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We quantified nesting activity and incidence of nest flooding in a population of the Magdalena River turtle (Podocnemis lewyana), which inhabits the climatic equator in northern Colombia, during two dry seasons when beaches formed (“verano”—December to March—and “veranillo”—July and August). Nesting activity was concentrated in the verano period, despite the presence of suitable nesting habitat in both dry season periods. More than half of all nests were harvested by local people, and 42.5% of the nests in both dry seasons that survived harvest were subsequently lost to flooding due to rises in the river to approximately a 4.15 m level. We used this value as a threshold value for the appearance of beaches and inspected a 44-year data base on river levels in this area. The verano and veranillo nesting periods did not differ in terms of opportunities for successful nesting, but there was evidence that the veranillo nesting season has increased significantly in duration in recent years, as well as experienced fewer flooding events. It is not clear why nesting each year is principally concentrated in the verano nesting season, but the evidence that this section of the Magdalena River is drying more in recent years during veranillo may entail a new threat to this population if it implies that non-nesting habitat (adjacent wetlands and channels) might eventually disappear.

Durante dos años, incubamos artificialmente bajo temperaturas constantes huevos de Podocnemis unifilis obtenidos del Parque Nacional Natural Cahunarí, Colombia. Una muestra de los neonatos fueron sexados para documentar la temperatura pivotal de esta población (32 °C). Aparentemente, en ambas estaciones de anidación, la mayoría de los nidos en la playa de estudio produjeron individuos de ambos sexos. El remanente de las tortugas obtenidas de las incubadoras por estación reproductiva fue mantenido en cautiverio por un año con el propósito de estudiar los efectos de factores pre y poseclosión en las tasas de crecimiento. En ambos años, documentamos un efecto materno en el tamaño de los huevos y en el tamaño inicial de los neonatos, pero no en las tasas de crecimiento posteriores. Las condiciones de incubación afectaron el tamaño inicial de los neonatos y sus tasas de crecimiento. Los individuos incubados a temperaturas cálidas emergieron con tamaños iniciales menores y luego presentaron tasas de crecimiento mayores. Para el final del primer año, estos individuos fueron significativamente más grandes que sus hermanos incubados a temperaturas más frías, lo cual es consistente con las predicciones de la hipótesis de Charnov y Bull sobre el valor adaptativo de la determinación sexual dependiente de la temperatura. También examinamos los efectos del tipo de dieta, la densidad y las oportunidades de soleamiento en las tasas de crecimiento, y encontramos que las tortugas que recibieron carne en sus dietas crecieron más rápidamente que las que se alimentaron exclusivamente de material vegetal. Las tortugas en la condición de densidad baja alcanzaron tamaños mayores en uno de los dos años del estudio, mientras que el acceso directo a la luz solar para el soleamiento no afectó significativamente las tasas de crecimiento.

Se realizó un inventario RAP (rapid assessment procedure) sobre la ictiofauna de la cuenca del río Aurra (San Jerónimo, Antioquia). El diseño de la selección de los sitios de muestreo tiene como fin evaluar posibles impactos antrópicos sobre la ictiofauna local. Empleamos la técnica de electropesca, que nos permitió muestrear ocho sitios el mismo día, colectando 374 individuos pertenecientes a diecisiete especies de cinco familias diferentes. Tres de las especies colectadas representan registros nuevos para la cuenca media del río Cauca. Encontramos una relación significativa negativa entre la diversidad íctica y la distancia del sitio al río Cauca. Aunque no detectamos un efecto de la granja de piscicultura, sí encontramos que los sitios más cercanos al casco urbano de San Jerónimo presentan valores menores de diversidad íctica, en comparación con otros sitios del estudio con distancias similares al río Cauca. Este estudio ilustra que los inventarios rápidos de la ictiofauna colombiana pueden aportar información valiosa sobre sus rangos de distribución dentro del país y sobre los efectos de las actividades antrópicas.

Cuantificamosla variación en el tamaño y forma del cuerpo y cabeza de Bolitoglossa vallecula en cuatro poblaciones de la Cordillera Central de Colombia. Dos de estas cuatro poblaciones ocurren en simpatría con B. ramosi una especie de salamandra ecológicamente similar que podría potencialmente competir con B. vallecula por recursos alimenticios. En ninguna de las poblaciones encontramos evidencias de dimorfismo sexual en el tamaño o forma de la cabeza, por lo tanto los datos de hembras y machos fueron agrupados. Las poblaciones difirieron significativamente en el tamaño promedio del cuerpo, pero esta variación no estuvo asociada con la elevación. Cuantificamos seis características de la forma de la cabeza asociadas con la morfología de la misma y las analizamos utilizando las proporciones de cada variable sobre la media geométrica, debido a que esta metodología es la más utilizada en la literatura para describir conformación mientras se controla por el efecto del tamaño. Una de las poblaciones simpátricas con B. ramosi (Bello) presentó diferencias significativas en la conformación de la morfología de la cabeza cuando se comparó con las poblaciones alopátricas, mientras que la otra población simpátrica no. Aunque en este trabajo la evidencia de desplazamiento de caracteres en respuesta a la competencia ecológica no es concluyente, este análisis destaca áreas de investigación que vale la pena adelantar en el futuro.

Large initial body size and rapid early growth rate are important in many species, both because predation rates decline as individuals grow and because females that attain a larger adult body size are more fecund. To identify possible factors contributing to size and growth rate variation in hatchling green iguanas, we artificially incubated six clutches at three constant temperatures to test for effects of incubation temperature and/or clutch effects on initial size and growth rate. Higher incubation temperatures resulted in significantly shorter incubation periods but did not influence initial body size. There were significant differences among clutches in egg size, and also in initial hatchling body size, even after correcting for differences in egg size among clutches. A subset of hatchlings from each nest was reared in semi-natural conditions for four months, with individuals from the high incubation temperature condition exhibiting the slowest longer-term growth rates. No clutch effects were detected in the growth rate analyses. The observed variation in early growth rate of juvenile iguanas seems to be selectively important and this variation may be due in part to the conditions the eggs experience during incubation, but clutch effects in this study were limited to egg size and initial hatchling body size variation, but were not found for subsequent growth rates.

This study aimed to document demographic parameters of an Andean dart frog, Andinobates opisthomelas. We used a photoidentification method to recognize recaptured individuals during a six month study of a population on a small island in a reservoir in the Cordillera Central of Colombia. Reproductively active males were identified based upon the presence of vocal sacs or observed calling or parental care behaviors (carrying from one to three tadpoles on their backs). Minimum size at first reproduction for males was estimated at 12.9 mm snout-vent length. Only 4% of captured individuals were smaller than this size; the remaining individuals were classified as either reproductively active males or other adults. The survival rates and detectabilities of these two groups were compared in both wet and dry season periods using maximum likelihood model fitting methods. Survival rates did not differ between groups but was related to body size, with smaller adult individuals having lower survival rates. R...

In freshwater turtles, movements have been shown to be influenced by seasonal changes in water levels, with members of the family Podocnemididae exhibiting some of the longest nesting migrations yet documented. In this study, we quantified linear home range sizes and seasonal movements of the Magdalena River Turtle (Podocnemis lewyana) using capture–mark–recapture and radio-telemetry techniques. We marked 924 turtles and recaptured 7.8% of these individuals one or more times, thereby documenting the movements of 41 juveniles, 13 males, and 18 females. Turtle movements differed significantly among sex/size classes, with males moving more. While 85% of all individuals had estimated linear home range sizes of less than 1 km, one juvenile moved 3.1 km, one female moved 2.5 km, and one male moved 4.8 km. We also obtained data on the movements of six reproductively mature females using radio telemetry. We documented seasonal movements out of channels into wetland or riverine habitats, increasing the estimates of total distance traveled for this sex/size class to a mean of 13.8 km (range = 6.9–18.7 km), with greater displacements documented during low water periods. Together, our results show that individuals of P. lewyana in the middle Magdalena River drainage occupy limited linear home ranges, but that reproductively mature females make extensive displacements during low water periods, presumably related to their need to access nesting beaches in riverine habitats. There are currently no protected areas within the range of this endemic species, but our results argue that any reserve created for protecting this critically endangered turtle must be large enough to cover all of its habitat requirements, including nesting beaches in the dry season that are separated from habitat where they maintain stable home ranges during the remainder of the year.

We conducted a four-year study of the life history parameters of the endangered freshwater turtle Podocnemis lewyana (Testudines: Podocnemididae) in four channels connecting wetlands to the Magdalena River in northern Colombia. Using capture–mark–recapture techniques, we documented body size growth rates, sex ratios, and size class distributions, and estimated survival rates for juveniles and adults. We also used body size/clutch size and body size/track width correlations to estimate the body sizes of females that nested in beaches in the Magdalena River near the study sites. The body size at first nesting (30 cm straight-line carapace length) was comparable to the estimate obtained by inspecting the reproductive tracts of 70 females using a sonograph. Growth rate analyses showed adult males to be smaller than adult females with an estimated size at sexual maturity of 20 cm straight-line carapace length. Females begin nesting at 5–6 years of age and may lay up to four clutches annually with a mean clutch...

We review the current practices of podocnemidid turtle conservation programs in South America and summarize the direct and indirect negative consequences that some of these practices may have on the populations we are attempting to manage. We argue that programs that only focus on nest transfer and head-starting as their conservation strategies would be better served by redirecting their efforts toward the protection of subadults and adults and in conducting monitoring programs designed to evaluate the impact of their management practices. Also, we make suggestions for other ways that the management of podocnemidid populations may be improved without resorting to manipulative ex situ practices that may well do more harm than good.

In oviparous species, preovulatory maternal effects such as investment in yolk quantity and composition or levels of yolk steroid hormones might potentially affect hatchling body sizes, growth rates, performance, and sex in species with temperature-dependent sex determination. We investigated the effects of egg mass and levels of testosterone and 17β-estradiol in the yolk on the phenotypes of hatchling Magdalena River Turtles (Podocnemis lewyana) in three populations in the Magdalena River drainage of northern Colombia. We hypothesized that, under homogeneous incubation conditions, the differences documented among clutches would be attributable to familial effects, caused by either heritable genetic factors or preovulatory maternal effects. Eggs were incubated artificially at the pivotal temperature for the species (33.4°C) and hatchlings were reared in the laboratory for 2 mo. Two eggs from each clutch were tested for testosterone and 17β-estradiol levels. Sex ratios, hatchling size, mass, and...

Esta tercera entrega del reporte anual de la biodiversidad en Colombia profundiza en la linea editorial iniciada el ano 2014 mediante nuevas propuestas analiticas y graficas, con la intencion de garantizar que la informacion llegue a todos los publicos y pueda ser discutida de manera amena sin sacrificio de calidad. La apuesta comunicativa sigue siendo central en el proyecto institucional y los nuevos lenguajes con los que estamos aprendiendo a conversar con la sociedad y las instituciones son un experimento que esperamos sea cada vez mas satisfactorio: ya estamos construyendo la version 2017 con el apoyo de las nuevas tecnologias digitales de manera que la potencia de la conexion vital colombiana se exprese en toda su capacidad. Por los contenidos es evidente que aun distamos mucho de tener una capacidad de seguimiento sistematico para la mayoria de temas relativos a la gestion de la biodiversidad y los servicios ecosistemicos, la unica manera de evaluar si las medidas de politica y las inversiones que realiza la sociedad estan teniendo los efectos deseados. De hecho, parte de las limitaciones reconocidas por robustamente los cambios positivos o negativos que afectan los diferentes niveles de organizacion de la vida planetaria, por lo cual las mismas metas de Aichi, nuestra carta de navegacion global, estan pendientes de verificacion. Un proposito adicional de este proceso es la invitacion a todos los colombianos para contribuir con la construccion y alimentacion de los indicadores basicos de seguimiento a la gestion, ya que es imposible identificar las tendencias de largo plazo en que estan inmersas la flora y fauna colombianas sin el apoyo de las instituciones, los investigadores y los ciudadanos: en el pais de la megadiversidad, el reto es inmenso. Por este motivo, este reporte ira abriendo sus paginas a expertos, incluso indigenas o de comunidades locales, para que presenten de manera sistematica y documentada sus perspectivas del cambio ambiental y sus efectos en la biodiversidad, con el animo de promover el compromiso de todos en su gestion. La unica manera de superar el riesgo de extincion es mediante un activo proceso de aprendizajes sociales que haga que todos los sectores asuman una parte de la compleja responsabilidad que significa proteger todas las formas de vida del pais, una decima parte mal contada de las planetarias. Agradezco a las decenas de personas que contribuyeron con este reporte, a quienes nos han apoyado en todas las etapas de produccion y a sus lectores y usuarios, quienes son en ultimo termino los jueces de su utilidad.

The citations contained in a recent literature review on the freshwater turtle and tortoise species of Colombia were analyzed. Publishing rates on these species have been increasing exponentially since the 1950s, although many of the publications would not be detected using internet-based literature searches. The most common topics of publications were systematics and phylogeography, nesting ecology, and management. In the 1970s and 1980s, the rate of publishing on the ecology and genetics of Colombian populations lagged behind the rate of publishing on these topics for populations of Colombian freshwater turtle and tortoise species located in other countries, but currently the production of the two regions is comparable. Also, in other countries there were trends towards publishing more over time in English and in journals with higher impact factors, but these trends were not significant for publications on Colombian populations. In Colombia, a disproportionate number of studies have been published on large-bodied species that face conservation problems. We argue that future studies of already well-studied Colombian species should focus on evaluating the effectiveness of management programs, and priority also should be given to increasing our knowledge of the many poorly-studied species in the country, especially those currently classified by the IUCN as data deficient (DD). RESUMEN Analizamos las referencias incluidas en una reciente revisión literaria sobre el estado de conocimiento de las tortugas continentales de Colombia. La tasa de publicaciones sobre estas especies ha incrementado exponencialmente desde los años 1950s, aunque muchas de éstas no podrían haber sido detectadas usando búsquedas de literatura por internet. Los tópicos más comunes de las publicaciones fueron sistemática y filo-geografía, ecología de anidación, y manejo. En los años 1970s y 1980s, la tasa de publicaciones sobre temas de ecología y genética de poblaciones ocupando el territorio colombiano, estuvo por debajo de publicaciones sobre estos dos tópicos con poblaciones de las mismas especies en otras regiones de Suramérica. Sin embargo, actualmente la producción en ambas regiones es comparable. En otros países, detectamos una tendencia temporal significativa de publicar cada vez más en inglés y en revistas de mayor impacto; esta tendencia no fue significativa para las publicaciones sobre poblaciones de tortugas colombianas. En Colombia, un número desproporcionado de las publicaciones son sobre especies de tamaños grandes que enfrentan problemas de conservación. Argumentamos que estudios futuros de las especies de tortugas continentales de Colombia relativamente bien conocidas, se deberían enfocar en evaluar la efectividad de los programas de manejo, y también debemos dar prioridad a investigaciones que aumenten el estado de conocimiento de las especies de tortugas continentales poco estudiadas en el país, especialmente de aquellas que actualmente están categorizadas por la UICN como con datos deficientes (DD).

This study determined the total mercury (THg) concentrations in pectoral muscle, blood and carapace tissue in turtles collected from Magangué and Lorica, Colombia. THg concentrations in μg/g (wet weight) were 0.39 ± 0.16 in muscle, 0.15 ± 0.08 in carapace and 0.07 ± 0.03 in blood for turtles from the Magdalena River and 0.25 ± 0.18 in muscle, 0.14 ± 0.09 in carapace and 0.06 ± 0.04 in blood for turtles from the Sinú River. Twenty-nine and ten percent of turtle muscle samples from Magangué and Lorica, respectively, exceeded the consumption advisory limit of 0.5 μg Hg/g for fish. There was a significant correlation between carapace length and THg levels for this specie, depending on the sample site. In addition, a significant correlation was observed in THg concentrations in carapace and muscle. However, significant differences were observed in the THg levels between the two study locations, with turtles caught in the Magdalena River having higher levels of THg.

We sampled the snake fauna in 13 landscapes along 80 km of highway and in the adjacent vegetation cover in the Colombian Llanos. We registered 119 snakes belonging to 33 species. Traffic levels significantly influenced rates of snake road kill, while adjacent vegetation cover, rainfall seasonality, and landscape structure and composition did not. We classified the species into seven ecological groups based upon foraging strategy, body length, and habitat preferences. Although most of the road-killed species had an active foraging strategy, all of the ecological groups contained some species that were killed on the highway, as well as some species that inhabited adjacent vegetation cover but that were not detected on the highway. The different ecological groups were not associated with different landscape characteristics. Six of the 13 landscapes that presented the lowest species richness of road-killed species had a different ecological group represented by each of the species documented as road kills. Thus, considering the ecological group that a species belongs to provides a complementary analytical approach that permits a fuller understanding of the ecological effects of roads on the functional role of the species in the ecosystem. We recommend focusing mitigation measures on highway sectors with the greater vehicular flow, employing both preventive measures such as posting driver advisories and installing speed radars and conducting environmental education programs to raise awareness of local drivers.

Two populations of the endangered Magdalena River turtle, Podocnemis lewyana, separated by 55 km in the Mom-pos Depression were sampled to quantify levels of genetic variation and inspect for evidence of genetic structure. Allozyme analyses resolved 22 presumptive gene loci, but only one resulted polymorphic. Genotype proportions at this locus departed from those expected under Hardy-Weinberg equilibrium, showing heterozygote deficiencies in both populations. However, allele frequencies at the locus did not differ between the two sites. The level of genetic variability documented is one of the lowest yet reported for a turtle species, and may reflect either a historical or recent bottleneck event. The lack of evidence for genetic structure suggests gene flow among the sites, at least historically, but the heterozygote deficiencies at each site also imply that inbreeding may be occurring presently within each deme.

During two nesting seasons we monitored 19 naturally incubated nests of Podocnemis lewyana obtained from two sites in the Mompos Depression of northern Colombia. We incubated another nine nests in the laboratory under similar humidity conditions, but at six different temperatures. We sexed the hatchlings obtained from all nests to confirm for the first time the occurrence of temperature-dependent sex determination in this species and quantify sex ratios and the pivotal temperature for this population. In both nesting seasons, the majority of the nests in the field produced hatchlings of both sexes, but sex ratios differed between study beaches/years. The pivotal temperature documented (33.4°C) appears to be among the highest reported for a turtle species. Incubation conditions in the naturally incubated nests also influenced hatching success rates and incubation periods, but not hatchling size or weight. Hatchlings obtained from the nests incubated in the laboratory were reared for one month in o...

We studied the population genetics of Podocnemis unifilis turtles within and among basins in the Orinoco and Amazon drainages using microsatellites. We detected high levels of genetic diversity in all sampled localities. However, ‘M-ratio’ tests revealed a substantial recent population decline in ten localities, in accord with current widespread exploitation. Our results reveal a consistent pattern across multiple analyses, showing a clear subdivision between the populations inhabiting the Amazon and Orinoco drainages despite a direct connection via the Casiquiare corridor, and suggesting the existence of two biogeographically independent and widely divergent lineages. Genetic differentiation followed an isolation-by-distance model concordant with hypotheses about migration. It appears that migration occurs via the flooded forest in some drainages, and via river channels in those where geographic barriers preclude dispersal between basins or even among nearby tributaries of the same basin. These observations caution against making generalizations based on geographically restricted data, and indicate that geographically proximate populations may be demographically separate units requiring independent management.

We obtained evidence of the continued presence of Podocnemis lewyana in 18 different sites within the Magdalena River drainage of northern Colombia. However, abundances at most sites were low, even in areas where the species had previously been reported as common. Although hunting of adults is no longer commercially viable, local people consume individuals that are captured incidentally while fishing. Hunting of eggs during the incubation period each year continues to be intensive. Turtle abundances were negatively related to human densities throughout this area. In the Chicagua River, where turtle abundances were highest, we conducted standardized shoreline censuses of basking adults and documented abundances of approximately 6 individuals/km2. Turtles often basked on mud banks, beaches, or emergent logs in aggregations made up of all size classes. Pilot trapping efforts also succeeded in capturing all size classes of turtles, which suggests that more intensive monitoring programs would be feasi...

By genetically characterizing adult individuals, we documented the presumed prefragmentation population structure of an endangered Andean tree, Magnolia espinalii. Our sample included all known surviving individuals for this species. Genetic diversity was high, but genetic distance was not related to geographic distance between sites. Magnolia espinalii apparently was originally distributed in numerous semi-isolated demes. The lack of evidence of recruitment around most adults in this species suggests a fragmentation-related disruption of their reproductive ecology. Artificial propagation projects should obviously attempt to involve all 23 known surviving trees.

Allozyme analyses were conducted on samples obtained from Trachemys scripta callirostris adults harvested in the Mompos Depression of Colombia. Genetic variability was low and there was no apparent genetic structure at either the micro- or macrogeographic scale, which contrasts markedly with the results of previous studies of a Trachemys population in the southeastern United States. These results have management implications for this subspecies and also suggest the need for further studies of the population genetics and systematics of other tropical Trachemys populations.

Trachemys callirostris is a turtle species endemic to northern South America. In northern Colombia it occurs in the middle and lower Magdalena River drainage and its principal tributaries (lower Cauca and San Jorge rivers) and in other minor drainages such as the lower Sinu River. In recent years, industrial, agricultural, and mining activities have altered natural habitats in Colombia where this species occurs, and many of the pollutants released there are known to induce genetic alterations in wildlife species. The micronucleus test and comet assay are two of the most widely used methods to characterize DNA damage induced by physical and chemical agents in wildlife species, but have not been employed previously for genotoxic evaluations in T. callirostris. The goal of this study was to optimize these genotoxic biomarkers for T. callirostris erythrocytes in order to establish levels of DNA damage in this species and thereby evaluate its potential as a sentinel species for monitoring genotoxic effects in freshwater environments in northern Colombia. Both genotoxic techniques were applied on peripheral blood erythrocytes from 20 captive-reared T. callirostris individuals as a negative control, as well as from samples obtained from 49 individuals collected in Magangue (Magdalena River drainage) and 24 individuals collected in Lorica (Sinu River drainage) in northern Colombia. Negative control individuals exhibited a baseline frequency of micronuclei of 0.78±0.58 and baseline values for comet tail length and tail moment of 3.34±0.24µm and 10.70±5.5, respectively. In contrast, samples from both field sites exhibited significantly greater evidence of genotoxic effects for both tests. The mean MN frequencies in the samples from Magangue and Lorica were 8.04±7.08 and 12.19±12.94, respectively. The mean tail length for samples from Magangue and Lorica were 5.78±3.18 and 15.46±7.39, respectively. Finally, the mean tail moment for samples from Magangue and Lorica were 23.59±18.22 and 297.94±242.18, respectively. The frequency of micronuclei in the samples was positively related to comet tail length and tail moment. Thus, this study showed that both genotoxicity biomarkers may be applied to T. callirostris erythrocytes as a sentinel organism for assessing the effects of environmental pollutants in freshwater ecosystems in northern South America.

Northwestern South America harbors one of the richest herpetofauna in the world. The connection among several biogeographic provinces along with climatic and orographic complexity makes this region an important contributor to the Neotropical biodiversity. Despite of this importance, the amphibian and reptile fauna in this area remains largely unknown as few herpetological collections has been made in recent decades. Motivated by this, the Herpetological Museum at the Universidad de Antioquia (Medellín, Colombia) has been increasing the collection in the last 16 years to better understand the herpetofaunal diversity and thus contribute to ecological, systematic, biogeographic and conservation research in the Neotropics. Here, we present the results of this effort and highlight how future collection will impact our understanding of the Neotropical herpetofauna.

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We quantified total mercury concentrations in eggshells, egg yolks, and embryos from 16 nests of the Colombian Slider (Trachemys callirostris). Nests were collected in different stages of development, but estimated time of incubation in natural substrates was not correlated with mercury levels in the eggs, suggesting that mercury was not absorbed from the substrate, but more likely passed on to the embryos during folliculogenesis by the reproductive females who had bioaccumulated the mercury from environmental sources. Mean mercury concentrations were higher in embryos than in eggshells or egg yolks, indicating that embryos also bioaccumulate mercury present in other egg tissues. Intra-clutch variation in egg yolk mercury concentrations was relatively high. Egg yolk mercury concentrations were not associated with any of the fitness proxies we quantified for the nests (hatching success rates, initial neonate sizes and first-month juvenile growth rates). After five months of captive rearing in a mercury-free laboratory environment, 86 % of the juveniles had eliminated the mercury from their tissues.

Over five years, 188 adult female green iguanas were captured one or more times, permanently marked, and measured at a nesting aggregation in Panama. Growth in these adult iguanas was very slow (averaging 6.8 mm/year) and appeared to be asymptotic, but there was substantial variability in the nesting female sizes observed (295 to 425 mm). This variation is biologically important because of the close relationship of female size to fecundity but little of this variation is explainable by differences in female ages (as estimated by skeletochronology) or in adult growth rates. Smaller females grew faster than larger ones but, controlling for size, younger iguanas did not grow faster than older ones. There is no evidence of alternative strategies with a trade-off between nesting sooner but smaller and nesting later but larger. Differences in adult sizes probably result from differences in juvenile growth rates, perhaps influenced by local differences in food quality and/or differences in the adult sizes at which growth trajectories asymptote. Energetic resources probably are not limiting for adult growth or reproduction. The high disappearance rate of iguanas from year to year (ca 60% per year) probably resulted mostly from mortality.

Two populations of the endangered Magdalena River turtle, Podocnemis lewyana, separated by 55 km in the Mompos Depression were sampled to quantify levels of genetic variation and inspect for evidence of genetic structure. Allozyme analyses resolved 22 presumptive gene loci, but only one resulted polymorphic. Genotype proportions at this locus departed from those expected under Hardy-Weinberg equilibrium, showing heterozygote deficiencies in both populations. However, allele frequencies at the locus did not differ between the two sites. The level of genetic variability documented is one of the lowest yet reported for a turtle species, and may reflect either a historical or recent bottleneck event. The lack of evidence for genetic structure suggests gene flow among the sites, at least historically, but the heterozygote deficiencies at each site also imply that inbreeding may be occurring presently within each deme. Dos poblaciones de la tortuga amenazada, Podocnemis lewyana, en la Depresión Momposina, separadas por 55 km fueron evaluadas para cuantificar los niveles de variación genética e inspeccionar evidencias de estructura genética. Mediante un análisis de alozimas resolvimos 22 presuntivos loci genéticos, pero sólo uno resultó polimórfico. Las proporciones genotípicas en éste locus difirieron significativamente a las esperadas bajo el modelo Hardy-Weinberg, mostrando en las dos poblaciones una deficiencia de individuos heterocigotos. Además, no se encontraron diferencias en las frecuencias alélicas entre los dos sitios. El nivel de variabilidad genética documentada en este estudio es una de las más bajas reportadas para una especie de tortuga, y podría reflejar un evento de cuello de botella histórico o reciente. La falta de evidencia de estructura genética sugiere flujo genético entre los sitios, por lo menos históricamente, pero la deficiencia de individuos heterocigotos en ambos sitios podría implicar que ha ocurrido entrecruzamiento reciente dentro de cada deme.

We studied the demography and nesting ecology of two populations of Iguana iguana that face heavy exploitation and habitat modification in the Momposina Depression, Colombia. Lineal transect data was analyzed using the Fourier model to provide estimates of social group densities, which was found to differ both within and among populations (1.05-6.0 groups/ha). Mean group size and overall iguana density estimates varied between populations as well (1.5-13.7 iguanas/ha). The density estimates were far lower than those reported from more protected areas in Panama and Venezuela. Iguana densities were consistently higher in sites located along rivers (2.5 iguanas/group) than in sites along the margin of marshes, probably due to vegetational differences (1.5 iguanas/group). There was no correlation between density estimates and estimates of relative abundance (number of iguanas seen/hour/person) due to differing detectabilities of iguana groups among sites. The adult sex ratio (1:2.5 males:females) agreed well with other reports in the literature based upon observation of adult social groups, and probably results from the polygynous mating system in this species rather than a real demographic skew. Nesting in this population occurs from the end of January through March and hatching occurs between April and May. We monitored 34 nests, which suffered little vertebrate predation, perhaps due to the lack of a complete vertebrate fauna in this densely inhabited area, but nests suffered from inundation, cattle trampling, and infestation by phorid fly larvae. Clutch sizes in these populations were lower than all other published reports except for the iguana population on the highly xeric island of Curaçao, implying that adult females in our area are unusually small. We argue that this is more likely the result of the exploitation of these populations rather than an adaptive response to environmentally extreme conditions.

We observed a green iguana (Iguana iguana) nesting aggregation in Panama over four successive nesting seasons that had radical differences in rainfall. More than a threefold variation in rainfall between years had little effect on the timing of nesting but a pronounced effect on hatching success. Excessive soil moistures late in the incubation period resulted in almost complete nesting failure in 1 yr and probably contributed to the failure of some clutches in years with more moderate rainfall. In the first 3 yr of the study an American crocodile (Crocodylus acutus) also nested at this site and frequently interrupted iguana nesting activities, especially early in the season. Each year, a complex burrow system was established so that later nesting iguanas laid deeper and were less susceptible to crocodile attack or to clutch disturbance by subsequent nesting iguanas. The earliest hatchling iguanas to emerge were more likely to have tick infestations. We also suggest that a parasitic fly may affect iguanas that hatch late in the

A population of green iguanas (Iguana iguana) that inhabits the forests around Gatun Lake in central Panama faces an apparent scarcity of suitable nesting sites. To investigate whether the disjunct distribution of nesting sites in this area and strong nesting site fidelity by female iguanas has contributed to genetic structuring of the population, samples obtained from females captured at three main nesting sites were analyzed electrophoretically. Significant allele frequency differences existed among nesting sites at one of the two polymorphic loci inspected. The pattern of allele frequency differences was consistent with what is known of iguana movement patterns and suggests that the genetic structure of the population has been influenced by nesting site availability and distribution. Additional electrophoretic analyses were conducted on samples obtained from three iguana populations from central Panama, western Panama, and Venezuela. Low levels of heterozygosity and polymorphism were observed in each of these populations, yet significant differences at three polymorphic loci were demonstrated. The management implications of the results are discussed.

made recognizable by one or more of three marking techniques: removing dorsal crest scales, attaching colored beads or applying reflective paint. Each recognition technique was evaluated in terms of its utility to the investigator and its effect on the lizards. Reflective paint is highly conspicuous to a searcher using artificial light at night, but dull and weakly translucent in daylight. Due to its reflectivity at night, unprecedented resighting rates of up to 96% were obtained for hatchling iguanas sleeping in dense foliage. All of the other techniques allowed long-term recognition of individuals at a distance. Distance recognition obviates the need for capture and handling, which were found to disrupt some natural movement patterns. AN ideal marking technique would provide easy permanent individual recognition at a distance without influencing the animal's behavior or fitness. Many techniques currently in use (Ferner, 1979) for example, toe-clipping, do not permit recognition at a distance and may