Validation of back‐calculated body lengths and timing of growth mark deposition in Hawaiian green sea turtles

Somatic growth rate data for wild sea turtles can provide insight into life‐stage durations, time to maturation, and total lifespan. When appropriately validated, the technique of skeletochronology allows prior growth rates of sea turtles to be calculated with considerably less time and labor than required by mark‐–recapture studies. We applied skeletochronology to 10 dead, stranded green turtles Chelonia mydas that had previously been measured, tagged, and injected with OTC (oxytetracycline) during mark–recapture studies in Hawaii for validating skeletochronological analysis. We tested the validity of back‐calculating carapace lengths (CLs) from diameters of LAGs (lines of arrested growth), which mark the outer boundaries of individual skeletal growth increments. This validation was achieved by comparing CLs estimated from measurements of the LAG proposed to have been deposited closest to the time of tagging to actual CLs measured at the time of tagging. Measureable OTC‐mark diameters in five turtles also allowed us to investigate the time of year when LAGs are deposited. We found no significant difference between CLs measured at tagging and those estimated through skeletochronology, which supports calculation of somatic growth rates by taking the difference between CLs estimated from successive LAG diameters in humerus bones for this species. Back‐calculated CLs associated with the OTC mark and growth mark deposited closest to tagging indicated that annual LAGs are deposited in the spring. The results of this validation study increase confidence in utilization of skeletochronology to rapidly obtain accurate age and growth data for green turtles.     

Structure of the femora and autotomous (postpygal) caudal vertebrae in the three-toed skink Chalcides chalcides (Reptilia: Squamata: Scincidae) and its applicability for age and growth rate determination

The limbs of the three-toed skink Chalcides chalcides are reduced to such a degree that the three digits are too small for skeletochronology. This study, performed on animals collected near Isernia (central Italy), describes the structure of the caudal vertebrae, which are often naturally lost due to autotomy, in order to determine whether they can be used to obtain data on age and growth with skeletochronological techniques. The reliability of the autotomous caudal vertebrae for skeletochronology was verified by performing skeletochronological analyses also on femora. Although the identification of the lines of arrested growth (LAGs) was easier in femora than in autotomous caudal vertebrae, a high correspondence of the LAG count between the two bones was observed. Females were larger and lived longer than males (4 and 3 years, respectively). For both sexes, the snout vent length (SVL) was significantly correlated with age. For both sexes, sexual maturity was attained after two hibernations from birth, beginning at the 20th month of age. At first reproduction, males had an SVL of 91–106 mm and females one of 111–150 mm. Von Bertalanffy growth curves of age versus SVL showed that females had slower growth rates than males for attaining their asymptotic SVL (females: 197 mm; males: 143 mm). The results provide the first data on age and growth of C. chalcide, and show that autotomous caudal vertebrae are reliable alternatives for obtaining such data for limb-reduced reptiles, avoiding the need to sacrifice or disable animals, as occurs when long bones are used.     

Skeletochronological assessment of age structure and population stability for two threatened frog species

Populations that fluctuate in size may become small at particular times and therefore be at risk of extinction. I used skeletochronology to examine the potential for fluctuations in population size in the threatened frog species Geocrinia alba and Geocrinia vitellina from southwestern Australia. The change in number of lines of arrested growth (LAG) in toe bones of recaptured frogs indicated that most individuals probably gain one LAG annually. Therefore, skeletochronology can be used for age determination. From a combination of skeletochronology and a mark–recapture study, both species appear to live for a maximum of six years. However, the majority of adult males only bred in a single year, which gave rise to a consistently dominant three-year-old age class. A drop in the number of two-year-old frogs and a large increase in the number of three-year-olds (up to 85%) from 1993 to 1994 in both species highlighted the potential for substantial fluctuations in population size. Widespread changes in abundance of between 25 and 50% may therefore be expected over periods as short as one or two years, due to variation in recruitment success.     

A skeletochronological study of age and growth in relation to adult size in the water frog Rana epeirotica

The age and growth of individuals in a population of the water frog Rana epeirotica, from northwestern Greece, were studied in 1998 and 1999 using skeletochronology. Analysis of the age structure was based on the enumeration of Lines of Arrested Growth (LAGs) in phalanges. Ages ranged from 1-5 years among 145 males and from 1-5 years among 173 females. The mean snout-vent length was 72.74 +/- 7.96 mm in males and 83.63 +/- 11.73 mm in females. The difference between the sexes in age and size was significant. Endosteal resorption may have eroded away the first LAG in only 9% of the studied individuals and was more frequent in females. Growth of adults was fitted by the Bertalanffy model. The growth coefficient (K) was 0.88 in males and 0.49 in females, reflecting faster male growth between metamorphosis and maturation.     

Reproductive ecology of female caecilian amphibians (genus Ichthyophis): a baseline study

The remarkable diversity of reproductive modes, including levels of parental care that are extensive relative to those of the other major amphibian groups, makes the limbless tropical caecilians ideally suited for evolutionary reproductive studies. Here we present key life history data for the oviparous caecilian Ichthyophis cf. kohtaoensis. We used non-invasive methods to analyse reproductive traits, seasonality of breeding and characteristics of oviposition sites in the field (Mekong valley, north-eastern Thailand). A correlation was established between reproductive activity and season, indicated by the age of egg clutches found in the field. Eggs at early developmental stages were found at the beginning of the rainy season, those with well-developed embryos at the peak of the monsoon. The body condition of females guarding younger clutches was superior to that of females with older clutches, indicative of a loss of energy reserves during the period of parental care. Maternal total length correlated positively with the number of eggs as well as with the total length of newly hatched larvae. The terrestrial oviposition sites of females were located close to temporary and permanent ponds, small brooks and rivers. It is hoped that the study will, in addition to contributing to our understanding of the evolution of caecilian reproduction, provide a basis for further comparisons of reproductive strategies among amphibians and other terrestrial tetrapods.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 207–217.     

Structure of the femora and autotomous (postpygal) caudal vertebrae in the three-toed skink Chalcides chalcides (Reptilia: Squamata: Scincidae) and its applicability for age and growth rate determination

The limbs of the three-toed skink Chalcides chalcides are reduced to such a degree that the three digits are too small for skeletochronology. This study, performed on animals collected near Isernia (central Italy), describes the structure of the caudal vertebrae, which are often naturally lost due to autotomy, in order to determine whether they can be used to obtain data on age and growth with skeletochronological techniques. The reliability of the autotomous caudal vertebrae for skeletochronology was verified by performing skeletochronological analyses also on femora. Although the identification of the lines of arrested growth (LAGs) was easier in femora than in autotomous caudal vertebrae, a high correspondence of the LAG count between the two bones was observed. Females were larger and lived longer than males (4 and 3 years, respectively). For both sexes, the snout vent length (SVL) was significantly correlated with age. For both sexes, sexual maturity was attained after two hibernations from birth, beginning at the 20th month of age. At first reproduction, males had an SVL of 91–106 mm and females one of 111–150 mm. Von Bertalanffy growth curves of age versus SVL showed that females had slower growth rates than males for attaining their asymptotic SVL (females: 197 mm; males: 143 mm). The results provide the first data on age and growth of C. chalcide, and show that autotomous caudal vertebrae are reliable alternatives for obtaining such data for limb-reduced reptiles, avoiding the need to sacrifice or disable animals, as occurs when long bones are used.     

Estimation of age structure by skeletochronology of a population of Hynobius nebulosus in a breeding season (Amphibia,Urodela)

Using skeletochronology, we determined the age structure of adult Hynobius nebulosus from Kyoto in the breeding season of 1998. From previously marked individuals, the lines of arrested growth proved to be formed once per year, indicating the number of winters each salamander experienced. The age at first reproduction was estimated to be 2.8-2.9 yrs of age in males and 3.8-3.9 yrs in females. The oldest males and females were 9.8-9.9 and 5.8-5.9 yrs of age, respectively, and, therefore the longevity in this species was estimated to be more than 9 yrs for males and 5 yrs for females. The growth curve of male's body size estimated indicated that the growth rate much decreases after males attained sexual maturity. Because body sizes of adults greatly vary even within an age class, it is dangerous to estimate individual age from the size frequency data at least in adults. We discussed age properties in Hynobius by comparing lentic and lotic breeders.     

Age structure of amphibian populations with endemic chytridiomycosis,across climatic regions with markedly different infection risk

Threatening processes, such as disease, can drive major changes in population demographics of the host. Chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), has led to the decline of at least 500 amphibian species across the globe and has been shown to truncate host age structure by lowering adult survival rates. This results in heavy reliance on annual recruitment and the inability to recover in the event of periodic recruitment failure. We used skeletochronology to determine the age structure, growth, and survival rates of populations of an endangered amphibian, Litoria raniformis, with endemic chytridiomycosis, across two climatically disparate regions in south‐eastern Australia: semi‐arid and temperate. Contrary to predictions, populations in the semi‐arid region (in which chytrid prevalence is substantially lower due to high temperatures) displayed a more truncated age structure than populations in the temperate study regions. Maximum recorded age was only two years in the semi‐arid region compared with up to four years in the temperate region. Wetland hydroperiod and average seasonal air temperature were correlated with age, and males had a slightly higher survival rate than females (0.31 for males and 0.27 for females). Despite the previously documented differences in chytrid prevalence between the two climatic regions, water availability and wetland hydroperiods appear the over‐riding determinants of the age structure and survival rates of L. raniformis. Targeted management which ensures water availability and improves survival of 1‐year‐old frogs into their second and third breeding season would reduce the impact of stochastic events on L. raniformis, and this may be true for numerous frog species susceptible to chytridiomycosis.     

Longevity and population age structure of the arroyo southwestern toad (Anaxyrus californicus) with drought implications

The arroyo southwestern toad is a specialized and federally endangered amphibian endemic to the coastal plains and mountains of central and southern California and northwestern Baja California. It is largely unknown how long these toads live in natural systems, how their population demographics vary across occupied drainages, and how hydrology affects age structure. We used skeletochronology to estimate the ages of adult arroyo toads in seven occupied drainages with varying surface water hydrology in southern California. We processed 179 adult toads with age estimates between 1 and 6 years. Comparisons between skeletochronological ages and known ages of PIT tagged toads showed that skeletochronology likely underestimated toad age by up to 2 years, indicating they may live to 7 or 8 years, but nonetheless major patterns were evident. Arroyo toads showed sexual size dimorphism with adult females reaching a maximum size of 12 mm greater than males. Population age structure varied among the sites. Age structure at sites with seasonally predictable surface water was biased toward younger individuals, which indicated stable recruitment for these populations. Age structures at the ephemeral sites were biased toward older individuals with cohorts roughly corresponding to higher rainfall years. These populations are driven by surface water availability, a stochastic process, and thus more unstable. Based on our estimates of toad ages, climate predictions of extreme and prolonged drought events could mean that the number of consecutive dry years could surpass the maximum life span of toads making them vulnerable to extirpation, especially in ephemeral freshwater systems. Understanding the relationship between population demographics and hydrology is essential for predicting species resilience to projected changes in weather and rainfall patterns. The arroyo toad serves as a model for understanding potential responses to climatic and hydrologic changes in Mediterranean stream systems. We recommend development of adaptive management strategies to address these threats.     

Care and parentage in a skin-feeding caecilian amphibian

An exceptional form of parental care has recently been discovered in a poorly known caecilian amphibian. Mothers of the Taita Hills (Kenya) endemic Boulengerula taitanus provide their own skin as a food source for their offspring. Field data suggest that nursing is costly. Females found attending young had a lower body condition and fat body volume than nonbrooding and egg-incubating females, and the female condition decreased substantially during parental care. Most mothers and their eggs or offspring were found in close proximity to other nesting females, in high-density nest sites that enhance the potential for social interactions and highlighting the possibility of communal breeding. Parentage was investigated using Amplified Fragment Length Polymorphism (AFLP) genetic markers in 29 offspring from six litters guarded by putative mothers. Our data provide the first evidence of multiple paternity in a caecilian, implying that two fathers sired one litter. Some young from two litters had genotypes not matching the guarding female suggesting that not all offspring are cared for by their biological mothers. This study provides evidence for alloparenting in an amphibian with cost-intensive parental care. J. Exp. Zool. 309A:460-467, 2008. (c) 2008 Wiley-Liss, Inc.     

The female cloaca of an oviparous caecilian amphibian (Gymnophiona): functional and seasonal aspects

Kuehnel, S., Herzen, J., Kleinteich, T., Beckmann, F. and Kupfer, A. 2011. The female cloaca of an oviparous caecilian amphibian (Gymnophiona): functional and seasonal aspects. —Acta Zoologica (Stockholm) 00 :1–14. Reproductive morphology is receiving increased attention in animals that have variable reproductive modes combined with internal fertilization. Exceptionally among amphibians all caecilian species practice internal fertilization via an intromittent organ: an everted part of the male cloaca (phallodeum or phallus). Because research has mostly concentrated on males, knowledge of the female cloacal morphology is scarce. Here, we present the first single‐species study of the functional morphology of the female cloaca of an oviparous, phylogenetically basal caecilian (Ichthyophis cf. kohtaoensis). We have analyzed female cloacal shape during the reproductive cycle combining conventional histology with 3D‐reconstruction. All females are similar in their overall cloacal structure with some differences in size and histology associated with the reproductive cycle. The female cloaca is divided into two distinct chambers similar to the male condition. The cranial chamber contains urogenital pockets into which oviducts and Wolffian ducts open and which may have function during oviposition. The caudal cloacal chamber bears a novel feature – dorsolateral blind sacs, which are homologous to the male condition, but are considerably smaller. The study of female cloacal morphology is essential to understanding the evolution of the caecilian reproductive system and contributes to the understanding of tetrapod genital morphology in general.     

A skeletochronological study of breeding females in a population of Japanese clouded salamanders (Hynobius nebulosus)

The age structure of breeding females of Hynobius nebulosus has not been studied sufficiently. We estimated the ages of 76 individuals from a population in Kyoto by using skeletochronology. The mean age and snout-vent length (SVL) of this population were 4.6 years and 55.7 mm, respectively. It was estimated that the youngest females breed two years post hatching at a mean SVL of 46.5 mm, but a larger number of individuals begins breeding at three years and a mean SVL of 52.2 mm. Because most males also start to breed at three years, there seems to be no gender difference in the timing of sexual maturation. The age of the oldest female was estimated to be 11.8 years. It is possible that the life history of H. nebulosus is characterized by early maturation and arrested growth, and short longevity.     

Intermediate Pond Sizes Contain the Highest Density,Richness, and Diversity of Pond-Breeding Amphibians

We present data on amphibian density, species richness, and diversity from a 7140-ha area consisting of 200 ponds in the Midwestern U.S. that represents most of the possible lentic aquatic breeding habitats common in this region. Our study includes all possible breeding sites with natural and anthropogenic disturbance processes that can be missing from studies where sampling intensity is low, sample area is small, or partial disturbance gradients are sampled. We tested whether pond area was a significant predictor of density, species richness, and diversity of amphibians and if values peaked at intermediate pond areas. We found that in all cases a quadratic model fit our data significantly better than a linear model. Because small ponds have a high probability of pond drying and large ponds have a high probability of fish colonization and accumulation of invertebrate predators, drying and predation may be two mechanisms driving the peak of density and diversity towards intermediate values of pond size. We also found that not all intermediate sized ponds produced many larvae; in fact, some had low amphibian density, richness, and diversity. Further analyses of the subset of ponds represented in the peak of the area distribution showed that fish, hydroperiod, invertebrate density, and canopy are additional factors that drive density, richness and diversity of ponds up or down, when extremely small or large ponds are eliminated. Our results indicate that fishless ponds at intermediate sizes are more diverse, produce more larvae, and have greater potential to recruit juveniles into adult populations of most species sampled. Further, hylid and chorus frogs are found predictably more often in ephemeral ponds whereas bullfrogs, green frogs, and cricket frogs are found most often in permanent ponds with fish. Our data increase understanding of what factors structure and maintain amphibian diversity across large landscapes.     

A skeletochronological study of age, growth and longevity in a population of the frog Rana ridibunda from southern Europe

Age at sexual maturity and longevity in a population of Rana ridibunda from north-eastern Greece were studied by skeletochronology performed on the phalanges. Analysis of the age structure was based on counting the lines of arrested growth (LAGs). Sexual maturity for both sexes arises during the first year or after the first hibernation. Ages ranged from 1 to 5 years (mean=2.96) among 52 males and from 1 to 5 years (mean=3.73) among 56 females. The mean snout-vent length was 69.03+/-12.6mm in males and 82.38+/-13.27 mm in females. The difference between the sexes in age and size was significant. Growth of individuals was fitted on? The von Bertalanffy model. The growth coefficient (K) was 0.57 in males and 0.54 in females, mainly due to faster male growth between metamorphosis and maturation.     

Characterization and distribution of neuropeptide Y in the brain of a caecilian amphibian

Neuropeptide Y (NPY) from the brain of an amphibian from the order Gymnophiona (the caecilian, Typhlonectes natans) was characterized. We cloned a 790 base pair cDNA encoding the caecilian NPY precursor. The open reading frame consisted of 291 bases, indicating an NPY precursor of 97 amino acids. Both deduced and isolated NPY primary structures were Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu(10)-Asp-Ala-Pro-Ala-Glu-Asp-Met-Ala-Lys-Tyr(20)-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu(30)-Ile-Thr-Arg-Gln-Arg-Tyr. NH2. In caecilian brain, we observed NPY immunoreactive cells within the medial pallium, basal forebrain, preoptic area, midbrain tegmentum and trigeminal nucleus. The prevalence of preoptic and hypothalamic terminal field staining supports the hypothesis that NPY controls pituitary function in this caecilian.     

A stem-group caecilian (Lissamphibia: Gymnophiona) from the Lower Cretaceous of North Africa

Of living amphibian groups, the limbless burrowing caecilians are amongst the most highly specialised, but are the least known. Their fossil record is extremely poor, leaving unresolved questions as to their origins, relationships and early distribution. We describe here caecilian remains from a Lower Cretaceous (Berriasian) microfossil locality near Anoual, Morocco. This material represents the second oldest record for the group, after the Jurassic Eocaecilia of North America, and the earliest caecilian record for Gondwana. It forms the basis of a new genus, Rubricacaecilia , which appears slightly more derived than Eocaecilia , but lacks major features of crown-group taxa. We support the use of Apoda Oppel, 1811 for the crown-group alone, and Gymnophiona Rafinesque 1814 for the clade comprising stem-group taxa + Apoda.     

Age Structure of Two Species of Odorous Frogs(Odorrana margaretae and Odorrana grahami)

Variation in age structure and body size benefits are identified to understand the evolution of life history. Here, we estimated the age structure and body size of two species of odorous frogs(Odorrana margaretae and Odorrana grahami) by using skeletochronology. The ages at sexual maturity of O. grahami and O. margaretae in both sexes were 1 and 2 years, respectively. For both sexes, the maximum age observed in O. margaretae was six years. For O. grahami, the maximum age observed in males and females were 4 and 5 years, respectively. Males and females did not differ in mean age in the two species.The average body size of both species considerably differed between sexes, with females being larger than males. The body size of females was also larger than that of males when the effect of age was removed. We also found positive correlations between body size and age within each sex in O. margaretae, but only for female in O. grahami. The female-biased sexual size dimorphism of the two species suggested that fecundity selection for larger female size may increase the reproductive output.     

Amphibians live longer at higher altitudes but not at higher latitudes

Why and how organisms differ in life‐history strategies across their range is a long‐standing topic of interest to evolutionary ecologists. Although many studies have addressed this issue for several life‐history traits, such as body size and clutch size, very few have been made for some others traits, including longevity. In the present study, we performed a comparative study aiming to develop general patterns of geographical variation in longevity of urodele and anuran amphibians using published information on demographic age derived from skeletochronology. We conducted within‐species meta‐analyses using datasets of two (ten urodele and 12 anuran species) and multiple (two urodele and nine anuran species) spatially‐separated populations and found that maturation, mean, and maximum age all increased with altitude but not with latitude in each sex of both amphibian groups. This geographical pattern held true across 33 urodele and 86 anuran species at common body sizes, independent of phylogeny. It is likely that metabolic rate, reproductive investment, and mortality risk, which are the key factors that affect longevity as suggested by ageing theory, vary systemically along altitudinal gradients but not along latitudinal gradients. The evolutionary causes behind these puzzling patterns deserve further investigation. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 623–632.