Carassius auratus L., were collected from a pond in Cambridge, Ontario from March until November 1981, and during April 1982. Based on histological examination, oocyte development was divided into five stages and the reproductive cycle into five periods. The origins of oogonia and the atresia process were examined. The gonadosomatic index (GSI) was found to be an accurate indicator of ovarian activity in the feral population. Based on the GSI, proportion of various oocyte stages and egg size, females older than 2 years appeared to spawn during two periods, May to June and late August; 2-year-old fish spawned in the first period. There was a reduction in the density, abundance and nuclear diameter of presumptive pituitary gonadotrops in early August, after the completion of ovarian development and before the completion of spawning.     

Communal Spawning in the Common Frog Rana temporaria– Egg Temperature and Predation Consequences

Females of the common frog, Rana temporaria, spawn synchronously at communal breeding sites, forming a communal egg mass of individual spawn clumps. A total of four spawning sites were studied. In the centre of the communal egg mass, daily maximum temperature was higher and minimum temperature lower than further out. Spawn clumps in the centre of the communal egg mass developed faster than single spawn clumps. In the centre of the egg masses, some spawn clumps suffered almost total egg mortality. This was probably the consequence of a cold spell with sub‐zero temperatures in combination with a tendency for low minimum temperatures in the centre. In a laboratory study, worm leeches, Erpobdella spp., fed readily on eggs of common frog, while horse leeches, Haemopis sanguisuga, hardly ate any eggs. At the spawning sites, most worm leeches were found in single spawn clumps, far from the communal egg mass. Females which spawned late, when most of the spawning was over, preferred to spawn in the centre of the communal egg mass. This suggests that there is a net advantage for eggs in spawn clumps laid in the centre.     

Characteristics of spawning sites of the common frog (Rana temporaria) with particular reference to acidity

Sixty-one ponds in northern England with pHs ranging from 4.2 to 8.9 were examined for the numbers of spawn clumps per unit area in the spring of 1985. In addition, measurements were made of 25 other chemical and physical variables in the ponds, including the concentration of aluminium, various heavy metals, pond area and depth. Thirty-one of the ponds contained from one to more than 1000 spawn clumps in densities ranging from 0.001 to 3.7 m⁻² of pond area. Contrary to the findings in other surveys, spawn clumps occurred in relatively high densities in ponds of low pH. This was possibly related to the fact that other (unmeasured) variables, conducive to high spawn densities, had a greater influence in ponds where pH was coincidentally low. However, it is emphasized that, although the selection of spawning sites may not be influenced by low pH, other stages in the life cycle may be affected. A comparison of the present results with those from an earlier survey led to the conclusion that the number of frogs in the Wear Valley had decreased over the last 10 years. Possible reasons for this decline were discussed.     

Competitive mate searching in male common toads, Bufo bufo

The reproductive behaviour of a population of individually marked toads Bufo bufo was studied at a pond where males outnumbered females by between four and five to one. There was intense competition between the males for mates and only 20·5 % of them bred successfully. Of the successful males, 38·5 % got mates by fighting and displacing other males from the backs of females (takeovers). Larger males enjoyed greater reproductive success because they were stronger and better able to achieve takeovers. When competing for females, some males searched at the spawn site while others searched away from spawn. The numbers searching in the two areas can be predicted by a model which assumes that unpaired males distribute themselves so that there is a spatial ESS, where individuals have equal expectations of finding a female both at and away from the spawning ground.     

Phytoplankton as a stimulus for spawning in three marine invertebrates

A distinct annual reproductive cycle with spring spawning was observed in Strongylocentrotus droebachiensis Müller, Tonicella lineata Wood and Tonicella insignis Reeve. This study gives evidence that the cue for spawning in these species is the spring phytoplankton bloom. In 1973 spawning occurred abruptly in early April at the time of the spring phytoplankton outburst, but in 1974 spawning was less abrupt corresponding to the slow development of the phytoplankton bloom in that year. Animals were collected prior to spawning and maintained in the laboratory under various temperature and light regimes: at 5 ° and 14 °C in darkness, and at 5 ° and 14 °C in light conditions similar to those in the field. These animals did not spawn when spawning occurred in the field, but animals returned to the field from the laboratory did spawn. In the laboratory a large proportion of animals spawned when they were exposed to phytoplankton collected with a 50μm mesh net. The results suggest that some substance bound to or released by phytoplankton stimulates spawning. For species with planktotrophic larvae the synchronization of spawning with the phytoplankton bloom increases the probability of favourable food and temperature conditions for the development of the larvae and juveniles.     

Movement patterns and spawning activity of individual nase Chondrostoma nasus (L.) in flow-regulated and weir-fragmented rivers

Eighteen adult nase Chondrostoma nasus (L.) (37.6–48.2 cm FL) from three highly fragmented Belgian rivers were tagged with surgically implanted radio transmitters and manually tracked from the banks of the rivers for 3–34 weeks. Their movements were mainly recorded during the circum reproduction period in 2001, 2002 and 2006 in river stretches delimited by physical barriers and/or minimum flow conditions. To reach the spawning grounds, nase displayed different patterns of movements that were mainly influenced by the configuration of the study site, the date of observation and the associated environmental conditions. Nase never cleared any physical obstacle but were able to spawn in minimum flow conditions or just downstream from physical obstacles. Nase were present on spawning grounds in late March in the warmest spring (2001) and from mid‐April to early May in the coldest spring (2006). After spawning, a major proportion of C. nasus migrated a substantial distance downstream, whereas others remained near their capture site and showed frequent movements, sometimes corresponding to group displacements from one river to another.     

The annual reproductive cycle of the freshwater mussel Dreissena polymorpha Pallas in lakes

Summary The annual development of the gonads of Dreissena polymorpha was studied at three sampling sites in two lakes over 3 and 1 1/2 years, respectively. A resting stage occurred after the last spawning in summer/autumn. Oogenesis (accompanied by multiplying segmentation of the oogonia and early growth processes of its oocytes) restarted in specimens at least 1 year old at low temperatures (below 10° C) during winter and early spring. At one location (Fühlinger See) the onset of the spawning season was correlated with an increase of water temperatures above 12° C. At 2 m depth, two main spawning periods in May and August were normally recognized, the first at temperatures of 12–16° C, the second at 16–21° C. It was clearly demonstrated for the first time in Dreissena polymorpha that the oocytes became mature in successive cohorts within one gonad. A female mussel may spawn several times during the reproductive season. At 9 m depth, the onset of spawning also started at about 12° C; this occurred in late summer, with two spawning periods within 1 month at a temperature range of 12–16° C. At another location (Heider Bergsee) the size of the gonads and the oocytes was reduced during April of both years studied, when food supply was low simultaneously with rapidly rising water temperatures in this shallow lake. There was no spawning period during spring. The major spawning period was delayed until July (temperatures 19–22°C). This shows (1) the synchronizing influence of low winter temperatures on the annual reproductive cycle and (2) a temperature threshold of at least 12° C for the start of the spawning processes. The results are discussed with regard to the geographical limits of further spread of Dreissena polymorpha.     

Changes in Structure and Function of Ventral Epidermis in Hyla arborea savignyi Aud. (Anura; Hylidae) Throughout Metamorphosis

The changes in epidermal ultrastructure during the metamorphic cycle of Hyla arborea are described. The number of cell layers increased from two to four in the late tadpole stages. The cell layers flatten and the process of stratification reaches its peak after the completion of metamorphosis. The mitochondria-rich cell appears early in the tadpole stages. Numerous flask cells are noticeable in the post-metamorphic stages. K+–p-NPPase activity was localized cytochemically in the epidermis of H. arborea during its metamorphic cycle. In the epidermis of the legless tadpole, evidence for K+–p-NPPase activity was confined intracellularly. During the later tadpole stages, preceding metamorphic climax, the main ATPase activity shifted to the baso-lateral cell membranes bordering with the intercellular spaces under the surface and later the stratum corneum. This continued after metamorphic climax in the juvenile toadlets, diminishing later in the adult stage.     

Disentangling reproductive biology of the Patagonian toothfish <Emphasis Type="Italic">Dissostichus eleginoides</Emphasis>: skipped vs obligatory annual spawning,foraging migration vs residential life style

Patagonian toothfish Dissostichus eleginoides Smitt 1898, is an important commercially targeted Notothenioid species in South-Atlantic waters. In this study we aimed to clarify several aspects of reproductive biology of Patagonian toothfish in the Falkland Islands waters. Histological examination of female gonads indicates that with the beginning of maturation females maintain at least two populations of oocytes, suggesting that toothfish requires up to two years for oocytes development. Females become mature at an average size of 79.1 cm indicating a decrease of first maturity size if toothfish females in the Falkland Island waters. The majority of females spawn at the size from 101 to 130 cm total length. Distribution of reproductive phases shows an increase of females at developing stage in December and March prior to the spawning peaks in May and August respectively. However, the majority of the toothfish population consist of non-spawning individuals remaining in regressing phase (55.8 to 85.6%) including the spawning period. The skip-spawning for toothfish has been defined as reabsorbing non-reproductive and resting types. The abbreviation of oocytes development in the gonads was observed from 1 to 22.1% of females which omitted the spawning season. Most likely females which remain in the spawning area have the opportunity to spawn more often, whereas females which undergo foraging migration toward Northern parts of the Falklands waters return to the spawning ground less often. Females remain Northern area longer to accumulate necessary amount of energy. This hypnotise is supported by the presence of females in immature, developing and regressing phase throughout surrounding Falkland Islands waters. Presence of post-spawning females in regressing stage throughout the Falklands waters suggest that toothfish may undertake irregular spawning/foraging migration when favourable for spawning condition occur.     

Biology of the amphioxus,Branchiostoma belcheri in the Ariake Sea,Japan II. Reproduction

We investigated the reproduction of the amphioxus Branchiostoma belcheri in the southern Ariake Sea, Japan, from 1999 to 2002. Gonads were very small or almost absent from September to December and began to develop in January. Changes in the gonad length index indicated that spawning began in mid June, after the gonads had attained maximum size. Although most gametes were extruded during the first spawning, some remained in the gonads. Shrunken gonads were much smaller but contained gametes, and the second spawning occurred around 10 July. It was unclear whether all adults spawned twice, but a large proportion of individuals did. After the first spawning, both males and females lost 30% of their body weight. Most one-year-old individuals did not spawn, and the minimum size at maturity was ca. 20 mm. We found no termination of reproduction among very large individuals. The average number of gonads was significantly larger on the right side of the body (26.2 in males and 26.1 in females) than on the left side (24.0 in males and 23.5 in females). We found two hermaphrodites in a total of 11,184 specimens examined. Each had four or three ovaries among a total of 45 or 54 gonads.     

Androgen directs sexual differentiation of laryngeal innervation in developing Xenopus laevis

In adult Xenopus laevis, innervation of the vocal organ is more robust in males than in females. This sex difference originates during tadpole development; at stage 56, when the gonads first differentiate, the number of axons entering the larynx is the same in the sexes, but by stage 62, innervation is greater in males. To determine if androgen secretion establishes sex differences in axon number, we treated tadpoles with antiandrogen or androgen beginning at stage 48 or 54 and counted laryngeal nerve axons at stage 62 using electron microscopy. When male tadpoles were treated with the antiandrogen hydroxyflutamide, axon numbers were reduced to female-typical values; axon numbers in females were unaffected by antiandrogen treatment. When female tadpoles were treated with the androgen DHT (dihydrotestosterone), axon numbers were increased to male-like values. These findings suggest that endogenous androgen secretion during late tadpole stages in males is required for the sexual differentiation of laryngeal innervation observed from stage 62 on. Because androgen treatment and laryngeal innervation affect myogenesis in postmetamorphic frogs, numbers of laryngeal dilator muscle fibers were determined for hormonally manipulated tadpoles. At stage 62, vehicle-treated males had more laryngeal axons than females; laryngeal muscle fiber numbers did not, however, differ in the sexes. Both male and female tadpoles, treated from stage 54 with DHT, had more muscle fibers at stage 62 than vehicle-treated controls. Thus, while endogenous androgen secretion during late tadpole stages is subthreshold for the establishment of masculinized muscle fiber numbers, laryngeal myogenesis is androgen sensitive at this time and can be increased by suprathreshold provision of exogenous DHT. A subgroup of tadpoles, DHT treated from stage 54 to 62, was allowed to survive, untreated, until postmetamorphic stage 2 (PM2: 5 months after metamorphosis is complete). Androgen treatment between tadpole stages 54 and 62 does not prevent the ontogenetic decrease in axon numbers characteristic of laryngeal development. In addition, the elevation in stage 62 axon numbers produced by DHT-treatment at late tadpole stages was not associated with elevated numbers of laryngeal muscle fibers at PM2. Juvenile males normally maintain elevated axon numbers (relative to final adult values) through PM2 and the presence of these additional axons may result from-rather than contribute directly to—laryngeal muscle fiber addition. 1994 John Wiley & Sons, Inc.     

A preliminary investigation of spawning migrations of grayling in a small stream as determined by radio-tracking

Adult grayling Thymallus thymallus migrated from 230 to 4980 m up the Aisne stream, Belgium, to spawn between 18 and 29 March, under decreasing floods, increasing temperature and low turbidity. Males ( n =4) arrived on spawning grounds several days earlier than females ( n =2), stayed there longer (10–19 v. 2–3 days), and occupied a single ground each, whereas females moved between several places. After spawning, all grayling homed precisely into the pool-riffle sequences where they were tagged in late February, and remained here until late June. These observations indicate that resident grayling are far less mobile than autumn-spawning salmonids, and that the environmental factors triggering spawning migrations resemble more closely those of spring-spawning cyprinids than of other salmonids. The implications of these restricted mobility patterns are discussed within the scope of population structure, and impact of river management.     

Rana temporaria metamorph production and population dynamics in the field – Effects of tadpole density,predation and pond drying

This study investigates factors of importance for tadpoles survival and metamorph production in the common frog Rana temporaria. It also assess the importance of this for the population dynamics of the species. Eighteen ponds were studied for up to 8 years. Data collected each year included: number of spawn clumps deposited, tadpole number and metamorph number. The permanency of the ponds was also recorded each year. Measures were taken of predator density. There was no suggestion of density dependence in the survival of tadpoles. In contrast, the number of spawn clumps deposited per pond area was highest for ponds with high survival. Density of predators (sticklebacks, newts and invertebrates) was negatively correlated to tadpole and metamorph survival. This was true both within (among years) and among ponds. Several of the study ponds dried completely before metamorphosis in some years. However, those ponds also were those with the smallest number of predators and in years with successful metamorphosis, these ponds produced more metamorphs than more permanent ponds. An analysis of the year to year dynamics showed that population size (number of deposited spawn clumps) was correlated to that in the previous year, suggesting a fairly high adult survival, but also on the number of metamorphs emerging two or three years before (corresponding to the age of sexual maturity of the species). It is concluded that the aquatic stage is not strongly limiting in these ponds but conservation efforts should be focused on the terrestrial habitat. Also, the study stresses the value of temporary ponds, despite the fact that recruitment often fails totally in these.     

Seamounts, New Moon and eel Spawning: The Search for the Spawning Site of the Japanese eel

After analyzing all the collection data for larvae of the Japanese eel, Anguilla japonica, in the western North Pacific, we found that the spawning site of this species appears to be near three seamounts in the West Mariana Ridge, 2000–3000km away from their freshwater habitats. These seamounts are located in the westward flow of the North Equatorial Current and are hypothesized to provide cues for migrating silver eels and to serve as possible aggregation sites for spawning. Back-calculated birth dates based on otolith microstructure of leptocephali indicate that the Japanese eel does not spawn continuously during the long spawning season from April to November, but is synchronized to spawn periodically once a month during new moon. This lunar periodicity of spawning and the seamount spawning hypothesis are new developments in the millennium-old mystery of eel spawning that has fascinated naturalists since the time of Aristotle.