The effects of kinship and density on growth and metamorphosis of the bronze frog (Rana temporalis) tadpoles

  Five clutches of Rana temporalis eggs collected along a stream were reared separately until formation of Gosner stage 25 tadpoles. The effect of kinship and density was then studied by rearing ten siblings in 1 (sib 1) or 5 (sib 5) l water, and mixed rearing of ten tadpoles (2 from each of the 5 clutches) in 1 (mix 1) or 5 (mix 5) l water; each group replicated five times. In all the groups tadpoles showed a sigmoid growth curve. Both kinship and density interacted to affect mean proportions of individuals reaching metamorphic climax (MC), mean body mass, and size frequency at MC (day 79). The proportion of tadpoles reaching MC was highest in sib 5 (82%) followed by mix 5 (77%), sib 1 (73%), and mix 1 (64%) groups. Crowding plus mixing significantly lowered the median developmental stage mean body mass and broadened the spectrum of developmental stages or size classes at MC. The size difference of individuals at MC was inversely related to density of rearing. Frequency of different developmental stages was comparable in sib 1, sib 5, and mix 5 groups. Interestingly, small individuals were significantly greater in number in the mix 1 group compared to sib 1. The above findings suggest that genotypic heterogeneity in conjunction with crowding retards growth rate of tadpoles in comparison with those reared in a genetically homogenous (sib) environment. Further, they suggest that the adverse effect of mixed rearing is context dependent. Received: 12 April 1999 / Received in revised form: 16 June 1999 / Accepted: 18 June 1999     

Effects of developmental and growth history on metamorphosis in the gray treefrog, Hyla versicolor (Amphibia, Anura)

In ecological models, the timing of amphibian metamorphosis is dependent upon rate of larval growth, e.g., tadpoles that experience a decrease in growth rate can initiate metamorphosis early. Recent authors have suggested that this plasticity may be lost at some point during the larval period. We tested this hypothesis by exposing groups of tadpoles of the gray treefrog, Hyla versicolor, to different growth schedules. In endocrine models, metamorphosis is dependent on thyroxine levels and thyroxine is antagonized by prolactin (amphibian larval growth hormone), consistent with the idea that a rapidly growing tadpole can delay metamorphosis. Thus, we also manipulated the rate of development by supplementing or maintaining natural thyroxine levels for half of the tadpoles in each growth treatment. All tadpoles that received thyroxine supplements metamorphosed at the same time regardless of growth history. They also metamorphosed earlier than tadpoles not treated with thyroxine. Tadpoles not given thyroxine supplements metamorphosed at different times: those growing rapidly during day 15-34 metamorphosed earlier than tadpoles growing slowly. Growth rate before day 15 and after day 34 had no effect on metamorphic timing. The difference in larval period between these rapidly growing tadpoles and their sisters given thyroxine treatments was less than the same comparison for tadpoles that grew slowly during the same period. This apparent prolactin/thyroxine antagonism did not exist after day 34. These results are consistent with the hypothesis of a loss of plasticity in metamorphic timing.     

Maternal effects on offspring growth and development depend on environmental quality in the frogBombina orientalis

Summary Differences in maternal investment and initial offspring size can have important consequences for offspring growth and development. To examine the effects of initial size variability in the frogBombina orientalis, we reared larvae (N=360) in one of two treatments representing different levels of environmental quality. We used snout-vent length at the feeding stage (stage 25, Gosner 1960) as a measure of maternal investment. In a “low quality” treatment, larvae were reared with two conspecific tadpoles and food was limited, whereas in a “high quality” treatment, larvae were reared individually and were fed ad libitum. Among tadpoles reared in the low quality treatment, individuals that were initially small had smaller body sizes through metamorphosis and longer larval periods than individuals that were initially large. Among tadpoles reared in the high quality treatment, initial size had only a weak influence on later larval size, and did not significantly affect metamorphic size of the duration of the larval period. This interaction between maternal investment and rearing conditions suggests that production of initially small offspring could be advantageous if these offspring develop in relatively benign environments, but disadvantageous if environments are more severe. These findings are discussed in light of previous studies that have demonstrated such interactions in organisms with complex life cycles.     

Influence of density and predators on metamorphic size in Rhinella schneideri tadpoles raised in mesocosm conditions

Amphibians exhibit extreme plasticity in the timing of metamorphosis, and several species respond to water availability, accelerating metamorphosis when their ponds dry. We analyzed the plasticity of the developmental response to water volume in Rhinella schneideri tadpoles. We raised tadpoles in mesocosm. Covariation between body size at metamorphosis and timing of development was positive. Nevertheless, the first approximately 53% of the metamorphoses finishing the cycle required between 34 and 56 days, and the covariation between body size at metamorphosis and timing of development was negative. For these tadpoles, the larval density and the presence of predators did not significantly affect their mass to metamorphosis. Nevertheless, predators affected time to metamorphosis. For the remainder of the tadpoles that reached metamorphosis at > 56 days, the relationship between body size at metamorphosis and timing of development was positive. For these tadpoles, larval density was important for mass at metamorphosis and presence of predators was also important for time to metamorphosis. Two dominant features were observed: (i) approximately 53% of metamorphs had morphological features similar to individuals developing in desiccating ponds, and (ii) the other individuals had morphological characteristics comparable to metamorphs developing in an unchanging environment.     

密度对大树蛙蝌蚪生长发育和存活率的影响

种群密度效应主要表现在影响和调节种群的死亡率、发育速率、繁殖率以及扩散、迁移等反应种群数量动态的重要参数。分析密度对大树蛙蝌蚪生长发育和存活率的影响,有助于探究外界环境因子导致大树蛙种群密度迅速下降的作用机制。设置了15、20、25只/L和30只/L 4个密度组,测量大树蛙蝌蚪的尾长、体长、发育时间和存活率。结果表明,在15—30只/L范围内,密度升高显著降低了大树蛙蝌蚪尾长和体长的生长速率,减小其变态期的尾长和体长大小,其中与15只/L相比,20、25只/L和30只/L 3组蝌蚪的尾长分别降低了11.6%、11.8%和13.9%,体长分别降低了11.1%、9.5%和12.9%;随着密度的升高,大树蛙蝌蚪发育至跗蹠部伸长期和前肢伸出期的所需时间显著延长;大树蛙蝌蚪生长后期的存活率随密度升高显著降低,但密度对蝌蚪生长早期的存活率影响不显著。因此,密度升高可显著减小大树蛙蝌蚪的尾长和体长、延长发育时间和降低其生长后期的存活率,可能影响大树蛙蝌蚪变态后的适合度。     

The ontogeny of functional design: metamorphosis of feeding behaviour in the tiger salamander (Ambystoma tigrinum)

The ontogeny of feeding behaviour was studied quantitatively in the tiger salamander, Ambystoma tigrinum , to elucidate the relative importance of morphological and environmental changes on form and function. High-speed films of prey capture provided data for a frame-by-frame analysis of seven kinematic parameters of feeding behaviour. By comparing underwater feeding of larval and metamorphosed individuals, the effect of morphological changes occurring at metamorphosis on the feeding kinematic pattern was determined. By comparing metamorphosed animals feeding in the water and on land, changes in feeding kinematics associated with the environmental transition (and thus the differing physical properties of water and air) were determined. Both univariate and multivariate analyses failed to demonstrate any differences between larval and metamorphosed aquatic feedings for seven kinematic variables. However, when individuals feed on land, a radical shift in hyoid kinematics was observed. In addition, multivariate analysis showed that terrestrial feedings differed from aquatic feedings in having longer duration head movements. The lack of a kinematic difference between larval and metamorphosed individuals feeding in the water indicates that the morphological changes occurring at metamorphosis do not impose any obligatory kinematic consequences. Rather, metamorphosed Ambystoma tigrinum acquire the ability to modulate their kinematic pattern depending on the environment.     

Interacting effects of predation risk and food availability on larval anuran behaviour and development

Age and size at metamorphosis are two important fitness components in species with complex life cycles. In anurans, metamorphic traits show remarkable phenotypic plasticity, especially in response to changes in growth conditions. It is also possible that the perception of risk directly determines changes in larval period and the size of metamorphs. This study examines how the perception of predation risk affects the timing of and size at metamorphosis in common frogs (Rana temporaria). I raised tadpoles at two risk levels (fish-conditioned water or unconditioned water) crossed with the availability or lack of food at night (all tadpoles had food available in the day). Tadpoles reacted to chemical cues from predatory fish by decreasing activity. A novel behavioural result was a predation×food interaction effect on refuge use, which also accounted for most of the predator main effect: predation risk only caused increased refuge use in the night-starved treatment. Despite these behavioural modifications, the perception of predation risk did not affect growth rate and mass at metamorphosis in a simple way: the effects of food regime on growth and size at metamorphosis were dependent on the level of predation risk as revealed by significant predation×food interaction effects. Tadpoles who had food withheld at night metamorphosed at the smallest size, suggesting a negative relationship between size at metamorphosis and refuge use. Tadpoles raised in fish-conditioned water had longer larval periods than those in unconditioned water, but these differences were significant only if food was available at night. These results conflict with the hypotheses that tadpoles should reduce their larval period or growth rates (and hence metamorphose at a smaller size) as the risk of predation increases. In contrast to predation risk, food availability strongly affected the length of the larval period: night-starved tadpoles metamorphosed relatively early with or without fish stimulus. Thus, early metamorphosis resulted from periods of low food availability, but not from a heightened ”perceived risk” of predation. This example counters the hypothesis of acceleration of the developmental rate (which shortens the time to metamorphosis) as a mechanism to escape a risky environment. Received: 18 August 1999 / Accepted: 10 January 2000     

Density But Not Kinship Regulates the Growth and Developmental Traits of Chinese Tiger Frog （Hoplobatrachus chinensis） Tadpoles

Kinship and density are believed to affect important ecological processes such as intraspecific competition, predation, growth, development, cannibalism, habitat selection and mate choice, In this work, we used Chinese tiger frog Hoplobatrachus chinensis tadpoles as an experimental model to investigate the effects of kinship and density on growth and development of this species over a 73 day period. The results showed that density can affect the growth and developmental traits （survival rate, larval period, size at the limb bud protrusion/metamorphic climax and body mass at different life stages） of H. chinensis tadpoles, while kinship does not. Tadpoles took longer to develop and potential metamorphosis was greater in high density groups of both sibling and non-siblings. The interaction of kinship and density did not significantly influenced growth traits of H. chinensis tadpoles during the experimental period. For coefficient variations of each growth trait, no differences were detected between sibling and non-sibling groups. These findings provide valuable information on the basic ecology of H. chinensis which will be helpful in future studies of other anuran species.     

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.     

Growth and development of larval green frogs (Rana clamitans) exposed to multiple doses of an insecticide

Our objective was to determine how green frogs (Rana clamitans) are affected by multiple exposures to a sublethal level of the carbamate insecticide, carbaryl, in outdoor ponds. Tadpoles were added to 1,000-l ponds at a low or high density which were exposed to carbaryl 0, 1, 2, or 3 times. Length of the larval period, mass, developmental stage, tadpole survival, and proportion metamorphosed were used to determine treatment effects. The frequency of dosing affected the proportion of green frogs that reached metamorphosis and the developmental stage of tadpoles. Generally, exposure to carbaryl increased rates of metamorphosis and development. The effect of the frequency of carbaryl exposure on development varied with the density treatment; the majority of metamorphs and the most developed tadpoles came from high-density ponds exposed to carbaryl 3 times. This interaction suggests that exposure to carbaryl later in the larval period stimulated metamorphosis, directly or indirectly, under high-density conditions. Our study indicates that exposure to a contaminant can lead to early initiation of metamorphosis and that natural biotic factors can mediate the effects of a contaminant in the environment.     

Influence of density and salinity on larval development of salt‐adapted and salt‐naïve frog populations

Environmental change and habitat fragmentation will affect population densities for many species. For those species that have locally adapted to persist in changed or stressful habitats, it is uncertain how density dependence will affect adaptive responses. Anurans (frogs and toads) are typically freshwater organisms, but some coastal populations of green treefrogs (Hyla cinerea) have adapted to brackish, coastal wetlands. Tadpoles from coastal populations metamorphose sooner and demonstrate faster growth rates than inland populations when reared solitarily. Although saltwater exposure has adaptively reduced the duration of the larval period for coastal populations, increases in densities during larval development typically increase time to metamorphosis and reduce rates of growth and survival. We test how combined stressors of density and salinity affect larval development between salt‐adapted (“coastal”) and nonsalt‐adapted (“inland”) populations by measuring various developmental and metamorphic phenotypes. We found that increased tadpole density strongly affected coastal and inland tadpole populations similarly. In high‐density treatments, both coastal and inland populations had reduced growth rates, greater exponential decay of growth, a smaller size at metamorphosis, took longer to reach metamorphosis, and had lower survivorship at metamorphosis. Salinity only exaggerated the effects of density on the time to reach metamorphosis and exponential decay of growth. Location of origin affected length at metamorphosis, with coastal tadpoles metamorphosing slightly longer than inland tadpoles across densities and salinities. These findings confirm that density has a strong and central influence on larval development even across divergent populations and habitat types and may mitigate the expression (and therefore detection) of locally adapted phenotypes.     

Sequential predator effects across three life stages of the African tree frog, <Emphasis Type="Italic">Hyperolius spinigularis</Emphasis>

While theoretical studies of the timing of key switch points in complex life cycles such as hatching and metamorphosis have stressed the importance of considering multiple stages, most empirical work has focused on a single life stage. However, the relationship between the fitness components of different life stages may be complex. Ontogenetic switch points such as hatching and metamorphosis do not represent new beginnings—carryover effects across stages can arise when environmental effects on the density and/or traits of early ontogenetic stages subsequently alter mortality or growth in later stages. In this study, I examine the effects of egg- and larval-stage predators on larval performance, size at metamorphosis, and post-metamorphic predation in the African tree frog Hyperolius spinigularis. I monitored the density and survival of arboreal H. spinigularis clutches in the field to estimate how much egg-stage predation reduced the input of tadpoles into the pond. I then conducted experiments to determine: (1) how reductions in initial larval density due to egg predators affect larval survival and mass and age at metamorphosis in the presence and absence of aquatic larval predators, dragonfly larvae, and (2) how differences in mass or age at metamorphosis arising from predation in the embryonic and larval environments affect encounters with post-metamorphic predators, fishing spiders. Reduction in larval densities due to egg predation tended to increase per capita larval survival, decrease larval duration and increase mass at metamorphosis. Larval predators decreased larval survival and had density-dependent effects on larval duration and mass at metamorphosis. The combined effects of embryonic and larval-stage predators increased mass at metamorphosis of survivors by 91%. Larger mass at metamorphosis may have immediate fitness benefits, as larger metamorphs had higher survival in encounters with fishing spiders. Thus, the effects of predators early in ontogeny can alter predation risk even two life stages later.     

Rana cascadae tadpoles aggregate with siblings: an experimental field study

Previous laboratory studies have shown that Rana cascadae larvae preferentially associated with siblings over non-siblings in choice tests. This study, conducted during three consecutive summers, tests the hypothesis that R. cascadae larvae aggregate nonrandomly with respect to sibship in natural ponds. Pairs of sibships were reared in separate tanks or together in the same tank in the laboratory. Each sibship within a pair was then stained with neutral red or methylene blue dye and released together in a natural pond. Over a period of several days, aggregations of tadpoles within test ponds were repeatedly captured, censused for sibship composition, and released. In control tests, two groups of tadpoles from the same sibship were dyed different colors and released together. In total, 25 different tests were conducted using tadpoles from 31 sibships and 456 aggregations were sampled. The distribution of color compositions of aggregations in control tests did not differ from an expected random distribution. Color compositions of aggregations in experimental tests differed from controls and from an expected random distribution. Aggregations in these tests tended to be dominated by one of the two colors (sibships). We conclude that R. cascadae tadpoles recognize and prefer to aggregate with siblings in natural field conditions. Circumstances of early rearing (i.e., whether tadpoles were reared with siblings or in mixed sibling/non-sibling groups) had no influence on preferences to associate with siblings, but there was an inverse correlation between group size and sibling association.     

Relatedness and competitive asymmetry – the growth and development of common frog tadpoles

Individuals can compete either through direct interference or uptake of limiting resources. If competing individuals are able to recognize their relatives, relatedness of competitors may evoke kin selection, which favours relatively even resource share among relatives. Resource competition is often size-symmetric, i.e. proportional to an individual's biomass, while interference competition is asymmetric giving large individuals a disproportionate advantage over small individuals. Kin-selection is predicted to reduce the intensity of direct interference and competitive asymmetry, leading to increased mean and decreased variation in individual size. We tested these predictions by investigating the effects of relatedness on age and size at metamorphosis in the common frog Rana temporaria tadpoles in a laboratory experiment. We reared related (full- and half-sibs) and unrelated tadpoles of different sizes (small, large, small and large together) at two densities until metamorphosis. Relatedness had little effect on mean growth, but it reduced size variation, as measured with coefficient of variation. Furthermore, there was a significant interaction between relatedness and density in size at metamorphosis, so that relatives always grew better in lower density, but growth was less affected by density among unrelated individuals. This indicates that the effects of relatedness on tadpole performance may be context dependent. Initial size differences in the mixed size treatment evened out during the course of the experiment, and initially small tadpoles were able to compensate the early growth losses, although it took longer for them to reach metamorphosis. We conclude that although relatedness may have rather small effects on the growth and development of R. temporaria tadpoles, it increases the symmetry of resource share decreasing between-individual variation in size at metamorphosis.     

An investigation of sibling recognition in Rana cascadae tadpoles

Sibling recognition was studied experimentally in tadpoles of the Cascades frog, Rana cascadae. Sibships were divided into two groups at an early developmental stage. One group was reared with siblings and the second with a mixture of siblings and non-siblings. Whe given a choice of associating with a sibling or non-sibling group, individuals reared with siblings preferred siblings. One mixed-reared group spent more time associating with unfamiliar siblings than unfamiliar nonsiblings. Tadpoles of another mixed-reared group preferred to associate with pure siblings over a mixture of siblings and non-siblings with which they were reared. When the stimulus animals were taken exclusively from the mixed-rearing tank, two mixed-reared groups showed no sibling preferences. Our results suggest that early association with non-siblings does not affect sibling recognition in this species.     

Competing tadpoles: Australian native frogs affect invasive cane toads (Rhinella marina) in natural waterbodies

The cane toad (Rhinella marina) is one of the most successful invasive species worldwide, and has caused significant negative impacts on Australian fauna. Experimental work in the laboratory and in mesocosms has shown that tadpoles of native frogs can affect survival, size at metamorphosis and duration of larval period of cane toad tadpoles. To test if these effects occur in nature, we conducted a field experiment using two temporary ponds where we set up enclosures with tadpoles of native green tree frogs (Litoria caerulea) and cane toads in treatments with a range of densities and combinations. The presence of green tree frog tadpoles significantly decreased the growth rate of toad tadpoles and increased the duration of their larval period in both ponds; in one pond, frog tadpoles also significantly reduced the body length and mass of metamorph toads. Toad tadpoles did not have any significant negative effects on green tree frog tadpoles, but there was strong intraspecific competition within the latter species: increased frog tadpole density resulted in increased larval period and reduced survival, growth rate and size at metamorphosis for frogs at one or both ponds. Our results are encouraging for the possibility of using native frogs as one component of an integrated approach to the biological control of cane toads.     

Ecological constraints on amphibian metamorphosis: interactions of temperature and larval density with responses to changing food level

Phenotypic plasticity is adaptive for an organism inhabiting a variable environment if the optimal phenotype of a trait that affects fitness varies with environmental conditions, and if the organism can perceive environmental conditions and respond appropriately. Wilbur and Collins have proposed that amphibian larvae might respond adaptively to changes in their resource environment. If conditions for growth in the aquatic environment deteriorate, then a tadpole should metamorphose earlier and smaller than a tadpole under constant high growth conditions. Several experiments on a variety of species have tested this prediction, but only one demonstrated such a response. That experiment involved Couch's spadefoot toads (Scaphiopus couchii) and employed a gradual decrease in food level, whereas the others all used an abrupt switch from high to low food. The purpose of the present experiment was to examine the response of S. couchii to an abrupt change in food level, and to determine if the response depended on the level of two other factors, density and temperature, that also affect larval development. The average effects of the abrupt change in food level were similar to those seen in studies on other species: age at metamorphosis was primarily determined by the early food regime, and size at metamorphosis was determined by food level late in the larval period, suggesting that the effect of decreased food depends on how the food change is done. However, the response to even an abrupt food change depended on interactions with other environmental factors. At high temperature, high initial food, and low density, development was very rapid and tadpoles switched from high to low food metamorphosed at about the same time and size as those at constant high food. In contrast, under high temperature and high initial food conditions, but at high density, tadpoles switched to low food metamorphosed somewhat earlier and smaller, on average, than tadpoles kept at high food. At low temperature, the direction of response depended on density: tadpoles metamorphosed much smaller and slightly, but significantly, earlier at low density, but smaller and later at high density. The developmental response to increased food also varied with temperature. Larvae at high temperature metamorphosed earlier and larger than those at constant low food. At low temperature, larvae metamorphosed larger, but at nearly the same time as their counterparts at constant low food. The combination of high density and constant low food prevented any tadpoles from metamorphosing at high temperature, and allowed relatively few metamorphs at low temperature. Under conditions which impose either very rapid or retarded development, the opportunity to respond to altered food level may be limited. Interactions among environmental factors, therefore, may constrain responses to changing conditions, and may even prevent completion of development. Received: 3 February 1997 / Accepted: 2 October 1997     

Reproductive biology of the fire-bellied toads, Bombina bombina and B. variegata (Anura: Discoglossidae): egg size, clutch size and larval period length differences

Clutch size, egg size, larval size and duration of larval period were estimated for samples of Bombina bombina and B. variegata from several populations. Bombina variegata lays fewer eggs per batch (mean 17.4) than B. bombina (mean 32.5). The volume of B. variegata eggs is 2.4 times greater and the dry weight 2.3 times greater than that of B. bombina. As a consequence, the volume of B. variegata hatchlings and their dry weight are respectively 1.9 times and 2.5 times greater than that of B. bombina. Analysis of variance showed that variation of egg size in B. variegata is significantly greater than in B. bombina. When reared under laboratory conditions freshly metamorphosed individuals of both species showed no difference in body size or weight. Although growth rates are equal, tadpoles of B. variegata reached metamorphosis 14 days earlier than B. bombina tadpoles because of differences in size of hatchlings. Differences in reproductive parameters found for the two European Bombina species can be interpreted as adaptations to contrasting environments in which they breed.     

Populational Changes of the Enteric Protozoans Opalina spp. and Nyctotherus cordiformis During the Ontogeny of Anuran Tadpoles

ABSTRACT. We studied ontogenetic population changes of Opalina and Nyctotherus cordiformis in eight species of tadpoles from 10 sites in east-central Mississippi. Most tadpoles acquired Opalina early in development, while the acquisition of N. cordiformis was variable. Developmental stage, species and collection site explained significant amounts of the variation in Opalina density of tadpoles ( F = 11.6; df = 27, 235; P < 0.0001) and metamorphs ( F = 7.31; df = 24, 84; P < 0.0001). Relationships between Opalina density and host stage showed either (1) a gradual decrease or (2) a gradual increase throughout host ontogeny. Opalina densities declined during metamorphosis. Density variations of N. cordiformis were explained by host species of tadpoles ( F = 9.30; df = 7, 142; P < 0.0001) and by host species and stage of metamorphs ( F = 5.85; df = 8, 62; P < 0.0001).
The length of larval period, habitat duration and generation time of the protozoans are suggested as major modifiers of the protozoan densities. Hosts with long larval periods show a decreasing population density and hosts with short developmental periods show a pattern of increasing density. Neither pattern was detected in tadpoles from temporary sites. Metamorphic declines in protozoan density, but not necessarily the loss of protozoans, reflect metamorphic alterations of the gut common to all hosts.     

POPULATION STRUCTURE AND COMPETITION AMONG KIN IN THE CHORUS FROG (PSEUDACRIS TRISERIATA)

In natural populations on Isle Royale, tadpoles of the chorus frog live in small pools on the shore of Lake Superior. Hatchling densities are high and sufficient to cause competitive impact on survivorship, growth, and development. The temporal and spatial pattern of egg laying indicates that tadpoles in many of the pools belong to single sibships. I calculated average coefficients of relationship among tadpoles under the assumption that eggs laid together are the products of the same breeding pair; the coefficients indicate that relationship among competing larvae averages approximately 0.35, and varies widely among larval subpopulations, from less than 0.1 to about 0.5. Two growth experiments were carried out in pens to test whether growth trajectories and larval characteristics at metamorphosis are influenced by relationship among competing tadpoles. In both experiments, initial density was crossed with average relationship; relationship was controlled by varying the number of sibships per pen from one to four. The same sibships were used in both experiments, but one experiment had lower initial densities and less water volume per pen than the other. In both experiments, density reduced growth, developmental rate, size at metamorphosis, survivorship to the onset of metamorphosis, and the proportion of survivors which actually attained metamorphosis by the end of the experiment. Kin effects occurred only in the experiment carried out in small pens at high initial densities: in this experiment, pure sib populations grew faster, and a higher proportion attained metamorphosis. However, there were no kin effects on larval period or body size at metamorphosis. The chorus frog appears to have a population structure conducive to kin-group selection. Furthermore, high variance in the average coefficient of relationship among pools should favor kin recognition and kin-specific interference behavior. The growth experiments suggest that the tadpoles respond to the genetic relationship of competitors, with significant effects on the distribution of fitness at metamorphosis among members of the group.