Vivian P. Páez

Complex evolution in the Neotropics: The origin and diversification of the widespread genus Leptodeira (Serpentes: Colubridae)

Lineage diversification in the Neotropics is an interesting topic in evolutionary biology but is also one of the least understood. The abiotic and biotic complexity of the region precludes generalizations that can be drawn regarding the historical evolutionary processes responsible for the diversity observed. The snake genus Leptodeira provides an excellent opportunity to investigate such processes because it spans the entire Neotropical region. In this study, we infer the phylogenetic position of Leptodeira within Dipsadinae, estimate evolutionary relationships among and within Leptodeira species, and estimate the diversification time and biogeography of the genus. Three mitochondrial gene regions were sequenced for individuals representing all the Leptodeira species and most subspecies currently recognized. Additionally, two nuclear protein-coding gene regions were sequenced for representatives of each species and several genera within the Dipsadinae. We infer that several Leptodeira species are either paraphyletic or polyphyletic as currently recognized, and that most recognized subspecies are not monophyletic lineages. Despite the taxonomic discordance with evolutionary relationships, clades appear to correspond very well to major biogeographic regions of Mexico, Central America and South America. Our results thus highlight the important role of the Miocene and Pliocene for lineage diversification in the Neotropics. Additionally, our time estimates suggest that recent intraspecific phylogeographic structure is likely the result of habitat and climatic fluctuations during the Pleistocene. Cumulatively, our inferences of lineage diversification within Leptodeira suggest a complex evolutionary scenario in the Mexican transition zone and a north to south expansion with a final colonization of the tropics in South America.

A Comparison of Maternal and Temperature Effects on Sex, Size, and Growth of Hatchlings of the Magdalena River Turtle (Podocnemis lewyana) Incubated under Field and Controlled Laboratory Conditions

Abstract 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 order to study the influence of pre-hatching factors on growth rates. In these nests we documented maternal effects on egg size, initial hatchling size, and weight and growth rates. Incubation temperature also influenced hatching success rates, sex ratios, growth rates, and hatchling size, but not hatchling weight.

MORPHOMETRIC VARIATION AND ITS EFFECT ON REPRODUCTIVE POTENTIAL IN FEMALE COLOMBIAN SLIDER TURTLES (TRACHEMYS CALLIROSTRIS CALLIROSTRIS)

We evaluated morphometric variation and reproductive effort in Trachemys callirostris callirostris females from nine populations in the Mompos Depression of northern Colombia. Two hypotheses were evaluated: (1) phenotypes of nesting females co-vary according to geographic distances among sites and/or specific environmental conditions at each site, and (2) female body size influences their reproductive potential and offspring characteristics. Populations were shown to differ in both mean female body size and body shape, with differences more related to local habitat characteristics than to geographic distances among sites. Larger females occurred in sites with higher annual precipitation and lower hunting pressure. Female size was highly correlated with clutch size and mass. Although habitat characteristics affected female size, habitat alone was not a predictor of reproductive potential. Specific habitat conditions and hunting both influence female phenotypes in this region and thereby also influence key demographic parameters, which have clear conservation implications for this highly exploited species.

Distribution and Status of Podocnemis lewyana in the Magdalena River Drainage of Colombia

ABSTRACT 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 feasible. Given the evidence of declines in most areas of the range of this species, the current lack of regulation of its exploitation, and the projections for continued human population growth in this area, we recommend its International Union for Conservation of Nature (IUCN) status be changed from Endangered to Critically Endangered (CR A2acd).

Reproductive Ecology of the Magdalena River Turtle (Podocnemis lewyana) in the Mompos Depression, Colombia

Abstract We studied various aspects of the reproductive biology of the Magdalena River turtle (Podocnemis lewyana) during 2 nesting seasons in 2 locations in the Mompos Depression in northern Colombia. We monitored 53 nests; 22 that completed incubation in situ, 24 that were transferred to protected areas (transferred nests), and 7 that were constructed using eggs removed from females that had been consumed by local people (“oviductal” nests). For each nest, we registered the oviposition date, distance to the nearest body of water, soil type, vegetative cover, exposure to sunlight, depth to the first egg, and maximum depth of the nest chamber. We also quantified egg dimensions and clutch sizes, mean incubation temperatures and duration of incubation periods, hatching success rates, and sex ratios. Most nests were located within 15 m of the shoreline, in open or grassy areas with permanent exposure to sunlight, and in sandy soils. The 3 nest types (natural, transferred, and oviductal) did not differ in hatching success rates. In both seasons, the majority of the nests produced hatchlings of both sexes, but the sex ratios differed between the nesting beaches and seasons. Incubation temperatures influenced incubation periods and hatching success rates, but not hatchling sizes or weights. The management implications of the findings are discussed.

Nest Site Selection by Colombian Slider Turtles, Trachemys callirostris callirostris (Testudines: Emydidae), in the Mompos Depression, Colombia

ABSTRACT Nest-site selection by female Trachemys callirostris callirostris was studied on an island in the Pijiño wetland of the Mompos Depression of Colombia. We quantified distances of nests to the shoreline and compared vegetative cover and soil types at nest locations and at randomly selected points on the island. Nests sites were concentrated in the first 5 m from the shoreline and were always located under vegetative cover. Such cover might reduce thermal stress to nesting females, lower the probability of nest detection by predators, and buffer the incubating eggs from environmental extremes. Females preferentially nested under water hyacinth, but it was not clear whether they selected directly for this vegetative cover type or simply preferred dirt substrates where it dominated, because dirt soils contained higher humidity.

Preovulatory Maternal Effects on Intra- and Interpopulation Variation in Sex Ratios and Phenotypic Characteristics of Magdalena River Turtles (Podocnemis lewyana)

Abstract:  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 17&bgr;-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 17&bgr;-estradiol levels. Sex ratios, hatchling size, mass, and righting times varied both between clutches within a site and between populations. Egg mass was positively related to hatchling body size and mass, both at hatching and at 2 mo of age. Levels of 17&bgr;-estradiol concentrations influenced hatching success rates and incubation periods. Sex ratios were marginally related to 17&bgr;-estradiol levels, with clutches and sites with higher levels tending to produce fewer males. Our results provide evidence that preovulatory maternal effects play a role in influencing phenotypic attributes related to hatchling survivorship such as size, growth rate, and performance, and also seem to interact with incubation temperature to determine the sex of each individual and the sex ratio of the clutch, which has implications for both parental and offspring fitness.

A Plea to Redirect and Evaluate Conservation Programs for South America’s Podocnemidid River Turtles

Abstract 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.

Life History and Demographic Characteristics of the Magdalena River Turtle (Podocnemis lewyana): Implications for Management

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 size of 22 eggs. The overall sex ratio was 1♀:0.72♂, but this parameter varied among study sites, as did size class distributions, with juveniles more abundant in the two shallower channels and adults more abundant in the two deeper channels. Survival estimates increased with increasing body sizes. We constructed a projection matrix using these estimates of the key life history parameters for this population and used an uncertainty analysis to create a distribution of possible asymptotic population growth rates (&lgr;), to estimate the vectors of stable age distribution and reproductive values, and conduct an elasticity analysis. Results indicated that the population is declining 8.8% annually, probably as a result of illegal over-exploitation of adults that are harvested as by-catch by local fishermen, and especially of reproductive females that are captured while nesting. Elasticity analyses indicated that the most effective way to help this population recover is to increase adult survival rates, since this transition alone accounted for 62% of the contribution of all vital rates to the population growth rate. Traditional management methods that rely entirely on nest transfer and head-starting will likely be of limited impact.

Population Genetics of the Slider Turtle (Trachemys scripta callirostris) in the Mompos Depression, Colombia

Abstract 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.