A new case of communal egg-laying by iguanas and American crocodiles (Crocodylus acutus Cuvier, 1807) from a Caribbean atoll of Mexico

Abstract

Communal egg-laying in oviparous animals occurs when two or more conspecific females deposit their eggs in the same nest cavity (Espinoza & Lobo 1996). Although this behavior appears to be more widespread among reptiles than initially thought (Doody et al. 2009), interspecific communal egg-laying, which involves different reptile species, has been reported less frequently in the literature (Alfonso et al. 2012, Escobedo-Galván et al. 2019). Recently, Escobedo-Galván et al. (2019) published a review of reptile species that have been observed depositing their eggs in crocodile nests. In addition, Platt et al. (2021) provide more information on some reptile species nesting in Crocodylus moreletii and hybrid (C. moreletii x C. acutus) nests in Belize. These studies revealed that interspecific communal egg-laying has been documented for eight (33.3%) of the 24 crocodilian species recognized by the IUCN crocodile specialist group (http://www.iucncsg.org/pages/Crocodilian-Species.html). Among these eight species, three are from the family Alligatoridae (Alligator mississippiensis, Caiman latirostris, and Melanosuchus niger) and five are from the family Crocodylidae (Crocodylus acutus, C. intermedius, C. moreletii, C. novaeguineae, and C. rhombifer) (Escobedo-Galván et al. 2019). There also exist cases of interspecific communal egg-laying in nests of C. acutus x C. moreletii hybrids in Belize (Platt et al. 2021). Twenty-five reptile species have been recorded to deposit their eggs in these crocodile nests: 15 turtles, six lizards, and four snakes (Escobedo-Galván et al. 2019, Platt et al. 2021). Here we report a new case of interspecific communal egg-laying between Crocodylus acutus and iguanas on Cayo Centro, Banco Chinchorro Atoll, Quintana Roo, Mexico. Banco Chinchorro Atoll is a Biosphere Reserve located off the southeastern coast of the Mexican state of Quintana Roo, on the Yucatan Peninsula (see description in Charruau 2021). Cayo Centro is by far the largest cay of the atoll (541 ha) and is located in the center of the reef lagoon (Charruau 2021). Since 2006, we have been monitoring (annually) the reproduction of a recovering population of American crocodiles (Crocodylus acutus) present on this cay (Charruau et al. 2005, 2010, 2013, 2022, Charruau & Hénaut 2012, Charruau 2012). On May 17, 2021, during our annual survey, we found a crocodile nest (18.57°N, -87.33°W) containing 16 iguana eggs beneath 17 C. acutus eggs (Fig. 1). The crocodile nest was a mound (140 cm wide x 150 cm long x 36 cm high) and the substrate consisted mainly of sand with some leaf litter and a black nylon rope (Fig. 2). Crocodile eggs (n = 17) had a mean length of 66.1 ± 2.2 mm (range: 63.2–71.7 mm), mean width of 42.3 ± 0.7 mm (range: 41.2–43.7 mm), and mean mass of 71.5 ± 4.5 g (range: 66.3–84.1 g). Iguana eggs (n = 15) had a mean width of 22.2 ± 0.6 mm (range: 21–23 mm), mean length of 32.1 ± 0.5 mm (range: 31–33 mm), and mean mass of 9.0 ± 0.6 g (range: 7.7–9.9 g). Unfortunately, it was not possible to determine the iguana species based on external egg characteristics. Two species of iguanids are present on the island, the green iguana (Iguana iguana) and the black iguana (Ctenosaura similis) (Charruau et al. 2015, 2020). The clutch and egg characteristics we obtained were within the range of measurements reported previously for these two species (Fitch & Henderson 1978, van Marken Lichtenbelt & Albers 1993, Alvarado et al. 1995, Muñoz et al. 2003, Campos & Desbiez 2013, Avery et al. 2014). Iguana iguana is already known