MHC class I antigens as surface markers of adult erythrocytes during the metamorphosis of Xenopus

An alloantiserum produced against Xenopus MHC class I antigens has been used to distinguish different erythrocyte populations at metamorphosis. By analysis using a fluorescence-activated cell sorter (FACS) analyzer, tadpole (stage 55) and adult erythrocytes have distinct volume differences and tadpole cells have no MHC antigens on the cell surface. Both tadpole and adult erythrocytes express a "mature erythrocyte" antigen marker, recognized by its monoclonal antibody (F1F6). During metamorphosis, immature erythrocytes, at various stages of differentiation, which express adult levels of cell-surface MHC antigens by 12 days after tail resorption, are found in the bloodstream. These immature cells are biosynthetically active, produce adult hemoglobin, and mature by 60 days after the completion of metamorphosis. Percoll gradient-density fractionation has shown that all of the cells in the new erythrocyte series express adult levels of MHC antigens but there is only a gradual increase in the amount of "mature erythrocyte" antigen. Tadpole erythrocytes, which are biosynthetically active during larval stages, produce small amounts of surface MHC antigens before the metamorphic climax and then become metabolically inactive. They are completely cleared from the circulation by 60 days after metamorphosis. Erythrocytes from tadpoles arrested in their development for long periods of time express intermediate levels of MHC antigens, suggesting a "leaky" expression of these molecules in the tadpole cells. The most abundant erythrocyte cell-surface proteins from tadpoles and adults, as judged by two-dimensional gel electrophoresis, are very different.     

The formation of new characteristics in life cycle of the marsh frog (Rana ridibunda) in thermal pond conditions

Using mark and recapture approach, the long-term population dynamics in the marsh frog (Rana ridibunda) was studied. Group-marking of metamorphs was conducted in a small thermal pond serving as a sedimentation basin for discharged waters from Nizhny Tagil metallurgic works. Depending on the time of metamorphosis, three groups of individuals could be singled out, namely: early ones (group I), middle ones (group II), and late ones that overwinter as tadpoles and complete metamorphosis in May of the next year (group III). Upon metamorphosis completion, individuals of group I were found to be significantly larger than those of group II, and individuals of both these groups to be significantly smaller than those of group III. After first wintering, immature individuals from group I were significantly larger than either individuals from group II or metamorphs from group III, though a growth rate of the latter was significantly higher than in groups I and II. These discrepancies were observed both between immature and adult individuals. Over the period from metamorphosis completion to the first wintering ending, survivorship in group I was significantly higher and did not differ between groups II and III. In adult frogs, maximum survivorship was registered in group III and minimum one in group II; the detected differences recurred in each age class till the fourth wintering. However, in age classes that overwintered 4 and 5 times, maximum survivorship was observed in group II, which can be treated as a compensation for rather low survivorship of this group at younger ages. All the events of tadpoles of this species overwintering (except in other thermal water bodies) that are described in literature, correspond to rare deviations from normal ontogenesis. Therefore, the revealed formation of a numerous group of overwintering tadpoles in successive generations should be considered as a new adaptation which sense is a decrease of competition between tadpole groups when using the highly productive resources of the thermal pond practically year-round. The advantage in body size and growth rate of not only tadpoles but also of metamorphs, immature and adult individuals of group III indicates that after metamorphosis the strategy of this group still remains successful. The reason for that is unusually large body size of metamorphs which provides higher postmetamorphic survivorship and greater female fecundity.     

Wide tissue distribution of axolotl class II molecules occurs independently of thyroxin

 Unlike most salamanders, the Mexican axolotl (Ambystoma mexicanum) fails to produce enough thyroxin to undergo anatomical metamorphosis, although a “cryptic metamorphosis” involving a change from fetal to adult hemoglobins has been described. To understand to what extent the development of the axolotl hemopoietic system is linked to anatomical metamorphosis, we examined the appearance and thyroxin dependence of class II molecules on thymus, blood, and spleen cells, using both flow cytometry and biosynthetic labeling followed by immunoprecipitation. Class II molecules are present on B cells as early as 7 weeks after hatching, the first time analyzed. At this time, most thymocytes, all T cells, and all erythrocytes lack class II molecules, but first thymocytes at 17 weeks, then T cells at 22 weeks, and finally erythrocytes at 26–27 weeks virtually all bear class II molecules. Class II molecules and adult hemoglobin appear at roughly the same time in erythrocytes. These data are most easily explained by populations of class II-negative cells being replaced by populations of class II-positive cells, and they show that the hemopoietic system matures at a variety of times unrelated to the increase of thyroxin that drives anatomical metamorphosis. We found that administration of thyroxin during axolotl ontogeny does not accelerate or otherwise affect the acquisition of class II molecules, nor does administration of drugs that inhibit thyroxin (sodium perchlorate, thiourea, methimazole, and 1-methyl imidazole) retard or abolish this acquisition, suggesting that the programs for anatomical metamorphosis and some aspects of hemopoietic development are entirely separate. Received: 15 July 1997 / Revised: 28 October 1997     

Simultaneous activation of genes encoding urea cycle enzymes and gluconeogenetic enzymes coincides with a corticosterone surge period before metamorphosis in Xenopus laevis

Amphibian tadpoles are postulated to excrete ammonia as nitrogen metabolites but to shift from ammonotelism to ureotelism during metamorphosis. However, it is unknown whether ureagenesis occurs or plays a functional role before metamorphosis. Here, the mRNA-expression levels of two urea cycle enzymes (carbamoyl phosphate synthetase I [CPSI] and ornithine transcarbamylase [OTC]) were measured beginning with stage-47 Xenopus tadpoles at 5 days post-fertilization (dpf), between the onset of feeding (stage 45, 4 dpf) and metamorphosis (stage 55, 32 dpf). CPSI and OTC expression levels increased significantly from stage 49 (12 dpf). Urea excretion was also detected at stage 47. A transient corticosterone surge peaking at stage 48 was previously reported, supporting the hypothesis that corticosterone can induce CPSI expression in tadpoles, as found in adult frogs and mammals. Stage-46 tadpoles were exposed to a synthetic glucocorticoid, dexamethasone (Dex, 10–500 nM) for 3 days. CPSI mRNA expression was significantly higher in tadpoles exposed to Dex than in tadpoles exposed to the vehicle control. Furthermore, glucocorticoid receptor mRNA expression increased during the pre-metamorphic period. In addition to CPSI and OTC mRNA upregulation, the expression levels of three gluconeogenic enzyme genes (glucose 6-phosphatase, phosphoenolpyruvate carboxykinase, and fructose-1,6-bisphosphatase 1) increased with the onset of urea synthesis and excretion. These results suggest that simultaneous induction of the urea cycle and gluconeogenic enzymes coincided with a corticosterone surge occurring prior to metamorphosis. These metabolic changes preceding metamorphosis may be closely related to the onset of feeding and nutrient accumulation required for metamorphosis.     

Biochemical evidence that equine leucocyte antigens W13, W22 and W23 are present on horse major histocompatibility complex class II molecules

A number of horse alloantisera were characterized biochemically as being directed against MHC class I or class II antigens by immunoprecipitation of the corresponding antigens from lysates of biosynthetically radioactively labelled lymphocytes and determination of their molecular weights by SDS-PAGE and fluorography. Sera recognizing A2 and A3 specificities precipitated antigens of 44,000 Daltons molecular weight (class I heavy chain), whereas sera with specificities W13, W22 and W23 precipitated antigens corresponding to class II dimers (30,000 and 32,000 Daltons). Comparison with antigens precipitated from horse lymphocyte lysates using (cross-reacting) antibodies to human class I and class II MHC molecules confirmed the results obtained.     

The major histocompatibility complex of the rat,RT 1

Recombinational analysis has shown that the rat MHC,RT1 is divided into two regions:RT1.A, which codes for class I (transplantation) antigens, andRT1.B, which controls the humoral immune response and proliferative response to allogeneic cells as well as the expression of class II (Ia) antigens. Serological and sequence studies suggest that there might be more than one antigen-coding locus within theRT1.A region. Results obtained by sequential immunoprecipitation reveal that both regions code for at least two gene products. By implication, theRT1 complex must therefore harbor at least four loci;RT1.A andD coding for class I glycoproteins (45,000 daltons); andRT1.B andE coding for class II (Ia) glycoproteins (35,000 and 28,000 daltons).     

Larval antigen molecules recognized by adult immune cells of inbred Xenopus laevis: two pathways for recognition by adult splenic T cells

During anuran metamorphosis, larval cells of the tadpole are completely eliminated and replaced by adult cells in the corresponding tissues of the frog for the adaptation to terrestrial life from an aquatic life. Before the metamorphic climax, most of the cells have already transformed from larval cells into adult-type cells, but the tail cells remain as larval cells even at the climax stages of metamorphosis. In our previous works, we demonstrated that larval skin grafts are rejected by an inbred strain of adult Xenopus and that the larval cells are recognized and made apoptotic by splenocytes obtained from adults and/or metamorphosing tadpoles in vitro (Y. Izutsu and K. Yoshizato, 1993, J. Exp. Zool. 266, 163-167; Y. Izutsu et al., 1996, Differentiation 60, 277-286). In the present study, it was found that there were two types of larval epidermal cells, classified according to the presence of major histocompatibility complex (MHC); one is the apical cell expressing both MHC classes I and II, and the other is the skein cell, which expresses no MHC. By a Percoll gradient, we were able to separate these two types of cells and examined the proliferative response of adult T cells to each of them. It was revealed that the apical cells (MHC-positive) were recognized directly by adult splenic T cells, whereas the skein cells (MHC-negative) were recognized by the T cells via the antigen presentation by adult splenocytes. Both of these proliferative responses were restricted to MHC class II. This is the first report showing how the larval-specific antigens present in different forms in epidermal cells are recognized as immunological targets by syngeneic adult T lymphocytes.     

Tolerogenic ability of thymocytes in organ-cultured thymus lobes.

It is generally believed that macrophages and dendritic cells are the major cell populations that present tolerogenic self antigens to developing thymocytes. However, it is still controversial whether self antigens expressed on thymocytes themselves work as tolerogens in the thymus. To evaluate this possibility, Thy-1 bright cells were sorted out from fetal thymus cells on the 15th gestation day, and were colonized into 2'-deoxyguanosine-treated allogeneic thymus lobes. The repopulated thymus lobes were organ-cultured, and the allo-specific killer activity of thymocytes recovered from the lobes was examined. These cells were tolerant to class I but not to class II-MHC of the donor haplotype, indicating that class I molecules expressed on the thymocytes worked as tolerogen. Tolerogenic ability of Thy-1+ cells was also demonstrated in another system. Upon intimate contact with allogeneic thymus lobes on a polycarbonate filter, thymus lobes fused with each other and Thy-1+ cells co-migrated (Eur. J. Immunol. 19:1525-1530, 1989). In thymus lobes rendered parabiotic from day 5, CTL tolerance was achieved against class I but not to class II MHC. These data indicate that thymocyte-thymocyte interaction is sufficient to induce class I CTL tolerance in developing thymocytes.     

Invasive equine trophoblast expresses conventional class I major histocompatibility complex antigens

Monoclonal antibodies and alloantisera were used in an indirect immunohistochemical assay to determine the expression of class I and class II Major Histocompatibility Complex (MHC) antigens by equine placental cells and the endometrial tissues at the fetal-maternal interface. MHC class I antigens were expressed at high density on the surface of the trophoblast cells of the chorionic girdle at days 32-36, just prior to their invasion of the endometrium. The mature gonadotrophin-secreting cells of the endometrial cups, which are derived from the chorionic girdle cells, had greatly reduced levels of MHC class I antigen expression while no MHC class I antigens were detectable on the non-invasive trophoblast cells of the allantochorion, except in small isolated patches. MHC class I antigens immunoprecipitated from chorionic girdle cells with either monoclonal antibodies or alloantisera had a relative molecular mass of 44,000, which was identical to that of MHC class I antigens precipitated from lymphocytes with the same reagents. MHC class II antigens were not detected on any trophoblast cells, although they were expressed at high levels by the endometrial glandular and lumenal epithelium immediately bordering the endometrial cups. MHC class I antigens were also expressed at high levels by endometrial tissues in the area of the cups. The high level of MHC class I antigen expression by endometrial glands within and bordering the cups was in sharp contrast to the greatly reduced class I antigen expression by the mature endometrial cup cells themselves.(ABSTRACT TRUNCATED AT 250 WORDS)     

中华大蟾蜍蝌蚪变态过程中脊椎骨化次序

两栖动物在幼体变态即由水栖到陆栖的环境转变中,骨骼系统会发生重塑。本文采用茜素红和阿利新蓝的双染色技术对不同发育阶段中华大蟾蜍(Bufo gargarizans)蝌蚪变态过程中(Gosner 38~46)脊椎骨的发育进程进行了形态学研究。结果显示,在中华大蟾蜍蝌蚪Gosner 39期,椎板中线处发生融合;荐前椎Ⅱ-Ⅷ和荐椎的椎体、椎弓起始骨化发生在Gosner 42期;其次荐前椎Ⅱ-Ⅷ和荐椎的横突、底索和荐后椎Ⅰ开始骨化;荐后椎Ⅱ骨化最晚;在Gosner 46期,尾杆骨最终形成。荐后椎愈合形成尾杆骨反映无尾类幼体由水栖环境转变为陆生环境中骨骼系统的机能适应。     

Ecological immunogenetics of life-history traits in a model amphibian

Major histocompatibility complex (MHC) genes determine immune repertoires and social preferences of vertebrates. Immunological regulation of microbial assemblages associated with individuals influences their sociality, and should also affect their life-history traits. We exposed Xenopus laevis tadpoles to water conditioned by adult conspecifics. Then, we analysed tadpole growth, development and survivorship as a function of MHC class I and class II peptide-binding region amino acid sequence similarities between tadpoles and frogs that conditioned the water to which they were exposed. Tadpoles approached metamorphosis earlier and suffered greater mortality when exposed to immunogenetically dissimilar frogs. The results suggest that developmental regulatory cues, microbial assemblages or both are specific to MHC genotypes. Tadpoles may associate with conspecifics with which they share microbiota to which their genotypes are well adapted.     

Metamorphic synchrony and aggregation as antipredator responses in American toads

Safety in numbers serves as an antipredator defense strategy in many organisms, as aggregation can reduce the probability of predation for individual group members. It has long been suggested that some organisms are under selective pressure to synchronize vulnerable life stages with conspecifics, but there have been very few experimental tests of this hypothesis. Furthermore, the role of aggregation of conspecific animals within cohorts during vulnerable life stages is poorly understood.
Previous studies indicate that predation pressure may select for synchronous metamorphosis and the subsequent formation of metamorphic aggregations in North American toad species. In a series of laboratory experiments, I demonstrated that 1) Bufo americanus tadpoles in the presence of a predator exhibit higher levels of aggregation than tadpoles maintained in the absence of predator stimuli, and 2) B. americanus exposed to predator chemical cues metamorphose more synchronously than control tadpoles. I also found that toads at the climax of metamorphosis exhibit higher levels of aggregation than pre-metamorphic individuals. These results support the hypothesis that predation pressure has played a role in selection for life stage synchrony, and that aggregation serves as an antipredator defense in animals with synchronous transitions.     

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.     

Hemoglobins of the tadpole of the bullfrog, Rana catesbeiana. Structure and function of isolated components.

Four major components of the hemoglobin of the bullfrog tadpole, Rana catesbeiana, have been isolated and characterized structurally and functionally. These components fall into two clear functional classes. Components I and II have substantially higher affinities for oxygen than do components III and IV. Components I and II predominate in very young tadpoles and are largely replaced by components III and IV in older tadpoles. The data (Broyles, R.H., and Frieden, E. (1973) Nature New Biol. 241, 207-209) indicate that component I arises in the kidney and components III and IV in the liver. The synchrony of appearance and functional similarity o components I and II suggest that component II probably also arises in the kidney. Thus the development of the tadpole is associated with the successive proliferation of three distinct populations of red cells, first from the kidney, then from the liver, and finally, after metamorphosis, from bone marrow...     

A Stem-line Model for Cellular and Chromosomal Differentiation in Early Mouse Development

Viability of allografts exchanged between the field-collected individuals of the common frog, R. temporaria , was long in tadpoles grafted during and immediately after closing of operculum; median survival time (MST) was 26 and 18 days, respectively. This probably reflected the immaturity of the host immune system and temporary tolerance to weak transplantation antigens. Allograft viability was the shortest in tadpoles grafted at foot-paddle stage (MST, 11 days). It was independent from the origin and size of the grafts. Such rate of rejection might reflect a maximal immunological potential of the host and the absence of any suppressor factors in response to highly polymorphic frog transplantation antigens. A gradual prolongation of allograft viability was observed in animals grafted at final stages of metamorphosis, in froglets, and in sexually mature adults (MST: 13, 17, and 28 days, respectively). In particular age groups viability of allografts from sibling donors was longer and from nonsibling ones shorter than MST values cited above.
Immunological memory of transplantation antigens did not disappear during the host metamorphosis, as MST (10 days) of second-set allografts in metamorphosing hosts sensitized during larval life was considerably shorter than the viability of the sensitizing grafts in the same age group.
The ontogeny of the response to alloantigens reflecting the immunological potential and the appearance of self-tolerance can be realized in different ways, depending on a particular amphibian species.     

Novel Rana keratin genes and their expression during larval to adult epidermal conversion in bullfrog tadpoles

The conversion of the larval to adult epidermis during metamorphosis of tadpoles of bullfrog, Rana catesbeiana, was investigated utilizing newly cloned Rana keratin cDNAs as probes. Rana larval keratin (RLK) cDNA (rlk) was cloned using highly specific antisera against Xenopus larval keratin (XLK). Tail skin proteins of bullfrog tadpoles were separated by 2-dimensional gel electrophoresis and subjected to Western blot analysis with anti-XLK antisera. The Rana antigen detected by this method was sequenced and identified as a type II keratin. We cloned rlk from tadpole skin by PCR utilizing primers designed from these peptide sequences of RLK. RLK predicted by nucleotide sequences of rlk was a 549 amino acid -long type II keratin. Subtractive cloning between the body and the tail skin of bullfrog tadpole yielded a cDNA (rak) of Rana adult keratin (RAK). RAK was a 433 amino acid-long type I keratin. We also cloned a Rana keratin 8 (RK8) cDNA (rk8) from bullfrog tadpole epidermis. RK8 was 502 amino acid-long and homologous to cytokeratin 8. Northern blot analyses and in situ hybridization experiments showed that rlk was actively expressed through prometamorphosis in larva-specific epidermal cells called skein cells and became completely inactive at the climax stage of metamorphosis and in the adult skin. RAK mRNA was expressed in basal cells of the tadpole epidermis and germinative cells in the adult epidermis. The expression of rlk and rak was down- and up-regulated by thyroid hormone (TH), respectively. In contrast, there was no change in the expression of RK8 during spontaneous and TH-induced metamorphosis. RK8 mRNA was exclusively expressed in apical cells of the larval epidermis. These patterns of keratin gene expression indicated that the expression of keratin genes is differently regulated by TH depending on the type of larval epidermal cells. The present study demonstrated the usefulness of these genes for the study of molecular mechanism of postembryonic epidermal development and differentiation.     

Molecular cloning of hepatic mRNAs in Rana catesbeiana responsive to thyroid hormone during induced and spontaneous metamorphosis

Amphibian metamorphosis affords a useful experimental system in which to study thyroid hormone regulation of gene expression during postembryonic vertebrate development. In order to isolate gene-specific cDNA probes which correspond to thyroid hormone-responsive mRNAs, we employed differential colony hybridization of a cDNA library constructed from poly(A)+ RNA of thyroxine-treated premetamorphic tadpole liver. From an initial screening of about 6000 transformants, 32 "potentially positive" colonies were obtained. The recombinant cDNA-plasmids from 13 of these colonies plus two "potentially negative" colonies were purified for further study. Southern blot analysis of the plasmid DNA was employed to determine whether different cDNAs encoded for the same mRNA. The effect of thyroid hormone on the relative levels of specific mRNA species was examined by Northern analysis of liver RNA from premetamorphic tadpoles, thyroxine-treated tadpoles, and adult bullfrogs. Three independent cDNA clones were obtained which encoded thyroid hormone-enhanced mRNAs. We also obtained two independent cDNA clones encoding thyroid hormone-inhibited mRNAs and three independent clones encoding thyroid hormone-unresponsive mRNAs. The levels of two thyroid hormone-enhanced mRNAs and one thyroid hormone-inhibited mRNA were essentially the same in the thyroid hormone-treated tadpole liver and adult liver, suggesting that thyroid hormone induces stable changes in liver gene expression during spontaneous metamorphosis. Using selected cDNAs, RNA dot blot analysis of liver mRNA from tadpoles at different stages of metamorphosis showed that the level of one thyroid hormone-enhanced mRNA increased during late prometamorphosis and metamorphic climax. Similarly, a mRNA which was strongly inhibited by thyroid hormone treatment was observed to decline during prometamorphosis and reach undetectable levels during metamorphic climax. One mRNA was detected which was reproducibly inhibited by thyroid hormone treatment but which remained essentially unchanged during spontaneous metamorphosis. These results provide the first direct evidence for the coordinate and selective pretranslational regulation by thyroid hormone of several liver genes during the developmental process of metamorphosis.     

Primary and secondary phenology. Does it pay a frog to spawn early?

This study examines the consequences of variation in the laying and hatching date for the time of metamorphosis in the common frog Rana temporaria . Field data are presented showing that eggs laid early tend to take longer to develop. Thus, the time advantage for early eggs is reduced at the time of hatching. There was an among-year variation in this phenomenon; it was not manifest in a phenologically late year. Also, field data revealed that mortality due to pond freezing is a real risk for early laid eggs. Finally, two experiments in tanks analyse the effects of hatching date variation for the time of metamorphosis. (1) When hatching was experimentally delayed by 7 or 11 days, this resulted in later metamorphosis, however, by only 2 and 5 days, respectively. (2a) When tadpoles from the same pond that naturally hatched at different times were compared, it was found that a hatching time difference of 6 days resulted in later metamorphosis by 2 days only. (2b) A comparison of tadpoles from two different ponds that hatched 11 days apart also resulted in only 2 days' difference in metamorphosis. In this case, the later but faster developing tadpoles metamorphosed at a smaller size. I suggest that eggs from these two ponds differed genetically in the growth and development strategy. Despite the obvious risks, and the moderate gain in terms of early metamorphosis, frogs breed dangerously early in spring. Possible reasons for this are discussed. These include external selective forces that promote early metamorphosis (also at a high cost), within-pond competition among tadpoles with an advantage for early and large tadpoles and finally factors relating to mate choice at the breeding site.     

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.