Ectoparasites are common on herpetofauna and can cause skin lesions, thermoregulatory complications,and hinder growth. Herein we present records from the literature and new data from the Calakmul Biosphere Reserveon ectoparasites of herpetofauna in the subclasses Acari (mites and ticks) and Hirudinea (leeches) from the MexicanYucatan Peninsula. Our new records fill important gaps in our knowledge of reptiles and amphibians affected by ectoparasitesand the geographic distribution of these interactions in Mexico. We also discuss conservation implications ofrecording ectoparasites particularly for vulnerable reptilian species as well as anthropological health issues that couldarise with diminishing natural habitats causing these animals and their parasites to live closer to humans.

When backcrosses are fertile, interbreeding between endangered taxa can lead to the admixture of gene pools under threat. One such case pertains to the Mesoamerican crocodile Crocodylus moreletii , a species which shows strong signatures of both recent hybridisation and historic intogression with the American crocodile C. acutus across large parts of its range . In the present paper, we use RAD-seq derived SNPs (4980 nuclear and seven mtDNA loci) to demonstrate that C. moreletii populations inhabiting the region of Calakmul in central Yucatan (Mexico) are rather unaffected by hybridization, despite being surrounded by coastal areas where pervasive admixture has previously been documented. All (based on fastSTRUCTURE) and 96% (based on NGSadmix) of 84 genotyped individuals from 18 sampled waterbodies (locally termed aguadas) were free from nuclear introgression of C . acutus DNA at at threshold of 0.95. Seven individuals (8%) possessed a C. acutus mtDNA haplotype, five of which were derived from two adjacent, rather peripheral aguadas. Spatial inferences based on a DAPC and fineRADstructure further showed that the region of Calakmul is inhabited by three genetic clusters spanning across a set of distinct aguadas each. Taken together, our findings reveal that central Yucatan contains the currently largest documented stronghold of C. moreletii populations only marginally affected by introgression, which has major implications for the conservation management of this important flagship species.

Syntopic species share the same habitat in time and space. Thus, although some species might have completely coinci-dent spatial distributions on a relatively broad scale, most are syntopic only in certain locations. Four species of caimans (Crocodylia:Alligatoridae) occur throughout the Amazon basin, but they are rarely found living in syntopy. In locations where all four caiman spe-cies coexist, their distributions and occurrences have not been studied simultaneously to determine to what degree they partitionspace. We carried out extensive spotlight night-surveys from 2013 to 2017 to better understand how the four caiman species coexist insympatry and quantify the degree to which they differ in habitat use and space occupancy. The strictly Amazonian species of caimans-Melanosuchus nigerandPaleosuchus trigonatus-were less likely to occur close to each other than other species pairs, suggestingthat these species occupy different sections within waterbodies in the same microbasin.Caiman crocodilushad the highest encounterrates and was mainly associated with varzeafloodplains and exhibited a high degree of spatial overlap withMelanosuchus niger.Paleosuchus trigonatuswas the only species showing encounter rates increasing with the proportion of nonflooded forest aroundwaterbodies but that relationship was not statistically significant. Based on spatial distributions,Paleosuchus palpebrosusseem to bethe species that most often shares space with other Amazonian caiman species, because it was the only regularly syntopic species. Thefact that each species represented its own most frequent neighbor indicates a clustered distribution of caimans, likely a result of habi-tat segregation among species. Although the phylogenetically related species tended to occupy the same ecosystem, habitat partition-ing may enable the coexistence of four crocodilian predators in one catchment

Estimates of animal abundance provide essential information for population ecological studies. However, the recording of individuals in the field can be challenging, and accurate estimates require analytical techniques which account for imperfect detection. Here, we quantify local abundances and overall population size of Morelet’s crocodiles ( Crocodylus moreletii ) in the region of Calakmul (Campeche, Mexico), comparing traditional approaches for crocodylians (Minimum Population Size—MPS; King’s Visible Fraction Method—VFM) with binomial N- mixture models based on Poisson, zero-inflated Poisson (ZIP) and negative binomial (NB) distributions. A total of 191 nocturnal spotlight surveys were conducted across 40 representative locations (hydrologically highly dynamic aquatic sites locally known as aguadas) over a period of 3 years (2017–2019). Local abundance estimates revealed a median of 1 both through MPS (min–max: 0–89; first and third quartiles, Q 1 –Q 3 : 0–7) and VFM (0–112; Q 1 –Q 3 : 0–9) non-hatchling C. moreletii for each aguada, respectively. The ZIP based N- mixture approach shown overall superior confidence over Poisson and NB, and revealed a median of 6 ± 3 individuals (min = 0; max = 120 ± 18; Q 1 = 0; Q 3 = 18 ± 4) jointly with higher detectabilities in drying aguadas with low and intermediate vegetation cover. Extrapolating these inferences across all waterbodies in the study area yielded an estimated ~10,000 (7,000–11,000) C. moreletii present, highlighting Calakmul as an important region for this species. Because covariates enable insights into population responses to local environmental conditions, N- mixture models applied to spotlight count data result in particularly insightful estimates of crocodylian detection and abundance.

The herpetofauna occurring in the Selva Maya is one of the richest assemblages in the Americas. We herein provide an updated list of herpetofauna species for the Calakmul region, located in the southern Yucatán Peninsula, Campeche, Mexico. This species list was compiled considering the results of herpetological surveys conducted between 2015-2019 in the Calakmul Biosphere Reserve, information gathered from previous literature, and sighting records from the website iNaturalist. All this information combined resulted in the identification of 109 species, 23 amphibians and 86 reptiles, belonging to 34 families. Furthermore, we hereby present new distribution records for 7 snakes, 2 lizards and 2 frogs not previously observed in the study region. Approximately 38% (n = 41) of the herpetofauna species are listed under a threat category by the environmental Mexican legislation (NOM-059-SEMARNAT-2010). The list presented in this study increases to 109 the number of species known to occur in the Calakmul region, and to 135 in Campeche, which therefore becomes the Mexican state of the Yucatán Peninsula with the highest herpetofauna diversity, followed by Quintana Roo with 133 species.

Crocodilians represent one of the oldest extant vertebrate lineages. They have co‐existed with humans throughout the Amazon basin for thousands of years, often having a strong cultural and economic influence on people's lives. Shifts in the socio‐economic and political reality of the Amazon basin during the last century have led crocodilian populations to face large variations in their numbers according to different levels of exploitation and strategies for their conservation. This article reviews the scientific knowledge obtained between 1945 and 2019 on the biology, conservation and management for the four Amazonian crocodilian (caiman) species ( Caiman crocodilus , Melanosuchus niger , Paleosuchus palpebrosus and Paleosuchus trigonatus ). It provides a general overview on past and current population status and research efforts involving caimans in the Amazon basin and discusses perspectives for the future. The most significant studies on the ecology, genetics and management strategies are examined in more detail and this information is contextualized to provide an overview of the most relevant findings that might explain caiman population trends over the last 75 years. Systems for sustainable management in the Amazon basin have been discussed for the past 20 years, but remain rarely applicable. It is necessary to develop new ways to maintain healthy caiman populations through innovative management programmes. Sustainable harvesting of wildlife has been shown to promote conservation targets, especially those initiatives based on community co‐management. In this article, we propose some general guidelines for future management schemes, in the expectation that the information provided by the scientific community will be considered fully without political agendas determining the priorities.

Assignment of Morelet's crocodile Crocodylus moreletii individuals into size groups or classes based on ecological and morphological similarities has not yet been associated with species‐specific ontogeny related changes. Age or size of first reproductive behavior is not precisely known for C. moreletii , but differences in allometric patterns and relative cranial size between juveniles and adults might be used as an indicator of sexual maturity. In this study, a regression tree analysis was used to investigate the relationship between age and body size in 1266 crocodiles by using both simple and generalized linear models, with gender and origin (captivity or wild) as factors. Total length (TL), snout–vent length (SVL) and cranial length (CL) were used as predictor variables and the logarithm of body mass as the response variable. Four length intervals with well‐defined thresholds (514, 899 and 1497 mm of TL) were established using all three predictors (TL, SVL and CL). Relationship between SVL and TL was described, and a strong positive relationship (r 2 = 0.98), unaffected by crocodile gender, was observed. The observed CL–TL and CL–SVL relationships were also positive but significantly different between males and females (p < 0.001) and length interval classes (p = 0.01). These results suggest that our estimated size thresholds seem to correspond to important ontogenetic changes in C. moreletii and that sexual maturity is closely related to size in this species, where sexual dimorphism in body length occurs, particularly in large individuals (size group IV).

The impact of microplastics on wildlife is a recent problem for which methods to evaluate exposure still need development. Being able to identify and quantify microplastics (particles < 5 mm) in the gastric contents of live crocodiles allows us to evaluate exposure, at both individual and population level, and also its contribution as transporter of other contaminants. The method was validated to determine and quantify microplastics in crocodile stomach contents recovered during an experiment where a known amount of this contaminant was given to crocodiles via oral administration. Through stomach flushing we were able to recover more than 80 % of the total volume of microplastic administrated to each crocodile. In summary, the method used during the experiment consists of 1) immobilization of the crocodile; 2) extraction of microplastics from stomach contents obtained through stomach flushing; 3) separation, identification and quantification of recovered microplastic fragments using microscopy and FTIR. •Low cost method that uses a small number of materials, does not take long to produce results and can easily be performed in the field or the laboratory.•Effective in extracting stomach contents (95 %).•High (>80 %) and good (>60 %) recovery efficiencies within two and four days after ingestion of microplastics by crocodiles.

Although nesting ecology is well studied in several crocodilian species, it is not known how nest attendance influences physiology and body condition of nesting females. In this study, we describe body condition and serum biochemical values of nesting female, non-nesting female and male spectacled caiman (Caiman crocodilus) and black caiman (Melanosuchus niger) in two areas of Central Amazonia. We also evaluated the effect of nest age and nest distance to water on body condition and blood parameters of nesting females. Body condition and plasmatic concentrations of glucose, triglycerides, lactate and uric acid of nesting females were significantly different from those of non-nesting females and males in C. crocodilus, but not in M. niger. Our study also demonstrated that nest age and distance to water had a negative effect on female body condition in C. crocodilus, but not in M. niger. Female C. crocodilus attending older nests or nests built further away from permanent water bodies tended to have lower body condition. Our results demonstrate that the nesting strategy of C. crocodilus has a metabolic cost associated with nest attendance for nesting females, which appear to depend on accumulated energetic reserves during nest attendance. In contrast, nest attendance had little effect on the physiology of female M. niger.

Although nesting ecology is well studied in crocodilians, there is little information on the diet and feeding habits of nesting females. During the annual dry season (November–December) of 2012, we studied the diet of female spectacled caiman (Caiman crocodilus) attending nests (n=33) and far from nests (n=16) in Piagaçu-Purus Sustainable Development Reserve (PPSDR), Central Amazonia, Brazil. The proportion of empty stomachs in nest-attending females was larger, and the occurrence of fresh food items was lower when compared to females not attending nests. Fish was the most frequent prey item for non-nesting females, while terrestrial invertebrates and snail operculae were the prey items most commonly recovered from stomachs of nesting females. Our study demonstrates that, despite enduring periods of food deprivation associated with nest attendance, nesting females of C. crocodilus still consume nearby available prey, possibly leaving their nest temporarily unattended.

We provide a list of amphibians and reptiles of the Calakmul Biosphere Reserve in the southern half of the Mexican Yucatan, in the state of Campeche. The study area was sampled through opportunistic, transect and pitfall trap surveys conducted for three successive years. These surveys resulted in a total of 2,359 amphibian and reptile encounters, belonging to 20 amphibian and 69 reptile species from 24 total families. We present herein the records for one snake, one chelonian and two salamander species not previously recorded in the area.

Predation is one of the major causes of crocodilian egg mortality. Many studies have suggested that opening nests, handling eggs, and capturing attending females may increase predation rates, but the influence of such activities on nest predation has not been quantified. For that reason, we studied the impacts of different research activities on nests of wild Spectacled Caimans (Caiman crocodilus crocodilus) from a flooded forest (varzea) in the Piagacu-Purus Sustainable Development Reserve, Central Amazonia. During the 2010 nesting season, predation on eggs in disturbed nests was generally higher than in nests without research activities found in the same area. However, natural predation rates in similar habitat were not significantly different, suggesting that predation rates on disturbed nests, though elevated, remain within the broad range found in undisturbed nests. We conclude that the benefits in knowledge gained from research activities will generally out-weigh the small increase in nest predation that could result from research activities.