Effects of climatic conditions on sex ratios in nests of broad‐snouted caiman

Abstract

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 sex‐determination pattern in crocodilians: A systematic review of three decades of research

“…Flow diagram of the study selection in the performed systematic search. The 25 studies included in the models that considered control of temperature were as follows: Ferguson and Joanen (, ), Webb, Manolis, and Buckworth (), Hutton (), Webb, Beal, Manolis, and Dempsey (), Joanen and McNease (), Lang, Andrews, and Whitaker (), Deeming and Ferguson (), Aguilar (), Guillette et al (), Lang and Andrews (), Rhodes and Lang (), Conley et al (), Leslie (), Pinheiro, Mourao, Campos, and Coutinho (), Mohanty‐Hejmadi et al (), Piña et al (), Stoker et al (), Charruau (), Marcó et al (), Elsey and Lang (), Simoncini et al (), López‐Luna et al (), Charruau, Martínez, Cantón, and Méndez de la Cruz () and Marcó et al (). The six studies also included in the models that did not consider control of temperature were as follows: Charruau (), Lance and Bogart (, ), Milnes, Allen, Bryan, Sedacca, and Guillette (), Milnes, Bryan, Medina, Gunderson, and Guillette () and Moore et al ()…”

“…264252). We thank Melina Simoncini and the Yacaré Project, and María Virginia Parachú Marcó for providing us with essential information not included in Simoncini, Cruz, Larriera, and Piña () and Marcó, Leiva, Iungman, Simoncini, and Piña (), respectively. We also thank Marc Girondot and five anonymous reviewers for their comments on earlier versions of the manuscript.…”

Influence of temperature variation on incubation period, hatching success, sex ratio, and phenotypes in Caiman latirostris

“…We know that C. latirostris incubated at certain constant temperatures (31°C, 33°C, or 34°C) produces hatchlings of only one sex (31°C only females, 33°C and 34°C only males). This does not happen when incubation is at 32°C, producing a strong clutch effect on the male: female ratio (Parachú Marcó et al, ; Simoncini et al, ), probably as a result of maternal factors deposited in eggs before oviposition; for example, estrogen levels (Elf, ; Elf, Lang, & Fivizzani, ; Uller, Hollander, Astheimer, & Olsson, ), and the stress level of females during follicle development (Lovern & Wade, ), or genetic influence (Holleley et al, ; Mrosovsky & Pieau, ). Because this study was done in 2 consecutive years, including different nests, we decided to analyze each year separately (our experimental design includes representatives from each clutch on every treatment of that year), first‐year treatments (a) and (b), second‐year treatments (c) to (f).…”

“…In crocodilians, most studies on TSD have been performed in the laboratory at constant temperatures (Charruau, ; Ewert & Nelson, ; Leslie & Spotila, ; Magnusson, Lima, & Sampaio, ; Piña, Siroski, et al, ). Additionally, we have to keep in mind that laboratory controlled conditions are different from the natural environment because in the wild, crocodilian nests experience daily thermal fluctuations during the incubation period (Packard, Paukstis, Boardman, & Gutzke, ; Simoncini, Cruz, Larriera, & Piña, ). Abiotic factors such as air temperature, rainfall, shade, wind, and photoperiod should be considered as crucial variables affecting the internal nest temperature during incubation that may produce thermal oscillations within the nest; and therefore, may have a more pronounced effect on sex determination in crocodilians than the mere mean incubation temperature.…”

“…These authors found that during colder nesting seasons C. latirostris nests produce a higher proportion of females (near 86.7%) and during hotter nesting seasons more males are produced (near 51.3%). Additionally, Simoncini et al () found that two nests in the wild despite showing the same mean incubation temperature (30.6°C) during the TSP but different variations in their temperatures ( SD of nest temperature = 1.15 and 1.87, respectively) gave different proportions of sexes (100% and 66% females, respectively). Thus, temperature variation has a strong effect on embryos; however, it remains unclear how temperature fluctuations affect the sex determination of these crocodilians during the TSP and the aftermath of these embryos in terms of survivorship and performance.…”