Egg inundation often results in poor hatching success in crocodylians. However, how tolerant eggs are to submergence, and/or how eggshell ultrastructure may affect embryo survival when inundated, are not well understood. In this study, our objective was to determine if embryo survival in Caiman latirostris is affected by eggshell surface roughness, when eggs are submerged under water. Tolerance to inundation was tested early (day 30) versus late (day 60) in development, using eight clutches (four per time treatments), subdivided into four groups: (N ¼ 9 per clutch per treatment; 9 Â 4 ¼ 36 eggs per group). 'Rough' eggshell represented the natural, unmodified eggshell surface structure. 'Smooth' eggshell surface structure was created by mechanically sanding the natural rough surface to remove surface columnar elements and secondary layer features, e.g. irregularities that result in 'roughness'. When inundated by submerging eggs under water for 10 h at day 30, 'smooth' eggshell structure resulted in more than twice as many dead embryos (16 versus 6, smooth versus rough; N ¼ 36), and fewer than half as many healthy embryos (6 versus 13, smooth versus rough, respectively; N ¼ 36). By contrast, at day 60, inundation resulted in very low hatching success, regardless of eggshell surface structure. Only two hatchlings survived the inundation, notably in the untreated group with intact, rough eggshells. Inundation produced a high rate of malformations (58% at day 30), but did not affect hatchling size. Our results indicate that eggshell roughness enhances embryo survival when eggs are inundated early in development, but not late in development. Apparently, the natural surface 'roughness' entraps air bubbles at the eggshell surface during inundation, thereby facilitating gas exchange through the eggshell even when the egg is submerged under water.

Caiman latirostris has temperature‐dependent sex determination and is potentially susceptible to environmental temperature fluctuations and, thus, to the global climate change phenomena. Considering the potential consequences of increasing temperatures for Ca. latirostris offspring, we examined the effects of climatic conditions on sex ratios produced by caimans in wild nests and in particular how climate variables affect nest temperature and the percentage of females produced. We also explored the potential consequences of a hypothetic 0.5 and 1.0°C increase in nest temperature on caiman populations. The proportion of females produced from nests in the wild varied among reproductive seasons, as mean nest temperatures varied between 27.1 and 33.9°C. However, after seven seasons the sex ratio biased toward females, and only during extreme events (strong El Niño Southern Oscillation event, La Niña) was there a reduction in the percentage of females produced in the wild. In the hypothetic scenarios of global warming, we predict a decrease of unisexual female nests, with nests containing both sexes or unisexual male nests becoming more frequent. Entire clutches might be lost if nest temperatures rise above 34.5°C for extended periods. However, it is possible that females modify their nesting timing and behavior to select thermally suitable nest environments.

The southern distribution of the Broad-snouted Caiman (Caiman latirostris Daudin 1802) in Argentina occurs in Santa Fe Province, where its population has been under management by "Proyecto Yacaré" since 1990. From 1997 to 2016, we captured 77 nesting female Broad-snouted Caimans in Santa Fe Province. Our results suggest that previously defined size classes for Broad-snouted Caiman do not adequately describe the reproductively mature female segment of the population. Here we propose to change size ranges for general size classes for Broad-snouted Caiman. In addition, we have observed that reintroduced reproductive females by Proyecto Yacaré represent about 32% of captured females. These results indicate that reintroduced females by the management program are surviving and reproducing in the wild at least up to 20 years.Keywords: management, size class, reproduction, sexual maturity. Tamanho de fêmeas nidificantes do jacaré-de-papo-amarelo (Caiman latirostris Daudin 1802)Resumo Na Argentina, a distribuição mais austral do jacaré-de-papo-amarelo (Caiman latirostris Daudin 1802) ocorre na Provincia de Santa Fe, sendo que suas populações são manejadas pelo "Proyecto Yacaré" desde 1990. Entre os anos de 1997 e 2016, nós capturamos 77 fêmeas nidificantes do jacaré-de-papo-amarelo em Santa Fe. Nossos resultados sugerem que as classes de tamanho definidas para o jacaré-de-papo-amarelo não representam a realidade dos animais capturados no presente estudo. Portanto, propõe-se uma alteração nas classes de tamanho para o jacaré-de-papo-amarelo. Nós também observamos que as fêmeas reintroduzidas pelo "Proyecto Yacaré" representaram 32% das fêmeas capturadas. Estes resultados indicam que fêmeas reintroduzidas pelo programa de manejo estão sobrevivendo e reproduzindo na natureza por, pelo menos, 20 anos.Palavras-chave: manejo, classe de tamanho, reprodução, maturidade sexual.

No abstract

Evaluation of factors associated with predation on Caiman latirostris nests (Crocodylia: Alligatoridae) in Argentina. Predation is a major cause of crocodilian egg loss. However, at present, the mechanisms by which predators detect nests is unknown. Previous studies have reported that predators are able to detect prey using both visual and olfactory cues. This study aims to determine the natural predation rate on Broad-snouted Caiman (Caiman latirostris whether olfactory or visual cues attract predators to caiman nests, and to evaluate the effect of maternal presence on nest predation. In December 2010, we searched for nests in the north of Santa Fe Province, Argentina. Each nest was assigned to one of the following treatments: (1) control nests (nests were observed from a distance to avoid disturbance), (3) olfactory attraction nests (nests were opened, one egg from the clutch was broken, and then the nests were covered again), (4) olfactory attraction from human disturbance (material was manipulated by researchers). The natural predation rate on broad-snouted caiman nests was found to be 21% during the nesting season. Both olfactory and visual cues were associated with increased predation rates, and human disturbance was strongly associated with increased nest predation at terrestrial sites. Predation rates were less at nests attended by female caiman. Management programs that harvest eggs in wild populations (ranching) are predicated on the assumption that removal of some eggs is the remaining hatchlings will have improved survival rates. To reduce nest predation of Broad-snouted Caiman between the time when the nest is found and when the eggs are they are found.Keywords: attraction, Broad-snouted Caiman, eggs, human disturbance, nesting, signs/ tracks, olfactory sensory cues, visual sensory cues. ResumenEvaluación de los factores asociados con la predación de nidos de Caiman latirostris (Crocodylia: Alligatoridae) en Argentina. de huevos de cocodrilianos. Estudios previos reportan que los predadores detectan a las presas mediante signos visuales u olfativos, por ejemplo los producidos por el hombre. Los objetivos de Caiman latirostris),olfativas o visuales atraen a los predadores a los nidos y si la presencia materna afectaría la predación de los nidos. Para este trabajo, buscamos nidos en el norte de la provincia de Santa Fe (Argentina) durante diciembre de 2010 y los asignamos a los siguientes tratamientos: "control" (nidos observados a la distancia para evitar disturbios), "atracción visual" (cintas amarillas atadas a la vegetación alrededor de los nidos), "atracción olfativa" (los nidos fueron abiertos, uno de los huevos fue roto, y se cubrieron nuevamente los nidos) y "atracción olfativa por disturbios humanos" (el material del nido fue manipulado por los investigadores). Encontramos que, durante una temporada reproductiva 21%. Observamos que rastros olfativos y visuales incrementan la tasa de predación, y los disturbios humanos estuvieron asociados al incremento de la tasa de predación de nidos...

Temperature is crucial for reptiles, also during embryonic development, particularly for species with temperature‐dependent sex determination. Under natural conditions, Broad‐snouted caiman (Caiman latirostris) eggs are influenced by thermal changes in the interior of the nest related to the external environmental temperature. As nests are subject to variations in temperature and most lab studies on crocodilian incubation have been carried out at constant temperatures, we were interested in determining how temperature fluctuations may affect the development of caiman embryos. We investigated the effects of incubation at constant temperatures (31°C, 32°C, and 33°C) and fluctuating temperatures (31 ± 2, 32 ± 1, and 32 ± 2°C) on the following aspects: incubation period duration, hatching success, sex ratio, total length, and body mass of C. latirostris hatchlings. Eggs incubated at 31°C produced 100% females, those at 32°C produced 71.6% females (however, the sex ratio was nest related), and at 33°C produced 100% males. We found a masculinizing effect when incubation was at 31 ± 2°C compared with a constant 31°C; and temperature fluctuations at 32°C (32 ± 1 and 32 ± 2°C) had a negative effect on hatchlings size and mass, and hatching success compared with constant incubation temperatures of 32°C and 33°C. Finally, the effect of temperature variation during the incubation period on sex ratio, hatching success, and phenotype depends on the mean temperature, as the fluctuation around 31°C affected the sex ratios and incubation period, and the fluctuation around 32°C affected hatchling success and size.

Reproductive aspects, like number of nests produced per season or clutch size (number of eggs per nest), of broad-snouted caiman (Caiman latirostris) may be affected by a climatic variables such as rainfall and temperature. The success of caiman reproduction is not only affected by the amount of rainfall, but also by the time elapsed during which it takes place. In this study, we present evidence of a positive relationship between the number of nests produced and the amount of precipitation on the water heads (“Bajos Submeridionales”) during March. Surprisingly, there was not a significant relationship when considering local rainfall and temperature. During one event of El Niño phenomena the number of caiman nests was the highest in eight years of monitoring, besides a remarkable low number of nests were produced during La Niña. There was not a significant relationship between clutch size and rainfall or temperature. This information is useful for the ranching programs, because managers will be able to estimate, nine months in advance, the number of nests for harvesting. Another positive aspect is that this information can be used to establish nests' searching strategies, and number of eggs to incubate and hatchlings to raise. Thus, this will help planning management strategies in support of conservation efforts for the species during extreme climatic events.

No abstract